Portable electronics: fuel cells eye the prize

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Volume 1 Issue 2 Aug/Sept 2004SOFCs target military marketsA faster take on fuel reformingStationary power ready to rollHydrogen codes and standards

An IOP Emerging Technology Review

THE

FUEL CELL REVIEWCOMPETIT IVE INTELLIGENCE ON HYDROGEN AND FUEL CELL TECHNOLOGIES

Portable electronics:fuel cells eye the prize

ISSN 1743-3029

http://www.greenlightpower.com

THE

FUEL CELL REVIEWVolume 1 Issue 2 Aug/Sept 2004

Shedding light on hydrogen storage p13

Common sense in fuel-cell cars p36

SOFCs get ready for battle p31

5 Leader

The view from Lucerne

7 News & Analysis

● Fuel-cell buses: a mixed outlook fordevelopers ● IEC puts focus on micro fuel cells ● Sweden, China team up onSOFCs ● Hydrogen safety: Q&A withRobert Walter Boyd, The BOC Group

13 R&D Focus

Unlocking the secrets of hydrogen storage ● Plankton fuel cells head for the depths ● Nanofabrication makes sense for hydrogen sensing

15 Patents

CEA ● FuelCell Energy ● BASF ● 3M● PolyFuel ● Foamex ● Therasense ●

Creavis ● UTC Fuel Cells

31 Technology Tracking

SOFCs gear up in the combat zone ●

Toshiba maintains that small is beautiful● Sustainable fuels for MCFCs ● Steamreforming just gets better ● Hydrogensensors: can’t get by without them

38 Talking Point

Hans Maru, CTO of FuelCell Energy, is atrue believer when it comes to the role thathigh-temperature fuel cells may one dayplay in stationary-power markets.

17 COMPONENTS & SYSTEMSResearchers redefine the DMFC roadmapPIOTR PIELA AND PIOTR ZELENAY

Consumer electronics giants like Toshiba and Sonyare investing big money in compact power sourcesbased on direct-methanol fuel cells. This two-partsurvey kicks off with a review of the fundamentalR&D on materials and components that promises to speed the time to market of micro fuel cells.

25 TECHNOLOGY TRANSFERDMFCs power up for portable devicesSHIMSHON GOTTESFELD

Incumbent battery suppliers, the US military andleading electronics companies are gearing up to takeadvantage of micro fuel cells. Even with that level ofmarket pull, however, significant innovations insystems design and engineering will be critical if thetechnology is to make the final transition fromprototype demonstrations to the mass market.

DEPARTMENTS SPECIAL REPORT: PORTABLE POWER

T H E F U E L C E L L R E V I E W | A U G U S T / S E P T E M B E R 2 0 0 4 3

Cover: Micro fuel cells are set to revolutionize power delivery inportable electronic devices pp17–29 (Victoria Le Billon)

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ISSN 1743-3029

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T H E F U E L C E L L R E V I E W | A U G U S T / S E P T E M B E R 2 0 0 4

LEADER

5

The organizers of the Lucerne Fuel CellForum know how to give their delegateswhat they want – and we’re not just talk-ing about beer at lunchtime and scenicevening cruises on Lake Lucerne. If it’shard technical information you’re afteron fuel-cell R&D, innovation and emerg-ing applications, then the historic Swisscity has established itself as the place to

head for when the summer conference circuit kicks in. Likeothers before it, this year’s event provided plenty of scope forattendees to get to grips with the fine detail of fuel-cell materi-als, components and systems development (165 presentations,60 poster contributions and 34 exhibitors from industry andacademia testify to that, as does a set of conference proceedingsrunning to 2200 pages).

Trouble is, sorting and evaluating the headline developmentsin a sprawling programme like this is no easy task. Of course,it helps to remember that there’s a bigger market picture in playhere and that, ultimately, fuel cells are a family of technologiesthat will be driven not by the prejudices of the scientists or engi-neers involved, but by the end-user. In this context, one of theencouraging aspects of the 2004 conference was the emphasisit placed on reporting field demonstrations and R&D projectsthat are focused squarely on getting fuel-cell technology out ofthe controlled confines of the laboratory.

Unsurprisingly, for an event with two parallel sessions onsolid-oxide fuel cells (SOFCs), close-to-market high-tempera-ture systems were very much to the fore. Swiss company SulzerHexis, for example, detailed an ambitious three-year pro-gramme of field trials involving deployment of 110 of itsHX1000 Premiere units (based on a 1 kW SOFC system).Working in partnership with the energy utilities, Sulzer hasbeen evaluating these “precommercial” prototypes for com-bined heat and power applications in single-family homes, aswell as in public buildings, laboratories and multitenant apart-ments. Now, with more than 500 000 h of accumulated operat-ing experience, the technical performance has made impressivestrides. Since the beginning of testing, says Sulzer, malfunctionshave been reduced by more than 80%, while downtime is lessthan 10% for 90% of systems tested since October 2002. On theback of this, a next-generation SOFC heating unit is already inthe works and should be ready for delivery in 2005.

Moving up several notches to the 250 kW regime, it appearsthat molten-carbonate fuel cells (MCFCs) are emerging as acredible, high-efficiency platform for decentralized cogenera-tion of electricity and heat using biofuels like sewage gas andlandfill gas (see p32). What’s more, this sustainable slant onMCFC technology could be ready for widespread commercial

application within the next five years, according to a presenta-tion from MTU CFC Solutions of Germany. MTU boasts animpressive pedigree in the development of integrated MCFCsystems. Its so-called HotModules have been put through theirpaces in a field-trial programme that’s been running since 2001.There are currently eight HotModule test sites across Germany,including hospitals, industrial plants and telecommunicationsexchanges (see photo, left).

Meanwhile, the US Army’s Construction EngineeringResearch Laboratory (CERL) elaborated on a simple yet effec-tive strategy for fuel-cell testing. Over the past decade, it hasimplemented a “kick it, and kick it hard” approach to evaluat-ing the performance of 30 200 kW phosphoric-acid fuel-cellpower plants and, more recently, 75 residential-scale polymer-electrolyte-membrane fuel-cell systems – all of them deployedat military and related facilities. CERL’s objective is to get awayfrom what it calls “the traditional approach of fuel-cell devel-opers” who “conduct carefully designed, tightly controlled fielddemonstrations”. The true test comes, it says, when the fuelcells are put into normal everyday operation and expected todeliver. The name of the game: to identify, in as short a time-frame as possible, any shortcomings associated with the fuelcells when they are exposed to a range of demanding conditions(i.e. high altitude, ground-water contamination and extremesof temperature/humidity).

Going forward, it’s clear that robust, no-nonsense approaches,like that of CERL, are going to be mandatory, and will ultimatelyenhance the commercial prospects of low- and high-tempera-ture systems operating at all power levels. It will be intriguing tosee how much progress is made on this score by the time the fuel-cell community meets up again in Lucerne next summer.

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Wry soundbite of the summer award goes to Michael J Binderof the US Army’s CERL. “There are a lot of people making smallfortunes in fuel cells today,” he told delegates in Lucerne.“Trouble is, they all started out with big fortunes.” If you don’twant to be one of the unfortunates in question, better makesure you’re reading The Fuel Cell Review. But remember, if youwant to carry on receiving the magazine you must become asubscriber. I urge you to subscribe today – using the card at thefront of the magazine or via our website.

Joe McEntee, Editor ([email protected])

There are encouraging signs that fuel-cell developers are getting their commercial priorities in order.

The headline view from LucerneConference report

MT

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mailto:[email protected]

NEWS &ANALYSIS

Also in this section

8 Micro fuel cells in the mix

8 Sweden, China and SOFCs

9 Opinion: hydrogen safety

10 Field trials show the way

They’re not cheap, but they are clean

A study from the United Nations GlobalEnvironment Facility offers a mixed bag of indi-cators for pioneers of fuel-cell buses (FCBs).First up, and most worryingly, the report con-cludes that FCB hardware and software (such ascodes, standards and training protocols) have“not progressed down the cost curve... in thepast two years as rapidly as originally antici-pated”. In other words, FCBs are still way tooexpensive – averaging out at around $2.3 m perbus, including the refuelling station. On the upside, the study claims that industry and govern-ment investment in FCBs is being sustained,with one key indicator of progress being thedoubling, between 2002 and 2003, of the cumu-lative number of FCBs that were built and oper-ated worldwide (the figure is now close to 70).

Urban transit buses provide an ideal testbedfor the optimization of fuel-cell-powered vehi-cles. For starters, bus companies have central-ized maintenance and fuelling depots, whichmakes the absence of a distributed hydrogen-fuelling infrastructure less of an obstacle thanit is for field trials of fuel-cell cars. Transit busesalso operate on regular – and very demanding –duty cycles, which means it is easier for devel-opers to compare the relative merits of differ-ent fuel-cell configurations.

Ticket to rideIn the US, California is setting the pace onFCBs. The state is a hot-bed of activity, thanksto a decree that all of its transit authoritiesmust operate some zero-emission buses by2010. The California Fuel Cell Partnership(CaFCP), for example, is currently involved inthree different trials: the Santa Clara ValleyTransportation Authority in San Jose; theSunline Transit Agency in Thousand Palms;and AC Transit in Oakland.

AC Transit, for its part, has been taking part inFCB trials for several years. And despite the highcost of prototype vehicles, the companyremains positive about the technology’s long-term prospects, according to Jaimie Levin, AC’sdirector of marketing and communications.Since September 2003, the group has been run-ning a 9 m long FCB which “has been quite

remarkable in its performance”, Levin says, cit-ing the vehicle’s 82% availability-for-service rat-ing. (AC Transit budgets for 85–90% availabilityfor its diesel buses.) The company has teamed upwith the fuel-cell provider UTC and ISE, a spe-cialist in hybrid-electric drive systems, to con-vert three diesel buses (supplied by Van Hool ofBelgium) to a fuel-cell/hybrid configuration thatwill run on hydrogen at atmospheric pressure.

Yet Levin acknowledges that the productionand storage of hydrogen fuel is a fundamentalchallenge for the transit authorities. “[Bus]companies would rather not be involved in theproduction of fuel; we would rather just buy it,”he explains. Although he’s optimistic about thefuture of FCBs, Levin does not expect ACTransit to have a substantial fleet of fuel-cellvehicles until about 2015. That view is in broadagreement with the US Federal TransitAdministration (FTA), which wants 10% ofnew US transit buses to be FCBs by 2015. Whilethere is a feeling in the industry that it may bepossible to produce a commercially viable FCBby 2010 – Toyota and MAN have announcedtheir intention to do so – it appears that thisheadline goal may be slipping.

Atakan Ozbek, director of energy researchat US-based ABI Research, believes there arecurrently fewer FCB pilot projects under waythan anticipated several years ago. This meansthat fuel-cell suppliers are not getting nearlyenough start-up manufacturing orders – a vital

part of the commercialization process. Hereckons that the US target of 10% FCB penetra-tion by 2015 is “a bit aggressive...When youlook at the technical developments, govern-ment policies and commercial realities, it doesnot look possible today”.

He continues: “No one believes that a fuelcell will be on cost parity with a diesel engineanytime soon. It won’t happen in the next 10 or15 years. Given the current progress I wouldexpect to see, say, 100 buses in one city in 2012or 2013.” That said, “the technology is pro-gressing at a reasonable pace”, he adds, “withGM, Toyota, Honda and Ballard all making sig-nificant improvements and investments”.

Meanwhile, the FTA’s 10% penetration targethas encouraged FCB projects beyond California.For example, UTC is developing a 200 kW poly-mer-electrolyte-membrane (PEM) fuel cell forFCBs in a project overseen by the NortheastAdvanced Vehicle Consortium. An FCB isexpected to be on the road in Connecticut by theend of this year.

The largest and most comprehensive FCBtrials to date, however, are the EuropeanUnion’s Clean Urban Transport for Europe(CUTE) and Ecological City Transport System(ECTOS) programmes, which involve the useof around 30 full-sized buses providing rev-enue service in 10 cities. The cities vary greatlyin size – from sprawling London to compactReykjavik – and climate – from northerly

Transportation

While the underlying technologies continue to advance, the wide-scale commercialization of fuel-cell buses is some way off.


Get on the bus: Beijing commuters will soon be able to ride in zero-emission FCBs from Daimler-Chrysler. The city will gain three hydrogen-powered Mercedes-Benz Citaro buses in 2005.

Little over 12 months after it was set up, a Sino-Swedish R&D collaboration looks to be mak-ing significant headway on low-temperaturesolid-oxide fuel cells (LTSOFCs), according toresults presented at the Sixth European SolidOxide Fuel Cell Forum in Lucerne, Switzerland,earlier this summer.

The initiative, which involves 12 Chinese andSwedish universities and research centres, is

developing ceria-based nanocomposite elec-trolytes, which exhibit excellent ionic conduc-tivities of 0.01–1 S/cm between 300 and 650 °C.In parallel, the scientists are working on a familyof compatible nickel and copper-based elec-trode materials. These electrolytes and elec-trodes have been used “to construct LTSOFCsthat demonstrated a performance from 100 to1000 mW/cm2 at temperatures between 400and 650 °C”, say the researchers. “In some cases,the LTSOFC could function at 300 °C.”

Another thrust of the work focuses on theunderlying mechanisms of LTSOFCs. Thisincludes internal reforming and electrochemi-cal processes for operation with carbonaceousfuels (such as gasoline, diesel, natural gas, coalgas, etc); microstructural analysis and reaction

dynamics at the electrode/electrolyte inter-faces; and hybrid proton and oxygen-ion con-duction and transport processes. Theseactivities are reinforced by a programme ofstack/system modelling and simulation.

Senior management at Stockholm’s RoyalInstitute of Technology (the Swedish coordinat-ing partner) is now looking to take things a stepfurther by establishing a Sino-Swedish jointresearch centre, in which LTSOFCs will formone of the main R&D programmes. The Chinesepartners in the LTSOFC initiative are TsinghuaUniversity, Beijing (coordinating partner);Dalian Maritime University; Tianjin University;University of Science and Technology, Hefei;and Institute of Energy Sources, Guangzhou.Joe McEntee, Lucerne

The International Electrotechnical Comm-ission (IEC) has established a new workinggroup (WG10) to draw up a standard coveringinterchangeability issues between micro fuelcells. The group will sit within IEC TC 105,which is the fuel-cell technologies technicalcommittee of the international standards body.

WG10’s objectives are to establish criteriafor interchangeability between micro-fuel-cellpower units and electrical devices, as well asbetween fuel cartridges and micro-fuel-cellpower packs. Why is this important? Becauseif a fuel cartridge is connected to an incorrectfuel-cell power unit there could be a safetyproblem, such as fuel leakage or an impropervoltage being supplied to an electrical device.The same problems could occur if a micro-fuel-cell power unit is connected to an incom-patible electrical device.

Toshiba’s Fumio Ueno, project leader onWG10, believes that the standardization ofmicro fuel cells will yield considerable benefits.“It will provide convenience for end-users whowish to use micro fuel cells for their portableelectronic devices,” he said. “End-users [will beable to] access the standard fuel cartridge atany outlet and there’ll be no chance of using theimproper cartridge, which will help in terms ofthe safety and performance of the device.”

He added: “As long as the reservoir is filledwith fuel, there is no limit in operating time andthe fuel reservoir allows products to be freefrom the limitations of the design and energystorage... but such a dream will be limited if youcannot get a proper cartridge at any time.”

Toshiba’s provision of a project leader is not

the only Japanese link to WG10. Indeed, theformation of the new group was proposed byJapan, with heavy-hitters like Hitachi, NEC andSony also involved. The US, France, Republicof Korea, China and the UK have said they willcontribute their own experts to WG10.

The 16 participating members of TC 105voted at the end of July to establish the newworking group. WG10 joins two other work-ing groups focused on micro fuel cells. Thefirst, WG8, was established in November lastyear to deal with the safety aspects of microfuel cells. The second group, WG9, was set upin June 2004 and is concentrating on fuel-celltechnical specifications and performance.

To ensure that the activities of the three work-ing groups are coordinated, their meetings willtake place at the same locations and on the samedates, according to a spokesperson for the IEC.Meanwhile, the initial tasks of WG10, saysUeno, are to tackle the core items required tomake fuel-cell power units interchangeable andto specify the fuel cartridge needed. The newgroup aims to produce a committee draft of thestandard in mid-2006. The full internationalstandard is planned for 2007. For furtherdetails, e-mail [email protected]ân Harris


NEWS & ANALYSIS

Standards bodies are working out the finedetail of micro-fuel-cell power sources.

Technology made easy

8

Portable power

Sweden and China have teamed up on the development of low-temperaturesolid-oxide fuel cells.

Working togetherResearch

Stockholm to as far south as Barcelona. In sev-eral projects, hydrogen fuel is manufacturedlocally. In Reykjavik, for example, hydrogen isgenerated through electrolysis using hydro-electric and geothermal energy. In Barcelona,solar panels will supply the electricity, while inHamburg wind energy will be used. Porto andStuttgart will use hydrogen reformed fromnatural gas and London will be the only city totrial the use of liquid (as opposed to gaseous)hydrogen generated at oil refineries.

All CUTE trials are using the Citaro FCBfrom DaimlerChrysler. The 12 m bus has a200 km range and can carry more than 60 peo-ple. The vehicle is powered by a 205 kW Ballardfuel cell supplied with hydrogen compressed at350 bar. The fuel-cell unit and storage cylinderssit in the roof of the vehicle and the electricmotor and transmission are located at the rearof the bus. Delivery of the buses began in 2003,and commercial services got under way in sev-eral cities towards the end of the year.

In Japan, meanwhile, Toyota has teamed upwith the bus manufacturer Hino to developFCBs. The companies launched their first vehi-cle in 1999, with a second generation of fourvehicles released in 2002. The latest buses are10.5 m long fuel-cell hybrids, which employtwo 90 kW PEM stacks. Elsewhere in Asia-Pacific, the Chinese government intends tohave 100 FCBs in service for the BeijingOlympic Games in 2008. The Ministry ofScience and Technology is currently funding a$106 m four-year programme to develop fuel-cell and hybrid-electric vehicles, with privatecompanies expected to invest as much as$300 m over the next five years. The fuel-cellsystems are being developed by ShanghaiShen-Li High Tech and Dalian Sunrise Power.The Shanghai Fuel Cell Vehicle PowertrainCompany is integrating the system in conjunc-tion with Tsinghua University. Hamish Johnston

On the go: micro fuel cells will benefit from theIEC’s latest moves on standardization.



NEWS & ANALYSIS

9

One of the fundamental challenges holdingback commercialization of hydrogen tech-nologies is “the lack of safety information onhydrogen components and systems used in ahydrogen fuel infrastructure, and the limitedavailability of appropriate codes and standardsto ensure uniformity and facilitate deploy-ment”. With no less an authority than the USDepartment of Energy (DOE) pushing thatrather downbeat view, it’s probably time to lis-ten up, especially as closer scrutiny reveals thatrising to the aforementioned challenge is likelyto be far from straightforward – and not justwhere the US is concerned.

For the time being, hydrogen and fuel-cellcompanies are caught between a rock and ahard place, most obviously when it comes todeployment of hydrogen systems in automo-tive and stationary-power applications. Forstarters, emerging technologies not yet recog-nized within all-encompassing codes and stan-dards are certain to experience difficulties withinsurance, and could well be vulnerable to hos-tile lawsuits. A lack of understanding of hydro-gen fuel and hydrogen systems among localgovernment officials, fire officers and the gen-eral public hardly helps. And competitionbetween standards and code-developmentorganizations complicates things yet further.

It may look messy, but when The Fuel CellReview spoke to Bob Boyd, project develop-ment manager, hydrogen energy, at The BOCGroup in the US, it found there are still reasonsto be optimistic that the hydrogen and fuel-cellindustry will be able to unify its efforts onsafety, codes and standards – and perhapssooner rather than later.

FCR: What is the commercial importanceof a coherent industry-wide approach tolegal codes and technical standardsrelating to hydrogen safety – specificallyin terms of vehicle applications?BB: It’s vital. Failure to develop harmonizedcodes, standards and legislation covering theuse of hydrogen in the public domain wouldprevent widescale adoption of hydrogen as afuel. Any organization wishing to sell hydro-gen-fuelled products on a commercial basismust be able to demonstrate that the safety riskhas been managed properly. At BOC, for exam-ple, we are participating in various workinggroups, committees and demonstrations that

contribute to establishing a harmonized frame-work supporting the whole supply chain –from production to application.

Excluding the changes being proposed toexisting codes, we currently have codes andstandards for industrial hydrogen systems,natural-gas-vehicle (NGV) fuelling applica-tions, and traditional small and standby powersystems. But it is a big headache having to usethe industrial-hydrogen standards and existingbuilding codes and standards to secure per-mitting for demonstration fuel-cell projects.

How much progress has been made, andremains to be made, in this context? In terms of vehicle and hydrogen-fuellinginfrastructure, North America appears to beon track to have codes and standards in placefor a major nationwide roll-out of fuel-cellvehicles by 2015. Here, much of the develop-ment on codes and standards going on todayhas been an outgrowth of the work of theCalifornia Fuel Cell Partnership (CaFCP).Through the CaFCP, almost all of the majorOEMs have found a forum to learn and collab-orate on both vehicle-development issues andhydrogen infrastructure standards.

Elsewhere, Japanese OEMs seem to be furtheralong towards an earlier commercialization ofhydrogen vehicles – certainly, they are ahead oncommercial hybrid-electric vehicles (see The FuelCell Review June/July 2004 p7). In terms of codesand standards, the general feeling is that there

are fewer roadblocks to commercial implemen-tation in Japan. ISO standards for compressed-and liquid-hydrogen-powered vehicles arebeing developed, although at about the samepace as in North America.

What role are the car makers playing?DaimlerChrysler, Ford, GM, Peugeot, Hyundaiand the Japanese OEMs are focusing on 35 and70 MPa on-board storage systems, leveragingthe composite storage-tank technology devel-oped for compressed NGVs. BMW and theOpel division of GM have been the only OEMsthat have shown an interest in on-board storageof liquid hydrogen. Both of these companieshave done a lot of development work, but therehas been little interest in on-board liquid hydro-gen outside Germany.

How important is government influencein the development of relevant hydrogensafety codes and standards? The DOE and National Renewable EnergyLaboratory (NREL) are doing a great job, withfewer resources than we would wish, to coor-dinate codes and standards development over awide range of organizations. Non-govern-mental agencies and industry-sponsoredorganizations, such as the National HydrogenAssociation (NHA) and Compressed GasAssociation (CGA), also play a vital role, work-ing with the DOE and NREL to bring the tech-nical issues and main players to the table.

At the same time, commercial companies –like BOC – are contributing the man-hoursneeded to support the code-developmentefforts. Some of that effort, to be sure, is therebecause these companies see commercialopportunities [that require new codes], but thehydrogen economy will not develop unlessthere is hope of commercial viability.

Clearly, many interested parties areinvolved in the development of hydrogensafety codes and standards, with differentand sometimes competing agendas. Doyou think that’s a problem?I think that the ad hoc approach is workingabout as well as we could hope. There is quite adiverse bunch of interested parties and the sup-port from DOE and NREL has been wellfocused on systems that support collaborationand harmonization.

They are viewed as a costly annoyance by many executives, but widely adopted codes and standards will be essential if hydrogen and fuel-cell technologies are to secure mainstream status.

Cracking the codes, setting the standardsHydrogen safety

“Any organization wishing to sell hydrogen-fuelled products on a commercial basis must beable to demonstrate that the safety risk hasbeen managed properly,” says BOC’s Bob Boyd.

▲▲

What codes and standards already existcovering the industrial applications ofhydrogen? And how relevant are these tothe storage and delivery of hydrogen forautomotive applications? Existing industrial codes and standards are rel-evant in that they are where you start todaywhen permitting a fuelling station. The flip sideis that they also present many challenges. Forstarters, the 25–75 ft set-back distances specifiedfor traditional hydrogen-storage systems fromcommon exposures can be very difficult toaccommodate in a commercial setting. At thesame time, today we must use compressed-NGV codes and standards as a basis for com-pressed-hydrogen vehicle systems – a weakposition in front of an AHJ [the local AuthorityHaving Jurisdiction], as the material-handlingproperties of hydrogen are unique.

Perhaps the most problematic issue of all isthat the high-pressure type 3 and type 4 NGVstorage tanks, which can currently be used as350 bar (hot-filled to 437 bar) on-boardhydrogen-vehicle storage systems, still can-not be used for commercial transportation ofcompressed hydrogen or for ground storageat fuelling stations. That’s despite the fact thatboth tank formats are approved by the USSociety of Automotive Engineers (SAE),ANSI-CSA America and ISO standards forcompressed-hydrogen vehicle systems.

How does the implementation of legalcodes and permitting work with respectto hydrogen safety in the US? There are now two code bodies – the NationalFire Protection Association (NFPA) and theInternational Code Council (ICC) – developingwhat are called “model codes”, which in turncompete for adopters. The competitionbetween the two model-code developers some-what complicates the whole issue, althoughthere is a significant degree of harmonizationbetween ICC and NFPA, and various “interestedparties” are proposing changes in the modelcodes that address the needs of the hydrogenand fuel-cell community.

Every municipal area has an AHJ and code-enforcement officials. Depending on thebudget and preferences of local agencies, eachwill adopt versions (typically not the latestversion) of the combination of codes they pre-fer. In some cases, whole states will adopt aseries of model codes. In other cases, there aredifferences at the county or city level, particu-larly regarding what “revision year” of a codehas been adopted by the AHJ. It’s a very frag-mented situation.

The primary organizations that I see drivingthese code changes are the CaFCP, the CGA,CSA America, DOE, ISO, NHA, NREL and the

SAE. Two of the most significant initiatives arebeing taken forward by the SAE, which isdeveloping on-board vehicle-hydrogen stan-dards and dispenser-to-vehicle interface stan-dards, and CSA America, which is developing ahydrogen-fuelling-station standard based onthe NGV standard. The CSA work is moving ata very fast pace to get an early first version outto support the current DOE demonstrations,beginning in early 2005.

The ICC recently announced a series ofupdated codes relating to hydrogenstorage. How significant is this?The changes being written into the 2004 ICCcodes are very important as they will form areference document that code officials andhydrogen-fuelling-station designers can use toenable some of the most current thinking. For

example, the new code has wording that willallow the underground storage of liquid hydro-gen, thus opening one door that may lead toreduced set-back distances.

The suggestion that the compressed-hydro-gen storage at a hydrogen fuelling station canbe mounted overhead, either on top of the dis-penser canopy or on top of the conveniencestore, is sensible, while the changes withrespect to metal-hydride storage systems willalso help to remove the barriers to commercialapplication of this technology.

Further readingA useful summary of hydrogen codes andstandards from the North American perspec-tive can be found at www.eere.energy.gov/hydrogenandfuelcells/codes/guidelines.html.Joe McEntee


NEWS & ANALYSIS

10

BOC describes itself as a provider of “safeengineering services” to the emerginghydrogen and fuel-cell energy market. “This is anatural fit for BOC because of the knowledgeand experience gained from building andoperating [industrial] hydrogen plants aroundthe world,” said Stewart Dow, manager,hydrogen energy and fuel cells for BOC GroupUK. “It is imperative that every installation is assafe as it can practically be for this embryonicindustry to succeed.”

The company is involved in a number ofhigh-profile hydrogen and fuel-cell projectsaround the world. In South Africa, for example,its local subsidiary Afrox worked with UK fuel-cell company Intelligent Energy on one of theregion’s first fuel-cell installations. Thehydrogen fuel cell provides primary power toan essential reservoir-level monitor.

“The safety challenge with the project wasthat it demanded the installation of compressedhydrogen in a non-industrial, non-secure,unmanned environment,” explained Dow. “Itwas felt that the only sustainable solution wasto put hydrogen cylinders into a secure cabinet,despite this not being normal procedure.”

In the absence of specific codes for fuel cells,the safety case for the installation was made bythe careful use of technology (excess flowvalves, hydrogen detection, pressure reliefvalves and assessment of ventilationrequirements) coupled with a detailed hazardand operability study. The team also workedclosely with the local fire service to address anyconcerns they might have had. Dow added:“Such an approach is acceptable for one-offinstallations but could never be justified on an

economic basis for a large number ofinstallations. The need for sensible codes andstandards is clear.”

He says that BOC always, as part of itsinternal procedures, develops a full safety caseand risk analysis for installing any hydrogensystem. “The rules and guidelines for hydrogensafety were developed for industrialapplications,” said Dow, “though these samerules need to be adapted for the new hydrogenand fuel-cell industry – and the best way to dothat is through demonstration projects.”

A case in point is the company’s involvementin the EC-sponsored CUTE (Clean UrbanTransport for Europe) bus project (see p7). Incollaboration with BP, engineers from BOCdesigned and constructed a hydrogen refuelleron the BOC Hackney gases site. The refuellerprovides hydrogen for London’s three fuel-cell-powered buses.

Real-world experience is what really counts

Power to the people: as part of its work on theCREST project in the UK, BOC deployed ahydrogen installation for a private house(above). Its team worked with the architect,the owner and health and safety officials.

http://www.eere.energy.gov/hydrogenandfuelcells/codes/guidelines.html

http://www.fuelcelltestingsystem.com

http://fcr.iop.org

http://www.umicore.com

Upton, NY: Researchers at the USDepartment of Energy’s Brook-haven National Laboratory and theNew Jersey Institute of Technologyhave taken a big step towards under-standing how titanium reacts withsodium alanate, a hydrogen-stor-age material, to catalyze the releaseand reabsorption of hydrogen.

The results, published in thejournal Applied Physics Letters (19July), may help scientists to learnhow similar catalysts work, whichcould lead to improved perform-ance and possibly the developmentof more efficient storage materialsfor hydrogen fuel cells.

In the late 1990s, it was discov-ered that adding a small amount oftitanium to sodium alanate allowsthe latter to reversibly release andreabsorb hydrogen. In a sense, thetitanium dopant acts like a molec-ular “key” to facilitate hydrogenabsorption. Until now, however,

the nature of that reaction was notwell understood.

“We found that the titaniumresides on the surface of sodiumalanate as a titanium–aluminiumcompound called titanium alu-minide, rather than entering the

bulk material and replacing otheratoms or occupying empty spotswithin the lattice,” said the study’slead author, Brookhaven physicistJason Graetz.

Graetz and his collaborators firstprepared two titanium-doped sam-ples by mechanically mixing tita-nium chloride and sodium alanateusing a planetary mill, a device thatgrinds substances together usingmarble-sized metal spheres. Theythen prepared four additional sam-ples, two from each of the maindoped samples: of these, one batchwas dehydrided (containing noabsorbed hydrogen) and the otherhydrided. The researchers werethen able to study the titanium’sproperties before and after hydro-gen absorption. This gave them onemore way to evaluate titanium’srole in the reaction.

The group probed the sampleswith high-energy X-rays at the

National Synchrotron Light Sourceat Brookhaven. From the resultantX-ray absorption spectra, they wereable to determine that the titaniumchloride reacted with sodiumalanate to form titanium aluminide.

“Our finding is the first steptoward an even more interestingdiscovery: determining exactlyhow titanium aluminide helps thehydride release and reabsorbhydrogen,” Graetz added. “Under-standing that mechanism may helpus identify better catalysts for thesodium-alanate system and help usfind dopants for new compoundsthat are currently impracticalenergy-storage materials, due tothe high temperatures and pres-sures required for the release andreabsorption of hydrogen.” ● For a detailed review of hydrogen-storage materials, see “Hydrogenstorage: the grand challenge” in theJune/July issue (p17).

R&D FOCUS


A survey of cutting-edge research, development and innovation.

Hydrogen storage is a complex affair

Key reactions: Brookhavenphysicist Jason Graetz hopes hiswork will lead to more efficientforms of hydrogen storage.

Newport, Ore: Over the past twoyears, scientists have successfullytapped the chemical reactions fromdecomposing organic matter onthe ocean floor to create demon-stration fuel cells that provide lowlevels of electrical power for manymonths. Earlier this summer,though, Oregon State University(OSU) researchers moved thingsforward by harnessing the samepower-producing decompositionactivity from plankton taken fromthe upper water column.

“We’ve only had the experimentsrunning for about four weeks,” saidClare E Reimers, a professor in theCollege of Oceanographic andAtmospheric Sciences at OSU, “butit is clear that we can use planktonas a fuel source and that the watercolumn is rich in microorganismsadept at shuttling electrons to fuel-cell electrodes.”

The seafloor fuel cells that OSUdeveloped previously are station-ary and designed to provide powerfor equipment that doesn’t move –

like the hydrophones used by theUS Navy or by OSU researchers forlistening for earthquakes.

“But by harnessing planktonpower,” Reimers added, “we couldpotentially fuel autonomous,mobile instruments that wouldglide through the water scoopingup plankton like a basking shark,and converting that to electricity.Such instruments carry sensorsand are used today to map thechanging chemical and physicalproperties of the ocean.”

In three seafloor experiments todate, OSU researchers and col-leagues at several US institutionshave tested prototype fuel cellsconsisting of graphite anodes shal-lowly embedded in marine sedi-ments and connected to graphitecathodes in the overlying seawater.They found that power was gener-ated both by the direct oxidation ofdissolved sulphide – which is aby-product of microbial decom-position – and by the respirationprocesses of microorganisms thatattached themselves to the anode.

Over the past couple of months,OSU has been testing the fuelcapacity of plankton. Using thesame principle as the seafloor fuelcells, the researchers have so farmanaged to direct about 10% of theenergy associated with planktondecomposition into a usablepower source. Reimers added:“Our focus is on developing powerfor oceanographic equipment.Who knows what spin-offs willdevelop beyond that?”

Plankton fuel cells take the plungeNanofabricationsenses new goalsAlbany, NY: Albany NanoTech,one of the world’s largest centres ofexcellence in nanotechnologyresearch, is extending its hydrogenand fuel-cell activities. With morethan $250000 of new funding in thebank – around 80% of it from theUS Department of Energy (DOE) –the centre has initiated a pro-gramme to develop a range of opti-cal sensors for fuel-cell applications.

The DOE cash will support thedevelopment of nanoscale chemi-cal sensors to monitor minuteamounts of hydrogen and otherhazardous gases in solid-oxidefuel-cell systems (operating at500–1000 °C). The rest of the funds(just over $60 000 from the NewYork State Energy Research andDevelopment Authority, orNYSERDA) will be channelled intoR&D on nanofabricated (20 nmthick) palladium alloy films, theoptical properties of which willform the basis of all-optical hydro-gen-safety sensors.

Plankton power: OSU’s researchon biological fuel cells is fundedby the US Department of Defense.

http://www.fideris.com

Superheating unit could well be hot stuff FuelCell Energy, US, has developed a fuel-cell-stack end unit thatcontains an integrated heat exchanger for superheating fuel gas beforedelivery into the stack (WO 2004/061998). It’s a set-up in which heat istransferred from the hot cathode outlet stream to the cool fuel inletstream in a space adjacent to the stack’s end plate. The end unit –designed as a hollow box to form a shell around the heat exchanger –has openings that allow fuel-cell process gas to be taken directly fromthe stack without the need for piping or duct-work to be attached tothin manifolds. According to the filing, “separate chambers areprovided for both the cathode-outlet and anode-outlet gas, therebyallowing all process connections to be made at one end of the stack”.The end unit also features a current-collection post that is separatedfrom the end cell of the stack by a number of members. These membersprovide structural support for the end unit and more uniformcollection of electrical current than a single, large current post.

Deionization helps to keep things coolA device for deionizing the cooling medium that circulates througha fuel-cell stack is detailed in international patent applicationWO 2003/061044 (revised 8 July 2004). Developed by BASFAktiengesellschaft, Germany, the deionizing unit sits within the fuelcell’s cooling circuit in such a way that a liquid deionizing agent canact upon the cooling medium on an intermittent basis. Thedeionization device can comprise static mixers, with membraneseparators connected downstream.

Material magic yields new-look membranesResearchers at Creavis Gesellschaft für Technologie und Innovation,Germany, have published details of a new class of proton-conductingceramic membrane based on zirconium phosphates(WO 2003/069712; revised 1 July 2004). Processing begins with theproduction of nanoscale zirconium phosphate in a microjet reactor.This material is then applied as a suspension onto a flexible carrier,after which it undergoes solidification. The result is a flexiblecation/proton-conducting membrane that is impermeable to othermaterials. Creavis claims that the new materials can form the basis of amembrane-electrode assembly “without any problem”.

Inner space: biological fuel cells power upTherasense, US, has unveiled details of a miniature biological fuel cellthat it claims could one day find applications as a power sourceimplanted inside the human body (WO 2003/106966; revised 1 July2004). The invention comprises an anode in electrical communicationwith an anode enzyme and a cathode in electrical communication

with a cathode enzyme. Redox polymers serve to “wire” the respectiveenzymes to their electrode, while the cathode enzyme operates underphysiological conditions. The inventors say that their fuel cell does notrequire a membrane seal or case.

There’s more than one right answer Two US companies have come up withdifferent takes on the storage and delivery ofliquid fuels for portable electronic devicespowered by polymer-electrolyte-membranefuel cells. Silicon Valley-based PolyFuel, forexample, detailed a removable fuel cartridge(shown left) comprising a flexible bladder, anexpandable pressure member (to maintain apositive pressure on the bladder) and ascalable exit port for the fuel

(WO 2004/051781). The delivery system channels fuel from the exitport to the fuel side of the polymer membrane. Meanwhile, Foamex ofPennsylvania revealed an orientation-independent fuel reservoircomprising a fuel container; a wicking structure from which the fuelmay be metered (such as by pumping); a retainer to hold the wickingstructure in a desired orientation; and a fuel outlet that links to thewicking element (WO 2004/027243).

Cathode protection can combat corrosionA fuel-cell design incorporating a corrosion-resistant and protectedcathode catalyst layer is described in international patent applicationWO 2004/061999, filed by UTC Fuel Cells, US. The cathode catalystlayer includes a platinum oxygen-reduction catalyst and an oxygen-evolution catalyst. The latter, selected from the group that is moreactive than platinum, can either be uniformly applied within thecatalyst layer or non-uniformly applied to high-corrosion areas. UTCsays the cathode catalyst may include heat-treated carbon supportmaterial and/or a heat-treated carbon black.

In fabrication, simplicity equals successA simplified method for bonding and edge-sealing a fuel-cellmembrane-electrode assembly (MEA) has been revealed by 3M ofthe US (WO 2004/062015). The key steps look like this: providing a suitable MEA lay-up; positioning an annular layer of thermoplastic;and applying pressure and heat sufficient to impregnate thethermoplastic into the fluid transport layer(s) of the MEA lay-up,simultaneously bonding those layers to the MEA’s polymer membrane(which may be perforated in its outer sealing area). 3M is also seekingpatent protection for MEAs made using the new approach.

PATENTS


Magnetic attraction is not a distractionScientists at the Commissariat à l’Energie Atomique, France, havedeveloped a fuel cell that exploits a magnetic cathode and astatic-pumping configuration to generate electrical power fromoxygen and hydronium ions (H3O+). According to internationalpatent application WO 2004/054018, the cathode comprises anactive layer and a proton electrolyte, with the latter sitting betweenthe anode and cathode. The invention also contains a network ofpermanent magnets to increase oxygen diffusion. Ideally, the centresof the magnets are distributed in a plane “that is disposed at theinterface between the electrolyte and the active layer... In this way, allof the poles of one polarity (S) are surrounded by the active layer, allof the poles of the opposite polarity (N) by the electrolyte”.

proton electrolyte active layer

anode

oxygen

S

S

S

S

N

N

N

N

array of permanent magnets

cathode

fuel

The pick of the latest international patent applications.

fuelbladder

pressure member

http://www.mst-technology.com


FEATURE: COMPONENTS & SYSTEMS

IS FUEL CELL technology on the verge of going mainstream?Could be – at least if the world’s leading consumer electronicsmanufacturers get their way. Heavyweight players such asSony, Toshiba and Nokia are investing serious money in thedevelopment and commercialization of the direct-methanolfuel cell (DMFC), a system in which methanol fuel is electro-oxidized directly, without any preprocessing, to generate elec-trical power. They’re betting that the payback will be anext-generation power source that revolutionizes the per-formance and ease-of-use of all sorts of portable electronicgadgets – including mobile phones, laptop computers, videocameras and plenty more besides. And what makes all thiseven more intriguing is the fact that some of these companiesare talking in terms of months rather than years when it comesto DMFC-based new product launches (see p25).

To put the emergence of the DMFC into context, however, it’sworth revisiting a few of the fundamentals of the fuel cell itself– in particular, the relative merits of different fuels. After all,from the electrochemical and specific-energy (energy per gram

of fuel) point of view, hydrogen is the most suitable fuel for fuelcells. The hydrogen oxidation reaction is a simple electro-chemical process, in which a diatomic molecule (H2) is con-verted to two hydrated protons (2H+

aq). The process takes placeefficiently on different electrode materials, of which platinum(Pt), palladium (Pd) and nickel (Ni) are the best performers.Unfortunately, hydrogen turns out to be difficult to store, espe-cially in portable applications.

No efficient, practical method of storing hydrogen for fuel-cell applications currently exists.1 So while liquefaction leadsto a form of hydrogen that’s potentially attractive for use inlarger fuel-cell systems, the energy density is low(2.70 Wh/cm3) because of the ultralow gravimetric density ofthe fuel. Furthermore, once the energy expended during theliquefaction process is taken into account, the energy densityis lowered still further, by as much as 40%. On the fringes of thetechnology spectrum, reversible storage of hydrogen in metalhydrides has been limited to date in terms of the achievablespecific energy (Wh/g hydride).

Researchers redefine the DMFC roadmap

PIOTR PIELA AND PIOTR ZELENAY

A two-part special report on direct-methanol fuel cells kicks off with a review of the R&D advances that have pushed the technology into the first phase of commercialization for portable power sources.

Mobile markets: but further innovation will be needed if electronics manufacturers are to fast-track the uptake of DMFC technology.

▲▲

It’s all about the fuelThe problems associated with hydrogen generation and stor-age have led the R&D community to focus on developing alter-native, mostly organic, fuels for use in polymer-electrolyte fuelcells (see table, “Fuels for direct-feed polymer-electrolyte fuelcells”). There are two main ways to utilize such fuels in a low-temperature polymer-electrolyte fuel-cell system:

● On-board processing, which involves extensive, multisteppurification of the fuel, after which the resultinghydrogen-rich gas mixture is supplied as a feed stream tothe fuel cell.

● Direct electro-oxidation of the fuel at the fuel-cell anode.

The former typically involves several catalytic reactors in series,a system often seen as too complex for reliable power deliveryover long timeframes and reasonably broad conditions of oper-ation. The latter approach is far simpler as it requires only one cat-alytic converter – the fuel cell itself. Nevertheless, there are majorchallenges, as high-rate, direct electro-oxidation of a carbona-ceous fuel molecule at the fuel-cell anode is far more demandingcatalytically than the electro-oxidation of dihydrogen.

When it comes to the choice of fuel, the energy content perunit weight or volume is one of the key figures of merit. Of thefirst five options listed in the table above, the four carbonaceousfuels can be oxidized only at temperatures much higher than100 °C, and even then not without problems. Of the two alco-hols next on the list, methanol can be electro-oxidized all theway to CO2 at temperatures well below 100 ºC, but ethanol can-not. This has been explained by the catalytically more demand-ing C–C bond activation in the case of ethanol.

Even so, other molecules with C–C bonds have been shown toelectro-oxidize completely to CO2 at temperatures well below100 ºC – one example being ethylene glycol.2 The big differenceseems to be the higher degree of “oxygenation” of the fuel mole-cule, reflected by an atomic oxygen:carbon ratio of ≥1. Thisapparent condition is fulfilled for methanol and ethylene glycol,but not for ethanol; and while the former two fully electro-oxi-dize to CO2 at low temperatures, the ethanol does not. Furtherdown the list are two substances – formaldehyde and formicacid – that are essentially partly oxygenated methanol. Both areeasy to oxidize to CO2 at low temperatures, as is oxalic acid

(though being highly oxygenated, they are less energy-dense). Health and environmental issues are likely to exclude the final

two options, ammonia and hydrazine, from widespread use infuel-cell systems. Of all the partly oxygenated fuel moleculesthat undergo complete electro-oxidation at low temperatures,methanol is the one that exhibits the best combination of energydensity and rate of electro-oxidation.

DMFC processesIn a DMFC, methanol (typically together with water) is suppliedto the anode, where it undergoes electro-oxidation to CO2 withthe release of six electrons to the load (figure 1). To date, mostof the systems described in the open literature involve a liquidmethanol–water feed, although in some platforms themethanol fuel can be supplied to the DMFC anode as a vapour.Electrons are subsequently transferred via the external circuit(which includes the load) to the cathode, where they are utilizedin the reduction of oxygen supplied to the cathode from air.

The reactants and mobile species in the electrolyte are inti-mately tied to the pH of the fuel-cell electrolyte. At low pH lev-els, water is consumed in the anode process together withmethanol, while protons are transported from the anode sideacross the electrolyte and consumed in the cathode process toform water. This is the case for the polymer-electrolyte fuel cell,as it is based on a proton-conducting poly(perfluoro-sulphonicacid), known as poly(PFSA), membrane.

In high-pH systems, on the other hand, the effect is reversed:water is now consumed on the cathode side of the cell in theoxygen-reduction process, forming hydroxyl ions. These ionsare transported across the cell to the anode, where they are con-sumed together with methanol fuel to form CO2. Equations 1


COMPONENTS & SYSTEMS

18

Fuel Fuel-cell reaction Specific Energy energy density(Wh/g) (Wh/cm3)

Hydrogen H2 + 0.5 O2 → H2O 33.0 2.7*

Carbon C + O2 → CO2 9.1 19.2

Methane CH4 + 2 O2 → CO2 + 2 H2O 14.2 6.0*

Propane C3H8 + 5 O2 → 3 CO2 + 4 H2O 13.3 6.6*

Decane C10H22 + 15.5 O2 → 10 CO2 + 11 H2O 12.9 9.4

Methanol CH3OH + 1.5 O2 → CO2 + 2 H2O 6.1 4.8

Ethanol C2H5OH + 3 O2 → 2 CO2 + 3 H2O 8.0 6.3

Ethylene glycol C2O2H6 + 2.5 O2 → 2 CO2 + 3 H2O 5.3 5.9

Formaldehyde CH2O + O2 → CO2 + 2 H2O 4.8 3.9*

Formic acid HCOOH + 0.5 O2 → CO2 + H2O 1.7 2.1

Oxalic acid C2O4H2 + 0.5 O2 → 2 CO2 + H2O 1.0 2.0

Ammonia NH3 + 0.75 O2 → 0.5 N2 + 1.5 H2O 5.5 3.9*

Hydrazine N2H4 + O2 → N2 + 2 H2O 5.2 5.3

* Based on the density of liquefied gas

Fuels for direct-feed polymer-electrolyte fuel cells

Low pH: 1.5O2 + 6 H+ +6 e →3H2OHigh pH: 1.5O2 + 3 H2O + 6 e →6 OH–

Equation 2. DMFC cathode reaction

Low pH: CH3OH + H2O →CO2 + 6 H+ + 6 eHigh pH: CH3OH + 6 OH– →CO2 + 5 H2O + 6 e

CO2 + OH– →HCO3–

Equation 1. DMFC anode reaction



19

and 2 describe, correspondingly, the anode and cathode reac-tions at both low and high pH levels. The overall methanol fuel-cell reaction, as shown in the table, is identical to that forcombustion of methanol by direct reaction with oxygen.

High-pH electrolytes can promote higher rates of methanoloxidation at a given temperature, because an alkaline environ-ment facilitates the formation of the active surface-oxygenspecies required for completion of the methanol electro-oxi-dation process. However, a serious obstacle associated withhigh-pH fuel cells is the absence of a hydroxyl-ion-conductingmembrane offering conductivity and reliability as good as thatof the poly(PFSA) membranes. Furthermore, the introductionof the liquid-alkaline electrolyte brings its own challenges:chiefly, the formation of bicarbonate ions (see equation 1).

As a consequence, most recent DMFC development activityhas focused on the proton-conducting polymer-electrolyteconfiguration shown in figure 1. The membranes in questionhave been primarily of the poly(PFSA) type, such as Nafion,although alternatives do exist at various stages of developmentand supply. One example of the latter is the Z1 membrane fromPolyFuel, based in Mountain View, California, US.

Methanol at the anodeElectro-oxidation of methanol is a six-electron process (see equa-tion 1) that, like other complex electrochemical reactions involv-ing multi-electron transfer, proceeds via a reactant adsorptionstep at the electrode surface, followed by a one-by-one transferof electrons from the molecule to the electrode. While providingsufficient bonding of a methanol molecule, Pt allows fastremoval of the four hydrogen atoms from the adsorbed moleculeonto adjacent Pt metal sites (dehydrogenation step), a processfacilitated by the high affinity of Pt metal sites to hydrogen atoms.

Thanks to this high level of dehydrogenation activity, theonset of electro-oxidation of methanol on pure Pt takes placeat a potential as low as 0.2 V on the hydrogen reference scale.However, this initial process is limited to dehydrogenationalone and is therefore not sustainable at such a low anode

potential. The adsorbed CO moiety, remaining on the Pt cata-lyst surface following the initial dehydrogenation step(s), canbe electro-oxidized at a Pt electrode only at a significantlyhigher electrode potential.

Consequently, continuous electro-oxidation of methanol toCO2 can be sustained at a Pt electrode only above 0.6–0.7 V. Atthese higher potentials, surface oxide (or hydroxide) startsforming on the Pt surface from adsorbed water. This surface-oxygen species is crucial for the completion of the methanoloxidation process, as it converts the adsorbed CO intermediateremaining after methanol dehydrogenation to CO2. The widelyaccepted mechanism of methanol oxidation on Pt reflects thissequence of methanol dehydrogenation followed by electro-oxidation of adsorbed CO, as shown in equation 3 overleaf.

Meanwhile, the search for a methanol electro-oxidation cat-alyst exhibiting higher activity than that of Pt has been directedat materials which, as well as maintaining high methanol dehy-drogenation activity, facilitate the rate-determining step of thereaction (i.e. CO electro-oxidation). Researchers have focusedprimarily on alloys of Pt with metals possessing a higher affin-ity with oxygen, with the most successful composition discov-ered to date being a binary alloy of Pt with ruthenium (Ru).

At 70 °C, for example, Pt–Ru alloys in which the atomic frac-tion of Ru varies between 0.3 and 0.6 will support complete,sustained methanol electro-oxidation at an anode potential of0.25–0.30 V. That’s well below the anode potential required forthe same process at a pure platinum catalyst. This methanolanode-potential range corresponds to an anode loss (DMFCcell voltage loss due to the anode) of 0.20–0.25 V. And consid-ering the “direct” nature of the fuel cell (no losses in fuel pro-cessing steps upstream of the fuel cell), such an efficiency lossdue to the anode (≤20% of total fuel energy content) is suffi-ciently low to make DMFC technology commercially viable.

So how does adding Ru to Pt lower the potential for completesix-electron methanol oxidation, compared with that foundusing Pt alone? One explanation that has been put forward isthe so-called bifunctional effect. This considers the significant

Operational principle of the proton-conducting, polymer-electrolyte DMFC. Methanol is supplied to the anode, usually with water,where it undergoes electro-oxidation to CO2. Electrons pass to the cathode, where they are used in the reduction of oxygen.

1. DMFCs: they’ve got the power

H+

H2O

CH3OH

Electroosmoticdrag

H+

H2O

CH3OH

Electroosmoticdrag

H+

H2O

CH3OH

Electroosmoticdrag

anode cathode

3H2OCO2 + 6H+ + 6e–

CH3OH + H2O

CH3OH(aq)

H2O

H+

electro-osmoticdrag

O2 (air), H2O

6H+ + 1.5O2 + 6e–

e–

CH3OH

methanol and, particularly, hydrogen affinity of Pt electrocat-alysts in aqueous environments and, on the other hand, thefacile oxidative water decomposition on Ru to form a surfaceoxygen species in aqueous electrolytes.3 Accordingly, thebifunctional mechanism involves the initiation of the surfaceprocess at a Pt–Ru catalyst with the dehydrogenation steps tak-ing place at Pt surface sites, whereas Ru sites assume the role ofproviding the oxide/hydroxide species required to complete theoxidation of surface CO. The overall anode process at Pt–Ru isthe same as in equation 3 down to the final two steps, which inthe case of the Pt–Ru alloy are described by equation 4.

Electronic effects provide another possible interpretation ofthe observed benefit of adding Ru to Pt.4 According to this the-ory, added Ru lowers the electron density in the 5d band of Pt,resulting in a shift of electronic charge from adsorbed CO to themetal catalyst and thereby facilitating oxidation of theadsorbed CO. Of the two interpretations offered, the formationof a bifunctional surface – with discrete sites of high dehydro-genation activity and of high surface-oxygen formation activity– is generally believed to be the more important.

As equation 4 suggests, the electrocatalytic process of anodicoxidation of methanol takes place on metal sites. What’s more,there’s compelling experimental evidence – collected on thehighly dispersed, unsupported Pt–Ru catalysts employed inDMFC anodes – that the significant amounts of various Ruoxide species present in such dispersed alloy samples have noactive role in the methanol electro-oxidation process. In fact,excess oxide coverage on the Pt–Ru metal alloy sites inhibits therate of methanol electro-oxidation – as evidenced, for example,by the benefits produced by prereduction treatments.5

Finally, it’s worth noting that the rate of methanol oxidationon Pt–Ru is strongly dependent on temperature, with high per-formance obtained near and above 100 ºC.6 Such a temperatureregime, however, is not compatible with simple stack/systemhardware and long-term performance stability – and is partic-ularly impractical for smaller, portable power sources. If suffi-cient methanol oxidation rates at 40–80 ºC are to be achieved,

the active surface area of the anode catalyst needs to be fairlyhigh, which in turn requires significant loading of Pt–Ru (typi-cally used in the form of a “black” or unsupported catalyst).

When aiming for maximum power, the Pt–Ru loading is ofthe order of several mg/cm2 of cross-sectional (geometric) areaof the electrode. Since similar precious-metal loading has beenrequired to date for the cathode as well, the overall precious-metal loading can be as high as 10 mg/cm2. However, the emer-gence of alternative DMFC membrane-electrode assemblies(MEAs) – such as those developed at Los Alamos NationalLaboratory – could allow system designers to cut down the cat-alyst loadings significantly, with relatively small losses in out-put power. This is possible because the power-outputdependence on catalyst loading in polymer-electrolyte DMFCsis highly nonlinear, with ever-decreasing incremental gains inpower for incremental increases in catalyst loading at a total cellloading exceeding 1 mg/cm2.

The dynamics of the cathodeJust like in a hydrogen fuel cell, the cathode reaction in a DMFC(equation 2) requires platinum to act as the oxygen-reductionelectrocatalyst. But while the major rate-limiting factor in thecathode process of hydrogen fuel cells is the sluggish interfa-cial kinetics of oxygen reduction, the DMFC cathode is addi-tionally challenged by penetration of methanol and waterthrough the membrane from the anode side of the cell. Highmethanol permeability in proton-conducting membranes isthe source of so-called “methanol crossover”. Once on the cath-ode side of the cell, methanol typically reacts with oxygen at thecathode catalyst to form CO2 and water. This amounts to a“chemical short” across the fuel cell, with the methanolcrossover corresponding to lost fuel.

In addition to the loss of fuel, the cell current at some givencathode potential (i.e. some given DMFC voltage) is lowered bya value corresponding to the current of methanol crossover atthat cell voltage. The result is a loss of output power. However,the flip side of the methanol crossover phenomenon is that it



20

DehydrogenationPt(electrode) + CH3OH →Pt(electrode)–COH + 3H+ + 3e

Pt(electrode) – COH →Pt(electrode)–CO + H+ + e

CO electro-oxidation (rate-determining step)Pt(electrode) + H2O →Pt(electrode)–OH + H+ + e

Pt(electrode) – CO + Pt(electrode) – OH→2 Pt(electrode) + CO2 + H+ + e

Equation 3. Mechanism of methanol oxidation on Pt

Ru(electrode) + H2O →Ru(electrode)–OH + H+ + ePt(electrode)–CO + Ru(electrode)–OH →Pt(electrode) + Ru(electrode) + CO2 + H+ + e

Equation 4. Final two steps of methanol electro-oxidation on Pt–Ru



21

can be used for two beneficial purposes: water generationwithin the cell when operating with 100% methanol feed (see“DMFCs power up for portable devices”, p25), and heat genera-tion to hike the temperature of the cell and bring it, at a higherrate, to some design temperature above ambient.

The permeation of water through the membrane and into thecathode is another cause for concern in DMFCs fed bywater/methanol liquid. Around 20 molecules of water appear inthe DMFC cathode per single methanol molecule oxidized at theanode, mainly as a result of electro-osmotic drag of water acrossthe membrane by protons. But a high water flux can easily“flood” the cathode, leading to performance loss. Consequently,effective removal of cathode water requires significant air flow atnon-zero pressure – such that the air pump (compressor) can bethe largest source of parasitic energy loss in the DMFC system.This also means that, to maintain the overall water balance, thesignificant mass of water leaving the cathode exhaust has to bereturned to the anode using condensers and pumps.

Alternative membranesOne of the fundamental challenges confronting DMFC pio-neers is the realization of proton-conducting polymers withreduced methanol permeability – particularly relevant for“mainstream” DMFCs based on water/methanol anode feeds.In these conventional designs, the high methanol permeabil-ity of poly(PFSA) membranes means that the local fuel con-centration in the anode flow field has to be maintained at levelsof less than 1 M methanol. This is necessary to achieve a suffi-ciently high ratio of cell current to crossover current, andthereby secure acceptable fuel utilization.

Yet operation with such a dilute solution was previously con-sidered impossible, based on a methanol permeation rate equiv-alent to about 0.1 A/cm2, measured across a 175 µm-thick Nafionmembrane (Nafion 117) in 1 M solution at approximately 70 °C.This rate of permeation is similar to the DMFC current densities,suggesting at first glance an unacceptable fuel utilization of no

better than 50%. Further work, however, has revealed that therate of methanol crossover can be cut significantly when the cellis under current, provided that the cell anode is designed to adjustthe concentration of methanol between the flow field and themembrane surface without, at the same time, generating a too-severe limitation on mass transport.7

By lowering the crossover in this way, it is now possible toachieve fuel utilizations as high as 90% with commercialpoly(PFSA) membranes such as Nafion, provided that the feedconcentration is dropped to ≤1 M. On this basis, a number ofcompanies have reported rapid and encouraging progress interms of the development and manufacture of viable DMFCsources. Still, it’s clear that further significant advantages willaccrue if the R&D community can come up with membranesthat combine lower methanol permeability with Nafion-levelprotonic conductivity. Such membranes will enable more con-centrated anode feeds; less exacting control of methanol con-centration in the anode feed loop; and an ability to maintainhigh fuel utilization under dynamic load conditions.

The key is going to be overcoming the strong tie between pro-tonic conductivity and high methanol permeability in polymermembranes (both properties scaling with water content). Theschemes attempted so far have been mostly based on either“seeding” the poly(PFSA) membrane with highly dispersedhydrophilic oxide, or varying the polymer nanopore networkstructure by modifying the polymer’s chemical nature toachieve essentially the same effect of enhancing the proton-to-methanol mobility ratio.

After several years of work along these lines, a number ofgroups have reported promising results. In 2003, PolyFuelannounced that it was ready to manufacture its proprietary Z1membrane.8 Compared with the most commonly usedNafion 117, the Z1 membrane is characterized by a threefoldreduction in both methanol and water permeation, without asignificant decrease in proton conductivity.

Elsewhere, a joint effort between Virginia Polytechnic

Performance matters: fuel-cell test set-up at Los Alamos National Laboratory. Inside the chamber is a high-power-density 23-cellDMFC stack, designed and built at Los Alamos. On the right is a close-up of the DMFC stack inside the test chamber.

Institute (Blacksburg, Virginia, US) and Los Alamos NationalLaboratory has resulted in the successful development ofDMFC membranes based on fully aromatic poly(arylene ethersulphone) copolymers, with comparable proton conductivityto that of the reference Nafion polymer, but almost three timeslower methanol permeability. In-cell testing of partially fluori-nated derivatives of poly(arylene ether sulphone) copolymersshowed excellent interfacial compatibility of such cell mem-branes with Nafion-based catalyst layers – a prerequisite foradvancing from membrane to complete MEA – resulting in bet-ter DMFC performance and comparable long-term stability tothat of the reference Nafion polymer.9

Performance stabilityWork on advanced catalysts and membranes notwithstanding,it is the long-term stability and durability of DMFCs that willgo a long way towards determining the success or otherwise ofcommercial products out in the marketplace. As with otherfuel-cell systems, however, the extensive study of DMFC per-formance decay over, say, 103–104 h of operation is very much awork in progress.

Figure 2 illustrates the measured drop in current with time ofa single-cell DMFC operating at 75 ºC with a 0.3 M methanolfeed. The total loss of about 40% of the initial current after 3000h can be resolved into recoverable and unrecoverable losses,where the recoverable portion is defined as the loss that can bereversed by interrupting the steady-state operation of theDMFC. The following phenomena have been identified as beingresponsible for the degradation of DMFC performance overextended operating periods:

● Surface oxidation of the cathode catalyst (recoverable);● Cathode flooding;● Ru migration from anode to cathode and subsequent

deposition of Ru at the cathode; and● Loss of active-catalyst surface area on either electrode.

Let’s take a look at each of these contributory factors in moredetail. When a DMFC is operated at a higher voltage targetinga high conversion efficiency (as in figure 2), the cathode poten-tial is sufficiently high (≥0.8 V) to encourage a slow, continuousprocess of Pt surface oxidation. This Pt surface-oxide build-up(and/or “ageing”) has been shown to significantly acceleratewith temperature at a given cathode potential inside the“Pt-oxide range”. Such surface-oxide formation inhibits the rateof oxygen reduction at the cathode, reflected in a gradual drop-off in DMFC performance over time. This decay-causingprocess can be reversed, however, by very short, periodic low-ering of the cathode potential (i.e. by brief lowering of the cellvoltage), resulting in electroreduction of the surface oxide andregeneration of active Pt sites. This component of the decay isconsequently recognized as being (a) recoverable, and (b) lesslikely to have similar magnitude at lower cell voltages.

The phenomenon of cathode flooding, meanwhile, has beenamply documented for low-temperature fuel cells in general. Itresults from slow accumulation of water at the cathode catalyst

layer and/or gas-diffusion layer (backing), often caused by amismatch between the water-generation rate under high cur-rent operation and the air flow/pressure; a temperature dropthat causes local condensation; or, particularly, by gradual lossof the hydrophobic properties of the backing. Flooding can bepartially reversed by stopping the cell and letting the cathodedry for a while, possibly assisted by a stream of dry air. Andwhile some of the performance loss is unrecoverable, becauseof the generally irreversible nature of the change in thehydrophobic properties of the cathode backing, it’s likely thatfurther improvements in overall design and wet-proofing ofthe backing layers will help to mitigate the problem.

Migration of Ru through commonly used DMFC mem-branes and its deposition at the cathode is another perform-ance-loss mechanism that was recently studied in detail at LosAlamos National Laboratory.10 Ru negatively impacts on thecathode performance, as the Ru-covered Pt surface is an infe-rior electrocatalyst for oxygen reduction and a better catalystfor oxidation of crossover methanol than pure Pt. Both effectstypically lead to a lowering of the cathode potential (cell volt-age) by as much as 40–50 mV, but in extreme contaminationcases, possibly resulting from cell “maltreatment”, this losscan reach 200 mV.

Ru migration appears to be caused by the nature of the activePt–Ru blacks (unsupported catalysts) commonly used in theDMFC anode. In liquid-fed DMFCs with significant net waterflux from anode to cathode, Ru species, most likely nanoparti-cles of RuO2 (abundant in Pt–Ru black catalysts), tend to leachfrom the anode catalyst, and ultimately end up on the other sideof the cell. The resulting cathode contamination by Ru is largelyirreversible. Evaluation of the phenomenon suggests that fur-



22

Scientists at Los Alamos National Laboratory recentlyperformed a 3000 h lifetime test on a single-cell, liquid-fedDMFC. Cell temperature was 75 °C; cell voltage was 0.5 V. Thecurrent spikes are caused by short interruptions in the steady-state operation of the cell, resulting in the reversal of“recoverable” performance loss.

2. Performance versus time



23

ther optimization of the anode catalysts – for example, reduc-tion in “loose” Ru oxide species in the anode catalyst – shouldhelp to minimize any migration.

Finally, it’s worth noting that the active surface area of bothelectrodes can be halved in less than 2000 h of cell operationunder the operation conditions shown in figure 2. And whilesurface-area loss of the anode is associated with a relativelysmall performance loss, a similar decrease in the surface areaof the cathode leads to a larger performance penalty.

Taking stockPolymer-electrolyte DMFCs have advanced on many fronts inrecent years. Alongside fundamental progress on the core elec-trocatalyst and MEA technologies, particularly Pt–Ru-basedanodes, an innovative approach to cell and system design hashelped developers get to grips with the problem of methanolcrossover – even when employing the “leaky”, but commer-cially available, Nafion membranes.

As a result, it is now possible to reach an areal power densityof 50 mW/cm2 at a relatively high cell voltage of 0.5 V (figure 2);a maximum areal power density (of between 200 and250 mW/cm2) is achievable at a voltage roughly 0.2 V lower atthe same cell temperature. This corresponds to a DMFC stackwith a potential power density and efficiency combination of150 W/dm3 and 30%. Figures of merit like this suggest thatDMFCs can provide a portable-power technology that is supe-rior to incumbent rechargeable batteries (see p25).

In summary, DMFCs are now about to enter the first phase ofcommercialization as small-scale power sources. Yet while thatcounts as a big leap forward, there is still plenty of scope for fur-ther progress – especially with respect to the kinetics of bothelectrode reactions. As far as fundamental research goes, thefollowing aspects need to be prioritized by the multidiscipli-nary teams tasked with moving things forward.

● Designing better and more stable anode catalysts thatincrease the rate of methanol oxidation, lower theprecious-metal loading and lower the cost.

● Developing methanol-tolerant cathode catalysts withPt-level activity.

● Increasing catalyst utilization through a combination of

better dispersion of catalyst particles and advanced designof electrode layers.

● Synthesizing polymer-electrolyte membranes withsignificantly reduced permeability to methanol and water,while maintaining high levels of protonic conductivityand performance durability.

When it comes to the catalyst, current DMFC MEA fabricationtechniques do not allow for utilization greater than 50–60%.What’s more, the possible advent of ultra-high-surface-area cat-alysts may actually lead to a further drop in utilization unlessmore sophisticated catalyst-layer-preparation techniques aredeveloped. Theoretical modelling of catalyst nano-array spatialgeometry will almost certainly shed light on this problem ini-tially, while further ahead the experimental use of nanotechnol-ogy tools for fuel-cell fabrication will open up all sorts ofintriguing opportunities for DMFC researchers.

Further reading1. R Harris, D Book, P Anderson and P Edwards 2004 “Hydrogen

storage: the grand challenge” The Fuel Cell Review June/July 17–23.2. E Peled, T Duvdevani, A Aharon and A Melman 2001 Electrochem. Solid-

State Lett. 4 A38.3. M Watanabe and S Motoo 1975 J. Electroanal. Chem. 60 275. 4. Y Tong, H S Kim, P K Babu, P Waszczuk, A Wieckowski and E Oldfield

2002 J. Am. Chem. Soc. 124 468.5. H Dinh, X Ren, F Garzon, P Zelenay and S Gottesfeld 2000 J. Electroanal.

Chem. 491 222.6. X Ren, M S Wilson and S Gottesfeld 1996 J. Electrochem. Soc. 143 L12.7. X Ren and S Gottesfeld 2001 US Patent No. 6 296 964.8. P Cox, S-Y Cha and A Attia 2003 Fuel Cell Seminar Book of Abstracts

977–980. Presented at 2003 Fuel Cell Seminar, Miami Beach, FL, US.9. Y S Kim, M J Sumner, W L Harrison, J S Riffle, J E McGrath and B S

Pivovar J. Electrochem. Soc. In press.10. P Piela, C Eickes, E Brosha, F Garzon and P Zelenay J. Electrochem. Soc.

In press.

Piotr Piela is a postdoctoral fellow and Piotr Zelenay is a technical projectleader in the Materials Science and Technology Division at Los AlamosNational Laboratory, New Mexico, US. The authors would like to acknowledgethe contribution of Shimshon Gottesfeld, vice-president and chief technologyofficer at MTI MicroFuel Cells, in drafting this article.

Editorial highlights coming up in issue 3 of The Fuel Cell Review:

Feature: Theoretical modelling of fuel cells – catalystsand membranes (Professor Michael Eikerling,Simon Fraser University, BC, Canada)

Feature: The emergence of a fuel-cell supply chain –an investment perspective (Neal Dikeman, Jane CapitalPartners)

Special report: Solid-oxide fuel cells – updates oncomponent reliability and testing; stack modelling anddevelopment; and low-temperature SOFCs.

Simply the best coverage ofhydrogen and fuel-cell R&D,technologies and applications.

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FEATURE: TECHNOLOGY TRANSFER

FUEL-CELL POWER sources have reached a defining moment onthe long and winding road to commercialization – at least as faras portable applications are concerned. In this low-power mar-ket segment, it’s now fair to say that micro fuel cells are meetingwith serious market pull, driven by consumer electronics man-ufacturers, incumbent battery suppliers and the US military.

For each of these interested parties, the end-game is the same:a next-generation power source with an energy density that sig-nificantly exceeds that of today’s leading-edge battery tech-nologies. In terms of the numbers, that means a source thatoffers an energy density well beyond 400 Wh/dm3 (0.4 Wh/cm3)and/or a specific energy of 200 Wh/kg (0.2 Wh/g), while alsoproviding the power required for the full dynamic range of theload in a given device.

Advanced power sources able to meet and beat those specifi-cations will allow greatly extended run times per recharge(refuel) for mobile phones, laptop computers and digital cam-eras – and the same goes for electronic gadgetry like night-vision goggles, global positioning systems and laser-targetingunits in the military arena. Perhaps even more significantly,higher-energy-density power sources are going to be essentialbuilding blocks in “converged” handheld communicationsdevices that combine the latest in colour-display technologywith voice, broadband data and video functionality – all in asingle power-hungry platform.

Fuel-cell system considerationsFor prospective manufacturers of fuel-cell power sources – inparticular, those based around direct-methanol fuel cells(DMFCs) – it’s time for a shift in mindset from prototypes anddemonstrators towards multigeneration product plans andlow-cost mass production. To take a closer look at the extent ofthis emerging opportunity, however, it is first necessary torevisit some of the key metrics of portable fuel-cell systemdesign and product engineering.

The big advantage of fuel cells over batteries in portable-power applications originates from the high energy density ofthe fuel. For low-temperature fuel cells (Tcell <100 °C) destinedfor handheld devices, the theoretical specific energies of the twomost suitable fuels are 33 Wh/g for hydrogen and 6.1 Wh/g for

methanol. By comparison, advanced rechargeable lithium-ionbatteries have a specific energy of around 0.2 Wh/g – less than1% of the energy density of hydrogen and 3% of that ofmethanol. In truth, such a comparison is skewed, because thebattery comprises a complete power source, with the chemicalreactants and the chemical-to-electrical energy-conversion

DMFCs power up for portable devices

SHIMSHON GOTTESFELD

Innovation in systems design and engineering will be critical if direct-methanol fuel cells are to make the final transition from prototype demonstrations into mass-market power sources.

Small times: a concept prototype of a DMFC power source basedon MTI Micro’s Mobion technology, shown integrated into anelectronic device. A Mobion fuel-cell array is shown separately.

components (the electrochemical cell) all in one package;whereas the fuel still has to be packaged with a chemical-to-elec-trical energy-conversion device (the fuel cell) plus any further“balance of plant”, including power conditioning and controls.

Furthermore, the actual effective energy content per unitmass of fuel carried in such a power pack is only a fraction ofthese theoretical values – that fraction being determined bythe energy-conversion efficiency of the fuel-cell system. Ifonly a fraction f wt

fuel of the total weight of a fuel-cell power sys-tem is the fuel itself, and the system’s overall energy-conver-sion efficiency (chemical-to-electrical energy) is ηsystem , thenthe specific energy, E wt

system (Wh/g), of the power pack will begiven by equation 1.

The specific energy of the complete fuel-cell power system,E wt

system , is the merit parameter that needs to be compared withthe specific energy of a rechargeable battery (which itself is acomplete power-generating system). So, for a fuel-cell power sys-tem in which methanol fuel accounts for 50% of the weight andthe system conversion efficiency is 25%, E wt

system is calculated,using equation 1, to be 0.75 Wh/g. In other words, the specificenergy advantage over a lithium-ion battery of 0.2 Wh/g is 3.75:1.

However, when it comes to carrying or supplying additionalenergy for extended use, the effective energy content of thereplacement fuel cartridge itself becomes the merit parameter.In applications involving multiple swaps of the cartridge, theweight of the fuel-cell system can be neglected altogether(equivalent to assuming f wt

fuel = 1 in equation 1). In this scenario,the specific-energy advantage of the fuel-cell system consid-ered above over a replacement lithium battery will be 7.5:1.

This significantly higher ratio (and stronger value proposi-tion) is relevant for cases of long use without recharge – in mil-itary applications, for example. It also comes into play in thecontext of the so-called “perfectly wireless world”, in whichlightweight replacement fuel cartridges could be used to elim-inate the need for cord connections between handheld devicesand a recharging power source. In the example given previ-ously, carrying replacement methanol cartridges for a cord-independent, fuel-cell-powered device will be 7.5 times moremass-effective than carrying replacement batteries.

Meanwhile, for really compact portable applications likemobile phones, it is often the volume rather than the weight ofthe power source that is the key figure of merit in terms of sys-tem packaging. Under these circumstances, it is the energy den-sity, rather than the specific energy, that is of greater interest.The equivalent of equation 1 will then be equation 2.

It is clear that designers must keep in mind the following pri-orities if they are to capitalize on the intrinsic energy-densityadvantage of the fuel in a fuel-cell power source.

● Maximize E wtfuel (equation 1) with:

a) Fuels of high energy density and significantelectrocatalytic activity at well below 100 °C;

b) Realistic fuel-storage options that maintain a largevolume/weight fraction of the neat fuel and that areacceptable for handheld, consumer electronicsapplications.

● Maximize f wtfuel (equation 1) by minimizing (1 – f wt

fuel), thefraction of the power-pack weight (or volume) occupiedby all energy-conversion components with no energycontent – i.e. the fuel cell plus any balance of plant (BOP).This necessitates:

a) Fuel-cell stack technology with the minimum weight(or volume) to generate the average power demand of aportable device. Put another way, a sufficiently highfuel-cell power density must be achievable under thebenign operating conditions dictated by handheldapplications;

b) A simple overall power system to minimize BOPweight/volume and increase overall reliability.

● Maximize ηsystem (equation 1) with a fuel-cell design thatmaximizes the two efficiency-determining factors:

a) Fuel utilization – that is, the conversion of fuel feed tocell current;

b) Fuel-cell voltage at the power demand by the load.

At present, the choice of fuel for portable power applications iseffectively limited to hydrogen and methanol. But, as discussedin the previous article (“Researchers redefine the DMFCroadmap”, p17), there are significant problems associated withthe storage of hydrogen for portable fuel-cell applications. Themost promising solution appears to be the use of metalhydrides or chemical hydrides (see “Chemical warfare”, The FuelCell Review June/July 2004 p10). In the former, controlled heat-ing is used to generate hydrogen, while the latter comprise ahydrogen-releasing solid (like sodium borohydride) that


TECHNOLOGY TRANSFER

26

E wtsystem = E wt

fuel × f wtfuel × ηsystem

Where E wtfuel is the theoretical specific energy of the fuel, expressed in

Wh/g of fuel actually stored in the system (for example, for a hydrideof 2% hydrogen by weight, E wt

fuel = 33 Wh/g ×0.02 = 0.66 Wh/g); f wtfuel

is the fuel-weight fraction in the fuel-cell system; ηsystem is the systemconversion efficiency for chemical energy of the fuel to electricalenergy to the load; and E wt

system (Wh/g) is the effective specific energyof the complete power pack.

Equation 1. Specific energy of the fuel-cell system

E vsystem = E vfuel × f vfuel × ηsystem

Here, E vfuel is the theoretical energy density of the fuel, expressed inWh/cm3; f vfuel is the fuel-volume fraction in the system; ηsystem is, asbefore, the system conversion efficiency for chemical energy of thefuel to electrical energy to the load; and E vsystem is the effective energydensity of the complete power system in Wh/cm3.

Equation 2. Energy density of the fuel-cell system


TECHNOLOGY TRANSFER

27

undergoes a controlled reaction with water. A variant has alsobeen proposed based on direct electrochemical oxidation of ahydride – employing potassium borohydride fuel dissolved inan aqueous alkaline solution.

The advantage of hydrogen fuel is its superior electrocat-alytic activity, particularly at low fuel-cell temperatures. It isfar easier to achieve higher power density with a hydrogen-fuelled cell stack, which in turn also means a higher energy-conversion efficiency (because a hydrogen–air fuel cell wouldbe likely to provide the power demand at a higher voltage percell). Unfortunately, however, a significant downside associ-ated with the potential use of hydrogen in portable-powerapplications is the limited energy packaging that is possiblewith realistic hydrogen-storage options. The overall weightpercent of hydrogen in relevant metal hydrides (those releas-ing hydrogen at temperatures under 100 °C) is as low as 1–2%;for the chemical hydrides, assuming the need to carry thewater for the reaction, this figure can reach 6–8%. At 8% byweight, Ewt

fuel reaches a value of 2.4 Wh/g. That’s about 40% ofthat of liquid methanol, which stores energy at 6.1 Wh/g.Additionally, whereas safety concerns arise regarding the useof hydrogen in mass-market consumer products, neatmethanol is a liquid that not only lends itself to simple pack-aging and distribution, but also raises little safety concern inhandling and/or disposal at the quantities needed for power-ing a portable electronic device.

DMFC engineering challengesThere are two prerequisites for achieving the target power den-sity in miniaturized DMFCs. First, there has to be sufficientlyhigh electrocatalytic activity per unit area of the DMFC elec-trodes at temperatures as low as 30–50 °C. Second, the fuel-cellhardware requires building blocks (electrodes, membrane sep-arators, current collectors and structural framing) of minimaloverall thickness. Delivering all of this is a considerable engi-neering challenge in the DMFC, a system that aims to capital-ize on the simplicity of direct use of unprocessed liquid fuel ofhigh energy density.

Nevertheless, with optimized Pt-Ru alloy catalysts and wellprepared electrode structures, DMFCs can generate a maximumareal power density in the range of 30–60 mW/cm2 at a temper-ature of around 45 °C. This is with no active air feed to the otherelectrode, so that the cell is said to be operating in “air breathing”mode. A volume power density of around 100 mW/cm3 is pos-sible under the same conditions. And while this figure of meritmay be five times lower than that of a hydrogen–air cell, theadvantages of methanol (as a liquid fuel of superior energy den-sity) and the simplicity of the DMFC system provide a winningcombination all the same (as shown in figure 1).

The plots in figure 1 reveal the potential lowering of the over-all system volume for 1 W fuel-cell systems compared with thevolume of a lithium-ion battery of energy density 0.2 Wh/cm3

– that’s as a function of overall energy content or use time (thenumber of Wh equals the number of hours of use at the 1 Wpower output considered). At a fuel-cell power density of 100mW/cm3 (100 W/dm3), the energy density of a DMFC systemwill exceed that of the lithium-ion battery for use times exceed-ing 4–6 h – assuming a BOP volume of 10 cm3 (equal to that ofthe fuel cell) and a system conversion efficiency of 20–30%.

The lowest of the three parallel lines in the figure shows that,at the projected volume of 20 cm3 for fuel cell plus BOP, sig-nificant volume savings over the battery are obtained for usetimes longer than 6 h. Furthermore, as the other two linesshow, similar savings are still possible at slightly longer usetimes of 7–10 h, even if the volume of the non-fuel-contain-ing part of the system is 50%, or even 100%, greater.Considering that the target use time per single refuelling istypically between several days and one week, figure 1 clearlyshows that the effective energy content of the fuel, E v

fuel, is themost significant parameter in establishing the energy-densityadvantage of the fuel-cell system.

DMFC technology platformsUntil very recently, DMFC system implementations wereoverly complex, largely because of the difficulties associatedwith management of the fuel and, primarily, water. (The previ-ous article provides a detailed discussion of the problemscaused by methanol crossover and water permeation throughthe electrolyte membrane; see p17.) The challenge for theDMFC system designer is to reconcile the target of using neat(100%) methanol in the fuel tank/cartridge – to achieve thegreatest energy-density advantage – with the need for a suffi-cient water supply to the anode. The mainstream approach to

Calculated total system volume as a function of the energycontent of three portable power systems: a prismatic lithium-ionbattery, a hydrogen–air fuel cell with metal-hydride fuel, and aDMFC. Projected energy-conversion efficiencies used togenerate these plots are 30% for the DMFC and 50% for thehydrogen–air fuel cell. The figure of merit quoted for the lithium-ion battery (0.2 Wh/cm3) is widely considered state-of-the-art,though some advanced lithium-ion batteries have recently beenreported with values as high as 0.4 Wh/cm3. A ceiling near0.5 Wh/cm3 is expected for rechargeable lithium batteries.

1. Cutting down the volume

0

120

140

160

100

80

60

40

20

02 4 6 8 10 12 14 16 18 20 22 24 26 28 30

volu

me

(cm

3 )

energy (Wh)

DMFC @1.5 Wheff/cm3 fuel

typical hydride @0.5 Wheff/cm3 fuel

prismatic Li- ion battery@ 0.2 Wheff/cm3

this problem has been to provide the water to the anode fromthe air-side of the DMFC, where it is a product of the cathodeprocess. This involves a so-called “active-system” approach, inwhich water collected from the cathode is pumped and mixedwith neat methanol from the fuel tank to provide a dilutemethanol/water mix as the anode feed.

The concept configuration for a system based on pumpingand mixing of fuel and water into a recirculating loop is shownschematically in figure 2, while the images on this page high-light different aspects of an active DMFC system of this generaltype. The system was built jointly by Ball Aerospace &Technologies Corporation (Boulder, Colorado, US) and LosAlamos National Laboratory (New Mexico, US), with the for-mer looking after BOP design and system integration and LosAlamos being responsible for the stack design and fabrication.Early tests indicate that the latest generation of active DMFCstacks built at Los Alamos will achieve a maximum stack-power density of 400–500 W/L at 75 °C – significantly better

than that of the stacks shown in the photographs.There is no doubt that the units developed by Ball Aerospace

and by others have been important in demonstrating the feasi-bility of a complete DMFC system with aqueous liquid feed forpower levels of 20 W and above. Especially notable is the imple-mentation of a complete water-management unit around thestack, which means the system is able to carry a tank of 100%methanol. Conversely, as figure 2 and its related images clearlyshow, DMFC systems have to date fallen short in terms of thesimplicity needed for portable power sources, particularly soat powers down to the 1 W level. The liquid plumbing requiresa number of moving parts with significant parasitic powerlosses – which all translates into serious reliability concerns forminiaturized power sources of the order of 1–3 W.

One way to achieve a simpler DMFC system at the expense ofenergy content is to include water as a component of the fuelcartridge, thereby eliminating the need to mix the anode feedon board the system. Unfortunately, the penalty associatedwith such an approach turns out to be prohibitive. Any sacri-fice of fuel space or weight in a DMFC system significantlyimpacts on the competitive edge of the system over incumbentbattery technology. (With the aid of figure 1, consider the effectof giving up, say, 50% of E v

fuel by carrying a 50% aqueousmethanol solution in the cartridge.)

Another take on this problem has been developed and imple-mented at the advanced prototype level by MTI MicroFuel Cells(Albany, New York, US). The two key innovations centrearound (a) fuel delivery to the anode, and (b) transport of suffi-cient water from the air cathode back to the methanol anode


TECHNOLOGY TRANSFER

28

A generic DMFC system utilizing an active flow-controlconfiguration. Water collected and pumped back from thecathode mixes with neat methanol pumped from the fuel tank to provide a dilute methanol/water anode recirculation loop.

2. Keep it in the loop

Fuel Cell

anode incathodeambientair

DC/DCconverter

pump driverand logic

MeOH feed pump

NeatMethanol

Fluidicsand Electronics

water recoverypump

recirculationpump

anode out

control logic

water

Bringing it all together: a 20 Wportable DMFC power systemdesigned by Ball Aerospace &Technologies Corporation forthe US military (top). Tworound cell stacks from LosAlamos are seen in the systemwith cover removed (above). Aside view of one of the 12-cellDMFC stacks is shown right.The overall system dimensionsare 23 ×11 ×6 cm.

two 12-cell DMFC stacks


TECHNOLOGY TRANSFER

29

within the cell (figure 3). For starters, the new fuel-deliverymode enables fine-tuning of the overall flux of neat methanolfrom reservoir to the anode – and in some implementations,this does not require any pumping. This controlled flux of 100%methanol mixes at the anode with water supplied from thecathode internally, across the thickness of the cell, eliminatingthe need for water collection and pumping. This new DMFCconcept provides the basis for an attractive combination of100% methanol feed and passive DMFC system. What’s more,the simplicity of the hardware is compatible with miniaturizedportable fuel-cell systems that can be easily embedded in con-sumer electronics devices (see photograph on p25).

Industrial demonstrationsOver the last three years, there has been a surge of industrialactivity on micro fuel cells. Many top-tier consumer elec-tronics manufacturers have revealed prototype fuel-cellpower packs, with most approaches so far being based onmethanol – some firms preferring the methanol-reformingoption (for example, Motorola and Casio) and a larger num-ber looking at DMFC-based systems (such as Toshiba,Samsung and Hitachi). Apart from the announcement by MTIMicroFuel Cells, though, these demonstrations have focusedon separate fuel-cell units that act as chargers for the batteryin an otherwise unmodified electronic device. Furthermore,most prototypes have been developed with laptop comput-ers in mind, in which miniaturization is a less daunting taskcompared with a handheld device.

Yet one manufacturer well on the road to commercialization

is Smart Fuel Cell (Brunnthal-Nord, Germany), which has justreleased a portable (though not man-portable) DMFC powersource operating in the 20 W regime. The company is initiallytargeting applications such as auxiliary power in recreationalvehicles, as well as primary power for road-side sensors andmonitors. These applications can tolerate the relatively highprice (more than $3000) charged for the early product, thoughentry into larger market sectors will likely require the price perwatt to drop by an order of magnitude.

The common denominator for most, if not all, of these early-stage fuel-cell power packs is that they are hybrid systems. Inother words, the fuel cell is there to provide the average powerover an extended period of use, while a small rechargeable bat-tery meets any additional peak-power requirements and, pos-sibly, assists with system start-up at lower temperatures.

The most effective way to simultaneously answer energy andpower demands is to use the fuel as the energy carrier and the bat-tery as the peak-power source, as can be seen from the energy-density ratio of the fuel (converted by the fuel cell) versus alithium-ion battery – around five with current DMFC technol-ogy – and the maximum power-density ratio of the battery to theDMFC – also around five. This simple observation explains whyhybridization of a fuel cell (with the maximum fraction of thevolume reserved for the fuel) with a small, rechargeable battery(required to ride through periods of peak-power demand) makessense on two levels: (a) satisfying the need for more energy pack-aged into same volume/weight, and (b) delivering the completespectrum of power demand by the relevant load.

Right now, while there is still no truly commercial micro-fuel-cell power-pack product for consumer electronics devices,there is a growing consensus that low-temperature fuel cellswill find their first killer application as the key component ofadvanced portable power sources either replacing or aug-menting rechargeable batteries. What’s more, with the cost ofincumbent battery technology pegged at several dollars perwatt of power (several thousand dollars per kW), the cost bar-rier for commercialization of fuel-cell products in this sector ismuch lower than in other emerging applications.

Shimshon Gottesfeld is vice-president and chief technology officer at MTI MicroFuel Cells in Albany, New York, US.

A prototype DMFC power source (trade name Mobion)developed at MTI MicroFuel Cells. The simple system exploits adirect feed of 100% methanol to the anode, without any waterpumping or recirculation, to facilitate packaging and maximizethe system energy density.

3. Simplicity is the secret

Fuel Cell

H2O

anode in

CO2 vent

cathodeambientair

DC/DCconverter

MeOH feed

NeatMethanol

Fluidicsand Electronics

Left: Toshiba is one of a number of Japanese electronicsmanufacturers working on DMFC power sources (prototypeshown rear) for laptop computers. Right: a 20 W DMFC powersource and fuel tank developed by Smart Fuel Cell.

http://www.sensistor.com

http://www.pdcmachines.com

http://www.fuelcellseminar.com

TECHNOLOGYTRACKING

Also in this section

32 Sustainable fuels in MCFCs

33 Small wonders at Toshiba

34 Fuel reforming: hot stuff

35 Hydrogen leak detection

Is the balance of power shifting?

The US military’s interest in all things fuel cellis set to intensify, following studies from Iraqover the past 12 months which concluded thatgenerators and batteries were in “high demandbut short supply” during the conflict – a stateof affairs that was found to limit both opera-tional speed and capability (The Fuel Cell Review,June/July p29). For the top brass, the challengeis clear: how best to deliver enhanced energyflows to the battlefield, while at the same timeimproving on the efficiencies that can beobtained from existing military fuels.

At present, armed forces the world over relyupon clunky, diesel-fuelled generators to sup-port an array of power-hungry battlefield sys-tems – everything from communications andsurveillance equipment through to weaponstargeting and auxiliary power. Trouble is, dieselgenerators are noisy and inefficient, yielding abest-case energy-conversion efficiency ofaround 20%. Add in the transportation andlogistics costs, and a litre of diesel on the battle-field can cost an order of magnitude more thanit does on the forecourt.

The question is: could fuel cells provide apractical generator alternative for the militaryin the near-to-medium term? The answer fromthe US Army appears to be a qualified “yes”,depending whether the platform in questionproves to be compatible with the traditionalsulphur-laden fuels already available in thefield (rather than the pure hydrogen ormethanol that many types of cells demand).With this in mind, the US Army’s ConstructionEngineering Research Laboratory recentlyawarded a $3.7 m contract to a collaborationinvolving the Gas Technology Institute (GTI) inIllinois and the Air Force Research Laboratory(AFRL). Their goal is to develop a 10 kWportable generator based around solid-oxidefuel cells (SOFCs) and either a diesel or mili-tary-logistics-fuel (known as JP8) feedstock.

Under the terms of the contract, GTI andAFRL are both contributing their own take onfuel-cell-processor technology. The main issuethat they need to address is the high sulphurcontent of the fuels, as sulphur poisons the fuel-cell catalyst and leads to rapid performance

degradation. GTI’s approach uses a sulphur-tol-erant steam-reforming process, followed bysulphur removal and tailoring of the methanecontent to the SOFC. AFRL’s system, on theother hand, fractionates the fuel and selectivelycracks the heavy portion; the lighter fractionsubsequently undergoes reforming followed bysulphur removal.

In the first phase of the programme, the tworesearch teams are each building a prototype3 kW SOFC system that will incorporate theirown fuel-processing technologies, as well asintegrating GTI’s proprietary sulphur-removaltechnique. The jury is still out on how muchsulphur the SOFCs can tolerate, but GTI’s tar-get is to reduce the amount of sulphur in thefuel to less than 1 ppm – a significant challenge,given that sulphur levels can be as high as3000 ppm in JP8 and higher still in diesel.

Division of labourGTI is focusing the development of its steam-reforming-based fuel processor on the opera-tional characteristics of the SOFC stack. Sincethe operating temperature of the stack is suffi-cient to effect direct internal steam-reformingof methane and some C2 species, and electro-chemically produced water is available in theanode compartment, the fuel compositionfacilitates stack cooling and simplifies the inte-grated power system. “Steam-reforming-

based processors overcome the disadvantageof partial-oxidation or autothermal methods,which produce a fuel diluted with nitrogen anda less than ideal hydrogen, carbon monoxideand methane content,” explained Gerry Runte,executive director of GTI’s Hydrogen EnergySystems Center.

The advantages offered by AFRL’s processsteps, on the other hand, are threefold: lighterhydrocarbons are less likely to form coke inthe steam reformer; the lighter hydrocarbonscontain a lower percentage of the sulphurspecies; and the sulphur-laden, heavier hydro-carbons are used for combustion to providethe energy for the endothermic reformingprocess. “This fuel-processing technique hasalready been tested at a subscale level, and willbe evaluated and modified for integration withthe SOFC stack provided by GTI during thefirst phase of the project,” said Runte. “In addi-tion, GTI will build and test a submodule of ahigh-temperature steam-reforming sectionthat may handle the diesel or JP8 fuels directlywithout preprocessing. This process is underconsideration at GTI for coal gasification pro-grammes [and] could convert oils or distillatefuels without coking.”

Both GTI and AFRL are working closely withVersa Power Systems, which will be buildingthe SOFC stacks and, ultimately, completefuel-cell systems incorporating the balance of

Military R&D

Solid-oxide fuel cells could one day provide the US Army with more efficient power generation for its battlefield systems.


Systems engineering: GTI’s Hydrogen Energy Systems Center supports a wide-ranging SOFCprogramme. Its capabilities include fuel reforming, desulphurization and cell and stack R&D.

plant. Versa Power is a US-based joint venturebetween GTI, FuelCell Energy, Materials andSystems Research Inc, the University of Utahand the Electric Power Research Institute.According to Runte, the collaboration withVersa Power enables the partners to work froma systems standpoint from day one. “Fuel-celland fuel-processing technologies are not plug-and-play, so you need to work closely with thesystem,” he explained.

By the beginning of next year, the goal is tohave both 3 kW SOFC prototypes ready forevaluation by another of the partners in thecontract, the US Department of Defense FuelCell Test and Evaluation Center (FCTec), whichis based in Johnstown, Pennsylvania. A rangeof technical specifications will be assessed,including fuel efficiency, stack performance,effectiveness of sulphur removal and durabil-ity of the SOFC stack. FCTec will also considerwhether the protocols that currently guide thedesign and manufacture of today’s militarygenerators are appropriate for next-genera-tion, fuel-cell-powered systems.

If things go to schedule, the evaluationprocess should be completed sometime inMarch 2005, after which the partners plan tocombine the best elements of their two systemsand scale up to a 10 kW SOFC platform. In thefinal phase of the project (which is currentlynot funded), the aim is to optimize the hard-ware into a beta prototype unit. The whole pro-gramme is expected to take around three years.

Looking ahead, it’s clear that SOFC genera-tors of this type could find plenty of applica-tions beyond the military arena. “The mostlogical non-military application is as auxiliarypower supplies for large trucks,” noted Runte.Use of SOFC generators would mean thattruckers would no longer have to idle theirengines to power climate-control systems andelectrical accessories (such as CD players andTVs) in the cab and sleeper compartments oftheir vehicles. It’s also worth noting that NASAand leading aircraft manufacturers like Boeingare looking into how they could use SOFCs inauxiliary power systems.Siân Harris


TECHNOLOGY TRACKING

32

GTI is a not-for-profit organization thatprovides research, development and training tothe natural-gas industry, as well as to emergingenergy markets such as those based onhydrogen and fuel-cell technology. The 38researchers reporting to Gerry Runte in theHydrogen Energy Systems Center are involvedin a range of activities embracing hydrogenenergy, alternative-fuelled vehicles, high- andlow-temperature fuel-cell components andsystems, and fuel processors and catalysts.

In addition to its work on SOFCs, forexample, the division is developing ways toimprove the cost of components (such asmembranes) in proton-exchange-membranefuel cells. It is also looking at direct-methanolfuel cells for low-power applications andundertakes outsourced R&D intomolten-carbonate fuel cells.

Meanwhile, other members of Runte’s team,led by Bill Liss, are building a hydrogen fuellingstation for the US Department of Energy andworking on prototype hydrogen-productionsystems. For the time being, these mostly runon natural gas but, according to Runte, “thereal deal is processing diesel and JP8”. Thedivision is also researching methods of storinghydrogen, such as solid-state storage in theform of metal hydrides.

In the near term, Runte hopes to receivefunding to research the use of solar power forhydrogen generation. Two solar projects are

being proposed at a test facility in the south-west of the US: one combines photovoltaic andmembrane technologies to break down water,while the other uses the sun’s thermal energy tocrack water at high temperatures.

GTI generates revenue from a number ofsources: contract research, technologydevelopment and education programmes;royalties and licence fees from GTItechnologies that have been incorporated intocommercial products and services; directsupport from its investors for medium-termR&D; and the activities of GTI subsidiaries andtechnology investments.

GTI’s work on the 10 kW SOFC generator isled by Mike Onischak, head of hydrogenproduction activities, and Robert Remick of thehigh-temperature electrochemistry group.

GTI takes the longer view Sustainable successStationary power

MTU has been evaluating the directconversion of sustainable biofuels inmolten-carbonate fuel cells.

Molten-carbonate fuel cells (MCFCs) are shap-ing up as a clean, high-efficiency platform fordecentralized cogeneration of electricity andheat using biofuels such as sewage gas and land-fill gas. And this sustainable slant on MCFCtechnology could be ready for widespread com-mercial applications within the next five years,according to a presentation from MTU CFCSolutions at the Fuel Cell World conference inLucerne, Switzerland, earlier this summer.

The German company knows a thing or twoabout MCFCs. For starters, it boasts an impres-sive track record when it comes to the develop-ment of integrated MCFC systems in the250 kW regime. Its so-called HotModules havebeen put through their paces in a comprehen-sive field-trial programme that’s been runningsince 2001 at eight test sites across Germany,including hospitals, industrial plants and tele-coms exchanges. All of these systems are basedon a natural-gas fuel supply.

At the same time, MTU and several Europeanpartners have been evaluating MCFC systemperformance with a range of biomass-basedsecondary gases – although only in laboratorydemonstrators so far. The studies have focusedon the development and design of adapted gasclean-up systems for agricultural applicationsand sewage-treatment plants. In each case, theresearchers report no problems when theMCFC stacks are operated using biogas and coalgas. Post-test analysis indicates no adverseinteractions between biogas or coal gas and thefuel-cell system components.

MTU reckons that its HotModule design is“perfectly adapted to the direct utilization ofhydrocarbons and synthesis gases” – such asbiogas, mining gas, synthesis gases from pyrol-ysis and other thermal-gasification products ofbiomass and/or waste materials. In their paperat the Lucerne conference, MTU’s AlexanderGienapp and Gerhard Huppmann point outthat the MCFC converts gases with a highmethane content to electricity with an effi-ciency of around 50% (which drops to around42% for synthesis gases such as hydrogen andCO). They conclude: “The utilization of bio-mass-based secondary gases is the most impor-tant and attractive application of the carbonatefuel cell. This would reduce [atmospheric] CO2

production enormously.”Volume manufacture of MTU’s HotModules

is slated to begin in 2006. ●

T H E F U E L C E L L R E V I E W | S E P T E M B E R 2 0 0 4

TECHNOLOGY TRACKING

33

It might be small, but it certainly packs a punch.In fact, Toshiba’s latest prototype direct-methanol fuel cell (DMFC) is compact enoughfor integration into a wireless headset for mobilephones, yet efficient enough to power an MP3music player for as long as 20 h on a single 2 cm3

charge of highly concentrated methanol.So far so impressive. Indeed, this is a case in

which the specifications really do speak forthemselves. The prototype’s dimensions arejust 22 × 56 × 4.5 mm (without the 2 cm3 fueltank). Even when the fuel tank is integrated,however, the height is just 9.1 mm and thewhole system comes in at a lean, mean 8.5 g(including fuel). According to Toshiba, the unitis able to provide a continuous output power of100 mW if the user tops up the fuel tank.

Not surprisingly, Toshiba is keeping much ofthe underlying technical innovation underwraps, although it is prepared to reveal somedetails. The prototype DMFC is based on a “pas-sive” fuel-supply system that feeds methanoldirectly into the cell without the need for apump or fan. Instead, it uses the concentrationgradient to deliver and circulate methanol andoxygen in the cell stack. The alternative “active”DMFC configuration may yield more energythan a passive system, says Toshiba, but it is alsomore complex.

According to company spokesman JunichiNagaki, the biggest challenges were the devel-opment of the internal component packagingand the use of highly concentrated (98%)methanol. The latter is desirable because itmeans that the fuel tank can be a lot smallerthan in traditional designs (in which themethanol concentration is less than 10%). Thedownside is that high concentrations ofmethanol exacerbate the problem of methanolcrossover – i.e. permeation of the methanolfuel through the cell membrane (usually a per-fluorinated ion-exchange polymer) from theanode to the cathode. Once at the cathode, themethanol is oxidized, which reduces the cath-ode’s potential and therefore the efficiency ofthe cell. However, the Japanese researchersclaim to have addressed the crossover problem“by optimizing the structure of the fuel cell’selectrodes and polymer-electrolyte membranethat trigger the reaction”.

And it seems that this is just the beginning.Toshiba expects to commercialize DMFCs forlaptop PCs this year, followed by DMFCs forsmaller handhelds, such as mobile phones and

digital audio players, in 2005. Nagaki wouldnot comment on the number of peopleinvolved in the manufacturer’s fuel-cell R&Dprogramme, or the size of its budget, but hepointed out that Toshiba has been working onboth passive and active DMFCs since the early1990s. “Within two to three years, we see thatthe power supply for handheld electronicdevices will become an issue and DMFCs willreplace batteries,” he added.

Of course, Toshiba is not the only Japaneseelectronics giant trying to miniaturize fuel cellsand address methanol crossover. Earlier thisyear, Fujitsu unveiled a new membrane-elec-trode-assembly (MEA) material that, it claims,

reduces methanol crossover to “one-tenth ofthat encountered with typical fluorinatedpolymers”. The other plus is that it enables theuse of concentrated methanol fuel.

Fujitsu’s MEA consists of an aromatic-hydro-carbon solid electrolyte covered with a high-density, platinum-based nanoparticle catalystwith methanol-blocking properties. There’senough power to drive a notebook PC for up to10 h when this MEA is incorporated into a pro-totype passive DMFC with 300 cm3 of 30%methanol. The prototype fuel cell has alreadybeen slimmed down to a thickness of 15 mmand can deliver output power levels of 15 W. Siân Harris

Japanese manufacturers are playing to their strengths in miniaturization when it comes to next-generation power sources.

Think small, win bigConsumer electronics

Pack it in: Toshiba claims to have developed the industry’s smallest DMFC (left), while Fujitsu’sprototype micro fuel cell (right) can power a notebook PC for up to 10 h without refuelling.

It’s not just Japan’s electronics manufacturersthat are getting serious about fuel cells. In July,KDDI, one of the country’s leading providers ofwireless and broadband telecommunicationsservices, announced a ground-breaking R&Dcollaboration with Toshiba and Hitachi onfuel-cell power sources for mobile-phonehandsets. Their goal is to realize a compact fuelcell that can be commercialized for the massmarket by the end of 2005.

Currently, most mobile phone makers areconcentrating their efforts on increasing thelifetime of conventional lithium-ion batteries.There’s just one snag. Mobile phones aregobbling up more and more electrical power,on the back of enhanced LCD screenfunctionality and the roll-out of new featuressuch as terrestrial digital broadcast receiversand online settlement systems.

Quite simply, traditional battery technologyis heading towards its limits, which means thesearch for a higher-energy-density, longer-lifetime power source is no longer optional – it’smandatory. With this in mind, KDDI and itsresearch partners will cover areas such asminiaturization, ease-of-use and all thetechnical considerations required forincorporating fuel cells into mobile phones.

Their aim is to complete an external, battery-charger-type model by the end of the year, and amobile-phone built-in model by the end of2005. The three companies are already active innational and international standardizationefforts related to fuel-cell technology.

KDDI hopes that the incorporation of fuelcells into mobile phones will contributesignificantly to ease-of-use by making lengthyrecharge times a thing of the past.

Market pull, not technology push

The road to the hydrogen economy is sure tobe a long and winding one – more a case ofevolution than revolution. Take the automo-bile industry. Right now, “blue-sky” thinkersfrom Detroit to Toyota City are trying to figureout the answer to their very own multibillion-dollar conundrum: how to transition fuel-cellcars from trade-show curiosity into mass-market phenomenon. More specifically, theywant to know how they can ensure that thetransition from A to B dovetails seamlesslywith the roll-out of an international networkof hydrogen-fuelling stations.

Yet with capital investment in that fuellinginfrastructure likely to be staggered overdecades rather than years, car manufacturerswill need to make some incremental moves inthe interim – one of which could involve thereforming of gasoline to hydrogen on board afuel-cell vehicle. The favoured technique uses afuel processor based on steam reforming, inwhich hydrocarbon fuel reacts with steam athigh temperatures over a catalyst to producehydrogen and carbon monoxide. Steam reform-ing is the most cost-effective method of generat-ing hydrogen, and is also the most efficient.

Unfortunately, there’s a snag. To date, thebest steam-reformer prototypes have takenaround 15–20 min to reach a temperature highenough to start generating hydrogen – a delaythat isn’t going to pass muster with the averagedriver intent on beating the morning gridlock.Now, however, engineers at Pacific NorthwestNational Laboratory (PNNL) in the US havemade what looks like a fundamental break-through: a compact steam reformer that canproduce large amounts of hydrogen-rich gasfrom liquid gasoline in only 12 s.

Hot stuffThe reformer is the highest-temperature com-ponent within a fuel-processing system, andtherefore represents the biggest hurdle torapid start-up. Hence the PNNL demonstratorlooks like a notable advance towards a com-plete on-board fuel processor that is able tostart up from cold in 30 s – a milestone that theUS Department of Energy (DOE) would like toreach before 2010. Central to PNNL’s successis the use of microfabrication techniques tofashion a series of tiny catalyst-loaded chan-nels inside the reforming reactor. Thesemicrochannels ensure low resistance to com-bustion gas flows, which in turn equates to

high rates of heat and mass transfer and rapidsteam-reforming kinetics.

“The key feature of the new design is that thereforming reactor and water vaporizer are con-figured as thin panels, with the hot gases flow-ing through the large surface area of the panel,”said Greg Whyatt, lead engineer on the project.“The panel configuration also allows highercombustion temperatures and flows withoutrisking damage to the metal structure.”

So what are the building blocks of the PNNLsystem, and how do they work? In outline, thesteam reformer consists of a number of vapor-izers, reactors, heat exchangers and a combus-tor linked together in the following way:● At start-up, the fuel is burned in a combustor,which provides heat to produce the steam. Thesteam generator is a microchannel devicedesigned to provide very low combustion-sidepressure losses. ● Steam from the generator flows through the

steam-reforming reactor, causing it to heat up.The reactor is also a microchannel device thatcontains supported catalysts inside its flowchannels. Additional heating is provided by thecombustion gases, which travel in a cross-flowarrangement.● After steam has flowed for a few seconds, fuelis injected into the steam plume and thefuel–steam mixture flows past the catalyst inthe reactor to produce syngas – a mixture ofhydrogen, carbon monoxide, carbon dioxide,methane and steam. Reformation occurs attemperatures of 650 °C and above. At thispoint, carbon monoxide (CO) concentrationsare relatively high – about 15 mole per cent atsteady state, with a steam:carbon ratio of 3.Since proton-exchange-membrane (PEM) fuelcells can only support about 10 ppm of CO atsteady state, its concentration needs to bereduced to acceptable levels by the subsystemsthat follow. On the other hand, the reformatecould be used as it stands for solid-oxide fuelcells, which can run on a CO feedstock.● From the steam-reforming subsystems, thegases flow into a high-temperature recupera-tor, which extracts enough of the heat for theflow to become compatible with the next part


TECHNOLOGY TRACKING

US researchers report significant progress in the race to make on-board fuel reforming a commercial proposition.

Fuel reforming: into the fast lane

34

Transportation

Above: system overview of PNNL’s rapid-startsteam reformer. The red elements are activeonly during the start-up phase, while the blueelements come into play only during steady-state operation. The new panel configuration(left) for the steam-reforming reactorprovides very short flow distances for theheating gas. Hot gases flow through the largesurface-area of the panel.

liquid fuel

air inlet

exhaustair recuperator

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reformate toWGS/PROX

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TECHNOLOGY TRACKING

35

of the system, the water-gas-shift subsystem.Recuperated heat is recycled to produce steam,and to drive the endothermic steam-reformingreactions. PNNL is also developing a new two-stage water-gas-shift subsystem that lowers theCO content by “shifting” it to carbon dioxideby reaction with the steam (and using catalystsfrom various commercial suppliers). ● The next stage is a preferential oxidation sub-system. This reactor lowers the CO content to10 ppm or less, by preferentially adsorbing thegas onto a catalyst surface, where it is oxidizedto carbon dioxide. A heat exchanger subse-quently adjusts the temperature of the refor-mate steam to ensure compatibility with aPEM fuel cell.● A condenser/vapour-liquid separator (devel-oped at PNNL) can then be used to adjust thevapour pressure in the reformate to the desiredlevel. This device is also intended to recovermoisture from gas flows leaving a PEM fuel cell.

A matter of prioritizationDespite the encouraging progress, PNNLacknowledges that there’s plenty of work stillto do. Top of the list is the systems engineering.“We need to integrate all of our subsystems sothat they operate together seamlessly,” LarryPederson, the project leader, told The Fuel Cell

Review. “This can be accomplished; it’s largelya budget issue rather than a technical barrier.”

He added: “We also need to continue to lowersystem mass, even though we are compatiblewith DOE targets now. As a national lab, we arefocused on showing the feasibility of ourapproach and not necessarily developing a pro-totype ready for large-scale manufacture. Assuch, our reactor designs tend to be overlyrobust, so they could be trimmed down.”

Lack of long-term stability in the presence ofsulphur (a common constituent of transporta-tion fuels) is another significant obstacle.Sulphur tends to adsorb onto catalyst surfacesand poison them. It also deposits onto the reac-tor walls and must be removed to very low lev-els in order to prevent rapid performancedegradation in PEM fuel cells. “We have a smalleffort in this area now and hope to expand it,”noted Pederson.

Meanwhile, as a prelude to commercializa-tion, the scientists will need to couple theirreformer into working fuel-cell systems tooptimize efficiency and long-term durability.With this in mind, Battelle Memorial Institutein Columbus, Ohio, which operates PNNL forthe DOE, is currently developing a microchan-nel fuel processor/PEM fuel-cell systemintended for use as an auxiliary power unit

(APU) on a military vehicle. Ultimately, thegoal is to operate the APU on diesel fuel. In arelated development, Battelle launched a spin-out company, Velocys, in 2001 to commercial-ize microchannel technology for merchant-hydrogen, ethylene production and otherchemical-industry applications.

“It is difficult to estimate when real large-scale commercial deployment will occur, butAPU development on the 1–5 kW scale couldhappen in the next five years or so,” claimedPederson. He cites the collaboration betweenDelphi Corporation and BMW, for example,which has already demonstrated an APU basedon solid-oxide fuel cells. That system operateson gasoline and uses a partial-oxidationreformer. The bottom line, says Pederson, isthat APUs are a key application for fuel cells –one in which “many of the technical require-ments of the reformer would be relaxed, suchas start-up time and start-up energy”. Belle Dumé, Paris

Further readingG A Whyatt et al. 2004 Development of arapid-start on-board automotive steamreformer. Presented at the American Institutefor Chemical Engineering 2004 SpringNational Meeting (New Orleans, Louisiana).

Handle with care. That’s a mantra that scien-tists, technologists and engineers would do wellto remember when working with hydrogenand fuel-cell systems. Whichever way you lookat it, hydrogen is a tricky gas to deal with. It’shighly volatile and flammable; it can explodewhen mixed with air in certain concentrations;and it leaks through small orifices more rapidlythan any other gas – 2.8 times faster thanmethane and 3.3 times faster than air.

A slippery customer like this demands spe-cial treatment. Specifically, that means a bul-letproof approach to fuel-cell system design –one that minimizes any fuel leaks as well asmonitoring for leaks on an ongoing basis dur-ing the system’s lifetime. Nowhere is this moreimportant than in early-stage fuel-cell vehicles,in which the considerable technical obstaclesto commercialization are matched, to a degree,by the negative public perception of hydrogencreated by more than 60 years of bad press.

“Many people are scared of using hydrogenbecause they have the story of the Hindenburgin the back of their mind,” says Elizabeth

Wasserle, product line manager for hydrogensensor modules at MST Technology (formerlyATMI), Germany. Yet that fear is somewhatmisplaced. In fact, hydrogen is no more or lessdangerous than many flammable liquid orgaseous fuels in common use today. The mini-mum concentration needed for detonation –

18% by volume at normal temperature andpressure – compares well to methane (6.3%)and propane (1.1%). Also, hydrogen’s lowerconcentration limit for ignition (4% by volume)is roughly the same as that of methane (4.4%),and a lot better than that of propane (1.7%).

Clearly, argues Wasserle, a well-thought-outstrategy on hydrogen detection and safety willgo a long way towards eliminating the risks ofignition or explosion in automotive fuel-cellapplications – even if putting such a strategyinto practice is far from straightforward.

Think safe, stay safeOn-board vehicle monitoring imposes a stringof exacting requirements concerning the per-formance and technical specifications of ahydrogen sensor. Long lifetime, cast-iron dura-bility and a compact footprint are a given as faras the car industry is concerned – as are lowpower consumption and a wide operationaltemperature range. Another must-have iscompatibility of the sensor’s signal output within-vehicle control systems (such as the

Talking sense on hydrogen sensingSafety

Fuel-cell vehicles require a fail-safe approach to hydrogen leak detection. Suppliers of high-end gas sensors are eager to help.

Drive on: hydrogen sensors can eliminate therisks of ignition or explosion in automotiveand industrial fuel-cell applications.

CANbus serial data communication protocolemployed by leading car makers, includingBMW, Volvo, Saab and Renault).

Taking all of this into account, MST claimsthat its intelligent H2 Sensormodule is the“ideal solution” for the detection of hydrogenin not only vehicular, but also stationary appli-cations. It’s an electrochemical three-electrodedevice that uses a special membrane to selec-tively distinguish hydrogen, while excludingother gases such as carbon monoxide, nitrogenoxide or gasoline. The sensor is capable ofdetecting hydrogen concentrations as low as100 ppm. Response time is less than 5 s andpower consumption is just 800 µA.

Wasserle says that one important advantageis the sensor’s size – the standard product meas-ures just 58 ×22 ×22 mm. This makes it suitablefor large-scale transport applications in cars,trucks and boats, although she claims that itcould also pave the way for integration intoportable electronic devices. And because thesensor is based on a modular design, Wasserlesays it can be adapted to fit custom require-ments as necessary.

Another critical factor is temperature per-formance. In-car systems must be able to han-dle seasonal variations, as well as geographicalextremes ranging from the blistering heat ofan Athens summer to the dead of winter indowntown Montreal. For this reason, MST’shydrogen sensor operates from –25 to 85 °C.“There are many hydrogen sensors available,but most have an upper limit of around 40 or50 °C,” claims Wasserle. “For many applica-tions this is fine, but fuel cells often operate athigher temperatures.”

Beyond the standard product that MSTlaunched last year, Wasserle reckons that there’splenty more innovation to come. “For our nextgeneration [sensor] we will use a new measure-ment principle that is independent of oxygen,”she says. The product, slated for commerciallaunch at the end of 2005, is based on a novelsolid-state gas sensor. “In addition to the newmeasurement principle, the sensor moduleswill have an extended temperature range (–40to 125 °C) and a longer lifetime (up to 10 years).”

Technology transfer However, having a good sensor is only part ofthe story, says Claes Nylander, managing direc-tor of Sensistor Technologies, Sweden. “Peoplecan go the wrong way with specifying sensitiv-ity and response time for sensors,” he explains.“With hydrogen-[fuelled] cars, for example,you need to know that you’ll get an early, rele-vant and reliable warning.”

Sensistor was set up in 1981 and specializesin the supply of digital leak-detection systemsfor a range of industrial applications. It’s got

some serious pedigree, evidenced by a cus-tomer base that includes Whirlpool, Electrolux,Bosch and GM. Early on, the company chose touse hydrogen as a “tracer” gas and developed afamily of dedicated sensors to support itsapproach. The tracer is normally a ready-madeindustrial gas mixture containing 5% hydrogenin a carrier gas such as nitrogen.

“We introduced hydrogen as a tracerbecause the molecules are very small and dis-sipate very quickly – ideal for pinpointing leaksin pipes and testing the tightness of industrialcomponents and systems,” adds Nylander.“Having been a supplier of hydrogen leak-test-ing equipment for many years we have a lot ofexpertise and know-how, so we think we have aunique position in the emerging [hydrogenand fuel-cell] market.”

Nylander identifies three areas in whichSensistor’s technology can help with thedesign and engineering of automotive hydro-gen and fuel-cell systems. First, there’s the iden-tification of leaks during development andproduction – whether the leak emanates fromthe fuel-cell stack itself or somewhere else in

the balance of plant. Second, there’s the loca-tion of leaks during repair and maintenance.And finally, there’s the 24/7 monitoring that’sneeded when a vehicle is out on the road.

For now, Sensistor is concentrating its ener-gies on the first two areas, although the firmalso has detectors installed in several prototypehydrogen and fuel-cell vehicles. When it comesto on-board systems, Nylander believes thatsimply identifying a higher-than-usual level ofhydrogen is not enough. Intelligent monitor-ing is what counts. “You don’t just want toknow that there is hydrogen in a car, becausethere are a number of other sources of hydro-gen, such as cigarette smoke or flatulence. Youwant to know if it [the hydrogen] is from thefuel and whether it’s dangerous.”

At the heart of Sensistor’s flagship product,the H2000, is a field-effect-transistor sensorthat is able to detect and locate leaks as smallas 5 × 10–7 mbar-l/s (or 0.5 ppm). The unitincludes a suite of powerful algorithms toevaluate the source of any hydrogen. A leak,for example, will yield a fairly constant supplyof hydrogen, while other sources (such ascigarette smoke) are characterized by concen-trated bursts of hydrogen that disperse rapidlywith proper ventilation.

Countermeasures aside, sensible vehicledesign and strict quality assurance will go along way towards minimizing the risks associ-ated with hydrogen leakage. For the engineer-ing teams at Ford, Toyota, Honda and the like,it’s not just a case of making sure that a fuel-cellsystem is leak-proof at the outset, but also oftaking into account the likely effects of wearand tear thousands of miles down the road.The fuel-cell system “may be leak-tight at thestart, but you have to consider what might hap-pen in two years’ time and ensure adequateventilation of critical areas”, adds Nylander.

One thing is clear: while the development ofhydrogen and fuel-cell vehicles may still be in itsinfancy, companies like MST, Sensistor and theirpeers are already betting that on-board hydro-gen monitoring will prove to be a long-termmoney-spinner. It won’t be an easy market tocrack, however. The car manufacturers aredemanding customers, and they will be pushingfor sensor/detector companies to deliver a“triple-whammy” of ongoing miniaturization,enhanced levels of intelligence and price reduc-tion in their next-generation products.

Even so, Nylander shares Wasserle’s view that,apart from anything else, hydrogen sensors aregoing to be essential tools for alleviating publicfears. “Hydrogen is odourless,” he concludes.“It’s psychological – people won’t accept hydro-gen-powered cars without [appropriate] sen-sors because they cannot smell it.”Siân Harris


TECHNOLOGY TRACKING

36

Smart sensing: the market for intelligenthydrogen-sensing modules will grow in linewith the commercial development and roll-outof fuel-cell vehicles. MST’s H2 Sensormodule(top) and Sensistor’s H2000 (bottom) are justtwo of the products that are currently beinglined up to meet the car makers’ needs.

International Trade Fair for Hydrogen and

Fuel Cell Technologies

Hamburg · 15– 17 Sept. 20049.00 – 17.00 hours

www.h2expo.de

Hamburg · 15– 17 Sept. 20049.00 – 17.00 hours

www.h2expo.de

Deutscher Wasserstoff- undBrennstoffzellen-Verband

Partners: Sponsor:Organizer:

Hydrogen and Fuel Cells 2004September 25-28, 2004

Toronto, Ontario, Canada

Have you registered? From BC's Hydrogen Highway to Toronto's Hydrogen Village to

Montreal's Hydrogen Airport, the conference will be the perfect

place to hear detailed information about fuel cell and hydrogen

projects in Canada. With over 200 speakers with diverse

perspectives this will be a great opportunity to learn about

technology advances, explore new business opportunities, and

network with industry and government specialists.

Key presentations this year focus on:

- Energy Producers, Utilities and Distribution

- International Hydrogen & Fuel Cell Developments

- Government & Industry Partnerships

- Hydrogen Infrastructure

- Demonstrations and technology applications

- Investment Opportunities

Full conference program at

www.hydrogenfuelcells2004.com/en/program/detailed.htm

www.hydrogenfuelcells2004.com

Jointly organized by:

Conference and Trade Show

Conference Secretariat:

(Attention: Hydrogen and Fuel Cells)

Suite 101 - 1444 Alberni St

Vancouver, BC V6G 2Z4 Canada

Telephone: 604.688.9655 ext2

Toll Free: 1.800.555.1099 ext2

Fascimile: 604.685.3521

Email: [email protected]

Website: www.hydrogenfuelcells2004.com

http://www.h2expo.de

http://www.hydrogenfuelcells2004.com

TALKING POINT


Where the fuel-cell industry has its say on emerging technologies.

Stationary power with a differenceDo high-temperature fuel cells have what it takes to deliver clean, efficient and economical electricpower generation in stationary applications? Siân Harris talks to someone who should know.

“MCFCs arenow at thepoint wherebaselinematerials andcomponentshave beenscaled up andare being usedin full-sizestacks.”

company’s DFC/H2 system – which is still at the R&D stage– separates the remaining 25% and subjects it to catalyticoxidation to generate heat for a range of applications.Alternatively, the hydrogen can be fed back into the fuel cellor collected to provide a hydrogen store for a fuellingstation or industrial plant.

While the DFC/H2 and DFC/T are for the future,FuelCell Energy has an installed base of commercialsystems deployed in an extensive field-trial programmearound the world. The first of these products, theDFC300A, has an output power of 250 kW and isoperating in around 30 locations, with many of theseunits also including waste-heat recovery. The Sheratonhotel chain, for example, has installed DFC300A units intwo hotels in New Jersey, US, and is interested in rollingout the technology to more sites. Other early adoptersinclude Mercedes-Benz and Caterpillar in the US, andDeutsche Telekom and RWE in Germany.

At higher-power regimes, FuelCell Energy’s DFC1500 iscurrently generating 1 MW of power from waste gasesgiven off at a municipal water-treatment plant inWashington State, US. This looks to be a “win–win”scenario, given that the utilities in charge of these facilitiesare under pressure to cut emissions of greenhouse gaseslike methane. A fuel-cell system that can use such gases asfuel is one way forward.

Every problem has a solutionNot surprisingly, getting MCFC technology into shape forcommercialization has involved its fair share of technicalchallenges – from basic materials and components throughto power-plant design. “In the early years of development,”explained Maru, “hot corrosion of the metallic hardware inthe carbonate environment was an importantconsideration, [though] properly engineered stainlesssteels now provide adequate protection.” Cost-effectiveprotection of the wet-seal surfaces has been another majorfocus, with aluminization found to eliminate the problem.“Low-cost aluminization approaches are also beinginvestigated,” added Maru. Equally significantly, researchon mechanically stable anodes turned up the Ni-Al alloy asthe preferred choice, while lithiated NiO emerged as the defacto cathode material.

According to Maru, “MCFC technology is now at thepoint where baseline materials and components have beenscaled up to full area (10 000 cm2) and are being used infull-size stacks.” Yet MCFC development is very much awork in progress, with power-density improvements andcost reduction top of the agenda at FuelCell Energy. “Thesearch for alternative cathode materials and electrolytes is continuing,” added Maru, “primarily to extend theuseful life of the fuel cell beyond the initialcommercialization goal of five years.” At the other end ofthe scale, Maru and his team are aiming to capitalize onthe wealth of experience they’ve gained from all thosefield installations to enhance the reliability andcost:performance of DFC power plants. ●

When it comes to power, Hans Maru likes to think big.That’s probably just as well, given his position as chieftechnology officer of FuelCell Energy, a Connecticut, US,company that’s developing molten-carbonate fuel cells(MCFCs) and stacks for stationary power plants. Maruhopes that one day soon, MCFC technology will be usedroutinely as the source for hundreds of kilowatts – or evenmegawatts – of power for large facilities such as hospitals,hotels, universities and factories. “These places need round-the-clock, reliable power, especially with high-qualitywaste heat [for recycling],” he told The Fuel Cell Review.

So what makes an MCFC tick? The electrolyte in MCFCsis a mixture of alkali-metal carbonates which, attemperatures of 600–700 °C, form a highly conductivemolten salt held in a ceramic sponge (or matrix). As inother fuel-cell systems, the main reaction is betweenhydrogen and oxygen; unlike all other fuel cells, however,carbon dioxide must be supplied to the cathode alongwith oxygen, with the former providing the basis of theion-transfer mechanism between cathode and anode. Thecarbon dioxide is generated from the hydrocarbon fuel,which also provides the hydrogen. And because MCFCscan operate on a wide range of fuels – such as natural gas,biogas, coal-mine methane and propane – they do notdepend upon a hydrogen infrastructure.

FuelCell Energy’s take on MCFCs is based around afamily of systems called Direct FuelCell (DFC), the keyfeature of which is the use of internal fuel reforming toextract hydrogen. The DFC solution brings the reformerinto the cell, with flat reformer plates placed betweenevery eight cells in the stack; a small amount of catalyst isalso placed in the fuel-cell passage to reform anyremaining hydrocarbons. As a result, “waste” heat fromthe core fuel-cell process can be recycled and put to gooduse in promoting hydrogen generation.

Currently, DFC systems offer electrical efficiencies of45–50%, although Maru says improvements are in theworks. Any waste heat that isn’t used to support hydrogengeneration, for example, can be fed into a turbine togenerate more electricity. In the long term, set-ups like thiscould yield electrical efficiencies of up to 75%. “The basicfeasibility of the DFC/T [DFC/turbine] concept is alreadybeing demonstrated at the 250 kW level with a Capstone60 kW microturbine,” said Maru, adding that further workon packaging and field demonstrations is in progress.

And there is yet more recycling to be done. In April,FuelCell Energy presented a paper at the National HydrogenAssociation (NHA) conference in Los Angeles about itsDFC/hydrogen system. In the standard DFC system, only75% of the hydrogen generated by the internal reformingprocess is used to produce electricity. However, the

Hans Maru, chieftechnology officer ofFuelCell Energy, US.

Student power: DFCinstallation at YaleUniversity in NewHaven, Connecticut.

http://www.astris.ca

http://www.boc.com

Portable electronics: fuel cells eye the prize

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