Solid Oxide Fuel Cell_ashutosh Singh

7/27/2019 Solid Oxide Fuel Cell_ashutosh Singh

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Contents

1) ABSTRACT

2) INTRODUCTION

3) WHAT IS SOLID OXIDE FUEL CELL AND THEIR TYPES ?

4) MATERIAL ISSUSE

5) CONSTRUCTION

6) HOW DOES IT WORK?

7) ANODE

8) ELECTROLYTE

9) INTERCONNECTED

10) CATHODE

11) STACK CONSTRUCTION

12) OPERATION

13) SOLIDE OXIDE ELECTROLYSER CELL

14) RESEARCH

15) APPLICATIONS

16) BLOOM ENERGY SERVER

17) ABOUT THE INVENTER OF BLOOM BOX

18) ADVANTAGES OF BLOOM ENERGY SERVER

19) BLOOM ENERGY IS DIFFERENT(PROPERTIES)

20) FUTURE ASPECTS

21) CONCLUSION


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22) SUMMARY

23) REFRENCES


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ABSTRACT

BLOOM ENERGY SERVER (Solid oxide fuel cells-

SOFCs), which will be operated at reducedtemperature, are becoming a frontier of RESEARCHand DEVELOPMENT. These compact size SOFCs willfit well with intermittent loads, of which share inenergy system is increasing today, whereas theconventional SOFCs will be effectively operatedwith stationary mode. For such compact size SOFCs,throttle down operation following intermittent loads

will be profitable because low current density giveshigher efficiency. SOFCs are not suitable for quickstart up. It was estimated that the hot standby modewould be more acceptable than cold start mode fromthe viewpoint of heat loss. The merit of internalreforming will also be lost for the reduced operationtemperature. Solid Oxide Fuel Cells are becoming themost revolutionary platforms in making a greener

earth with low cost electricity production. Within itscategory SOFC is the cheapest, high temperatureworking and output efficient. The project containsthe explanation of primary elements for SOFC likeanode, cathode and electrolyte with 3D diagram andactual working of SOFC. Applications andmerits/demerits are concisely discussed. Bloomingnew technologies within SOFC and improvements

after its foundation and the new process stacks aredefined. Bloom Energy Server, which is the powerplant box containing Solid Oxide Fuel Cells is therevolutionary product in large scale applications isdiscussed.


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1


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INTRODUCTION

Solid oxide fuel cells are a class of fuel cellcharacterized by the use of a solid oxide material asthe electrolyte. In contrast to proton exchangemembrane fuel cells (PEMFCs), which conductpositive hydrogen ions (protons) through a polymerelectrolyte from the anode to the cathode, the SOFCsuse a solid oxide electrolyte to conduct negativeoxygen ions from the cathode to the anode. Theelectrochemical oxidation of the oxygen ions withhydrogen or carbon monoxide thus occurs on theanode side.

They operate at very high temperatures,typically between 500 and 1,000C. At thesetemperatures, SOFCs do not require expensive

platinumcatalyst material, as is currently necessaryfor lower temperature fuel cells such as PEMFCs, andare not vulnerable to carbon monoxide catalystpoisoning. However, vulnerability to sulfur poisoninghas been widely observed and the sulfur must beremoved before entering the cell through the use ofadsorbent beds or other means.

Solid oxide fuel cells have a wide variety ofapplications from use as auxiliary power units invehicles to stationary power generation with outputsfrom 100 W to 2 MW. Theoretical efficiency of aSOFC device can exceed 60 percent. The higheroperating temperature make SOFCs suitablecandidates for application with heat engine energyrecovery devices or combined heat and power, which

further increases overall fuel efficiency.
http://en.wikipedia.org/wiki/Oxidehttp://en.wikipedia.org/wiki/Electrolytehttp://en.wikipedia.org/wiki/Proton_exchange_membrane_fuel_cellhttp://en.wikipedia.org/wiki/Proton_exchange_membrane_fuel_cellhttp://en.wikipedia.org/wiki/Protonshttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Anodehttp://en.wikipedia.org/wiki/Platinumhttp://en.wikipedia.org/wiki/Catalystshttp://en.wikipedia.org/wiki/Proton_exchange_membrane_fuel_cellhttp://en.wikipedia.org/wiki/Sulfurhttp://en.wikipedia.org/wiki/Adsorptionhttp://en.wikipedia.org/wiki/Heat_enginehttp://en.wikipedia.org/wiki/Combined_heat_and_powerhttp://en.wikipedia.org/wiki/Oxidehttp://en.wikipedia.org/wiki/Electrolytehttp://en.wikipedia.org/wiki/Proton_exchange_membrane_fuel_cellhttp://en.wikipedia.org/wiki/Proton_exchange_membrane_fuel_cellhttp://en.wikipedia.org/wiki/Protonshttp://en.wikipedia.org/wiki/Hydrogenhttp://en.wikipedia.org/wiki/Anodehttp://en.wikipedia.org/wiki/Platinumhttp://en.wikipedia.org/wiki/Catalystshttp://en.wikipedia.org/wiki/Proton_exchange_membrane_fuel_cellhttp://en.wikipedia.org/wiki/Sulfurhttp://en.wikipedia.org/wiki/Adsorptionhttp://en.wikipedia.org/wiki/Heat_enginehttp://en.wikipedia.org/wiki/Combined_heat_and_power


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Because of these high temperatures, lighthydrocarbon fuels, such as methane, propane andbutane can be internally reformed within the anode.SOFCs can also be fueled by externally reformingheavier hydrocarbons, such as gasoline, diesel, jetfuel (JP-8) or biofuels. Such reformates are mixturesof hydrogen, carbon monoxide, carbon dioxide,steam and methane, formed by reacting the

hydrocarbon fuels with air or steam in a deviceupstream of the SOFC anode. SOFC power systemscan increase efficiency by using the heat given off bythe exothermic electrochemical oxidation within thefuel cell for endothermic steam reforming process.

Thermal expansion demands a uniform and well-regulated heating process at startup. SOFC stacks

with planar geometry require on the order of an hourto be heated to light-off temperature. Micro-tubularfuel cell design geometries promise much faster startup times, typically on the order of minutes.

Unlike most other types offuel cells, SOFCs canhave multiple geometries. The planar fuel cell designgeometry is the typical sandwich type geometry

employed by most types of fuel cells, where theelectrolyte is sandwiched in between the electrodes.SOFCs can also be made in tubular geometrieswhere either air or fuel is passed through the insideof the tube and the other gas is passed along theoutside of the tube. The tubular design isadvantageous because it is much easier to seal airfrom the fuel. The performance of the planar design

is currently better than the performance of thetubular design however, because the planar designhas a lower resistance comparatively. Othergeometries of SOFCs include modified planar fuel celldesigns (MPC or MPSOFC), where a wave-like
http://en.wikipedia.org/wiki/Fossil_fuel_reforminghttp://en.wikipedia.org/wiki/Volumetric_thermal_expansion_coefficienthttp://en.wikipedia.org/wiki/Fuel_cellhttp://en.wikipedia.org/w/index.php?title=Planar_fuel_cell_design&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Modified_planar_fuel_cell_design&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Modified_planar_fuel_cell_design&action=edit&redlink=1http://en.wikipedia.org/wiki/Fossil_fuel_reforminghttp://en.wikipedia.org/wiki/Volumetric_thermal_expansion_coefficienthttp://en.wikipedia.org/wiki/Fuel_cellhttp://en.wikipedia.org/w/index.php?title=Planar_fuel_cell_design&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Modified_planar_fuel_cell_design&action=edit&redlink=1http://en.wikipedia.org/w/index.php?title=Modified_planar_fuel_cell_design&action=edit&redlink=1


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structure replaces the traditional flat configuration ofthe planar cell. Such designs are highly promising,because they share the advantages of both planar

cells (low resistance) and tubular cells.

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SOFC technology dominates competing fuel celltechnologies because of the ability of SOFCs to usecurrently available fossil fuels, thus reducing

operating costs. Other fuel cell technologies (e.g.molten carbonate, polymer electrolyte, phosphoricacid and alkali) require hydrogen as their fuel.Widespread use of such fuel cells would require anetwork of hydrogen suppliers, similar to our familiargas stations.

High efficiency and fuel adaptability are not the

only advantages of solid oxide fuel cells. SOFCs areattractive as energy sources because they are clean,reliable, and almost entirely nonpolluting. Becausethere are no moving parts and the cells are thereforevibration-free, the noise pollution associated withpower generation is also eliminated.


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4

MATERIAL ISSUSE

Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) use a hard, non-porous ceramic compound as the electrolyte.Because the electrolyte is a solid, the cells do not

have to be constructed in the plate-like configurationtypical of other fuel cell types. SOFCs are expectedto be around 50%60% efficient at converting fuel toelectricity. In applications designed to capture andutilize the system's waste heat (co-generation),overall fuel use efficiencies could top 80%85%.

Solid oxide fuel cells operate at very high

temperaturesaround 1,000C (1,830F). High-temperature operation removes the need forprecious-metal catalyst, thereby reducing cost. Italso allows SOFCs to reform fuels internally, whichenables the use of a variety of fuels and reduces thecost associated with adding a reformer to thesystem.

SOFCs are also the most sulfur-resistant fuel celltype; they can tolerate several orders of magnitudemore of sulfur than other cell types. In addition, theyare not poisoned by carbon monoxide (CO), which


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can even be used as fuel. This property allows SOFCsto use gases made from coal.

High-temperature operation has disadvantages.It results in a slow start up and requires significantthermal shielding to retain heat and protectpersonnel, which may be acceptable for utilityapplications but not for transportation and smallportable applications. The high operatingtemperatures also place stringent durabilityrequirements on materials. The development of low-cost materials with high durability at cell operatingtemperatures is the key technical challenge facingthis technology.

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Scientists are currently exploring the potential

for developing lower-temperature SOFCs operatingat or below 800C that have fewer durabilityproblems and cost less. Lower-temperature SOFCsproduce less electrical power, however, and stackmaterials that will function in this lower temperaturerange have not been identified.


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HOW DOES ITS WORK?

A solid oxide fuel cell is made up of four layers,three of which are ceramics (hence the name). Asingle cell consisting of these four layers stackedtogether is typically only a few millimeters thick.Hundreds of these cells are then connected in series

to form what most refer to as an "SOFC stack". Theceramics used in SOFCs do not become electricallyand ionically active until they reach very hightemperature and as a consequence the stacks haveto run at temperatures ranging from 600 to 1,000C.Reduction of oxygen into oxygen ions occurs at thecathode. These ions can then diffuse through thesolid oxide electrolyte to the anode where they can

electrochemically oxidize the fuel. In this reaction, awater byproduct is given off as well as two electrons.These electrons then flow through an external circuitwhere they can do work. The cycle then repeats asthose electrons enter the cathode material again.

Anode

The ceramic [anode] layer must be very porous

to allow the fuel to flow towards the electrolyte. Likethe cathode, it must conduct electrons, with ionicconductivity a definite asset. The most commonmaterial used is a ceramic made up of nickel mixedwith the ceramic material that is used for theelectrolyte in that particular cell, typically YSZ (yttriastabilized zirconia). The anode is commonly thethickest and strongest layer in each individual cell,

because it has the smallest polarization losses, andis often the layer that provides the mechanicalsupport. Electrochemically speaking, the anodes job


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is to use the oxygen ions that diffuse through theelectrolyte to oxidize the hydrogen fuel.

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The oxidation reaction between the oxygen ionsand the hydrogen produces heat as well as waterand electricity. If the fuel is a hydrocarbon, forexample methane, another function of the anode isto act as a catalyst for steam reforming the fuel intohydrogen.

This provides another operational benefit to thefuel cell stack because the reforming reaction isendothermic, which cools the stack internally

Electrolyte

The electrolyte is a dense layer of ceramic thatconducts oxygen ions. Its electronic conductivitymust be kept as low as possible to prevent lossesfrom leakage currents. The high operatingtemperatures of SOFCs allow the kinetics of oxygenion transport to be sufficient for good performance.However, as the operating temperature approachesthe lower limit for SOFCs at around 873 K, the

electrolyte begins to have large ionic transportresistances and affect the performance. Popularelectrolyte materials include yttria stabilized zirconia(YSZ) (often the 8% form Y8SZ) and gadoliniumdoped ceria (GDC) The electrolyte material has


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crucial influence on the cell performances.Detrimental reactions between YSZ electrolytes andmodern cathodes such as LSCF have been found,

and can be prevented by thin (


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together and a mechanism for collection of electricalcurrent needs to be provided, hence the need forinterconnects. The interconnect functions as the

electrical contact to the cathode while protecting itfrom the reducing atmosphere of the anode.

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The high operating temperature of the cellscombined with the severe environments means thatinterconnects must meet the most stringentrequirements of all the cell components: 100% electricalconductivity, no porosity (to avoid mixing of fuel andoxygen), thermal expansion compatibility, and inertnesswith respect to the other fuel cell components. It will beexposed simultaneously to the reducing environment ofthe anode and the oxidizing atmosphere of the cathode.

For an YSZ SOFC operating at about 1000 C, thematerial of choice is LaCrO3 doped with a rare earthelement (Ca, Mg, Sr, etc.) to improve its conductivity.Ca-doped yttrium chromate is also being consideredbecause it has better thermal expansion

compatibility, especially in reducing atmospheres[Chou]. Interconnects are applied to the anode byplasma spraying and then the entire cell is co-fired.

Cathode

The cathode, or air electrode, is a thin porouslayer on the electrolyte where oxygen reduction

takes place. The overall reaction is written in Krger-Vink Notation as follows:


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Cathode materials must be, at minimum,electronically conductive. Currently, lanthanumstrontium manganite (LSM) is the cathode material of

choice for commercial use because of itscompatibility with doped zirconia electrolytes.Mechanically, it has similar coefficient of thermalexpansion to YSZ and thus limits stresses built upbecause of CTE mismatch. Unfortunately, LSM is apoor ionic conductor, and so the electrochemicallyactive reaction is limited to the triple phaseboundary (TPB) where the electrolyte, air and

electrode meet. LSM works well as a cathode at hightemperatures, but its performance quickly falls asthe operating temperature is lowered below 800C.

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In order to increase the reaction zone beyondthe TPB, a potential cathode material must be able toconduct both electrons and oxygen ions. Composite

cathodes consisting of LSM YSZ have been used toincrease this triple phase boundary length. Mixedionic/electronic conducting (MIEC) ceramics, such asthe perovskite LSCF, are also being researched foruse in intermediate temperature SOFCs as they aremore active and can makeup for the increase in theactivation energy of reaction. The charge carrier inthe SOFC is the oxygen ion (O2-). At the cathode, the

oxygen molecules from the air are split into oxygenions with the addition of four electrons. The oxygenions are conducted through the electrolyte andcombine with hydrogen at the anode, releasing fourelectrons. The electrons travel an external circuitproviding electric power and producing by-productheat.

Anode Reaction: 2 H2 + 2 O2- => 2

H2O + 4 e-

CathodeReaction:

O2 + 4 e- => 2 O2-


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Overall CellReaction:

2 H2 + O2 => 2 H2O

The operating efficiency in generating electricityis among the highest of the fuel cells at about 60%.Furthermore, the high operating temperature allowscogeneration applications to create high-pressuresteam that can be used in many applications.Combining a high-temperature fuel cell with a turbineinto a hybrid fuel cell further increases the overallefficiency of generating electricity with a potential of

an efficiency of more than 70%.

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Fig: Solid oxide fuel cell (SOFC) stacks

Stack construction

Stack construction is concerned with thepreparatory steps formaterial-connected joints between the metallic partsof the SOFC (casing, cover, interconnects, endconnectors).

Operation

SOFCs operate at extremely high temperatures(600C1000C) resulting in a significant timerequired to reach operating temperature andresponding slowly to changes in electricity demand.It is therefore considered to be a leading candidate

for high-power applications including industrial andlarge-scale central-electricity generating-stations.

The very high operating temperature of theSOFC has both advantages and disadvantages. Thehigh temperature enables them to tolerate relativelyimpure fuels, such as those obtained from thegasification of coal or gasses from industrial process

and other sources. However, the high temperaturesrequire more expensive materials of construction.


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Solid Oxide Electrolyser Cell:

A solid oxide electrolyser cell (SOEC) is a solidoxide fuel cell set in regenerative mode for theelectrolysis of water with a solid oxide, or ceramic,electrolyte to produce oxygen and hydrogen gas. Aregenerative fuel cell (mode) or reverse fuel cell(RFC) is a fuel cell run in reverse mode, whichconsumes electricity and chemic to producechemical A.


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Bloom energyserver is Different:

Bloom Energy's versatile fuel cell technology is

essentially a flexible energy platform, providingmultiple benefits simultaneously for a wide range ofapplications. In addition to clean, reliable, affordableelectricity, Bloom customers can realize a multitudeof other advantages:

Reverse Backup:

Businesses often purchase generators andother expensive backup applications that sitidle 99% of the time, while they purchase theirelectricity from the grid as their primarysource. The Bloom solution allows customersto flip that paradigm, by using the EnergyServer as their primary power, and onlypurchasing electricity from the grid to

supplement the output when necessary.Increased asset utilization leads todramatically improved ROI for Bloom Energy'scustomers.

Time to Power:

The ease of placing Bloom Energy Serversacross a broad variety of geographies andcustomer segments allows systems to beinstalled quickly, on demand, without theadded complexity of cumbersome combinedheat and power applications or large spacerequirements of solar. These systems'environmental footprint enables them to beexempt from local air permittingrequirements, thus streamlining the approvalprocess. Fast installation simply requires aconcrete pad, a fuel source, and an internetconnection.


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DC Power:

Bloom systems natively produce DC power,which provides an elegant solution toefficiently power DC data centers and/or bethe plug-and-play provider for DC charging

stations for electric vehicles.

Hydrogen Production:

Bloom's technology, with its NASA

roots, can be used to generateelectricity and hydrogen. Coupled withintermittent renewable resources likesolar or wind, Blooms future systemswill produce and store hydrogen toenable a 24 hour renewable solutionand provide a distributed hydrogenfueling infrastructure for hydrogenpowered vehicles.

Carbon Sequestration:

The electrochemical reaction occurringwithin Bloom Energy systems generationelectricity, heat, some H2O, and pure CO2.

Traditionally, the most costly aspect ofcarbon sequestration is separating theCO2 from the other effluents. The pureCO2 emission allows for easy and cost-effective carbon sequestration from the


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Bloom systems. Bloom is proud to deliverone of the most robust and dynamicenergy platforms on the market today.

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FUTURE ASPECTS:

Overview: Bloom Energy is

changing the way the world

generates and consumes energy.

The companysunique on-site powergeneration systems utilize an

innovative new fuel cell technology

with roots in NASAs Mars program.

Derived from a common sand-like

powder, and leveraging breakthrough

advances in materials science,

Bloom Energys technology is able to

produce clean, reliable, affordable

power, practically anywhere, from a

wide range of renewable or

traditional fuel sources, including

natural gas, wind, solar, and

biomass. Bloom Energy Servers areamong the most efficient energy

generators available, providing for

significantly reduced electricity costs


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and dramatically lower greenhouse

gas emissions. By generating power

on-site where it is consumed, Bloom

Energy offers increased electrical

reliability and improved energy

security, providing a clear path to

energy independence.

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Founded: 2001

Headquarters: Sunnyvale, California

Primary Investors: Kleiner PerkinsCaufield & Byers, New EnterpriseAssociates, MorganStanley.

Management team: KR SRIDHAR , ph.d; principal co-

founder and chief executive officer BILL KURTZ;chief financial officer and chief commercial officerGIRISH PARANJPE; managing director of bloom energyinternational GARY CONVIS; chief operations officer

VENKAT VENKATARAMAN .

company 2001 Company founded

2002 First round of funding

2003-2005Research and

development


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2006-2007 Field trials product testing

and validation

2008 First commercial shipment

2009 Sales and manufacturing

ramp

2010 Public launch

2011 Bloom electrons service

launch

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Announced Customers: Adobe, AT&T,

Bank of America, BD, Caltech,The Coca-

Cola Company, Cox Enterprises, eBay,

Fedex, Firemans Fund, Google, Kaiser

Permanente, NTT, Safeway.


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Statistics: Since the companys

initial commercial

installation in 2008,

Bloom Energy has

produced more than

100 million kilowatt

hours for its customers

and reduced their

carbon foot- prints by

over 140 million lbs.

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RESEARCH:

Research is going now in the direction of lower-temperature SOFC (600C) in order to decrease thematerials cost, which will enable the use of metallicmaterials with better mechanical properties andthermal conductivity.

Research is currently underway to improve thefuel flexibility of SOFCs. While stable operation hasbeen achieved on a variety of hydrocarbon fuels,these cells typically rely on external fuel processing.For the case of natural gas, the fuel is eitherexternally or internally reformed and the sulfurcompounds are removed. These processes add to

the cost and complexity of SOFC systems. Work isunderway at a number of institutions to improve thestability of anode materials for hydrocarbonoxidation and, therefore, relax the requirements for


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fuel processing and decrease SOFC balance of plantcosts.

Research is also going on in reducing start-uptime to be able to implement SOFCs in mobileapplications. Due to their fuel flexibility they may runon partially reformed diesel, and this makes SOFCsinteresting as auxiliary power units (APU) inrefrigerated trucks.

Specifically, Delphi Automotive Systems aredeveloping an SOFC that will power auxiliary units in

automobiles, while BMW has recently stopped asimilar project. A high-temperature SOFC willgenerate all of the needed electricity to allow theengine to be smaller and more efficient. The SOFCwould run on the same gasoline or diesel as theengine and would keep the air conditioning unit andother necessary electrical systems running while theengine shuts off when not needed (e.g., at a stop

light).

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Rolls-Royce is developing solid-oxide fuel cells

produced by screen printing onto inexpensiveceramic materials. Rolls-Royce Fuel Cell Systems Ltdis developing a SOFC gas turbine hybrid systemfueled by natural gas for power generationapplications on the order of a megawatt (e.g.Futuregen).

Ceres Power Ltd. has developed a low cost and

low temperature (500-600 degrees) SOFC stackusing cerium gadolinium oxide (CGO) in place ofcurrent industry standard ceramic, yttrium stabilizedzirconium (YSZ), which allows the use of stainlesssteel to support the ceramic.


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Solid Cell Inc. has developed a unique, low costcell architecture that combines properties of planarand tubular designs, along with Cr-free cermets

interconnect.

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APPLICATIONS:

Using planar SOFCs, stationary power

generation systems of from 1-kW to 25-kW size have

been fabricated and tested by several organizations.

Several hundred 1-kW size combined heat and power

units for residential application were field tested by

Sulzer Hexis; however, their cost and performancedegradation was high and stack lifetime too short.

With improved sealing materials and sealing

concepts, planar SOFC prototype systems in the 1- to


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5-kW sizes have recently been developed and are

being tested by various organizations with greater

success. Using tubular (cylindrical) SOFCs, Siemens/

Westinghouse fabricated a 100-kW atmosphericpower generation system (Figure 4). The system was

successfully operated for two years in the

Netherlands on desulfurized natural gas without any

detectable performance degradation. It provided up

to 108 kW of ac electricity at an efficiency of 46% to

the Dutch grid and approximately 85 kW of hot water

for the local district heating system. At theconclusion of the operation in The Netherlands, the

system was moved to a German utility site in Essen,

Germany, where it operated successfully for another

4,000 hours. After replacing some cells, the system

was then installed and operated in Italy, for over two

years, again with very stable performance.

Siemens/Westinghouse tubular cells have also beenused to fabricate and field test over a dozen 5-kW

size combined heat and power units, each about the

size of a refrigerator. These units gave excellent

performance and performance stability on a variety

of hydrocarbon fuels. However, at present, their cost

is high; future such units are expected to use higher

power density alternate tubular geometry cells to

drive down the cost.

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Another application of SOFC systems is in thetransportation sector. The polymer electrolytemembrane fuel cell is generally regarded as the fuel

cell of choice for transportation applications.

These fuel cells require pure hydrogen, with nocarbon monoxide, as the fuel to operate successfully.However, presently no hydrogen infrastructure


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exists, and on-board reformer systems to producehydrogen from existing fuel base (gasoline, diesel)are technically challenging, complex, and expensive.

Furthermore, it is difficult to eliminate the carbonmonoxide entirely from the reformate stream. Incontrast, SOFCs can use carbon monoxide along withhydrogen as fuel, and their higher operatingtemperature and availability of water on the anodeside makes on-cell or in-stack reformation ofhydrocarbon fuels feasible. Also, no noble metalcatalysts are used in SOFCs reducing cost of the

cells. The initial application of SOFCs in thetransportation sector will be for on-board auxiliarypower units. Such auxiliary power units, operating onexisting fuel base, will supply the ever increasingelectrical power demands of luxury automobiles,recreational vehicles, and heavy-duty trucks. DelphiCorporation has developed a 5-kW auxiliary powerunit using anode-supported planar SOFCs. This unit is

intended to operate on gasoline or diesel, which isreformed through catalytic partial oxidation. Thebuilding blocks of such an auxiliary power unitconsist of an SOFC stack, fuel reformation system,waste energy recovery system, thermalmanagement system, process air supply system,control system, and power electronics and energystorage (battery) system. Delphi has reduced the

mass and volume in successive generation auxiliarypower units to meet the stringent automotiverequirements; the remaining issues of start up timeand tolerance to thermal cycling are presently beingworked on.

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SOFCs are of high interest to the militarybecause they can be established on-site in remotelocations, are quiet, and non-polluting. Moreover, theuse of fuel cells could significantly reduce


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deployment costs: 70% by weight of the materialthat the military moves is nothing but fuel.Stationary installations would be the primary or

auxiliary power sources for such facilities as homes,office buildings, industrial sites, ports, and militaryinstallations. They are well suited for mini-power-gridapplications at places like universities and militarybases. SOFC technology is ideal for such anexpansion, since much of the anticipated demand isexpected to come from growing economies withminimal infrastructure. SOFCs can be positioned on-

site, even in remote areas; on-site location makes itpossible to match power generation to the electricaldemands of the site.

Stationary SOFC power generation is no longerjust a hope for the future. Siemens Westinghousehas tested several prototype tubular systems, withexcellent results. A plant in the Netherlands hasbeen operational for two years and an earlierprototype installation has been operating for 8 years.

The fuel cells have been through over 100 thermalcycles and the voltage degradation during the testtime has been minimal less than 0.1%/thousandhours. Siemens Westinghouse expects to have itsfirst fully operational tubular fuel cell plant in placeby October 2003 [Siemens]. Meanwhile, in Australia,

Ceramic Fuel Cells, Ltd. has been operatingprototype planar fuel cell plants since 2001 andexpects to be ready with market-entry products in2003 [CFCL].

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In the transportation sector, SOFCs are likely tofind applications in both trucks and automobiles. Indiesel trucks, they will probably be used as auxiliarypower units to run electrical systems like airconditioning and on-board electronics. Such unitswould preclude the need to leave diesel trucksrunning at rest stops, thereby leading to a savings indiesel fuel expenditures and a significant reduction

in both diesel exhaust and truck noise. Meanwhile,automobile manufacturers have invested at least$4.5 billion in fuel cell research (not all SOFC)[ceramic]. There are an estimated 600 millionvehicles worldwide, 75% of which are personalautomobiles, and the number is expected to grow by30% in the next 10 years [SECA]. With morestringent environmental restrictions in the United

States and European Union, automobilemanufacturers are under growing time pressure tobring non-polluting cars to the marketplace. SOFCsare attractive prospects because of their ability touse readily available, inexpensive fuels.


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26

Bloom Energy Server:The Bloom Energy Server is a solid oxide fuel

cell made by Bloom Energy, of Sunnyvale, California,that uses liquid or gaseous hydrocarbons (such asgasoline, diesel or propane produced from fossil orbio sources) to generate electricity on the site whereit will be used; Bloom Energy representatives assertthat it is at least as efficient as a traditional large-

scale coal power station.

According to the company,a single cell (one 100mm 100mm metal alloy platebetween two ceramic layers) generates 25 watts.

Fig: Bloom Energy Server


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The Bloom Energy Server uses thin whiteceramic plates (100mm 100mm) which are madefrom sintered modified zirconia (an oxide derivedfrom common beach sand). Each ceramic plate iscoated with a green Nickel oxide -based ink on oneside (anode) and another black (probably Lanthanumstrontium manganite) ink on the other side(cathode). According to the San Jose Mercury News,"Bloom's secret technology apparently lies in theproprietary green ink that acts as the anode and theblack ink that acts as the cathode--" but in fact thesematerials are widely known in the field of solid oxidefuel cells. Wired reports that the secret ingredientmay be yttria-stabilized zirconia based upon a 2006patent filing (7,572,530) that was granted to Bloomin 2009; but this material is also one of the mostcommon elecrolyte materials in the field. To savemoney, the Bloom Energy Server uses inexpensivemetal alloy plates for electric conductance betweenthe two ceramic fast ion conductor plates. In lowertemperature fuel cells, platinum is required at thecathode.

Advantages of Solid Oxide Fuel Cells

One advantage of SOFC is that hydrogen and

carbon dioxide are used as fuel in the cell. Thismeans that SOFC can use many commonhydrocarbon fuels such as natural gas, diesel,gasoline and alcohol without the need to reform thefuel into pure hydrogen. In other fuel cells, such asthe polymer electrolyte fuel cell, which are fueledwith pure hydrogen, the carbon dioxide is a poison.

SOFC have a potentially lower cost due to theabsence of precious metals, compared to protonexchange membrane and phosphoric acid fuel cellswhich use platinum as a catalyst. Some other fuel


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cell types use liquid electrolytes, similar to batteryacid that can have a corrosive effect on components.Since SOFC use one piece solid state ceramic cells,

they are easier to maintain due to the lack of thiscorrosion.28

Disadvantages of Solid Oxide Fuel Cell:

A major disadvantage of the SOFC, as a result ofthe high heat, is that it places considerable

constraints on the materials which can be used forinterconnections. Another disadvantage of runningthe cell at such a high temperature is that otherunwanted reactions may occur inside the fuel cell. Itis common for carbon dust, graphite, to build up onthe anode, preventing the fuel from reaching thecatalyst.


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Conclusion:Forty years have passed since the first

successful demonstration of a solid oxide fuel cell.Through ingenuity, materials science, extensiveresearch, and commitment to developing alternativeenergy sources, that seed of an idea has germinatedand is about to bloom into a viable, robust energyalternative. Materials development will certainlycontinue to make SOFCs increasingly affordable,efficient, and reliable.

SummaryThe challenge in successfully commercializingSOFCs offering high power densities and long termdurability requires reduction of costs associated withthe cells and the balance-of-plant. Additionally, fortransportation auxiliary power unit applications,ability for rapid start up and thermal cycling needs tobe developed.


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References:

1) [Weisberg] J. Weissbart, R. Ruka, "A SolidElectrolyte Fuel Cell," Journal of theElectrochemical Society, Vol. 109, No. 8, 1962,pp 723-726.

2) [Singhal] S. C. Singhal, "Science and Technologyof Solid-Oxide Fuel Cells," MRS Bull. Vol.25, No.3,2000, p.16-21.

3) [Park] S. Park, John M. Vohs, Raymond J. Gorte,"Direct Oxidation of Hydrocarbons in a Solid-Oxide Fuel Cell," Nature, Vol. 404, 16 March2000, pp. 265-267.

4) [Liou] Jiann-Hwa Liou, Po-Jou Liou, Tzer-ShinSheu, "Physical Properties and Crystal Chemistryof Bismuth Oxide Solid Solution," Processing andCharacterization of Electrochemical Materials

and Devices. Proc. Symp. Indianapolis, 25-28April 1999, pp 3-10. Ceram. Trans. 109.5) [Seabaugh] Matthew M. Seabaugh, Scott L.

Swartz, William J. Dawson, "Developing ColloidalFabrication Processes for YSZ Solid ElectrolyteMembranes," Processing and Characterization ofElectrochemical Materials and Devices. Proc.Symp. Indianapolis, 25-28 April 1999, pp 21-30.

Ceram. Trans. 109.6) [Ralph] J. M. Ralph, J. A. Kilner, B. C. H. Steele,

"Improving Gd-doped Ceria Electrolytes for LowTemperature Solid Oxide Fuel Cells," NewMaterials for Batteries and Fuel Cells. Proc.


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Symp. San Francisco, 5-8 April 1999, pp 309-314.

7) [Moon] J-W. Moon, H-J. Hwang, M. Awano, K.

Maeda, "Preparation of NiO-YSZ tubular supportwith radially aligned pore channels," MaterialsLetters, vol. 57, no. 8, pp. 1428-1434, February2003.

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Solid Oxide Fuel Cell_ashutosh Singh

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