Materials Science & Technology Division Los Alamos National … · 2006. 3. 8. · Materials...

Materials Science & Technology, MST-11Fuel Cell ResearchOAAT Program Review, May 2002

Annual OAAT Fuel Cells Program ReviewNational Renewable Energy Laboratory, Golden, CO, May 2002

DIRECT METHANOL FUEL CELLS

Piotr Zelenay

Materials Science & Technology DivisionLos Alamos National Laboratory


Major Contributors to DMFC Effort in FY 2002

Eric Brosha (TSM) - Ultrasonic spray/freeze dryJohn Davey (Tech) - MEA research; technical supportChristian Eickes (PD) - ElectrocatalysisRobert Fields (TSM) - Controls & softwareMichael Hickner (GRA) - Membrane & MEA researchFrançois Le Scornet (GRA) - Single cell & stack testingDon McMurry (Tech) - Controls & softwareBryan Pivovar (TSM) - Membrane & MEA researchGerie Purdy (Tech) - Testing & general supportJohn Ramsey (GRA) - Flow & hardware modelingJohn Rowley (Tech) - Technical supportMahlon Wilson (TSM) - Cell/stack design & engineeringChristine Zawodzinski (TSM) - Cell/stack design & engineeringTom Zawodzinski (TSM) - Membrane & MEA researchPiotr Zelenay (TSM) - Project management & electrocatalysisYimin Zhu (PD) - Electrocatalysis


Status by the End of FY 2001

• Composition of anodes with reduced catalyst loading optimized

• 5 gPt/kW successfully demonstrated in a 45-cm2 five-cell stack with a total Pt loading of 0.53 mg cm-2

• Several membranes with higher selectivity and lower electro-osmotic drag of water identified; improved overall efficiency demonstrated with several alternative membranes

• Fourth-generation 30-cell 80-W DMFC stack delivered and integrated by Ball Aerospace into a complete demonstration system for the military

• Design/modeling study of a ~500 W APU stack initiated


Response to Selected Reviewers’ Comments

“Need more emphasis on automotive applications.”

Manufacturing capability resulting from the likely market-entry of DMFCs for portable power applications should reduce the cost andfacilitate commercialization of PEM fuel cells for higher power applications, automotive transportation in particular. Portable power -transportation synergy in fuel cell R&D appears to be the best commercialization strategy.

“Not sure that LANL should be developing fuel cell stacks.”

Fundamental research has been and will remain the focus of direct methanol fuel cell program at LANL. Few stack prototypes have been built to prove practical viability of core DMFC technology developed at LANL, identify possible scale-up issues and verify adaptability of the technology to complete systems.

R

R


Major Collaborations & Commercial Interactions ( )C

• Collaboration with Motorola on fundamental DMFC technology and high-temperature RHFC membrane for portable power in final stage of re-instating via CRADA; common research to begin in mid-May.

• Partnership with Ball Aerospace in FY 2002:

Complete 60 W (net power) DMFC system demonstrated to the military;

Three-year Palm Power research project started in mid-2001, focusing on fundamental research as well as stack development; first 22 W stack delivered to Ball for system integration in March 2002;

Operating conditions for the APU system agreed upon; first stack will be shipped from LANL in the fall of 2002.

R


Major Collaborations & Commercial Interactions (II)

• Catalyst research:

Johnson Matthey – Effect of atomic composition, morphology and crystallography of Pt-Ru blacks on DMFC anode activity;

OMG – New carbon-supported cathode catalyst with improved methanol tolerance;

Superior MicroPowders – Carbon-supported catalysts for PEM and DMFC cathodes; DMFC MEAs (planned).

• Membrane/MEA research & development; polymer fabrication:

Virginia Tech – Development of alternative polymers (BPSH) and MEAs with significantly improved selectivity;

Hydrosize Technologies, Inc. – Fabrication of BPSH initiated; first two batches of BPSH polymer ordered and synthesized; polymer to be shipped to LANL within a week.


Cathode ResearchCarbon-Supported vs. Unsupported Pt Catalysts

Cathode Loading (mgPt cm-2)

0 1 2 3 4 5 6

i DM

FC @

0.4

5 V

(A c

m-2

)

0.0

0.1

0.2

0.3

0.4

40% Pt / C Cathode (80°C)

0.46 sLm - 10 psig

0.46 sLm - 30 psig0.05 sLm - 30 psig

0.05 sLm - 10 psig

Cathode Loading (mgPt cm-2)

0 1 2 3 4 5 6

i DM

FC@

0.4

5 V

(A c

m-2

)

0.0

0.1

0.2

0.3

0.4

Pt Black Cathode (80°C)

0.46 sLm - 10 psig

0.46 sLm - 30 psig0.05 sLm - 30 psig

0.05 sLm - 10 psig

Pt < 1.0 mg cm-2 - Pt / C catalyst

Pt > 1.0 mg cm-2 - Pt black catalyst


Cathode ResearchNafion Content; Improved Cell Performance with Low Total Pt Loading

Cell Current Density (A cm-2)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Cel

l Vol

tage

(V)

0.0

0.2

0.4

0.6

0.8

Power D

ensity (W cm

-2)

0.00

0.04

0.08

0.12

0.16

80°CTotal Pt: 1.2 mg cm-2

Pt-X / C

Nafion Weight Fraction(Cathode)

0.1 0.2 0.3 0.4 0.5

H2-

Air

Cel

l Vol

tage

@ 0

.2 A

cm

-2 (V

)

0.70

0.75

0.80

0.85

0.90

Pt / C

80°C

Achievements: (1) Nafion content in the cathode optimized at a low Pt loading (0.6 mg cm-2)

(2) Very good performance demonstrated at 80°C with 1.2 mg cm-2 total Pt loading


Cathode ResearchNew Binary Catalyst with Improved O2 Activity & Methanol Tolerance

Current Density (A cm-2)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Cel

l Vol

tage

(V)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Pt-X / C

Pt / C

80°C, 30 psig0.6 mgPt cm-2 (cathode) 80°C

Potential (V vs. DHE)0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

Cur

rent

(mA

)

-60

-40

-20

0

20

40

60

80

Pt / C

Pt-X / C

Achievement: Even at low a Pt loading of ~ 0.6 mg cm-2, the new binary Pt-X / C catalyst shows significantly better activity in oxygen reduction and improved methanol-tolerance over commercial Pt / C catalyst (E-Tek).

Collaboration with OMG (formerly Degussa-dmc2)C


(111)

(311)

(200)

(222)(220)

aPt = 3.910Å

0

500

1000

1500

2000

2500

3000

3500

20 40 60 80 100

Inte

nsity

(c.p

.s)

Two-Theta (degrees)

In-House Catalyst EffortNew Carbon-Supported Pt Catalyst: 80wt%Pt / C

Ultrasonic-spray / free-dry method10-µm droplets quickly frozen in LN26.1 nm Pt particle size determined by whole-profile fitting of XRD dataPt very well dispersed Pt (SEM)DMFC performance very close to that of best cathode catalysts commercially available!

Pt 80°C

Current Density (A cm-2)0.0 0.1 0.2 0.3 0.4 0.5 0.6

Cel

l Vol

tage

(V)

0.0

0.2

0.4

0.6

0.8Cathode: ~ 0.6 mgPt cm

-2

_____ In-House 80 wt% Pt / C Cathode Catalyst________ 6 Commercial Pt

/

C Cathode Catalysts


Anode ResearchPt-Ru Blacks: Catalytic Activity vs. Atomic Ratio

XRu,bulk [%]0 20 40 60

j [A

cm

-2]

0.0

0.1

0.2

0.3

0.4

0.580°C 60°C40°C

Achievement: Optimum bulk composition of the anode catalyst found to be 55 ± 5 at% Ru, regardless of temperature.

Collaboration with Johnson MattheyC


Membrane / MEA ResearchEffect of Processing on Membrane Performance

Membrane MeOH Permeability Conductivity Selectivity Relative ED10^6 (cm2/s) mS/cm 10 -̂6 mS s/cm3 Selectivity

N117 2.73 84.7 31.0 1.0 ~3.3

BPSH-40 (A) 0.50 38.5 76.3 2.5 ~1.5BPSH-35 (B) 0.81 43 53.1 1.7 1.3BPSH-40 (B) 1.40 38.1 27.2 0.9 2.7

(a) (b)

(c) (d)

A B

BPSH-40

BPSH-35

A B

A – Membrane before processingB – Membrane after processing

Processing greatly affects BPSH polymer properties and morphology; after processing, BPSH-35 (B) becomes similar to BPSH-40 (A).


Membrane / MEA ResearchDMFC MEAs with Alternative Polymers

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 50 100 150 200 250

Current Density (mA cm-2)

Volta

ge (V

)

0

20

40

60

80

100

120

140

0 100 200 300 400 500

Current Density (mA cm-2)

Cro

ssov

er C

urre

nt (m

A c

m-2

)

N117

N117

BPSH-35 (B)

BPSH-35 (B)

Achievement: In short-term testing, with ambient air at 80°C and 1.0 M MeOH anode feed, BPSH-35 (B) offers significantly reduced methanol crossover and comparable performance to Nafion 117.

Collaboration with Virginia Tech C


Membrane / MEA ResearchMEA Issues Critical to Further Progress

Membrane Fuel Cell

Conductivity (mS cm-1)

Membrane Conductivity

(mS cm-1)

Fuel Cell Relative

Selectivity

Membrane Relative

Selectivity

Nafion 117 85 110 1.0 1.3 BPSH-40 (A) 38 80 2.5 4.4 BPSH-50 (A) 40 100 1.3 3.8 BPSH-60 (A) 52 170 1.1 2.5

Ion Clad 26 130Tricoli 1.5 5.7

• Based on membrane properties alone, relative selectivity of “alternative” MEAsshould be higher than observed in DMFC testing.

• “Fuel cell conductivity” needs to be improved.• More research required - with Nafion-free catalyst layers in particular.


22 W DMFC Stack for Portable PowerHigh Efficiency, Ambient Pressure & Low Cathode Air Flow


0.00 0.05 0.10 0.15

Stac

k Po

wer

(W)

0.00

5.00

10.00

15.00

20.00

25.00

30.00

60°C

70°C

80°C

fMeOH = 3.0 mL min-1 cell-1

fAir = 0.1 sLM cell-1

pAir = 0.76 atm (ambient)

Achievement: Very good performance demonstrated at ambient cathode pressure (0.76 atm), low air flow (λ < 3) and relatively high stack voltage of ~12V (0.55 V cell-1).

Collaboration with Ball AerospaceC


500 W Prototype Stack / System Development for APUOn Track with Stack Deliverable in Fall 2002


0.0 0.1 0.2 0.3 0.4 0.5 0.6

Cel

l Vol

tage

(V)

0.0

0.2

0.4

0.6

0.8

Cell Pow

er (W)

0

6

12

18

24

100 cm2 MEA, 80°C

Stoich 2.1

APU Stack: High-conductivity 100-cm2 graphite hardware used in the first-generation APU cell. Performance recorded:

2.1 air stoich, 30 psig cathode back pressure: ~ 21 W1.3 air stoich, ambient cathode pressure: ~ 11 W


APU Hardware & Flow ModelingPressure Drop – Air Flow – Stack Hardware

0.0

0.4

0.8

1.2

1.6

2.0

0 200 400 600 800 1000

Cathode Feed Rate (sccm)

Cel

l Pre

ssur

e D

rop

(psi

)

Calculated Pressure Drop

Experimental Data

100-cm2 Cell Pressure Drop

Manifold Flow Models

Air flow: 0.6 m/s

Alternative Compression Approach


FY 2002: Summary

Reduction in Catalyst Loading:

Composition of cathodes with reduced Pt loading optimized; good performance with a total precious metal loading of 1.2 mgcm-2 demonstrated at 80°C – task completed

Catalyst Research:Alternative Pt-X cathode catalyst identified (patent pending)In-house catalyst fabrication capability established; system used to make - commercially unavailable - 80wt%Pt/C cathode catalystStudy of the effect of Pt-to-Ru atomic ratio on anode performance at different cell operating temperatures – task completed


FY 2002: Summary (II)

Membrane Research:Well-performing BPSH (sulfonated poly(arylene ether sulfone))MEAs with significantly reduced methanol crossover demonstrated – task completedDemonstration of short stack with 3× better selectivity – pending

Stack R&D:

Components for 22 W DMFC stack for portable power applications designed, fabricated and optimized in single-cell and short-stack testing; first 22 W stack built and delivered to Ball Aerospace

Components for 500 W stack for auxiliary power applications under development; single cell operation of 100-cm2 hardware demonstrated with good results – task on schedule (stack delivery planned for the fall of 2002)


FY 2003 Plans

• Continue fundamental research and development in electrocatalysis of methanol oxidation and oxygen reduction; improve performance by optimizing hydrophilic/hydrophobic properties of the cathode (Sep 03)

• Study and report on the effect of sulfonation on performance of BPSH membranes in direct methanol fuel cells; narrow the gap between bench-top and fuel-cell selectivity of alternative membranes to no more than 30% (May 03)

• Demonstrate for at least 500 hours durability of Nafion and alternative MEAs (no more than 15% performance loss) (May 03)

• Demonstrate for at least 100 hours sustained operation of a “portable power” DMFC stack with air stoich below two (May 03)

• Investigate composition of the DMFC cathode exhaust as a function of cell operating conditions (Sep 03)

Materials Science & Technology Division Los Alamos National … · 2006. 3. 8. · Materials...

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Transcript of Materials Science & Technology Division Los Alamos National … · 2006. 3. 8. · Materials...