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Performance Measurement of MEAs

214th Meeting of the Electrochemical Society-HTM Working GroupHonolulu, HI, Thursday, October 16th, 2008

Shyam S. Kocha*(Advanced Electrocatalysts Group, Fuel Cell Laboratory,

Nissan Research Center, Japan.*Currently: NTCNA-Fuel Cell Laboratory, Farmington Hills, MI)

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Outline

1. Measurement of MEA Performancei. Measurement of ECAii. Measurement of ORR activityiii. Effect of RH and T on

a) Performance/Activityb) Membrane resistancec) Catalyst Layer resistance

2. Current Status - PEMFC3. Overview of Requirements &Testing

i. Expected MEA operating environmentii. Electrolyte membrane target performanceiii. Electrolyte membrane durabilityiv. Target cost of membranev. Automotive fuel cell MEA degradation map

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3

Measurement of MEA Performance

4

4

25cm2

72mm

72m

m

50mm

50m

m

Membrane

Catalyst Coated Area

Fuel Cell Specification

Typical subscale cell used intesting of MEA performanceand durablity.

5

-60

-40

-20

0

20

0 0.2 0.4 0.6 0.8 1

Potential / V vs. RHE

Cur

rent

Den

sity

/ m

Acm

-2

5

N2 Flow Rate at Cathode*Cell TemperatureCell RH

CathodeAnode

80 oC

N2 0.5 SLPM

e-

Cell Temperature 80 oCN2 Flow Rate 0.5 SLPM

? H20.5 SLPM

Hads

H2Cross Over

Cyclic Voltammograms- Issues

*M. Uchimura and S. S. Kocha, AIChE Abstracts Fall 2007.

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-20

-15

-10

-5

0

0.0 0.1 0.2 0.3 0.4

Potential / V vs. RHE

Cur

rent

Den

sity

/ m

Acm

-2

2.0 SLPM0.25 SLPM 0 SLPM Water

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1) R. Woods, J. Electroanal. Chem., 49, 217-226 (1974).2) D. A. J. Rand and R. Woods, J. Electroanal. Chem., 35, 209 (1972).

H2 Evolution Onset Shift

Cell Temp. 30 oC

High N2 flow rates result in a shift of the H2 onset towards positive potentials-leading to smearing of Hads peaks.

Zero N2 flow rate is recommended for ECA diagnostics.

Effect of N2 Flow Rates on CV

M. Uchimura and S. S. Kocha, ECS Transactions 11, 1215 (2007).

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-10

-8

-6

-4

-2

0

0.0 0.1 0.2 0.3 0.4

Potential / V vs. RHE

Cur

rent

Den

sity

/ m

Acm

-2

30 oC45 oC60 oC80 oC

30 oC45 oC60 oC80 oC

7

-10

-5

0

5

10

0.0 0.2 0.4 0.6 0.8 1.0Potential / V vs. RHE

Cur

rent

Den

sity

/ m

Acm

-2

Ph.D. Disseration of M. Oudenhuijzen“Support Effects in Heterogeneous Catalysis”, Chapter 6, p.104 (2002).

-23 oC

175 oC

75 oC

PtH

Effect of Cell Temperature on CV

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Effect of RH - CV

Onset of oxide formation shifts positively as RH decreases.

-40

-30

-20

-10

0

10

20

30

40

0.0 0.2 0.4 0.6 0.8 1.0Potential / V vs. RHE

Cur

rent

Den

sity

/

mA

cm-2

RHa/RHc=90/90%RHa/RHc=70/70%RHa/RHc=50/50%RHa/RHc=30/30%

Should one measure CVs at low or high RH toevaluate I-V performance at low RH?

Nissan, unpublished data.

Hads

Onset of oxide formation

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0

20

40

60

80

100

Sample Number

ECA

/ m

2 g-1

N2 Flow Rate / SLPM 0Cell Temperature / oC 30Voltage Scan Range / V 0.04 - 0.9

ECA Measurement Conditions

78±3 m2g-1

0 5020 30 4010

78

100

0

30

60

90

120

Half CellHClO4

In-situMEA

Pt S

urfa

ce A

rea

/ m2 g-1

Reproducibility and Utilization

80% Utilization

M. Uchimura and S. S. Kocha, ECS Transactions 11, 1215 (2007).

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Reasons for ScatterCatalyst LoadingSurface AreaOperating ConditionsProtocol Used• Pre-conditioning• Intermediate-conditioning• Direction of Sweep

Oxide Coverage

ORR Activity

Scatter in values of ORR activity reported in the literature.

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Nissan Abstracts on Pt - Oxides : This meeting

Abstract 914The Influence of Pt-oxide Coverage on the ORR Reaction Order in PEMFCsM.Uchimura and S. Kocha

Abstract 919MEA Performance Modeling for Breakdown of Catalyst Layer Polarization Components.Y. Suzuki, S. Sugawara, N. Horibe, S. Kocha and K. Shinohara

Abstract 1036Simultaneous Electrochemical Measurement of ORR Kinetics and Pt Oxide Formation/ReductionS. Sugawara, K. Tsujita, S. S. Kocha , K. Shinohara, S. Mitsushima and K. Ota,

214th Meeting of the Electrochemical SocietyHonolulu, HI, 2008

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12

i / A

Time

Inter.-Cond. (1 A/cm2)

Inter.-Cond. (OCV)

Cell Temp. 80 oC, RH 100 %, PO2 : ~ 70 kPa

i / A

Time

(+)

(+)

(-)

(-)

i / A i / A

Time Time

Schematic of Measurement Protocols

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0.80

0.85

0.90

0.95

0.01 0.10 1.00

Current Density / Acm-2

iR-F

ree

Volta

ge /

V

Negative(-)

Positive(+)

0.80

0.85

0.90

0.95

0.01 0.10 1.00

Current Density / Acm-2

iR-F

ree

Volta

ge /

V

0.80

0.85

0.90

0.95

0.01 0.10 1.00

Current Density / Acm-2

iR-F

ree

Volta

ge /

V

Negative(-)

Positive(+)

Solid : w/o Inter.-conditioningHollow : w/ Inter.-conditioning

Positive(+)

PositiveNegative

4224

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i0.9 / mAcm-2

×1.75

ORR Activity - Tafel Plots

Benchmarking data from different laboratories is difficult

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ORR Activity – Modeling

Importance of Pt Oxide Film on ORR Kinetics

Adsorbed oxygen species can(1) block the adsorption of O2 on active Pt sites.(2) alter the adsorption energy of reaction intermediates.

N.M. Markovic, et al., J. Electroanal. Chem., 467, 157 (1999).

( ) ⎟⎠⎞

⎜⎝⎛−⎟

⎠⎞

⎜⎝⎛−−=

RTθrγ

RTηFβθnFKCi expexp1

2O

Effect of oxide on activity was included and fitted to MEA ORR results.

Abstract 919 (214th Meeting of the Electrochemical Society, Honolulu, HI, 2008)MEA Performance Modeling for Breakdown of Catalyst Layer Polarization Components.Y. Suzuki, S. Sugawara, N. Horibe, S. Kocha and K. Shinohara

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0.6

0.7

0.8

0.9

1.0

1.1

0.001 0.01 0.1 1 10

H2 X-over Corrected Current density / A cm-2

iRFr

ee V

olta

ge /

V

(+)

Model

- Extended Butler-Volmer Eq.

- Resistance-EIS + Finite trans. model

- Oxide Coverage (θ)

- Single i0

(-)H2-O2; 15 mins/point

ORR Activity – Modeling

Abstract 919MEA Performance Modeling for Breakdown of Catalyst Layer Polarization Components,Y. Suzuki, S. Sugawara, N. Horibe, S. Kocha and K. Shinohara

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Effect of RH

- Catalyst Activity- Membrane Resistance- Catalyst Layer Resistance

The key parameters that need to be measured to characterize high temperature/low RH membranes using MEAs in subscale fuel cells are the following:

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Effect of RH: Activity

Kinetic reaction order: < 1ECA : Small effectTafel : Higher at lower RHActivity: decreases at low RH below 50%

“Effect of Elevated Temperature and Reduced RH on ORR Kinetics for PEM Fuel Cells”Hui, Xu, Ying Song, H. Russell Kunz, and James M. Fenton, J. Electrochem. Soc., 152 (9), (2005)

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Effect of RH – IV Peformance, HFR

HFR increases and performance decreases as RH decreases.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6Current Density / Acm-2

Cel

l Vol

tage

/ V

0

200

400

600

800

1000

1200

1400

1600

HFR

(@R

img=

0) /

mΩ

cm2

RHa/RHc=30/30%RHa/RHc=50/50%RHa/RHc=70/70%RHa/RHc=90/90%

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Effect of RH – Catalyst Layer R

Ionomer resistance in the catalyst layer increases at lower RH.

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

Zreal / Ωcm2

Zim

ag /

Ωcm

2

RHa/RHc=90/90%RHa/RHc=70/70%RHa/RHc=50/50%RHa/RHc=30/30%

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Current Status - PEMFC

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Current Status – Improved Stacks

MEA (Membrane Electrode Assembly): Double the power density is achieved through improved conductivity of the electrolyte layer within the MEA, where the main chemical reaction occurs, coupled with a more densely-packed cell structure.

Cell Structure: A more densely-packed cell structure is achieved through the replacement of the carbon separator with a new thin metal separator. The separator functions to break down the hydrogen, oxygen and cooling water necessary for the chemical reaction. A specific coating applied to the separator helps improve conductivity and prevents chemical corrosion, leading to increased efficiency and durability throughout the fuel cell stack’s life-cycle.

Electrode: Higher durability electrode material results in a 50% reduction of the platinum required compared to the previous generation. This in turn, provides a significant breakthrough in the cost of these components.

Stack size and cost: The combined improvements in the cell result in double the power density, which enables a downsizing of the fuel cell stack size by one-third and significant cost reduction, without sacrificing performance. Compared to the previous generation, the new generation stack’s power output is increased 1.4 times from 90kW to 130kW, which can power larger vehicles. Stack size is reduced by 25% to 68L from 90L, which allows for improved packaging flexibility.

Need further improvementsin terms of a HTM-MEA that operates at high T and low RH to achievePEMFC system cost targets.

Not Enough!

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Overview of Requirements &Testing

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PEMFC: Targets and Protocols in Japan

FCCJ

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Operating Environment & Target Performance

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Membrane Durability

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Membrane Durability - Map

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END