Degradation behavior of PEMFC - eLib - DLR

DLR.de • Chart 1

Degradation behavior of PEMFC P. Gazdzicki, J. Mitzel, A. Dreizler, M. Schulze, K.A. Friedrich German Aerospace Center (DLR), Institute of Engineering Thermodynamics, Pfaffenwaldring 38-40, 70569 Stuttgart, Germany

DLR.de • Chart 2

Contents • Motivation • Irreversible Degradation • Reversible Degradation • Performance vs Pt-loading • Degradation vs Pt-loading • Summary

DLR.de • Chart 3

Requirements for PEMFC development  Reduction of manufacturing cost at increased durability in order to compete with conventional technologies

Challenge Cost

[Multi-Annual Work Plan (2014-2020), FCH JU]

Durability

Performance

[U.S. DOE 2015 Annual Merit Review]

 Most promising regarding cost reduction: catalyst layer (45 % of stack cost) • Low loadings • Alternative catalysts

DLR.de • Chart 4

Motivation Performance targets clearly defined and well verifiable, BUT determination of degradation rates is not well defined. How to determine if durability goals are achieved? Discrimination between reversible and irreversible degradation needed

• •

j = 1 A/cm2 Refresh interruptions

• •

j = 0.5 A/cm2 Refresh interruptions

www.DLR.de • Chart 5

Evaluation of irreversible degradation Durability tests consist of several test blocks of an operation period and a recovery procedure

Test block

automotive Operation period

Recovery procedure

stationary

www.DLR.de • Chart 6

Evaluation of irreversible degradation Durability tests consist of several test blocks of an operation period and a recovery procedure

Test block

automotive

stationary

Operation period

Single FC-DLC cycle

20 min Recovery procedure

DLR.de • Chart 7

Evaluation of irreversible degradation Use voltage values before or after refresh?

MEA Y

DLR.de • Chart 8

Evaluation of irreversible degradation Use voltage values before or after refresh?

MEA X

MEA Y

DLR.de • Chart 9

Evaluation of irreversible degradation Constant and non-constant reversible degradation  decay rate(…): combination or reversible an irreversible degradation  decay rate(---): irreversible degradation MEA X

MEA Y

DLR.de • Chart 10

Recovery of reversible degradation

- Water management plays major role in recovery - Reason for recovery at low loads unclear Gazdzicki et al. (2016) J. Power Sources, doi: 10.1016/j.jpowsour.2016.07.049

www.DLR.de • Chart 11

Reversible degradation

const. load 80%RH const. load 50%RH OCV transient

• Reversible degradation very sensitive to operation conditions  mitigation by e.g. OCV transient

www.DLR.de • Chart 12

Reversible degradation Improved MEA components

• Reversible degradation very sensitive to operation conditions  mitigation by e.g. OCV transient • Mitigation by MEA modification

www.DLR.de • Chart 13

Evaluation of reversible degradation Mathematical description of reversible degradation

membrane failure

1A/cm2

Amplitude of exp. part responsible for increase of reversible degradation with operation time

DLR.de • Chart 14

Pt-Loading Rainbow Stack Study

DLR Rainbow-Stack Pt-loadings at anode/cathode in mgPt/cm2

Different Pt loadings

Different Pt loadings

DLR.de • Chart 15

Performance Vs Pt-loading BoT Voltages versus Loading

Const. anode loading

Const. cathode loading

• Clear dependence of Cell Voltage on cathode Pt loading • No dependence of Cell Voltage on anode Pt loading

DLR.de • Chart 16

Performance Vs Pt-loading BoT Voltages versus Loading

Const. anode loading

Const. cathode loading

• Clear dependence of Cell Voltage on cathode Pt loading • No dependence of Cell Voltage on anode Pt loading • Onset of mass transport issues observed at cathode loading 1 A/cm2

DLR.de • Chart 17

Performance Vs Pt-loading

SOURCE: A. Kongkand and M.F. Mathias, J. Phys. Chem. Lett. (2016), 7, 1127

BoT Voltages versus Loading

Const. anode loading

Const. cathode loading

0.1 mgPt/cm2

• Clear dependence of Cell Voltage on cathode Pt loading • No dependence of Cell Voltage on anode Pt loading • Onset of mass transport issues observed at cathode loading 1 A/cm2

DLR.de • Chart 18

Degradation Vs Pt-loading

~500 h FC-DLC degradation test 20 min 1.00 A/cm2

0.42 A/cm2 0.05 A/cm2

DLR.de • Chart 19

Degradation Vs Pt-loading: evaluation of rev. degradation

-0.6

Degradation Rate / mV h-1

-0.5 -0.4 -0.3 -0.2 -0.1 0

1.00 A/cm2 Irreversible Degradation rates - voltage 1 h after refresh Degradation rates - voltage 1 h before refresh

DLR.de • Chart 20

Degradation Vs Pt-loading: evaluation of rev. degradation Degradatioon rate before -after refresh / mV h-1

0.4

1.00 A/cm2

0.3 0.2 0.1 0 -0.1 0

5 Cathode ECSA / C

-0.6

Degradation Rate / mV h-1

-0.5 -0.4 -0.3 -0.2 -0.1 0

1.00 A/cm2 Irreversible Degradation rates - voltage 1 h after refresh Degradation rates - voltage 1 h before refresh

10

DLR.de • Chart 21

0.4 Degradatioon rate before -after refresh / mV h-1

Degradation Vs Pt-loading: evaluation of rev. degradation

1.00 A/cm2

0.3 0.2 0.1 0 -0.1 0

5

10

Cathode ECSA / C Degradatioon rate before -after refresh / mV h-1

cathode loading 0.4 mg cm-2

=0.4 mg cm-2