Water management plays major role in recovery. - Reason for ... mitigation by e.g. OCV transient ... Clear dependence of Cell Voltage on cathode Pt loading.
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