DLR.de Chart 1. Determination of Degradation Rates. Pawel Gazdzicki, DLR

Transcription

1 DLR.de Chart 1 Determination of Degradation Rates Pawel Gazdzicki, DLR

2 DLR.de Chart 2 Contents Motivation Evaluation of irreversible degradation Evaluation of reversible degradation Recovery of reversible degradation Degradation vs Pt-loading Summary

3 DLR.de Chart 3 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/cm 2 Refresh interruptions

4 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 Questions: j = 1 A/cm 2 1. How to determine irreversible Refresh interruptions degradation? 2. How to describe reversible degradation? 3. Does refresh procedure lead to full recovery of reversible losses?

5 DLR.de Chart 5 Evaluation of irreversible degradation

6 DLR.de Chart 6 Evaluation of irreversible degradation Durability tests: several test blocks of operation period followed by a recovery procedure FC dynamic load cycle (FC-DLC) according to FCH-JU StackTest project Automotive conditions Test block automotive Operation period 20 min Single FC-DLC cycle Recovery procedure

7 DLR.de Chart 7 Evaluation of irreversible degradation FC dynamic load cycle (FC-DLC) according to FCH-JU StackTest project Pseudo I-V curve obtained from each cycle 0.00 A/cm A/cm A/cm A/cm A/cm A/cm 2 FC-DLC cycles

8 DLR.de Chart 8 Evaluation of irreversible degradation Use voltage values at start of each test block, i.e. after refresh MEA Y

9 DLR.de Chart 9 Evaluation of irreversible degradation Use voltage values at the end of each test block, i.e. before refresh MEA Y

10 DLR.de Chart 10 Evaluation of irreversible degradation MEA X MEA Y

11 DLR.de Chart 11 Evaluation of irreversible degradation Constant and non-constant reversible degradation MEA X MEA Y

12 DLR.de Chart 12 Evaluation of irreversible degradation Constant and non-constant reversible degradation decay rate( ): combination or reversible an irreversible degradation MEA X decay rate(---): irreversible degradation MEA Y

13 DLR.de Chart 13 Evaluation of irreversible degradation Constant and non-constant reversible degradation decay rate( ): combination or reversible an irreversible degradation MEA X decay rate(---): irreversible degradation MEA Y Need to define time period to calculate mean U values

14 DLR.de Chart 14 Evaluation of reversible degradation

15 DLR.de Chart 15 Evaluation of reversible degradation Systematic FC-DLC test for accurate determination of reversible degradation 1A/cm 2 Reversible degradation can be described by a linear-exponential function

16 DLR.de Chart 16 Evaluation of reversible degradation Systematic FC-DLC test for accurate determination of reversible degradation membrane failure 1A/cm 2 Amplitude of exp. part responsible for increase of reversible degradation with operation time

17 DLR.de Chart 17 Recovery of reversible degradation

18 DLR.de Chart 18 Recovery of reversible degradation Test of conditions that occur during shutdown recovery procedure and could be the reason for recovery Stop gas supply Drying reduction of T cell OCV period purging anode with air potential sweep low potential, N 2 purge Switch off load stop gas supply let cell cool down to RT

19 DLR.de Chart 19 Recovery of reversible degradation Recovery by shutdown could not be exceeded by any other procedure It is assumed that shutdown leads to full recovery of reversible losses Gazdzicki et al. (2016) J. Power Sources, doi: /j.jpowsour

20 DLR.de Chart 20 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: /j.jpowsour

21 DLR.de Chart 21 Degradation Vs Pt-loading DLR Rainbow-Stack Pt-loadings at anode/cathode in mg Pt /cm 2

22 DLR.de Chart 22 Degradation 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

23 DLR.de Chart 23 Degradation 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 <=0.2 mg/cm2 and j>1 A/cm2

24 DLR.de Chart 24 Degradation Vs Pt-loading ~500 h FC-DLC degradation test 20 min 1.00 A/cm A/cm A/cm 2

25 DLR.de Chart 25 Degradation Vs Pt-loading: evaluation of irrev. degradation Significant increase of irrev. degradation for cathode loading <0.2 mg/cm 2 and high loads Determination of irrev. degradation (cells 4..9)

26 DLR.de Chart 26 Degradation Vs Pt-loading: evaluation of rev. degradation Degradation Rate / mv h A/cm 2 Irreversible Degradation rates - voltage 1 h after refresh Degradation rates - voltage 1 h before refresh

27 DLR.de Chart 27 Degradation Vs Pt-loading: evaluation of rev. degradation Degradatioon rate before -after refresh / mv h A/cm Cathode ECSA / C Degradation Rate / mv h A/cm 2 Irreversible Degradation rates - voltage 1 h after refresh Degradation rates - voltage 1 h before refresh

28 DLR.de Chart 28 Degradation Vs Pt-loading: evaluation of rev. degradation Degradatioon rate before -after refresh / mv h -1 <0.4 mg cm -2 >=0.4 mg cm A/cm cathode loading <0.4 mg cm -2 cathode loading >0.4 mg cm -2 Degradatioon rate before -after refresh / mv h Cathode ECSA / C 0.42 A/cm Cathode ECSA / C MEAs with cathode loading <0.4 mg cm -2 exhibit non-constant reversible degradation Effect strongest at high current density Degradatioon rate before -after refresh / mv h A/cm Cathode ECSA / C

29 DLR.de Chart 29 Summary

30 DLR.de Chart 30 Summary o Irreversible degradation rate: linear regression of voltage values after refresh

31 DLR.de Chart 31 Summary o Irreversible degradation rate: linear regression of voltage values after refresh o Reversible degradation described by linearexponential function with c i responsible for acceleration of reversible degradation

32 DLR.de Chart 32 Summary o Irreversible degradation rate: linear regression of voltage values after refresh o Reversible degradation described by linearexponential function with c i responsible for acceleration of reversible degradation o Voltage recovery: water management, removal of anodic contaminants

33 DLR.de Chart 33 Summary o Irreversible degradation rate: linear regression of voltage values after refresh o Reversible degradation described by linearexponential function with c i responsible for acceleration of reversible degradation o Voltage recovery: water management, removal of anodic contaminants o Degradation Vs Pt-loading: accelerated rev. degradation for cathode loadings <0.4 mg cm -2 increased irrev. Degradation for cathode loading <0.2 mg cm -2

34 DLR.de Chart 34 Thank you for your attention. The research leading to these results has received funding from the European Union s Seventh Framework Programme (FP7/ ) for Fuel Cell and Hydrogen Joint Technology Initiative under Grant n o (Impact).