Fuel Cell-Performance and Durability--Modeling, Evaluation

1

2016 DOE Fuel Cell Technologies Office Annual Merit Review

2016 DOE Hydrogen and Fuel Cells Program Review

XYZ: Thrust Area # Co-ordinatorRod & Adam: FC PAD Directors

Wednesday, June 8th, 2016

FC-PADFuel Cell – Performance and Durability

FC139 – Modeling, Evaluation, CharacterizationPresenter : Rangachary Mukundan

This presentation does not contain any proprietary, confidential, or otherwise restricted information.


June 8th, 2016

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Overview - Relevance

Project start date: 11/20/2015Project end date: 09/30/2020

• Durability of PEMFC stacks, which must include tolerance to impurities and chemical and mechanical integrity, has not been established

• Sufficient durability of fuel cellsystems operating over automotivedrive cycles has not beendemonstrated

• Development and implementation ofaccelerated stress tests (ASTs) areneeded to shorten the time requiredto address durability issues

• MEA Targets:• 300mA @ 0.8V• 1W/cm2 @ rated power• 5000 hour durability

Timeline Barriers

National Labs• ANL, LANL, LBNL, NREL, and ORNL

• IRD, New Mexico• Umicore, Germany• GM, USA• W. L. Gore, USA• Ion Power, USA• Tanaka Kikinzoku Kogyo (TKK), Japan• National Physical Laboratory, United

Kingdom

External Collaborators

5


Overview - Approach (Operando Evaluation/Durability)

Refine ASTs• Proposed new membrane and electrocatalyst ASTs

Evaluate durability of Pt-alloy catalyst based MEAs and proposemethods to improve durability• Operando evaluation, Characterization and Modeling

Impurity effects on fuel cell performance• Reversible/Recoverable degradation (membrane degradation fragments)• Sulfate anion poisoning

Benchmark SOA MEA• Obtained MEA with membrane from Gore and SOA catalyst from GM

Develop/Apply advanced electrochemical characterizationtechniques• Reference electrodes

6


Accomplishments : Adoption of Membrane ASTSevere degradation of DuPont XL® after 307 hours @ OCV

No degradation of DuPontXL® 20098 RH Cycles

Degradation of DuPont XL®

9934 RH Cycles in OCV

Mechanical : RH cycling @ 80 oC, Air (saturated = 2mins, dry = 2mins)Target = 1333 hours (20,000 cycles)Chemical: OCV hold at 90 oC, 30%RHTarget = 500 hoursCombined : RH cycling @ 90oC; H2/Air (saturated = 30s, dry = 45s)Target = 500 hours (24,000 cycles)

• 30sec wet and45sec dry cycles inH2/Air

• Similar RH stressesas determined byHFR

• Cycling time needsto be adjustedbased on HFR

See additional slide for FCTT adopted AST

7


Accomplishments : Adoption of Electrocatalyst AST

Target = 133 hours

0.6 to 1.0V cycles

Target = 50 hours

0.6 to 0.95V cycles

0

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0 1000 2000 3000 4000 5000 6000

% E

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Los

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Time (hrs)

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0 20000 40000 60000 80000 100000

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# of Potential Cycles

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See additional slide for FCTT adopted AST

• New AST 20X faster than oldAST and 100X faster thanFCTT durability protocol

Higher N2 flow rates (200sccm vs 75sccm)

8


Accomplishments : Refined catalyst AST

• Acceleration factor can be increased with increasing N2 flow rate• High N2 flow (200 sccm) results in 100X acceleration while low N2

flow (75 sccm) results in 25X acceleration• Spatial variation in degradation is greater at the higher flow rate• Use 75sccm N2: 5X acceleration over old AST

0

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0 50 100 150

% E

CSA

Loss

Time (hrs)

0.15mg.Pt/cm2 of Pt/C-HSA

New AST (1-serp)

Modified Old AST (0.6V to 0.95V) 1-serp

New AST (4-serp)

New AST (4-serp, high flow)

4.9nm to 5.4nm

4.3nm to 4.6nm3.6nm

4.8nm

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0 1000 2000 3000 4000 5000

% E

CSA

Loss

Time (hrs)

Pt/C @ 0.15mg.Pt/cm2

FCTT : Drive cycle: TEC10E20E

Old AST (5X): TEC10E20E

New AST (25X) : TEC10E20E

New AST Low flow 4-serp (25X) : TEC10E20E

New AST High flow 4-serp (100X) : TEC10E20E

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Cathode half-cell model extending from gas channel to CCL

Nearly uniform ORR flux in CCL for Rc/Rf = 0.05

Non-uniform ORR flux in CCL for Rc/Rf = 5

14


Accomplishments : Modeling

O2 Transport Resistances in Saturated Alloy catalyst

Rg: Gas channel resistanceRd: GDL resistanceRcf: Combined resistance of CCL pores and ionomerRc: CCL pore resistanceRf: ionomer resistance

Assumptions O2 transport in GDL is by molecular diffusion: diffusivity is inversely

proportional to pressure O2 transport in 20-100 nm CCL macros is by Knudsen diffusion: diffusivity

weakly dependent on P O2 transport in ionomer film and micro pores is independent of pressure Water breaks through GDL because gas channel RH is 100%: Rd = Rd(P, i) Ionomer is saturated with water and CCL pores contain liquid water : Rcf =

Rcf(i)

0

25

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125

150

0.0 0.5 1.0 1.5 2.0 2.5

R, s

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Current Density, A.cm-2

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2.5 atm

Rcf

1.5 atm

1.1 atm

Rd

Rg

0

50

100

150

0.0 0.5 1.0 1.5 2.0 2.5

R, s

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Current Density, A.cm-2

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Rc

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Rc and RfTransport ResistancesCathode catalyst layer pore resistance and GDL resistance are primary contributors at high current density (100% RH)

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16


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20% PtCo-Vulcan

• Noticeable poisoning effect by sulfates in RDE• PtCo alloy catalyst shows a larger decrease in performance with sulfate anions

• 10 mV shift for Pt/C ; 30 mV shift for PtCo/C• Pt and PtCo alloy catalyst show full recovery after removal of the anions• Onset of OH ads. shifts to higher potentials• ORR inhibition affected by scan rate and direction (anodic vs cathode scan)

Accomplishments – Sulfate ORR Inhibition (Ex situ)

20% Pt-Vulcan

Shift in onset of Pt-Ox ORR inhibition and recovery

17


Accomplishments – Sulfate Anion Contamination (In situ)

• Sulfate infusion causes degradation in fuel cell performance at 0.6 A/cm2 when the cathode loading is 0.1 mgPt/cm2 (no effect at 0.2 A/cm2 and 0.4 mgPt/cm2)

• The adsorption of sulfate anions on the cathode catalyst resulted in performance loss of ∆V1 = 24 mV

• Membrane resistance (HFR) was not affected by sulfate contaminant• Voltage loss not recovered when infusion was stopped (∆V2 = 28 mV).• Sulfate caused degradation appears to be reversible after potential cycling

recovery step.• Low voltages and high RH’s have been reported to result in recovery

18


• After infusion, Pt CV shows a decrease in ECSA• After several CVs from low (0.085V) to high (1V)

potentials, ECSA was partially recovered andperformance almost fully recovered

• Recovery potential needs to be <= 0.3V for sulfateanions

• Cathode environment irrelevant between: N2 or Air• Liquid water injection observed to hurt recovery

Accomplishments – Sulfate Anion Contamination (recovery)

Recovery of Pt-Ox

OCV tests

Infusion recovery

11 mV/hr

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Benchmarking

• W. L. Gore provided 18 µm membrane to GM• GM applied SOA catalyst layer of 0.1mgPt/cm2

@ cathode• MEA meets DOE BOL Mass activity target (FC

137)• Will be used in durability protocol, membrane

AST protocols, and catalyst/support ASTprotocols to benchmark SOA MEA

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22


Collaborations

Institutions Role

FC-PAD Consortium ANL, LBNL, ORNL, LANL, NREL

Umicore, TKK Supply SOA catalysts for evaluation

IRD, Ion Power Supply SOA catalysts and/or MEAs for evaluation

NPL Reference electrode Setup

GM/W.L. Gore Supply SOA MEA for Benchmarking

23


Proposed Future Work

• Plans for the remainder of FY16o Complete durability evaluation of PtCo alloy catalyst based MEAso Complete development of reference electrode setupo Systematically evaluate effect of sulfate infusion as a function of potential

and during durability cycling protocolo Quantify effect of reversible degradation under durability cycling protocol

• Plans for FY 17o Evaluate durability of PtNi and advanced carbon based MEAso Use segmented/reference cell to evaluate effect of operating parameters

on durabilityo Model durability of MEAs under both AST and durability cycling protocolso Benchmark durability of SOA MEA (durability cycling , membrane AST, and

support AST)o Adopt a differential cell for single cell durability testingo Evaluate effect of system contaminants on low loaded SOA MEAs

24


Summary

• Relevance: Evaluate durability of SOA MEAs, determine degradation mechanisms, propose mitigation strategies to meet DOE 2020 durability targets for MEAs that can meet the DOE 2020 Pt loading and BOL performance targets. Refine ASTs to evaluate the durability of MEAs.

• Approach: Our approach involves developing advanced diagnostics, modeling and characterization techniques to evaluate SOA MEAs and provide insights to improve the durability of the MEA components to meet DOE 2020 performance and durability targets.

• Accomplishments and Progress: 2 new ASTs have been adopted by the DOE. Durability studies of SOA MEAs meeting BOL targets have been initiated. Benchmarking of SOA MEA initiated. Reference electrode setup being developed for durability studies.

• Future work: Identify all degradation mechanisms in SOA alloy catalysts and quantify voltage losses (especially in the mass transport region). Develop mitigation strategies. Complete the development of advanced tools and models.

25

2016 DOE Fuel Cell Technologies Office Annual Merit ReviewSupplemental Slides

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Table A5 Membrane Chemical/Mechanical Cycle and Metrics (Test Using a MEA)

a. Step durations of 30 s dry and 45 s wet were selected in testing at LANL so that the HFR at the end of the drystep was 2.5 times the HFR at the end of the wet step, which is approximately equal to the HFR ratio that occurswhen running the mechanical test (Table A4). Depending on hardware used, these step times may need to beadjusted to achieve the same HFR variation.

b. Tested in MEA on H2, 80°C, fully humidified gases, 1 atm total pressure. See M. Inaba, et. al. ElectrochimicaActa, 51, 5746, 2006. Crossover recorded after 2 min of drying under 0% RH conditions.

c. Hydrogen crossover and OCV targets should be achieved at 0 kPa pressure differential and at 50 kPa anodeoverpressure, providing sensitivity to global membrane thinning and to hole formation, respectively.

d. A protocol such as the one in Table A9 should be used to recover reversible losses at least once every 24 h andprior to each measurement of metrics.

e. Measured at 0.5 V applied potential, 80ºC, 100% RH N2/N2. Compression to 20% strain on the GDL.

Cycle ycle 0% RH (30 s) to 90oC dewpoint (45 s), single cell 25-50 cm2

Total time Until crossover >15 mA/cm2 or 20,000 cyclesTemperature 90°C Relative Humidity Cycle from 0% RH (30 s) to 90°C dewpoint (45 s)a

Fuel/Oxidant H2/Air at 40 sccm/cm2 on both sides Pressure Ambient or no back-pressure

Metric Frequency Target F- release or equivalent for non-fluorine membranes

At least every 24 h No target – for monitoring

Hydrogen Crossover (mA/cm2)b,c

Every 24 h <15 mA/cm2

OCVc,d Continuous Initial wet OCV ! 0.95 V, <20%OCV decrease during test

High-frequency resistance Every 24 h at 0.2 A/cm2 No target – for monitoring Shorting resistancee Every 24 h >1,000 ohm cm2

Documents

Fuel Cell-Performance and Durability--Modeling, Evaluation