Highly-Accessible Catalysts For Durable High-Power Performance

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FC144Highly-Accessible Catalysts forDurable High-Power PerformanceAnusorn Kongkanand (PI)General Motors LLC, Fuel Cell BusinessMay 30, 2020This presentation does not contain any proprietary, confidential, or otherwise restricted information

OverviewTimeline Project start date: 1 Apr 2016Project end date: 31 Mar 2020Percent complete: 100%Barriers B. Cost– A. Durability– Budget Total Funding Spent as of 3/31/20: 3.23M*Total DOE Project Value: 3.99MCost Share: 21.7% Improve kinetic activity and high currentdensity performanceC. Performance– Decrease amount of precious metals.Achieve and maintain high current densitiesat acceptably-high voltagesPartnersSubcontractors:–––––3M CompanyCarnegie Mellon UniversityCornell UniversityDrexel UniversityNRELProject lead: General Motors LLC*Amounts shown are based on invoices to DOE and do not reflect finalinvoice amounts with remaining subcontractor expenditures.2

Relevance:Mass-transport Voltage LossesChallenge: Local Transport LossesCathodemgPt/cm2PtCo, 0.20PtCo, 0.10PtCo, 0.050.90.81.75 A/cm2 on a 0.10mgPt/cm2 cathode0.7Lower Pt loadingVoltage (V)O20.60.5O2O2 through Ionomer/Pt InterfaceO2H , O2ionomerH2/air, 94 C, 250/250 kPaabs,out, 65/65% RHin, st 1.5/2-0.400.511.5H and O2 through CarbonMicropores-2--Pt-Current Density (A/cm²)carbonIonomer & Ionic LiquidCarbon FC087 Dealloyed PtCo and PtNi met Catalyst Targetsdensity, HCD). At HCD, high flux of O2 and proton per a given Pt area causes large voltage loss on low-Pt cathode. The ‘local transport resistance’ dominates the mass transport related loss (purple). Likely a sum of H and O2 resistance at ionomer/Pt interface and in carbon micropores. Want to reduce apparent RPt from 25 s/cm to 10 s/cm, or double the Pt ECSA.(activity and durability)but not MEA Targets (high currentJ. Phys. Chem. Lett. (2016) 1127.3

Approach:Work Focuses in the Past YearSolid New Carbon SupportsPorousAccessiblePorous814O2, H Study local transport using MEA electrochemical diagnostics,microscopy, and simulation. Understand support effects on durability. Optimize PtCo on accessible carbon with emphasis onstabilityKineticTransportkW/gPtO2 Electrolyte-Pt Interfaces: Ionomer and Ionic Liquid Develop process to add ionic liquid in MEA and study itseffect. Identify new electrolyte-Pt interface affects fuel cellperformance.8ionomer-----Pt-carbon Ordered Intermetallic Alloys Use advanced in-situ techniques to optimize activity/stabilityvs Pt-particle-size growth Effects of Co2 and Ce3 Validate cation performance model with in-situ visualization.4

Relevance:MetricTargets and StatusPtCo/KBUnits20162PGM total loading (both electrodes)mg/cmMass activity @ 900 mViR-freeLoss in catalytic (mass) activityPerformance at 0.8V (150kPa, 80 C)A/mg PGM% lossPower at rated power (150kPa, 94 C)W/cmPower at rated power (250kPa, 94 C)Ordered- OrderedPtCo/HSC-fPtCo/HSC-fPtCo/HSC-f PtCo/KB0.125 0.075 (0.025 0.10)†(0.015 0.06)††††DOE2020TargetProjectTarget 0.125 tbd 0.44 40% 0.3 20.80.950.94tbd0.91 1.0-21.011.311.291.151.23- 1.1PGM utilization (150kPa, 94 C)W/cmkW/gPGM6.47.67.5tbd12.1 8 PGM utilization (250kPa, 94 C)kW/gPGM8.110.510.39.216.4- 9.12439*258tbd 30 500 500tbdtbdtbd 30-Catalyst cycling (0.6-0.95V, 30k cycles)Support cycling (1.0-1.5V, 5k cycles)2A/cmmV loss at0.8A/cm2mV loss at1.5A/cm2Reduce overall stack cost byimproving high-current-density (HCD)performance adequate to meet DOEheat rejection and Pt-loading targets. Maintain high kinetic mass activities. Minimize catalyst HCD degradation. Must meet Q/ΔT 1.45or 0.67 V at 94 C* Meet target in absolute term (e.g. 0.26 A/mgPGM)† MA at 0.9VRHE in cathodic directionObjectives Green: meet targetRed: not yet meet targetBlack: NAThis Year Target Highlights No change in status regarding targets. However, validation test result by NREL supports keyimprovement reported earlier by the project.

Approach:Milestones and Go/No GoTASK 1 - Development of Highly-Accessible Pt CatalystsGo/No-go criteria: 1.0 W/cm2, 8 kWrated/gPt, and Q/ΔT 1.7 with Pt/C Downselect carbon support, ionomer, ionic liquidMeasure the effect of leached Co2 and Pt surface areaDevelop dealloyed catalyst from ordered intermetallic alloyVisualize carbon structure and Pt location on selected catalystsModel baseline material 2019 SK 2 - Development of Dealloyed Catalyst with Preferred Catalyst DesignGo/No-go criteria : 0.44 A/mgPGM, 40% mass activity loss with preferred design Develop dealloyed catalyst on preferred supportImplement selected ionomer and ionic liquid with selected catalystsVisualize fresh PtCo/C and post-AST Pt/CModel PtCo/C before and after AST100%100%100%100% 100%100%100%100%TASK 3 - Optimization for Durable HCD and LCD PerformanceMilestone: 1.1 W/cm2, 9.1 kWrated/gPt, and Q/ΔT 1.45 Identify root cause and improve durability and performance of PtCo/CEvaluate effect of selected ionomer/IL on HCD and durability of improved PtCo catalystIntegrate new catalyst design with other state-of-the-art FC componentsMake available to DOE the improved catalyst in 50 cm2 MEAsVisualize and model improved catalyst2016Improved HCD withPt/C2017Durable ORRactivity PtCo/CGo/No-go2018Durable HCDand 2020Diagnostics& ValidationMilestone6

Materials d PartnersProf. MullerElectron MicroscopyProf. LitsterModelingX-ray CTCation effectDr. HaugIonomerDr. Neyerlin Prof. LenertMEA diagnosticsProf. AbrunaCatalyst dev’tCatalyst dev’tMEA integrationDr. BorupCation effectUnfundedPartnersProf. SnyderIonic LiquidDrs. Wang & SasakiCatalyst dev’tAPS & Dr. MyersSAXS, XRF, XASSuppliersCatalyst dev’tProf. ThompsonSupport dev’t7

Technical Accomplishment:SOA Integration & DOE ValidationSOA ComponentsCathode:30 wt.% Intermetallic ordered Pt3Co/HSC-f at 0.06 and 0.10 mgPt/cm2,PFSA ionomer (D2020), 900 EW, I/C ratio of 0.8,Anode:Pt/HSC, 0.015 mgPt/cm2PEM:PFSA with reinforcement layer, 18 μm thickGDL: 210 and 120 μm thick carbon fiber layer with 30 μm MPL. Water proof.MetricPtCo/KBUnitsPtCo/HSC-f2016PGM total loading (both electrodes)Mass activity @ 900 mViR-freeLoss in catalytic (mass) activityPerformance at 0.8V (150kPa, 80 C)Power at rated power (150kPa, 94 C)Power at rated power (250kPa, 94 C)2mg/cmA/mg PGM% loss0.125 Ordered- OrderedPtCo/HSC-fPtCo/HSC-f PtCo/KB 0.075 (0.025 0.10)†(0.015 0.06)††††DOE2020TargetProjectTarget 0.125 tbd 0.44 40% 0.320.80.950.94tbd0.91 1.0-21.311.291.151.23- 1.12A/cmW/cm PGM utilization (150kPa, 94 C)W/cmkW/gPGM1.016.47.67.5tbd12.1 8 PGM utilization (250kPa, 94 C)kW/gPGM8.110.510.39.216.4- 9.12439*258tbd 30 500 500tbdtbdtbd 30-Catalyst cycling (0.6-0.95V, 30k cycles)Support cycling (1.0-1.5V, 5k cycles)mV loss at0.8A/cm2mV loss at1.5A/cm2 As a deliverable, project catalysts were integrated into an MEA with other SOAsubcomponents (within confidentiality constraint), and evaluated at both GM and NREL. Anode Pt loading was further reduced by using high-ECSA Pt/HSC catalyst.8

Technical Accomplishment:DOE Validation at GM LabVoltage at 2 A/cm210000300000.60-0.95V, TZWPtCo/HSC-f, 0.10, GDL-APtCo/HSC-f, 0.06, GDL-APtCo/HSC-f, 0.06, GDL-Bi-PtCo/HSC-f, 0.10, GDL-Ai-PtCo/HSC-f, 0.06, GDL-Ai-PtCo/HSC-f, 0.06, 9Voltage at 2 A/cm2 (250 s Activity (A/mg-Pt)ORR Mass Activity0.30 cycles10k cycles30k cyclesPtCo/HSC-f, 0.10, GDL-Ai-PtCo/HSC-f, 0.10, GDL-APtCo/HSC-f, 0.06, GDL-Ai-PtCo/HSC-f, 0.06, GDL-APtCo/HSC-f, 0.06, GDL-Bi-PtCo/HSC-f, 0.06, GDL-BH2/air, 94 C, 250/250 kPaabs,out, 65/65% RHin, st 1.5/2 The prepared MEAs were first tested at GM, with two GDLsloadings (0.10&0.06 mgPt/cm2).(240&150 μm thick)and two Pt Although for this validation study, we were not able to use some of our best MEAsubcomponents (electrode ionomer, membrane, and GDL) due to confidentiality, the GM tests resultslargely agree with prior conclusion. Annealed PtCo to encourage ordered intermetallic structure show slightly higher BOL and EOT mass activity. Annealed PtCo lost less ECSA after voltage cycling leading to higher HCD at EOT.9

Technical Accomplishment:DOE Validation at NREL Agree with GM results10

Technical Accomplishment:DOE Validation at NRELin anodic direction Agree with GM results11

Technical Accomplishment:Accessible Carbons StructureCarbonClose-up STEM TomographyPtCo/KBAccessible-PtCo/HSCPtCo particles Closer examination with TEM tomography led us to conclude that while some larger carbonpore openings are observable, they are not abundant enough to be the primary factor. Even though the accessible carbons have larger pores and thinner shells, they do not show significant increase inthe number and size of pore openings Instead, it is the larger interior pore volume, thinner carbon shell, and less tortuous diffusionpath together that help lower the O2 transport resistance. At the same time, small pore openings effectively exclude ionomer from entering carbonpores and poisoning Pt surfaces. This enables high ORR activities12

Technical Accomplishment:X-CT indicates potential CCL compactionfresh30k cycles Noticeable drop in cathode pore volume wasobserved after AST test. Similar observation has been reported earlier using electronand optical microscopes but with less confidence level. This could explain the sharp drop in voltage atHCD of PtCo/KB after AST, previously notunderstandable with known parameters. When consider the operating window, the decreasein pore volume is unlikely due to carbon corrosion. Itcould be due to electrode compaction from cellcompression. Need further study.13

Technical Accomplishment:Co-doping of Co2 & Ce3 Cell Voltage (V)0.58Cathode Proton Resistance(Ohm-cm2)H2/air, 87 C, 250/250 kPaabs,out, 80/80% RHin, high stoich0.61Vu, f(Ce)0.55Pt/HSC with Co2 and 8% Ce3 0.52Pt/V with Co2 and 8% Ce3 HSC, f(Ce)Vu, f(Co)HSC, f(Co)0.49010203040Acid Exchange Rate (%)Rsheet @ 75%RH, Vulcan0.080.070.060.050.040.030.020.010Pt/V with Co2 and 8% Ce3 Pt/V with Ce3 010203040Acid Exchange Rate (%) While the effects of Co2 and Ce3 were studied earlier, the effect when both cations arepresent was not systematically studied. We found that the effect was about the same as the combined effect of individual cation, i.e.,the interaction was small. The study also confirmed previous findings. At LCD, both Co2 and Ce3 have negligible effect. At HCD, Co2 causes larger voltage loss and larger increase in electrode and membrane proton resistance.14

Technical Accomplishment:Dynamic ORR Model DevelopmentORR kineticOxide coverage0.15 mgPt/cm2 Pt/V with NR212 membrane75 C, 100% RHin, high stoich of O2 or N2 Because fuel cell is operated in a transient mode most of the time, understanding ORR kinetic as a functiontime is important, not only to predict its performance, but also understanding its durability. Preliminary results showed that Pt oxide follows logarithm growth behavior, while ORR kinetic currentfollows logarithm decay behavior. This indicates that oxide-coverage kinetic can be applied for transientORR as well. Measurement and model development underway for Pt and PtCo catalysts.15

Technical Accomplishment:PtPd ML catalysts on Mesoporous Carbons0.730k cyc0 cyc0.6Mass Activity (A/mgPt)10k cyc1401201008060402010k cyc2530k cyc200.5PtPd onsolid carbon0.40.315100.250.1000PtCo/KBPtPd onPtPd/NE-Hsolid carbonPtPd onPtPd/PC-AHSC-amean 4.4 nm%0 cyc160PtPd onPtPd/PC-BPtCo/KBHSC-kPtPdonPtPd/NE-Hsolid carbonPtPd onPtPd/PC-APtPd fter V-cycling35mean 4.4 nm3025PtPd onHSC-a20% With some discussion with GM, NECC independentlydeveloped PtPd monolayer catalyst on mesoporouscarbons.1510 Thanks to high ECSA of ML catalysts, HCD issueassociated with local O2 transport is absent. On the other hand, significant improved stability wasobserved with mesoporous carbons. The following areconfirmed: Better retention of HCD performance, ECSA, and ORR activity Less number of aggregated particles Less Pt and Pd losses from the catalyst5012345678after-V cycleing910 11 12Particle size/nm50mean 3.1 nm4030PtPd onHSC-k%ECSAHAD (m2/gPt)after V-cycleingGM 38 cm2 platform. 0.07 mgPt/cm2 with Gen1 membrane&GDL180201001234567Particle size/nm891016

Future WorkThe project has concluded.2016Improved HCD withPt/C2017Durable ORRactivity PtCo/CGo/No-go2018Durable HCDand LCDGo/No-go20192020Diagnostics& ValidationMilestone17

Responses to Last Year AMR Reviewers’ Comments “ionomer-related progress lags behind” This complication arises because, a 3M-led project(FC155) solely focusing on this ionomer topic wasawarded by DOE after our project has started. Whilethis accelerates our learning, it isn’t done within thisproject. As a result, the ionomer scope was reducedand a portion of this DOE funding was returned. “how the ILs are limiting catalyst dissolution” This is also a question we are interested in. Whilewe do not have resources to take this on at themoment, we see opportunity to leverage a modelthat was developed within the project to study this,i.e., CMU’s Pt dissolution in absent of ionomer model. “keep durability in focus and conduct sensitivity studies at higher (Pt) loading. The impact on MEA cost isunderstood, but durability is critical” This is a important point. However, it cannot be done under the scope of this project. Pt loading sensitivity mustbe done under realistic operating condition (i.e., not AST), and this is strongly dependent on applications. FCPADconsortium will be more suited to study this. That being said, as shown in this work, the improved local transport property of the developed materials doesenable a more durable MEA despite slightly faster ECSA degradation. This benefit will be transferrable to a widerange of applications, as long as the FCS design limiting factor is the power, and not efficiency. “understanding the impact of the IL system on durability” “Evaluating the leaching of IL from theelectrode matrix ” Unfortunately, in this very last phase of the project, we could not address this technically challenging task. Wehope the new project led by Drexel on block copolymer-IL composites (FC309) will shed some light.

Summary Validation test at NREL confirmed improved HCD performance with catalyst with accessiblecarbon. Stability improvement from the ordered intermetallic PtCo on accessible carbon was less thanon baseline porous carbon (consistent with earlier result) The cause still unknown. Could be due to more open structure, shallower pores, less carbon corrosiontolerance, etc. Improved understanding of low-PGM electrode TEM tomography revealed the nanostructure of accessible carbons and how it can affect O2 transport. Experiment and simulation study highlight the role of internal pore structure on adsorbing/condensingwater and conducting proton. Quantified the effects of cation when both Co2 and Ce3 coexist in the membrane. Performancemodel development ongoing. Dynamic ORR kinetic model development underway. PtPd ML catalysts development demonstrated that different catalysts may have differentrequirement for their supports. (e.g. catalyst with high ECSA prefers a support that promote stability over a supportwith good local transport)Product: 21 published articles, 6 planned articles, 52 talks, 2 patent applications19

AcknowledgementsDOE–Greg Kleen (Program Manager)–Donna Ho (Technology Manager)–Shaun OnoratoGeneral Motors LLC–Aida Rodrigues, Yevita Brown, Carissa Miller, SherylForbes, Charles Gough (Contract Administration Group)–Venkata Yarlagadda–Michael K. Carpenter–Yun Cai–Thomas E. Moylan–Joseph M. Ziegelbauer–Ratandeep Singh Kukreja–Wenbin Gu–Srikanth Arisetty–Roland Koestner–Cristin L. Keary–Qiang Li and team–Peter Harvey and team–Kathryn Stevick and team–Tim Fuller–Shruti Gondikar–Mohammed Atwan–Nagappan Ramaswamy–Dave Masten–Swami Kumaraguru–Craig Gittleman–Mark F. Mathias3M Company–Dr. Andrew Haug (sub-PI)–Matthew Lindell–Tyler MatthewsCarnegie Mellon University–Prof. Shawn Litster (sub-PI)–Shohei Ogawa–Jonathan Braaten–Leiming Hu–Yuqi GuoCornell University–Prof. David A. Muller (sub-PI)–Prof. Héctor Abruña–Elliot Padgett–Matthew Ko–Barnaby Levin–Yin Xiong–Yao YangDrexel University–Prof. Joshua Snyder (sub-PI)–Yawei LiNREL–Dr. K.C. Neyerlin (sub-PI)–Guanxiong Wang–Luigi Osmieri–Jason Christ–Shaun Alia–Jason ZackANL / APS–Dr. Deborah J. Myers–Dr. Nancy N. Kariuki–Dr. Ross N. Andrews–Dr. Jan IlavskyLANL–Dr. Andrew M. Baker–Dr. Rangachary Mukundan–Dr. Rod L. Borup

Target Project Target PtCo/HSC-f Ordered-PtCo/HSC-f PtCo/HSC-f Ordered-PtCo/KB 8 SOA Integration & DOE Validation Technical Accomplishment: Cathode: 30 wt.% Intermetallic ordered Pt 3 Co/HSC-f at 0.06 and 0.10 mg Pt /cm2, PFSA ionomer (D2020), 900 EW, I/C ratio of 0.8, Anode: Pt/HSC, 0.015 mg Pt /cm2 PEM: PFSA with reinforcement layer, 18 μmthick

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