carbon corrosion effects in fuel cells - fuel cell … conference...carbon corrosion effects in fuel...
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Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Gordon Research Conference on Fuel CellsGordon Research Conference on Fuel CellsJuly 22July 22--27, 2007 Bryant University, Smithfield, RI, USA27, 2007 Bryant University, Smithfield, RI, USA
Carbon Corrosion Effects in Fuel CellsCarbon Corrosion Effects in Fuel Cells
Paolina AtanassovaPaolina Atanassova, Gordon Rice,, Gordon Rice, JianJian--Ping Ping ShenShen, , Yipeng Yipeng SunSun
Cabot Fuel Cells, Albuquerque, NMCabot Fuel Cells, Albuquerque, NM
MadhusudhanaMadhusudhana DowlapalliDowlapalli,, PlamenPlamen AtanassovAtanassov
Department of Chemical & Nuclear EngineeringDepartment of Chemical & Nuclear EngineeringUniversity of New Mexico, Albuquerque, NMUniversity of New Mexico, Albuquerque, NM
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Carbon Corrosion Effects in Fuel CellsCarbon Corrosion Effects in Fuel Cells
• Impact of carbon corrosion on catalysts/MEA Impact of carbon corrosion on catalysts/MEA durabilitydurability
•• Corrosion resistant carbon (CRC) supportsCorrosion resistant carbon (CRC) supports•• Fundamentals of carbon black supportsFundamentals of carbon black supports
•• Requirements for carbon as support for FC Requirements for carbon as support for FC electrocatalystselectrocatalysts
•• Structural and oxidation resistance test methodsStructural and oxidation resistance test methods
•• Performance and durability of alloy Performance and durability of alloy electrocatalysts based on CRC supportselectrocatalysts based on CRC supports
•• HydrogenHydrogen--air FC materials solutionsair FC materials solutions
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Cabot Fuel Cell Materials Development Cabot Fuel Cell Materials Development
• Low Precious Metal Alloy Electrocatalysts• Advanced Carbon Supports• Optimized Electrode Layers and MEA Structures• Tailored to FC operating conditions
CostCostgPtgPt/kW; $/kW/kW; $/kWPerformancePerformance
mWmW/cm/cm22DurabilityDurability
5000 h5000 h
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Cabot Fuel Cell Materials Development Cabot Fuel Cell Materials Development
Combination of Combination of ddurable Pt alloy catalysts with corrosion resistant urable Pt alloy catalysts with corrosion resistant carbon supports is a viable way for next generation automotive fcarbon supports is a viable way for next generation automotive fuel cell uel cell materialsmaterials
Alloy Electrocatalysts:Alloy Electrocatalysts:Two fold mass activity improvement by PtTwo fold mass activity improvement by Pt--alloy catalystsalloy catalysts
High absolute performance combined with low precious metal High absolute performance combined with low precious metal loadings in a single cell and short stackloadings in a single cell and short stack
Significant Significant durability improvement under cycling protocolsdurability improvement under cycling protocols
Advanced Carbon Supports:Advanced Carbon Supports:Surface modification of carbon supports effectively enhances Surface modification of carbon supports effectively enhances
carbon corrosion resistance and enables operation at low relativcarbon corrosion resistance and enables operation at low relative e humidity operating conditions humidity operating conditions
No performance loss after 120 hours of standard corrosion No performance loss after 120 hours of standard corrosion protocol (1.2 V) without sacrificing initial performanceprotocol (1.2 V) without sacrificing initial performance
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Impact of Carbon Corrosion on Impact of Carbon Corrosion on Catalyst/MEA DurabilityCatalyst/MEA Durability
• Carbon support durability is considered to be a major Carbon support durability is considered to be a major barrier for commercialization of automotive fuel cellsbarrier for commercialization of automotive fuel cells
•• Electrochemical oxidation of carbon in acid occurs by at Electrochemical oxidation of carbon in acid occurs by at least two anodic reaction pathwaysleast two anodic reaction pathways
CarbonCarbon surface groupssurface groups COCO22CarbonCarbon COCO22
•• Carbon corrosion is accelerated:Carbon corrosion is accelerated:
•• during start/ stop cycles during start/ stop cycles
•• at high voltage,OCVat high voltage,OCV
•• at high temperature operating conditionsat high temperature operating conditions
•• at low humidity operating conditionsat low humidity operating conditions
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Impact of Carbon Corrosion on Impact of Carbon Corrosion on Catalyst/MEA DurabilityCatalyst/MEA Durability
• Type of Catalyst/MEA Type of Catalyst/MEA performance losses related to performance losses related to carbon corrosioncarbon corrosion
•• Pt sintering due to loss of active Pt sintering due to loss of active phase/support interactionphase/support interaction
•• Oxidation of carbon surface leads to Oxidation of carbon surface leads to layer flooding effectslayer flooding effects
•• Break down in carbon/carbon Break down in carbon/carbon interfaceinterface
•• Formation of reactive species Formation of reactive species affecting membrane durabilityaffecting membrane durability
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Long Term Performance Losses Related Long Term Performance Losses Related to Carbon Corrosionto Carbon Corrosion
OH
~
OH
OH
•• Surface groups are Surface groups are formed during corrosionformed during corrosion
•• Hydrophilic in natureHydrophilic in nature
•• Flooding of electrodes
•• Loss of interaction between Pt Loss of interaction between Pt particles and carbon surface particles and carbon surface (undercutting)(undercutting)
•• Sintering, loss of active areaSintering, loss of active area Flooding of electrodes
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Long Term Performance Losses Related Long Term Performance Losses Related to Carbon Corrosionto Carbon Corrosion
Naf
ion
Naf
ion
Naf
ion
Naf
ion
Percolation effects in conductivity/connectivity of porous matriPercolation effects in conductivity/connectivity of porous matrixesxes
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Carbon Corrosion Effects in Fuel CellsCarbon Corrosion Effects in Fuel Cells
• Impact of carbon corrosion on catalysts/MEA Impact of carbon corrosion on catalysts/MEA durabilitydurability
•• Corrosion resistant carbon (CRC) supportsCorrosion resistant carbon (CRC) supports•• Fundamentals of carbon black supportsFundamentals of carbon black supports
•• Requirements for carbon as support for FC Requirements for carbon as support for FC electrocatalystselectrocatalysts
•• Structural and oxidation resistance test methodsStructural and oxidation resistance test methods
•• Performance and durability of alloy Performance and durability of alloy electrocatalysts based on CRC supportselectrocatalysts based on CRC supports
•• HydrogenHydrogen--air FC materials solutionsair FC materials solutions
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Fundamentals of Carbon BlacksFundamentals of Carbon Blacks
•• Mostly Carbon Mostly Carbon Graphitic Graphitic crystallites or amorphouscrystallites or amorphous
•• Defects, dislocations, and Defects, dislocations, and discontinuities at the edges of discontinuities at the edges of layer planeslayer planes
•• Variable amount of disorganized Variable amount of disorganized tetrahedrallytetrahedrally bonded carbon can bonded carbon can often be found crossoften be found cross--linking linking different layers.different layers.
•• Total oxygen content usually Total oxygen content usually less than 1%less than 1%
•• Phenols, Phenols, ketonesketones, acids, etc., acids, etc.•• Hydrogen content ~ 0.2%Hydrogen content ~ 0.2%•• The carbon surface is The carbon surface is
essentially inert to most organic essentially inert to most organic reaction chemistryreaction chemistry
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Fundamentals of Carbon BlacksFundamentals of Carbon Blacks
• CB is homologous to graphite.• ca. 18 x 24 Å sheets.
• 3-4 parallel layers
• Separation of layers: 3.5 - 3.8 Å for CB
3.35 Å for graphite
• Disordered layers - Turbostratic Structure
• Form primary particles
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Fundamentals of Carbon BlacksFundamentals of Carbon Blacks
• Aggregates consist of fused primary particles
• The primary particle size, aggregate size, surface area and structure are controlled during CB production
• Agglomerates consist of aggregates held together with Van der Waals forces
• Surface area: 20 - 1500 m2/g
Dpp
Dagg
Dpp = 10-75 nmDagg= 50-400 nm
Dagglomerate = 100 -1000 nm
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Fundamentals of Carbon BlacksFundamentals of Carbon Blacks
Low Structure, Small Particle Size
Low Structure, Large Particle Size High Structure, Large Particle Size
High Structure, Small Particle Size
Vulcan XC 72Vulcan XC 72KetjenKetjen BlackBlack
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Ability to Control Carbon Support PropertiesAbility to Control Carbon Support Properties
Particle Size
Structure
Surface Chemistry
Combination of morphology controland surface modification allows for rational design of carbon materials
• Carbon black morphology can be controlled to design the length scale of gas and water transport channels
• Various degrees of carbon support graphitization can be achieved
• Carbon support surface chemistry can be modified
+ N YN+
Carbon Black Diazonium SaltModified Carbon Black
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Carbon Corrosion Effects in Fuel CellsCarbon Corrosion Effects in Fuel Cells
• Impact of carbon corrosion on catalysts/MEA Impact of carbon corrosion on catalysts/MEA durabilitydurability
•• Corrosion resistant carbon (CRC) supportsCorrosion resistant carbon (CRC) supports•• Fundamentals of carbon black supportsFundamentals of carbon black supports
•• Requirements for carbon as support for FC Requirements for carbon as support for FC electrocatalystselectrocatalysts
•• Structural and oxidation resistance test methodsStructural and oxidation resistance test methods
•• Performance and durability of alloy Performance and durability of alloy electrocatalysts based on CRC supportselectrocatalysts based on CRC supports
•• HydrogenHydrogen--air FC materials solutionsair FC materials solutions
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Desirable Properties of EC SupportsDesirable Properties of EC Supports
Surface areaMin 100-300 m2/gPreferably higher, 400-1000 m2/g
PorosityMinimal micro - porosity, less than 1 nmMeso - porosity preferred, 10 nm - 100 nm pore size
Stable in acidic mediaLow solubility at pH 1-2Related to impurities and effect to proton conductor poisoning
Stable to corrosion under electrochemical conditions Graphitization levelPassivation surface chemistry Suppression of hydrogen peroxide formation
Electronic conductivity
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Importance of Carbon Purity Importance of Carbon Purity –– estimate estimate
Considered to be a factor for long term stability, various opinions, no solid proof
Metal cations can be leached out and end up in the membrane decreasing proton conductivity Calculations on the level of impurities that can negatively affect the membrane conductivity
Nafion 112 membrane Iononomer in the electrocatalyst layers – order of magnitude less proton sides, even easier to poison by impuritiesConclusion: metal impurities of typical carbon grades show that carbon purity is sufficient
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Carbon Corrosion Root Cause Carbon Corrosion Root Cause
•• Electrochemical oxidation of carbon Electrochemical oxidation of carbon in acid occurs by several reaction in acid occurs by several reaction pathwayspathways
CarbonCarbon hydroxyl, hydroxyl, ketoketo, , carboxilyccarboxilycCOCO22
Carbon Carbon COCO22
•• Active sites for carbon corrosion are Active sites for carbon corrosion are associated with carbon atoms at associated with carbon atoms at edges, defects, dislocations and edges, defects, dislocations and singlesingle--layer planes (amorphous).layer planes (amorphous).
~OH
OH
O
OH
O
C
O
CO2
•• Removal, reduction and inhibition of those active sites in carboRemoval, reduction and inhibition of those active sites in carbon is n is expected to slow down carbon corrosionexpected to slow down carbon corrosion
•• Conventional approaches for improving carbon durability lead to Conventional approaches for improving carbon durability lead to trade offs between durability, absolute performance and catalysttrade offs between durability, absolute performance and catalystink propertiesink properties
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Approaches to Durable EC SupportsApproaches to Durable EC Supports
Conventional approaches used to reduce/avoid carbon Conventional approaches used to reduce/avoid carbon corrosion issuecorrosion issue
Graphite supportsGraphite supportsGraphitization of carbon blacks Graphitization of carbon blacks Addition of Addition of dopants dopants (B) in carbon(B) in carbon
Radically different nonRadically different non--carbon supports carbon supports Nitrides, carbides, or metal oxides that are:Nitrides, carbides, or metal oxides that are:
Stable in acidic conditionsStable in acidic conditionsHigh surface areaHigh surface areaElectrically conductiveElectrically conductive
Cabot’s approach to corrosion resistant carbon (CRC)Cabot’s approach to corrosion resistant carbon (CRC)Carbon blacks treatment to adjust graphitization level and Carbon blacks treatment to adjust graphitization level and
morphology morphology Surface modification to adjust surface propertiesSurface modification to adjust surface propertiesCombined with sprayCombined with spray--conversion method for EC manufacturingconversion method for EC manufacturingTailored to FC OEM operating conditionsTailored to FC OEM operating conditions
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Carbon Corrosion Effects in Fuel CellsCarbon Corrosion Effects in Fuel Cells
• Impact of carbon corrosion on catalysts/MEA Impact of carbon corrosion on catalysts/MEA durabilitydurability
•• Corrosion resistant carbon (CRC) supportsCorrosion resistant carbon (CRC) supports•• Fundamentals of carbon black supportsFundamentals of carbon black supports
•• Requirements for carbon as support for FC Requirements for carbon as support for FC electrocatalystselectrocatalysts
•• Structural and oxidation resistance test methodsStructural and oxidation resistance test methods
•• Performance and durability of alloy Performance and durability of alloy electrocatalysts based on CRC supportselectrocatalysts based on CRC supports
•• HydrogenHydrogen--air FC materials solutionsair FC materials solutions
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Characterization of Corrosion Resistant Characterization of Corrosion Resistant CarbonsCarbons
•• Matrix of carbon blacks treatment and surface Matrix of carbon blacks treatment and surface modification conditionsmodification conditions
•• Structural characterizationStructural characterization–– BET, pore volume and pore size distributionBET, pore volume and pore size distribution–– XRD for XRD for crystallinitycrystallinity/graphitization evaluation/graphitization evaluation
•• ExEx--situ electrochemical measurementssitu electrochemical measurements•• High voltage test in MEA High voltage test in MEA
–– Performance, ECSAPerformance, ECSA–– CO/COCO/CO22 measurementsmeasurements
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XX--Ray DiffractionRay Diffraction
(002)
(10)
(004) (110)
La
Lc/2
•• The smaller The smaller dd(002)(002) space space (ideally 0.3354nm), the (ideally 0.3354nm), the higher the level of higher the level of graphitization of carbon graphitization of carbon blacks, and the better blacks, and the better the carbon corrosion the carbon corrosion resistanceresistance
•• The presence of (110) The presence of (110) also indicative of also indicative of carbon corrosion carbon corrosion resistanceresistance
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Characterization of Conventional Characterization of Conventional Graphitized CarbonsGraphitized Carbons
C 2610-1 - File: C 2610-1.RAW - Type: PSD fast-scan - Start: 10.000 ° - End: 89.586 ° - Step: 0.014 ° - Step time: 0.1 s - Temp.: 25 °C (Room) - Time Started: 0 s - 2-Theta: 10.00C 3379 - File: C 3379.RAW - Type: PSD fast-scan - Start: 10.000 ° - End: 89.586 ° - Step: 0.014 ° - Step time: 0.1 s - Temp.: 25 °C (Room) - Time Started: 0 s - 2-Theta: 10.000 ° - C 3293 - File: C 3293.RAW - Type: PSD fast-scan - Start: 10.000 ° - End: 89.586 ° - Step: 0.014 ° - Step time: 0.1 s - Temp.: 25 °C (Room) - Time Started: 0 s - 2-Theta: 10.000 ° -
Lin
(Cou
nts)
0
100
200
300
400
500
600
700
800
900
2-Theta - Scale10 20 30 40 50 60 70 80 90
KB EC 600
HT-1200C, 2hrs
HT-1800C, 2hrs
(002)
(10)(004)
(110)
0200400600800
100012001400
Ketjen
Blac
k EC60
0 HT-
1200
C, 6hr
HT-12
00C, 2
hr
HT-15
00C, 2
hrHT-
1800
C, 2hr
HT-21
00C, 2
hr
HT-24
00C, 2
hr
BET
SA
(m^2
/g)
50.0
60.0
70.0
80.0
90.0
100.0
Pore
Vou
me
(5nm
~100
nm) (
%)
•• Graphitized carbons can meet Graphitized carbons can meet the corrosion requirements but the corrosion requirements but the obtained carbon through the obtained carbon through high temperature treatment will high temperature treatment will not be suitable for making high not be suitable for making high performance catalyst due to:performance catalyst due to:
•• Low surface areaLow surface area. Most of . Most of graphitized carbons do not graphitized carbons do not have sufficient surface area for have sufficient surface area for making highly dispersed making highly dispersed catalysts. catalysts.
•• Inert carbon surfaceInert carbon surface. Low . Low surface energy is mostly surface energy is mostly responsible for forming larger responsible for forming larger precious metal particles,easier precious metal particles,easier metal sintering, etcmetal sintering, etc
Gra
phiti
zatio
n
Temperature, time
Surf
ace
area
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ExEx--situ Electrochemical Measurementssitu Electrochemical Measurements
Gas‐Diffusion Electrode Half‐Cell Set‐up
Fuel Chamber (for full cell)
c
c c
c
Electrolyte Chamber
Cathode GDE
Anode GDE (full cell) or Counter Electrode (Half cell)
Reference Electrode Port
Oxygen Chamber
Room Temp, 2M H2SO4Hg/HgSO4 reference electrode
1. Three Electrode System2. Air Breathing Gas-Diffusion Electrode3. Teflonized Carbon Backing
24
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Carbon Blacks Corrosion Measurements: Carbon Blacks Corrosion Measurements: Carbon Layer on GasCarbon Layer on Gas--Diffusion ElectrodeDiffusion Electrode
Carbon Blacks are mixed withNafion and Teflon
press
press
Active Layer
500mg of Teflonized carbon
Gas Diffusion Layer
65mg of carbon black+ 35 mg Teflonizedcarbon black
Current Collector
press
Carbon black matrix
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Corrosion Resistance of Carbon BlacksCorrosion Resistance of Carbon Blacks
+ N YN+
Carbon Black Diazonium SaltModified Carbon Black
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Corrosion Resistance of EC and Carbon Corrosion Resistance of EC and Carbon BlacksBlacks
Pt/Carbon Black electrocatalysts express higher corrosion currents than the support itself.
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Corrosion Resistance of Carbon BlacksCorrosion Resistance of Carbon Blacks
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ExEx--Situ Electrochemical TestingSitu Electrochemical Testing
• Delivers valuable information on corrosion resistance of carbon blacks and electrocatalysts
• Quantitative analysis can be based on:– Normalized current (per m2 of support or catalyst) for similar
surface area catalysts– Total current for fixed amount of support or catalyst
• Protocol modified to potentiostatic test at conditions similar to high voltage test in MEA– 0.8 V,1.0 V, 1.2 V, 1.4 V, 1.5 V– Potentiostatic and galvanostatic protocols deliver identical
results when test is performed below 1.2 V
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
ExEx--situ Electrochemical Measurement of situ Electrochemical Measurement of Carbon Corrosion at Various VoltagesCarbon Corrosion at Various Voltages
At 0.8V
0
5
10
15
20
25
0 200 400 600 800 1000 1200
Time, sec
Cur
rent
, mA
C2610-KB
C2547-VXC72
C3071-Timcal
C3625-KB-2700
C3625-L4
KB EC 600Vulcan XC 72
Graphite
HT KB
Cabot CRC
• Under the same voltage,the lower current (mA) means the carbon is less corrosive
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
ExEx--situ Electrochemical Measurement of situ Electrochemical Measurement of Carbon Corrosion at Various VoltagesCarbon Corrosion at Various Voltages
At 1.0V
0
10
20
30
40
50
60
70
80
90
0 200 400 600 800 1000 1200
Time, sec
Cur
rent
, mA
C2610-KB
C2547-VXC72
C3071-Timcal
C3625-KB-2700
C3625-L4
KB EC 600Vulcan XC 72Graphite
HT KBCabot CRC
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
ExEx--situ Electrochemical Measurement of situ Electrochemical Measurement of Carbon Corrosion at Various VoltagesCarbon Corrosion at Various Voltages
At 1.2V
0
20
40
60
80
100
120
140
160
180
200
0 200 400 600 800 1000 1200
Time, sec
Cur
rent
, mA
C2610-KB
C2547-VXC72
C3071-Timcal
C3625-KB-2700
C3625-L4Cabot CRC
KB EC 600
Vulcan XC72
Graphite
HT KB
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
ExEx--situ Electrochemical Measurement of situ Electrochemical Measurement of Carbon Corrosion at Various VoltagesCarbon Corrosion at Various Voltages
At 1.4V
0
50
100
150
200
250
300
350
0 200 400 600 800 1000 1200
Time, sec
Cur
rent
, mA
C2610-KB
C2547-VXC72
C3071-Timcal
C3625-KB-2700
C3625-L4
KB EC 600
Vulcan XC72
Graphite
HT KB
Cabot CRC
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
ExEx--situ Electrochemical Measurement of situ Electrochemical Measurement of Carbon Corrosion at Various VoltagesCarbon Corrosion at Various Voltages
At 1.5V
0
50
100
150
200
250
300
350
400
450
0 200 400 600 800 1000 1200
Time, sec
Cur
rent
, mA
C2610-KB
C2547-VXC72
C3071-Timcal
C3625-KB-2700
C3625-L4
KB EC 600
Vulcan XC72
Graphite
HT KB
Cabot CRC
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
SummarySummary
•• Combination of physical and electrochemical exCombination of physical and electrochemical ex--situ situ characterization allows for pre characterization allows for pre -- screening of carbon supports screening of carbon supports based on selection criteriabased on selection criteria
•• Cabot CR carbons exhibit corrosion currents as low as or lower Cabot CR carbons exhibit corrosion currents as low as or lower than traditionally graphitized carbons and commercial high than traditionally graphitized carbons and commercial high surface area graphite while maintaining greater than 2x surface area graphite while maintaining greater than 2x advantage in BET surface areaadvantage in BET surface area
•• Down selected carbon supports are used as catalyst supports and Down selected carbon supports are used as catalyst supports and Pt and PtPt and Pt--alloy based catalysts are manufacturedalloy based catalysts are manufactured
•• Active phase loading and spray processing conditions are varied Active phase loading and spray processing conditions are varied to ensure optimized active phase dispersionto ensure optimized active phase dispersion
•• CRC CRC –– based catalyst are tested in MEA configuration:based catalyst are tested in MEA configuration:–– Initial performanceInitial performance–– High voltage testHigh voltage test–– Load cycling Load cycling –– Intermediate evaluation of performance, ECSAIntermediate evaluation of performance, ECSA–– Final performanceFinal performance
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Carbon Corrosion Effects in Fuel CellsCarbon Corrosion Effects in Fuel Cells
• Impact of carbon corrosion on catalysts/MEA Impact of carbon corrosion on catalysts/MEA durabilitydurability
•• Corrosion resistant carbon (CRC) supportsCorrosion resistant carbon (CRC) supports•• Fundamentals of carbon black supportsFundamentals of carbon black supports
•• Requirements for carbon as support for FC Requirements for carbon as support for FC electrocatalystselectrocatalysts
•• Structural and oxidation resistance test methodsStructural and oxidation resistance test methods
•• Performance and durability of alloy Performance and durability of alloy electrocatalysts based on CRC supportselectrocatalysts based on CRC supports
•• HydrogenHydrogen--air FC materials solutionsair FC materials solutions
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Electrocatalyst Corrosion at High Voltage Test in MEA
•• Investigate and evaluate theInvestigate and evaluate the corrosivecorrosivebehaviorbehavior ofof catalystscatalysts in single MEA fuelin single MEA fuelcell cell
•• Corrosion resistance evaluation protocol Corrosion resistance evaluation protocol adopted from GM/DOEadopted from GM/DOE–– Polarization curves test conditions Polarization curves test conditions
8080°°C,C, stoichstoich flows A/C = 3/3, 50% RH, flows A/C = 3/3, 50% RH, 7 psig7 psig
•• Study the effect of platinum loading, Study the effect of platinum loading, surface modification and morphology of surface modification and morphology of the carbon blacks on the corrosive the carbon blacks on the corrosive behavior of electrocatalysts.behavior of electrocatalysts.
•• Goal Goal –– less than 30 mV loss at 1 A/cmless than 30 mV loss at 1 A/cm22
after 100 hrs corrosion test at 1.2V, 80after 100 hrs corrosion test at 1.2V, 80°°CC
Start-up Cell
Conditioning(12 to 16 hours)
Measure Polarization Curves
Apply 1.2V - 100% RH H2/N2 for 15 hours
Measure Polarization Curves
Apply 1.2V - 100% RH H2/N2 for 5 -15 hours
t <100 hours?
No
Yes
Shutdown Cell
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Severe Corrosion Losses with Standard Severe Corrosion Losses with Standard SupportsSupports
60% Pt / Ketjen Black
• > 100mV loss at 1A/cm2 only after 15h
• > 50% Loss in ECSA after 45h of standard corrosion protocol
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5Current Density (A/cm2)
Volta
ge (V
)
0hr15hr20hr25hr30hr35hr40hr45hr
Polarization curves test conditions:
80/80/80°C,stoich flows A/C = 3/3, 50% RH, 7 psig
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Long Term Performance Losses Related Long Term Performance Losses Related to Carbon Corrosionto Carbon Corrosion
OH
~
OH
OH
•• Surface groups are Surface groups are formed during corrosionformed during corrosion
•• Hydrophilic in natureHydrophilic in nature
•• Flooding of electrodes
•• Loss of interaction between Pt Loss of interaction between Pt particles and carbon surface particles and carbon surface (undercutting)(undercutting)
•• Sintering, loss of active areaSintering, loss of active area Flooding of electrodes
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Long Term Performance Losses Related Long Term Performance Losses Related to Carbon Corrosionto Carbon Corrosion
Naf
ion
Naf
ion
Naf
ion
Naf
ion
Percolation effects in conductivity/connectivity of porous matriPercolation effects in conductivity/connectivity of porous matrixesxes
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Severe Corrosion Losses with Standard Severe Corrosion Losses with Standard SupportsSupports
0.00
0.20
0.40
0.60
0.80
1.00
1.20
0 10 20 30 40Time (hrs)
Cur
rent
Den
sity
(A/m
2)
At 0.5V
At 0.7V
At 0.85V
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 10 20 30 40
Time (Hrs)%
Los
s
%Loss Mass transport regime
%Loss Ohmic regime
%Loss Kinetic regime
%Loss EC Area
60% Pt / Ketjen Black
• > 70 - 90 % Losses in kinetic, ohmic and mass transport regime • > 50% Loss in ECSA after 45 h of standard corrosion protocol
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Surface Modification Effectively Surface Modification Effectively Enhances Carbon Corrosion ResistanceEnhances Carbon Corrosion Resistance60% Pt / Modified Carbon Black (MCB)
• > 100mV Loss at 1A/cm2 after 50h, ~3 fold improvement • Improvement is related to the coverage of functional groups on
carbon surface• Functional groups stabilize the carbon surface
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4
Current Density (A/cm2)
Volta
ge (V
)
0hr15hr20hr25hr30hr35hr40hr45hr50hr
Polarization curves test conditions:
80°C, stoichflows A/C = 3/3, 50% RH, 7 psig
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Surface Modification Effectively Surface Modification Effectively Enhances Carbon Corrosion ResistanceEnhances Carbon Corrosion Resistance
0.00
0.20
0.40
0.60
0.80
1.00
1.20
0 10 20 30 40 50
Time (hrs)
Cur
rent
Den
sity
(A/m
2)
At 0.5VAt 0.7VAt 0.85V
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 10 20 30 40 50
Time (Hrs)%
Los
s
%Loss Mass transport regime
%Loss Ohmic regime
%Loss Kinetic regime%Loss EC Area
60% Pt / Modified Carbon Black (MCB)
• < 35 % Losses in kinetic, ohmic and mass transport regimes • < 60% Loss in EC Area after 50 h of standard corrosion protocol• Performance loss observed is relatively low compared to loss in
EC Area
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• ~ No Loss at 1A/cm2 after 45hrs• < 10 % change in performance
in kinetic, ohmic and mass transport regimes
• A maximum of 25% loss in EC area is observed after 45 hours.
• Relative performance loss observed is very low compared to loss in EC Area
0.00
0.20
0.40
0.60
0.80
1.00
1.20
0 10 20 30 40Time (hrs)
Cur
rent
Den
sity
(A/m
2)
At 0.5VAt 0.7VAt 0.85V
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 1.10 1.20
Current Density (A/cm2)
Volta
ge (V
)
0hr15hr20hr25hr28hr33hr45hr
Superior Corrosion Resistance with Superior Corrosion Resistance with Cabot CRC SupportCabot CRC Support
0%5%
10%
15%20%
25%
30%
35%40%
45%
0 10 20 30 40 50Time (Hrs)
% L
oss
%Loss Mass transport regime
%Loss Ohmic regime
%Loss Kinetic regime
%Loss EC Area
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Significant Improvement in Durability with Significant Improvement in Durability with no Performance Trade Offsno Performance Trade Offs
0.00.10.20.30.40.50.60.70.80.91.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0Current Density (A/cm2)
Volta
ge (V
)0hr15hr30hr45hr60hr75hr90hr105hr120hr
60% Pt / Corrosion Resistant Carbon (CRC)
•• Both MCB and CRC supports show significant improvement in carbonBoth MCB and CRC supports show significant improvement in carbondurabilitydurability•• CRC materials exhibit no performance loss at 120 hrs after highCRC materials exhibit no performance loss at 120 hrs after highvoltage test at 1.2 Vvoltage test at 1.2 V
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Carbon Loss during FC testingCarbon Loss during FC testing
Paul T. Yu, Wenbin Gu, Hubert A. Frederick T. Wagner, GM, ECS meeting, Cancun, Oct-Nov 2006
The higher corrosion resistance carbon release less carbon spices (CO/CO2 ) – direct measurement in FC
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Cabot Fuel Cell Materials Development Cabot Fuel Cell Materials Development
• Low Precious Metal Alloy Electrocatalysts• Advanced Carbon Supports• Optimized Electrode Layers and MEA Structures• Tailored to FC operating conditions
CostCostgPtgPt/kW; $/kW/kW; $/kWPerformancePerformance
mWmW/cm/cm22DurabilityDurability
5000 h5000 h
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Cabot Electrocatalyst PlatformCabot Electrocatalyst Platform
Liquid delivery Atomization Gas Phaseprocessing
Collection Product
Effluent gasGas feed
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Process in MotionProcess in Motion
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1 PtCoCu2 PtCoFe3 PtFeCu4 PtNiCu5 PtNiFe6 PtPdCu7 PtPdCo8 PtPdFe9 PtMnFe10 PtPdMn11 PtNiCo12 PtCoAg13 PtFeAg14 PtNiAg15 PtPdNiCo
Test Conditions:
• Non IR corrected, 50 cm2 MEA, NafionTM 112
• Loadings: Cathode: 0.2 mgM/cm2, Anode: 0.05 mgPt/cm2
• 80ºC, 1.5 H2/2.5 air at 1A/cm2, 100% RH, 30 psig, 10min/point
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0 1 2 3 4 5 6 7 8 9 10
A/mg Pt cathode
Cel
l Vol
tage
(V)
20% PtCoCu/C
20% PtNiCo/C
20% PtCo/C
20% PtNiFe/C
20% Pt/C
20% PtNi/C
Best Pt alloy compositions show up to 2 fold mass activity improvement in hydrogen air fuel cell
Two Fold Mass Activity Improvement Demonstrated byTwo Fold Mass Activity Improvement Demonstrated byTernary PtTernary Pt-- Alloy Supported CatalystsAlloy Supported Catalysts
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MEA Performance at Low Precious Metal MEA Performance at Low Precious Metal LoadingsLoadings
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0 0.8 0.9 1.0
Current Density (A/m2)
Cel
l Vol
tage
(V)
MEA loadings: 0.15 mg Pt/cm2 total loading Cathode: 0.1 mg Pt/cm2; Anode: 0.05 mg Pt/cm2
0.8 V, 0.6 g Pt/kW 0.75 V, 0.4 g Pt/kW
0.7 V, 0.3 g Pt/kW
Test Conditions:• 50 cm2, NafionTM 112 • 80°C, 1.5 H2/2.5 air at 1A/cm2, 100% RH, • 30 psig, 10 min/point, Non IR corrected
Pt (111): 40.36 (2θ); a: 3.87 Å
Highly Dispersed Alloy Catalysts
3-5 nm
20 nm
2-3 nm
10 nm
Control of crystallite size
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High Absolute Performance Combined High Absolute Performance Combined with Low Precious Metal Loadingswith Low Precious Metal Loadings
Test Conditions:• Non IR corrected 50 cm2, NafionTM 112, cathode: as listed; anode: 0.05 mgPt/cm2,• 80°C, 1.5 H2/2.5 air at 1A/cm2, 100% RH, 30 psig, 10 min/point
Current Density (A/cm2)
Cel
l Vol
tage
(V)
0.00.10.20.30.40.50.60.70.80.91.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
A: 0.3 mgPt/cm2, Pt alloy/KB
B: 0.5 mgPt/cm2, 50 wt.% Pt/KB
2006
• High Metal Loading Catalyst on High Surface Area Carbon Support
• Identical performance at approximately half of the Pt content
• At 0.8 V a power density of 0.32 W/cm2 was achieved
• At 0.7 V approximately 0.56 W/cm2 (total PM loading, anode plus cathode of 0.35mgPt/cm2), which corresponds to approximately 0.6 gPt/kW.
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LongLong--Term Durability Under Cycling Term Durability Under Cycling ProtocolsProtocols
Normolized Specifc Surface Area vs. CV Cycle
0%
20%
40%
60%
80%
100%
120%
initial 15 K cycles 30 K cycles
Spec
ific
Surf
ace
Are
a [%
of in
itial
]
Pt/C Pt alloy/C
1000000
10
20
30
40
50
60
70
80
90
100
1000 10000
Number of CyclesN
orm
aliz
ed P
t EC
SA (%
)Test Conditions: 50 cm2 MEA, cycling under H2/air at 80°C and 100% RH between 0.7 and 0.9 V IR-free voltage (30 s hold at each potential) combined with periodical evaluation of the Pt surface area using cyclic voltammetry and performance.
Pt alloy catalyst shows 30% loss of surface area after 20 K cycles and no further loss is observed until 30K cycles
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Performance After Cycling ProtocolsPerformance After Cycling Protocols
0.00
0.20
0.40
0.60
0.80
1.00
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00Current Density (A/cm2)
Volta
ge (V
) 0 cycle3840 cycles10680 cycles30600 cyclesVoltage
loss (mV)50 mA/cm2 6400 mA/cm2 13
Test conditions:• Single MEA 50 cm2 test cell, Nafion 112, Cell temperature 80°C• Anode/cathode constant flow rates = 510/2060 mL/min H2/air (1.5H2/ 2.5 air stoich at 1 A/cm2)• 30 psig pressure on both anode and cathode, 100% humidification of gases, 80C dew point
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Corrosion Resistant Supports Combined Corrosion Resistant Supports Combined with Pt Alloyswith Pt Alloys
1.00
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90Current Density (A/cm2)
Vol
tage
(V)
Pt/CRC
PtCo/CRC
Standard Polarization Curves Test Conditions: 80C, constantflow - 520/2040 mL/min A/C, 100% RH, 30 psig
• By combining alloy catalysts with Corrosion Resistant Carbons, Cabot is able to make materials with the same resistance towards electrochemical oxidation while increasing the overall performance
• Even for the alloy electrocatalysts the hydrophobic nature of the CRC supports pose challenges for low RH operation.
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Carbon Corrosion Effects in Fuel CellsCarbon Corrosion Effects in Fuel Cells
• Impact of carbon corrosion on catalysts/MEA Impact of carbon corrosion on catalysts/MEA durabilitydurability
•• Corrosion resistant carbon (CRC) supportsCorrosion resistant carbon (CRC) supports•• Fundamentals of carbon black supportsFundamentals of carbon black supports
•• Requirements for carbon as support for FC Requirements for carbon as support for FC electrocatalystselectrocatalysts
•• Structural and oxidation resistance test methodsStructural and oxidation resistance test methods
•• Performance and durability of alloy Performance and durability of alloy electrocatalysts based on CRC supportselectrocatalysts based on CRC supports
•• HydrogenHydrogen--air FC materials solutionsair FC materials solutions
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Cabot Fuel Cell Materials Development Cabot Fuel Cell Materials Development
• Low Precious Metal Alloy Electrocatalysts• Advanced Carbon Supports• Optimized Electrode Layers and MEA Structures• Tailored to FC operating conditions
CostCostgPtgPt/kW; $/kW/kW; $/kWPerformancePerformance
mWmW/cm/cm22DurabilityDurability
5000 h5000 h
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
Surface Modification Enables Operation at Low Surface Modification Enables Operation at Low Relative Humidity ConditionsRelative Humidity Conditions
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00
Current Density (A/cm2)
Volta
ge (V
)100 % relativehumidity50% relativehumidity
• 100 % relative humidity test: flow stoich = 2.0 (A/C), cell temperature 80°C back pressure =10 psig ( A/C), RH=100% (A/C)
• 50 % relative humidity test: flow stoich = 2.0 (A/C), cell temperature 80°C back pressure =10 psig ( A/C), RH=50%/50% (A/C)
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Qualitative Test on Hydrophobic CharacterQualitative Test on Hydrophobic Character
TraditionalPartially Graphitized
Carbon BlackCabot Treated Carbon – L2
Cabot Treated Carbon – L1
Cabot Treated Carbon – L3
Along with the increased durability towards electrochemical oxidation, the Cabot “treatment” also alleviates the problem of high hydrophobic character of traditionally graphitized carbons
Floats on Water
Wetted by water
Gordon Research Conference, 07_25_07Gordon Research Conference, 07_25_07
SummarySummary
• Cabot has developed a series of moderately high surface area carbons which have equivalent durability towards electrochemical oxidation as traditionally graphitized carbons and commercial high surface area graphites
• Unlike traditionally graphitized carbons, Cabot’s carbons do notsuffer from high levels of hydrophobic character which can create problems with active phase dispersion and ink formulations
• Further integration with alloys active phase and manufacturing optimization is in progress
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Status and Future WorkStatus and Future Work
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.41.5
1.6
90 10080 12011070FC Operating Temperature, oC
Hig
h Vo
ltage
Tes
t, V
Cabot CRC Gen 1
Cabot CRC Gen 2 Future
generationscombined with HT membrane
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Gordon Research Conference on Fuel CellsGordon Research Conference on Fuel CellsJuly 22July 22--27, 2007 Bryant University, Smithfield, RI, USA27, 2007 Bryant University, Smithfield, RI, USA
Cabot Facility in Albuquerque, NMCabot Facility in Albuquerque, NM
Thank you for your attention !Thank you for your attention !
Questions?Questions?