Carbon Corrosion Effects in Fuel Cells - Fuel Cell … Conference...Carbon Corrosion Effects in Fuel...

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



• 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


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



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


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


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


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



Naf

ion

Naf

ion

Naf

ion

Naf

ion

Percolation effects in conductivity/connectivity of porous matriPercolation effects in conductivity/connectivity of porous matrixesxes


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



• 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



• 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



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


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


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


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


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


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


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


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


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


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


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


Corrosion Resistance of Carbon BlacksCorrosion Resistance of Carbon Blacks

+ N YN+

Carbon Black Diazonium SaltModified Carbon Black


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.


Corrosion Resistance of Carbon BlacksCorrosion Resistance of Carbon Blacks


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


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



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



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



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



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


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


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


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



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



Naf

ion

Naf

ion

Naf

ion

Naf

ion

Percolation effects in conductivity/connectivity of porous matriPercolation effects in conductivity/connectivity of porous matrixesxes


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


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


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 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


• ~ 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


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 Ohmic regime

%Loss Kinetic regime

%Loss EC Area


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


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






5000 h5000 h


Cabot Electrocatalyst PlatformCabot Electrocatalyst Platform

Liquid delivery Atomization Gas Phaseprocessing

Collection Product

Effluent gasGas feed


Process in MotionProcess in Motion


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


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


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


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.


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


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


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.






5000 h5000 h


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


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)


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


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


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


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?

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