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Center for Electrochemical EngineeringUniversity of South Carolina
Novel Non-Precious Metals for PEMFC: Catalyst Selection Through Molecular Modeling and
Durability Studies
2005 DOE Hydrogen, Fuel Cells Infrastructure Technologies Program Review
Branko N. PopovDepartment of Chemical Engineering
University of South Carolina, Columbia, South Carolina 29208
May 24, 2005
Project ID# FC15This presentation does not contain any proprietary or confidential information
Overview
Center for Electrochemical EngineeringUniversity of South Carolina
Technical Barriers and TargetsElectrode performance
Perform at least as good as the conventional Pt catalysts currently in use in MEAs
Durability2000 hours operation with less than 10% power degradation
Material Costcost at least 50% less as compared to a target of 0.2 g (Pt loading)/peak kW
Partners / CollaborationsCase Western University
Molecular ModelingNortheastern University
Structural Studies / Chalcogenides
BudgetTotal Project Funding
DOE Share- $ 1376.292 KContractor Share - $351.207K
FY 03: $ 200KFY 04: $ 125KFY 05: $ 425KFY 06: $ 395KFY 07: $ 231.292K
TimelineProject Start Date
31/9/2003
Project End Date30/9/2007
Percent Complete35%
Center for Electrochemical EngineeringUniversity of South Carolina
ObjectivesDevelop transition metal supported catalysts for oxygen reduction using:- Low cost transition metal and nitrogen precursors- Modified carbon support
Optimize number of the catalytic sites as a function of – Carbon pretreatment.– Chemical composition of catalyst.– Post treatment of catalyst.
Improve understanding of reaction mechanism of oxygen reduction on non-precious catalysts through
Theoretical molecular modeling. (Case Western Reserve University)Electrochemical characterization.Structural studies (XPS, EXAFS, XANES). (North Eastern University)Correlation between the catalyst composition, heat treatment and catalytic sites for oxygen reduction.
Accomplish low cost catalyst through– Mass production methods.– Non precious metals.– Low cost precursors.
Accomplish stable non precious catalysts with – High durability (corrosion resistant alloy catalysts).– Low peroxide generation.– High activity towards oxygen reduction.
Center for Electrochemical EngineeringUniversity of South Carolina
Our Approach
Carbon Surface Modification
Surface Modifiers
Bimetallic Alloys
New Nitrogen Precursors
• Introduce carbon surface functional groups to increase the adsorption and dispersion of Co metal chelate.
• Increase porosity, dispersion and surface area of the Co catalyst with the use of surface modifiers.
• Development of bimetallic alloys such as Co-Fe and Ru-Fe.
• Development of Co based alloys from nitrogen containing precursors.
Molecular Modeling
Structural Studies
RRDE/ MEA Test Durability Studies
Center for Electrochemical EngineeringUniversity of South Carolina
Accomplishments
• Metal free catalyst was developed with carbon surface modification. – Onset potential for oxygen reduction = 0.7 V vs. RHE.– FOUR electron pathway for ORR.
• Active Co-chelate /C catalysts was developed with the use of activated carbon– A methodology was developed to increase the active sites of the catalyst. Introduction
of quinone- hydroquinone groups on the carbon surface increases the number of active sites by favoring the anchoring of Co chelate complexes on carbon substrate.
– FOUR electron pathway for ORR.
• Active Co-chelate/ C catalyst was developed with the use of surface modifiers.– Two surface modifiers were identified (SM1 and SM2- USC product) to increase the
activity of the non precious metal catalyst (Co, Fe and Co-Fe).– FOUR electron pathway for ORR.
• Ru based catalyst synthesized by our methodology has a performance equivalent to that of ETEK 20% Pt/C catalyst under RRDE test conditions.
• Bimetallic Ru-Co and Ru-Fe prepared by the methodology developed at USC shows performance comparable to that of ETEK 20% Pt/C catalyst under RRDE test conditions.
Center for Electrochemical EngineeringUniversity of South Carolina
Development of Metal Free CatalystModeling : Structure Model for Nitrogenated Carbon
Radical e- is calculated to delocalize onto adjacent C atoms.
H bonds by 1.02 eV on N and Uo = -1.0 V for the reaction
H+ + e- + surface H-surface H bonds by 2.31 eV on C, and Uo = 0.2 V.This means H will be oxidatively removed from the surface to create a catalytically active radical site.
surface + H2O2O2 + H+ + e- + surface
Uo = 0.88 V Uo = 0.51 VH+ + e-
Introducing various oxygen and nitrogen groups on the surface of the carbon increases the activity towards oxygen reduction
However, oxygen reduction is predominantly through TWO electron pathway.
This agrees with the structure model for nitrogenatedcarbon.
Disk Potential E/V vs SHE0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
K1
K2 + NH3
K2
K1 – Un-Oxidized, K2 – Oxidized
Center for Electrochemical EngineeringUniversity of South Carolina
Development of Metal Free Catalysts
Oxidation of carbon by HNO3 introduces quinone groups on the carbon which favors nitrogen adsorption.
Adsoprtion of monomeric nitrogen precursors on oxidized carbon
Onset potential for ORR – 0.7 V vs. RHETWO electron pathway for ORR
Adsorption of polymeric nitrogen precursors in oxidized carbon
Onset potential for ORR - 0.7 V vs. RHEFOUR electron pathway for ORR
Disk Potential E/V vs NHE0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
-0.8
-0.6
-0.4
-0.2
0.0
K2-PolymericK2-Monomeric
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
0.00
0.02
0.04
0.06 K2-PolymericK2-Monomeric
Rin
g C
urre
nt i/
mA
Dis
k C
urre
nt i/
mA
O
O
Quinone
K1-Unoxidized carbon
K2- Oxidized carbon
Disk Potential E/V vs NHE
Center for Electrochemical EngineeringUniversity of South Carolina
Effect of Carbon Activation on Co-chelate/C Performance to Oxygen Reduction Reaction
Disk Potential E/V vs SHE0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
-0.8
-0.6
-0.4
-0.2
0.0
K2-Co-ND1K1-Co-ND1E-TEK 20% Pt 14µg/cm2
Dis
k C
urre
nt i/
mA
Disk Potential E/V vs SHE0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Dis
k C
urre
nt i/
mA
-0.6
-0.4
-0.2
0.0
K2-CoEDA(HT)K2-EDA(HT)E-TEK 20% Pt/C,14µgPt/cm2
O
O
OH
HO
Presence of quinone groups on carbon surface favors nitrogen adsorption.
Introduction of Co in the catalyst structure increases the activity and shifts ORR mechanism from two electron to four electron.
Developed chelate catalysts show less than 100 mV overpotential in comparison to ETEK 20% Pt/C
Quinone /Hydroquinone
K1 – Un-Oxidized, K2 – Oxidized ND – Chelating Agent
Center for Electrochemical EngineeringUniversity of South Carolina
Investigating Relative Amounts of Oxygen Using XPS
The decrease in the intensity of Co peak can be attributed to the formation of a graphitic envelop around the transition metal with high temperature treatmentOxidation increases only the amount of quinone groups on carbon and not the total oxygen content.After heat treatment more amount of oxygen is retained in the catalysts dispersed on oxidized carbon. Thus quinone groups help in activity in addition to increasing dispersion.
O 1s SpectraCo 2p Spectra
6000
5000
4000
3000
2000
1000
Cou
nts/
sec
540538536534532530528526Binding Energy (eV)
Binding Energy (eV)
Cou
nts/
sec
K1-CoEDA
K2-CoEDA
K1-CoEDA(HT)
K2-CoEDA(HT)
K1
K2
6000
5000
4000
3000
2000
1000
Cou
nts/
sec
540538536534532530528526Binding Energy (eV)
Binding Energy (eV)
Cou
nts/
sec
K1-CoEDA
K2-CoEDA
K1-CoEDA(HT)
K2-CoEDA(HT)
K1
K2
4500
4000
3500
3000
Cou
nts/
sec
790785780775Binding Energy (eV)
Binding Energy (eV)
Cou
nts/
sec
4500
4000
3500
3000
Cou
nts/
sec
790785780775Binding Energy (eV)
Binding Energy (eV)
Cou
nts/
sec
K2-CoEDA
K1-CoEDA
K1-CoEDA(HT)
K2-CoEDA(HT)
3500
3000
2500
2000
1500
Cou
nts/
sec
406404402400398396394Binding Energy (ev)
Binding Energy (eV)
Cou
nts/
sec
K1-CoEDA
K2-CoEDA
K1-CoEDA(HT)K2-CoEDA(HT)K1K2
3500
3000
2500
2000
1500
Cou
nts/
sec
406404402400398396394Binding Energy (ev)
Binding Energy (eV)
Cou
nts/
sec
K1-CoND1
K2-CoND1
K1-CoND1(HT)K2-CoND1(HT)K1K2
3500
3000
2500
2000
1500
Cou
nts/
sec
406404402400398396394Binding Energy (ev)
3500
3000
2500
2000
1500
Cou
nts/
sec
406404402400398396394Binding Energy (ev)
Binding Energy (eV)
Cou
nts/
sec
K1-CoEDA
K2-CoEDA
K1-CoEDA(HT)K2-CoEDA(HT)K1K2
3500
3000
2500
2000
1500
Cou
nts/
sec
406404402400398396394Binding Energy (ev)
3500
3000
2500
2000
1500
Cou
nts/
sec
406404402400398396394Binding Energy (ev)
Binding Energy (eV)
Cou
nts/
sec
K1-CoND1
K2-CoND1
K1-CoND1(HT)K2-CoND1(HT)K1K2
N 1s Spectra
K – Ketjen Black EC 300 J, V – Vulcan XC-72, B – Black Pearl 20001 – Un-Oxidized, 2 – Oxidized, ND – Chelating agent , HT – After heat treatment
Center for Electrochemical EngineeringUniversity of South Carolina
Activity to Oxygen Reduction Reaction of Co-chelate Loaded on Different Carbons
Disk Potential E/V vs SHE0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
-0.6
-0.4
-0.2
0.0 K2-Co-ND (HT)V2-Co-ND (HT)B2-Co-ND (HT)
Disk Potential E/V vs SHE0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
0.00
0.01
0.02
0.03
0.04
0.05
0.06
K2-Co-ND (HT)V2-Co-ND (HT)B2-Co-ND (HT)
Dis
k C
urre
nt i/
mA
Rin
g C
urre
nt i/
mA
Carbon Area (m2/g)
Micropores (m2/g)
Mesopores (m2/g)
Vulcan XC 72 254 118 100
Ketjen Black EC 300J 886 55 680
Black Pearl 2000 1500 720 540
Ketjen Black EC-300 J (K) with the highest mesoporous area shows the highest activity (highest disk and lowest ring currents)
1 – Un-Oxidized, 2 – Oxidized, ND – Chelating agent
Center for Electrochemical EngineeringUniversity of South Carolina
TEM image of Co-chelate Loaded on Different Carbons
K2-Co-ND (9.5 nm)
K1-Co-ND (23.7 nm)
Co-chelate/Un-oxidized Ketjen Black EC 300 JCo-chelate/Oxidized Ketjen Black EC 300 J
V2-Co-ND (40 nm)B2-Co-ND
(12.5 nm)
Co-chelate/Oxidized Black Pearl 2000 Co-chelate/Oxidized Vulcan XC-72
K – Ketjen Black EC 300 J, V – Vulcan XC-72, B – Black Pearl 20001 – Un-Oxidized, 2 – Oxidized, ND – Chelating agent
Center for Electrochemical EngineeringUniversity of South Carolina
The Effect of Nitrogen Donors and Surface Modifier
Potential (V vs. NHE)
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
Cur
rent
(A)
-0.0014
-0.0012
-0.0010
-0.0008
-0.0006
-0.0004
-0.0002
0.0000
20 wt% Co -NH3 / C
20 wt% Co -ND1 / C
20 wt% Co-ND3/C
20 wt% Co -ND1 / C - SM1
The scan rate is 5mV/s. Rotation rate 900 rpm in 0.5M H2SO4.Potential (V vs. NHE)
0.0 0.2 0.4 0.6 0.8
Cur
rent
(mA
)
-1.0
-0.8
-0.6
-0.4
-0.2
0.0AD1 = [0]AD1 = [0.62]AD1 = [3.2]
The activity of the catalyst is dependent on the nitrogen donor used.Surface modifier increases the activity of the catalyst
Increases the dispersion.Forms part of the catalytic site.
Center for Electrochemical EngineeringUniversity of South Carolina
Effect of Surface Modifiers
SM1 = [0.62]6 nm
SM1 = [0]17 nm
100 nm
SM1 = [46]16 nm
SM1 = [3.2]12 nm
Center for Electrochemical EngineeringUniversity of South Carolina
Stability Test for Co Catalyst in RRDE Test Conditions
Potential (V vs. NHE)
0.0 0.2 0.4 0.6 0.8
Cur
rent
(mA
)
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0Open system-FreshAD1 = [0.62]+AD3 = [0.62]Open system-10 hrs.AD1 = [0.62]+AD3 = [0.62]
Initial After 10 h
The scan rate is 5mV/s. Rotation rate 900 rpm in 0.5M H2SO4.
Center for Electrochemical EngineeringUniversity of South Carolina
Performance Studies of Co-based Catalysts in Fuel Cell Station after 24 hrs
Operating Conditions: H2/O2, 75oC, 1atm, Nafion 112
Anode: 0.4mg/cm2 of 20wt% Pt/C
Current (A)
0 1 2 3 4 5 6
Pote
ntia
l (V
)
0.0
0.2
0.4
0.6
0.8
1.00.4 mgCo/cm2
0.8 mgCo/cm2
1.2 mgCo/cm2
1.6 mgCo/cm2
Center for Electrochemical EngineeringUniversity of South Carolina
Ru Chelate Catalyst for Oxygen Reduction Reaction
E/V vs. NHE
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
I/mA
-1.2
-1.1
-1.0
-0.9
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
Ru-ND2/C (USC )
Ru-ND2 SM1/C
Mo-Ru-Se (Chalcogenide)
E/V vs. NHE
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
I/mA
0.000
0.001
0.002
0.003
0.004
0.005
0.006
0.007
Ru- ND2/Carbon
Ru- ND2 S M1/Carbon
Mo-Ru-Se (Chalcogenide)
E/V vs. NHE
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
H2O
2%
0
1
2
3
4
5
6
Ru-Organic ND-2/Carbon
Ru-ND2- SM1/Carbon
Mo-Ru-Se (Charcogenide)
Ru catalysts prepared by USC chelatemethod show improved activity than MoRuSecatalysts.
%H2O2 produced is less than 2% for the synthesized catalysts.
ND: Nitrogen containing compound SM: Surface modifier
Center for Electrochemical EngineeringUniversity of South Carolina
TEM Image of Ru Chelate and Chalcogenide Catalyst
RuNx MoRuSe
Center for Electrochemical EngineeringUniversity of South Carolina
Bimetallic Catalysts for Oxygen Reduction Reaction
RuFeNx Catalysts for ORR
E/V vs. NHE
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
I/mA
-1.2
-1.1
-1.0
-0.9
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.120wt% FeNx
20wt% RuFeNx (Ru:Fe=1:1 atomic)20wt% RuNx
13wt% RuNx
The scan rate is 5mV/s. Rotation rate 900 rpm in 0.5M H2SO4.E/V vs. NHE
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
%H
2O2
0
5
10
15
20
25
30
35
FeNx
RuFeNx Ru:Fe=1:1 (atomic)RuNx
Alloying 13wt% Ru with 7 wt% Fe show comparable performance to ETEK 20% Pt/C and 20%Ru/C.
Synergistic effect between Ru and Fe is observed.
Center for Electrochemical EngineeringUniversity of South Carolina
Bimetallic Catalysts for Oxygen Reduction Reaction
ORR - Various Bimetallic Catalysts Stability of RuCo Catalysts
Ru:Me = 1:1 (atomic)
E/V vs. NHE
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1
I/mA
-1.4
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
Ro-CoRu-CrRu-TiRu-FeRu-Pb The scan rate is 5mV/s. Rotation rate 900 rpm
Electrolyte 0.5M H2SO4.
Ta – 77 ºC, Tc - 75 ºC, Tcell - 75 ºC, 5 cm2, Nafion112Loading – 1.2 mgRu/cm2, Ambient Pressure.
Activity of Ru catalyst with alloying follow
Ru > RuFe > RuCo > Ru-Cr > Ru-Ti > Ru-Pb
Ru and Ru-Fe catalysts show activity similar to ETEK 20% Pt/C.
Center for Electrochemical EngineeringUniversity of South Carolina
Comparison of Performance of USC Co and Ru Based Catalyst vs. Pt
E/V vs. NHE
0.0 0.2 0.4 0.6 0.8 1.0 1.2
I/A
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
0.0
0.2
20% ETEK Pt/C 20 µg/cm2
20% Ru-ND2 -SM1 (USC)Co-ND1-SM1 (USC)CoTMPP (USC)20% RuFe-ND2-SM1 (USC)
Dis
k C
urre
nt i/
mA
Ru catalysts prepared by USC chelate method with surface modifiers show performance close to that of 20% ETEK Pt/C catalysts
Center for Electrochemical EngineeringUniversity of South Carolina
Initial In-situ/Ex-situ XAFS Results (NEU)
Energy, eV
• In-situ XAFS studies to analyze the stability on Ru based catalysts
• Analyze the evolution of catalyst structure of Co and Fe catalyst with heat treatment.
• Develop cluster model to predict the structure of the active site.
Center for Electrochemical EngineeringUniversity of South Carolina
Response to Reviewer’s Comments
• Lack of Industrial Collaboration– USC has collaboration with Fuji Film Inc, Faraday Technologies which
are complimentary to this research.– Northeastern University’s collaboration with ETEK is complimentary to
this research.• Approach is a “Wish List”. Tasks listed are very large and difficult
– Initial studies were primarily aimed at screening the catalysts.– Current research focuses on Co, Fe and Co-Fe bimetallic catalysts.
• NEU and CWRU don’t seem actively engaged in the effort.– The project was at initial stages during the 2004 review program.– CWRU has been contributing to understand the role of nitrogenated
species on the activity.– In situ and ex-situ XAFS studies are being conducted by NEU to analyze
the catalyst structure and stability.
Center for Electrochemical EngineeringUniversity of South Carolina
Future Work
• Enhancement of the intrinsic activity of Co based catalysts.
• Development of Fe chelate based catalysts.
• Development of Fe-Co chelate based catalysts.
• Effect of chain length and different surface functionalities on the ORR kinetics.
• Extensive material characterization/ structural analysis of the developed Co chelate catalyst – Attain insight on the nature of the active site.
• Search for new surface modifiers and carbon surface treatments to increase the number of active sites.
Activity Stability
• Modify carbon surface functional groups to anchor chelate metal catalysts strongly.
• To increase the reversibility of the redox system for oxygen reduction.
• Use of Pressure / Temperature variants to increase the stability.
• Encapsulation of the catalyst in more stable materials such as carbide, nitride and zeolite.
• Extensive fuel cell testing to evaluate the stability of the catalyst
Center for Electrochemical EngineeringUniversity of South Carolina
Publications and Presentations
Publications
1. N.P.Subramanian, S.P.Kumaraguru, H.Colon, B.N. Popov, “Studies on Co Based Electrocatalysts on Modified Carbon Substrates for PEMFC Applications”, Submitted to J. Power Sources.
2. N.P.Subramanian, H.Colon, S.P.Kumaraguru, B.N. Popov, “Development of Metal Free Catalysts for Oxygen Reduction”, submitted to Carbon
Presentations
• S. P. Kumaraguru, N. Subramanian, H. Colon, K. Hansung and B.N. Popov, “Novel Non Precious Metal Catalysts for PEMFC Applications”, 206th meeting of the Electrochem Soc., Honolulu, HI, October, 2004.
• N.P.Subramanian, S.P. Kumaraguru and B.N. Popov “Analysis of Carbon Substrates used in Non-Precious Metal Catalysts for Fuel Cell Applications”, 206th meeting of the Electrochem Soc., Honolulu, HI, October, 2004.
Center for Electrochemical EngineeringUniversity of South Carolina
Hydrogen Safety
• All reactors are operated in a vented area.
• Hydrogen detector is placed near the hydrogen source.
• Reactors using high concentrations of hydrogen have additionally installed a burning flame to eliminate exhausting gas
• All the reactors have being design using leak-proof joints
• Ambient atmosphere pressures are used at all times in the reaction vessels and fuel cell stations
• Only personnel trained in how to operate the reactors and emergency procedures is allowed to use the reactor set-up– At least one person trained must present during runs in case of an
emergency shutdown
Center for Electrochemical EngineeringUniversity of South Carolina
Safety Equipment
Furnace for Hydrogen Treatment at High Temperature
and Safety Equipment
PEM Fuel Cell Dual Station with a Hydrogen Sensor
Center for Electrochemical EngineeringUniversity of South Carolina
Safety Questions for Hydrogen Review Program
1. What is the most significant hydrogen hazard associated with this project? Please be specific in your answer.The most significant hydrogen hazard is the fuel cell test station that we use to test the catalysts. However, the hydrogen flow rate used does not exceed 600 cm3/min.
2. What are you doing to deal with this hazard? Please list pertinent safety measures you are implementing and/or plan to implement.In order to prevent any accident safety features such as fail close H2valve, fail open N2 valve, low voltage trip, low gas flow trip, high temperature alarm, and H2 sensor with audible alarm are activated when the system is in operation. In addition, the system is positioned close to the hood in order to vent the used gas. Operation and emergency procedures are accessible in the case of an accident.