in-situ and operando xafs studies of fuel cell...
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In-situ and operando XAFS studies of fuel cell catalysts
Carlo Segre
Physics Department&
Center for Synchrotron Radiation Research and InstrumentationIllinois Institute of Technology
October 30, 2013
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 1 / 37
Outline
• The CSRRI & MRCAT
• X-ray absorption spectroscopy
• Operando synchrotron fuel cells
• Oxygen reduction at the NiPt cathode
• Methanol oxidation on a PtRu catalyst
• Ru@Pt core-shell methanol catalysts
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 2 / 37
CSRRI @ IIT
PhysicsCarlo Segre
Jeff Terry
David Gidalevitz
Bhoopesh Mishra
Tomohiro Shibata (MRCAT)
Soma Chattopadhyay (MRCAT)
John Katsoudas (MRCAT)
Bill Lavender (MRCAT)
Weifeng Shang (BioCAT)
Materials EngineeringKeith Bowman
Leon Shaw
BiologyTom Irving
Andy Howard
Joseph Orgel
Olga Antipova (BioCAT)
Srinivas Chakravarty (BioCAT)
ChemistryAdam Hock
Social SciencesElizabeth Friedman
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 3 / 37
MRCAT - historical timeline
1993 – MRCAT started with materials physics focusNotre Dame, Northwestern, Purdue, IIT, Amoco
1995 – Construction begins on Insertion Device lineUniv. of Florida, Argonne/CSE joins
1997 – First light on Insertion Device line
1998 – Argonne/ER joins
2002 – Honeywell, Sandia fund initial Bending Magnet line
2005 – EPA joins
2007 – UOP joins Bending Magnet line buildout begins
2009 – Bending Magnet line operational
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 4 / 37
MRCAT - present membership
Current active membershipUniversity of Notre Dame
Illinois Institute of Technology
Argonne Chemical Sci. & Eng.
Argonne Biosciences
Environmental Protection Agency
UOP Honeywell
BP plc
General users – catalysisUC Davis, Purdue, Penn State
Illinois, UIC, UC Santa Barbara
Rice, LSU, UC Berkeley, Michicgan
Wisconsin, Ohio State, MIT, ORNL
ID LineXAFS (4 keV - 33 keV)
Continuous scan (¡ 2 min)
Very dilute samples
8-circle goniometer
Microprobe
Microdiffraction
BM LineXAFS (4 keV - 30 keV)
X-ray lithography
High energy tomography
Photochemistry
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 5 / 37
The EXAFS experiment
Io = incident intensityIt = transmitted intensityIf = fluorescence intensity
x = sample thicknessµ(E ) = absorption coefficient
It = Ioe−µ(E)x µ(E )x = ln
(IoIt
)µ(E ) ∝ If
Io
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 6 / 37
The x-ray absorption event
νh
νhk
∆t
Ni
Pt
Pt
Ni Pt
χ(k) =∑j
NjS20 fj(k)
kR2j
e−2k2σ2j e−2Rj/λ(k) sin [2Rj + δj(k)]
fj(k): scattering factor for the pathλ(k): photoelectron mean free pathδj(k): phase shift for the jth path
Nj : number of paths of type jRj : half path lengthσj : path “disorder”
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 7 / 37
Pt foil XAFS analysis
11500 12000 12500
E(eV)
-2
-1.5
-1
-0.5
0
0.5
ln(I
o/I
)
remove background andapply k-weighting
0 5 10 15
k(Å-1
)
-0.2
-0.1
0
0.1
0.2
χ
extract structural pa-rameters for first shell ormore distant atoms asappropriate
0 2 4 6
R(Å)
0
5
10
15
20
25
30
χ(R
)
take Fourier Transformand fit with a structuralmodel
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 8 / 37
Pt foil XAFS analysis
11500 12000 12500
E(eV)
0
0.5
1
ln(I
o/I
)
remove background andapply k-weighting
0 5 10 15
k(Å-1
)
-0.2
-0.1
0
0.1
0.2
χ
extract structural pa-rameters for first shell ormore distant atoms asappropriate
0 2 4 6
R(Å)
0
5
10
15
20
25
30
χ(R
)
take Fourier Transformand fit with a structuralmodel
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 8 / 37
Pt foil XAFS analysis
11500 12000 12500
E(eV)
0
0.5
1
ln(I
o/I
)
remove background andapply k-weighting
0 5 10 15
k(Å-1
)
-0.2
-0.1
0
0.1
0.2
χ
extract structural pa-rameters for first shell ormore distant atoms asappropriate
0 2 4 6
R(Å)
0
5
10
15
20
25
30
χ(R
)
take Fourier Transformand fit with a structuralmodel
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 8 / 37
Pt foil XAFS analysis
11500 12000 12500
E(eV)
0
0.5
1
ln(I
o/I
)
remove background andapply k-weighting
0 5 10 15
k(Å-1
)
-0.2
-0.1
0
0.1
0.2
χ
extract structural pa-rameters for first shell ormore distant atoms asappropriate
0 2 4 6
R(Å)
0
5
10
15
20
25
30
χ(R
)
take Fourier Transformand fit with a structuralmodel
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 8 / 37
Pt foil XAFS analysis
11500 12000 12500
E(eV)
0
0.5
1
ln(I
o/I
)
remove background andapply k-weighting
0 5 10 15
k(Å-1
)
-0.2
-0.1
0
0.1
0.2
χ
extract structural pa-rameters for first shell ormore distant atoms asappropriate
0 2 4 6
R(Å)
0
5
10
15
20
25
30
χ(R
)
take Fourier Transformand fit with a structuralmodel
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 8 / 37
Mark I operando fuel cell
R. Viswanathan et al., “In-situ XANES study of carbon supportedPt-Ru anode electrocatalysts for reformate-air polymer electrolytefuel cells”, J. Phys. Chem. B 106, 3458 (2002).
• Transmission mode
• <1 mm of graphite
• Pt/Ru on anode
• Pd on cathode
• 35◦C operating temp
• 1-2 min scan time
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 9 / 37
Mark II operando fuel cell
E.A. Lewis et al., “Operando x-ray absorption and infraredfuel cell spectroscopy”, Electrochim. Acta. 56, 8827 (2011).
• FTIR & x-rays
• Air-breathing cathode
• Pd on anode
• 1.2 mg/cm2 loading
• 50◦C operating temp
• Pt L3 and Ni K edges
• Continuous scan mode @
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 10 / 37
Oxygen reduction at a PtNi cathode
U.S. Department of Defense (DoD) Fuel CellTest and Evaluation Center (FCTec)
Anode: 0 V vs. SHE
2 H2 −−→ 4 H+ + 4 e–
Cathode: 1.23 V s. SHE
O2 + 4 H+ + 4 e– −−→ 2 H2O
breaking O−O bond is rate limiting
(a) (b) (c) (d)
H + e+
H + e+
2H + 2e+
Pt
O O
Pt
O O
Pt
O O
H+
.
Pt
O O
H H
Pt
2H O2
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 11 / 37
Fuel cell performance and open questions
0 20 40 60 80 100
Current Density [mA/cm2]
0
200
400
600
800
1000
1200
Pote
ntial [m
V]
1229 mV
860 mV
780 mV
PtNi/Pd has higher open circuitvoltage, similar performance toPt/Pd.
Pt: How do reactants adsorb on platinum sur-face?
• Do all faces of Pt adsorb equally well?
• Is there a change in location withcoverage?
PtNi: Why is ORR improved with bimetalliccatalyst?
• Pt electronic structure modified
• Pt catalyst geometric structure modified
• Static oxygen adsorbates inhibited
• Overpotential reduced
How do real catalysts differ from model sys-tems?
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 12 / 37
Fuel cell performance and open questions
0 20 40 60 80 100
Current Density [mA/cm2]
0
200
400
600
800
1000
1200
Pote
ntial [m
V]
1229 mV
860 mV
780 mV
PtNi/Pd has higher open circuitvoltage, similar performance toPt/Pd.
Pt: How do reactants adsorb on platinum sur-face?
• Do all faces of Pt adsorb equally well?
• Is there a change in location withcoverage?
PtNi: Why is ORR improved with bimetalliccatalyst?
• Pt electronic structure modified
• Pt catalyst geometric structure modified
• Static oxygen adsorbates inhibited
• Overpotential reduced
How do real catalysts differ from model sys-tems?
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 12 / 37
Data quality: Pt LIII edge in Pt/C
• Merge of 10-20 scans
• Data good to k=13
• Pt-O peak just below 2 A
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 13 / 37
Data quality: Ni K edge in PtNi/C
• Merge of 10-20 scans
• Data good to k=11
• Large change from OCV
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 14 / 37
Pt/C and PtNi/C comparison
11550 11575
Energy (eV)
0.00
0.02
550 mV
750 mV
900 mV
0.00
0.02
∆µ
(E)
11550 115750.0
0.5
1.0
µ(E
)
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 15 / 37
PtNi Structural model
Attempt to get global information about the oxygen
Fit all potentials with same metal core parameters for eachcatalyst
Simultaneous fit of Pt and Ni edges in PtNi/C with constrainton Pt-Ni distance
Fit in k, k2, and k3 weighting simultaneously
M-O path constraints
• length common across potentials
• σ2fixed to 0.01
• Pt-O in PtNi/C are refined with a single occupation #
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 16 / 37
Example fits
0.0
0.5
1.0
|χ(R
)| [Å
-3]
0
1
0.0
0.5
1.0
0
1
χ(q
) [Å
-2]
0 2 4 6R [Å]
0.0
0.5
1.0
0 4 8 12
q [Å-1
]
0
1
Pt in Pt/C
Pt in PtNi/C
Ni in PtNi/C
Ni-O
Pt-O
Pt-O
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 17 / 37
Fit results
Pt/C PtNi/C
Pt Ni
NPt 8.7± 0.2 NPt 6.1± 0.3 NNi 3.7± 0.2
RPt-Pt 2.749± 0.001 RPt-Pt 2.692± 0.003 RNi-Ni 2.572± 0.006
NNi 3.4± 0.1 NPt 8.9± 0.5
RPt-Ni 2.635± 0.004
NTotal 9.5± 0.4 NTotal 12.6± 0.7
RPt-O 2.02± 0.01 RPt-O 2.09± 0.03 RNi-O 1.90± 0.01
Note the Pt-Pt and Pt-O bond lengths as well as total metal near neighbors
Q. Jia et al, “In Situ XAFS studies of the oxygen reduction reaction on carbon supportedPt and PtNi(1:1) catalysts”, J. Phys. Conf. Series 190, 012157 (2009).
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 18 / 37
What does Ni really do?
Resides predominantly in metal core of nanoparticle
Eliminates static Pt-O bonds at all potentials
Number of O near neighbors “increases” with potential
Lengthens Pt-O and shortens Pt-Pt bond
Reduces Pt white line in most reduced state (0 mV)
Open circuit voltage is increased (reduction in overpotential)
Can we use modeling to establish specific mechanism?
• Pt-Pt bond reduction (weakening of Pt-O bond)?
• Electron donation to Pt d-band (weakening of Pt-O bond)?
• Stronger affinity for oxygen?
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 19 / 37
Pt cluster modeling
By using FEFF8.4, which performs full multiple-scattering self-consistent calculations, we can explore the implications of the“ligand effect” and the “strain effect” on the electronic state ofPt.
Separate the effects of
(a) Shorter Pt-Pt distance
(b) charge transfer from subsurface Ni
Use experimentally determined distances
Calculate local density of states
Calculate XANES spectrum
Q. Jia, et al., “Structure-property-activity correlations of Pt-bimetallic nanoparticles: atheoretical study” Electrochimica Acta bf 88, 604 (2013).
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 20 / 37
Cluster calculation results
Strain effectshorter Pt-Pt bond → broader and lower Pt d-band
• serves to weaken the Pt-O bond
• White line at absorption edge is reduced
• In agreement with DFT calculations (Nørskov et al.)
Ligand effectsubsurface Ni → sharpens and reaises Pt d-band
• Raises chemisorption energy
• Increases white line
Net effect dominated by strain effect
Predictive ability• Moving down periodic table (Ru, Ag)
• Moving left across periodic table (towards Mn)
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 21 / 37
Methanol oxidation by a PtRu anode
U.S. Department of Defense (DoD) Fuel CellTest and Evaluation Center (FCTec)
Anode: 0.02 V vs. SHE
CH3OH+H2O −−→ 6 H+CO2+6 e–
Cathode: 1.23 V s. SHE32 O2 + 6 H+ + 6 e– −−→ 3 H2O
Pt surface poisoned by CO
The presence of Ru promotes Co oxidation through a “bi-functional mechanism”
Pt−(CO)ads + Ru−OH −−→ Pt + RuCO2 + H+ + 2 e–
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 22 / 37
Pt LIII edge
• Potential dependent EXAFS at 0.1M.Pt EXAFS has excellent fit with atotally metallic environment. All dataare nearly identical.
• FT range for k space is 2–13 A.
• Fit range for R space is 1.5–3 A.
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 23 / 37
Ru K edge
• Potential dependent EXAFS at 0.1MCh3OH
• Ch3OH dependent EXAFS
• Model fit at 350 mV
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 24 / 37
Ru EXAFS fitting
• Addition of Ru-O/C neighbors improves the EXAFS fit
• The peak at about 1.3 A is ascribed to oxygen bound to Ru
• The asymmetric distribution of the Ru-O/C peak isconsistent with disorder
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 25 / 37
Metal nanoparticle structure
• First shell analysis
• Fit Pt and Ru EXAFS simultaneously at each potential. Nopotential dependence observed
• Simultaneously fit Pt and Ru data at all potentials. Identicaloverall average coordination was observed
• Use fractional coordination numbers, x (Pt around Ru) and y(Ru around Pt) and total coordination number about eachatom, N
• Bond lengths and Debye-Waller factors are consistent withliterature values for C supported Pt-Ru catalyst (Russel 2001,Camara 2002)
N 8.2± 0.2x 0.54± 0.02y 0.27± 0.02
[Ru]
[Pt]=
y
x= 0.50
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 26 / 37
Metal core restucturing
As-received catalyst
Ru oxidation ∼ 58 %
N = 5.6
[Ru]
[Pt]=
y
x= 0.44
Pt-O bonds present
# Ru-O bonds ∼2.8
In-situ catalyst
Ru oxidation ∼ 15 %
N = 8.2
[Ru]
[Pt]=
y
x= 0.50
No Pt-O bonds
# Ru-O/C bonds ∼0.24
• Inner core has more Pt than Ru
• Ru on surface and outside of metallic nanoparticle
S. Stoupin, et al., “Pt and Ru X-ray absorption spectroscopy of PtRu anode catalystsin operating direct methanol fuel cells” J. Phys. Chem. 110, 9932 (2006).
S. Stoupin, et al., “Structural analysis of sonochemically prepared PtRu versus JohnsonMatthey PtRu in operating direct methanol fuel cells” Phys. Chem. Chem. Phys. 10,6430 (2008).
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 27 / 37
Role of Ru in Co oxidation?
• PtRu bifunctional catalyst improves performance
• In commercial PtRu catalysts there is always a lot ofinactive Ru-oxide (?)
• Ru signal dominated by metallic Ru environment
• How does Ru behave in the presence of reactantsadsorbed on platinum surface?
Core-shell nanoparticles can resolve these questions
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 28 / 37
Ru-decorated Pt nanoparticles
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 29 / 37
Electrochemical performance
-0.2 0 0.2 0.4 0.6 0.8
Potential [V]
-0.004
-0.002
0
0.002
Curr
ent [A
]
PtRu
Pt
Without Methanol
Low V peaks are H+ stripping
Dip 0.5 V is oxygen stripping
Ru shifts potential on all peaks
With Methanol
Continual current growth is due tomethanol oxidation
Ru improves current by removing theCO which blocks active sites
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 30 / 37
Electrochemical performance
-0.2 0 0.2 0.4 0.6 0.8
Potential [V]
0
0.02
0.04
0.06
0.08
Cu
rre
nt
[A]
PtRu
Pt
Without Methanol
Low V peaks are H+ stripping
Dip 0.5 V is oxygen stripping
Ru shifts potential on all peaks
With Methanol
Continual current growth is due tomethanol oxidation
Ru improves current by removing theCO which blocks active sites
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 30 / 37
Ru EXAFS
No methanol
0 1 2 3 4 5
R [Å]
0
0.2
0.4
0.6
0.8
1
|χ(R
)| [Å
-3]
-225 mV
+175 mV
+375 mV
+575 mV
+675 mV
With methanol
0 1 2 3 4 5
R [Å]
0
0.2
0.4
0.6
0.8
1
|χ(R
)| [Å
-3]
-225 mV
+375 mV
+675 mV
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 31 / 37
Ru EXAFS
No methanol
0 1 2 3 4 5
R [Å]
0
0.2
0.4
0.6
0.8
1
|χ(R
)| [Å
-3]
-225 mV
+175 mV
+375 mV
+575 mV
+675 mV
With methanol
0 1 2 3 4 5
R [Å]
0
0.2
0.4
0.6
0.8
1
|χ(R
)| [Å
-3]
-225 mV
+375 mV
+675 mV
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 31 / 37
Fit example: -225 mV without methanol
0 1 2 3 4 5 6 7 8 9 10 11
R [Å]
-0.4
-0.2
0
0.2
0.4
0.6
k2 χ(k
) [Å
-2]
-225 mV - no MeOH
0 1 2 3 4 5
R [Å]
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
|χ(R
)| [Å
-3]
-225 mV - w MeOH
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 32 / 37
Fit example: 675 mV without methanol
0 1 2 3 4 5 6 7 8 9 10 11
R [Å]
-0.5
0
0.5
1
k2 χ(k
) [Å
-2]
675 mV - no MeOH
0 1 2 3 4 5
R [Å]
0
0.2
0.4
0.6
0.8
1
|χ(R
)| [Å
-3]
675 mV - no MeOH
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 33 / 37
Fit example: 675 mV with methanol
0 1 2 3 4 5 6 7 8 9 10 11
R [Å]
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
k2 χ(k
) [Å
-2]
675 mV - with MeOH
0 1 2 3 4 5
R [Å]
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
|χ(R
)| [Å
-3]
675 mV - with MeOH
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 34 / 37
Fitting results
-0.2 0 0.2 0.4 0.6
Applied Potential [V vs Ag/AgCl]
2.5
2.6
2.7
2.8
2.9
3
3.1
R [Å
]
-0.2 0 0.2 0.4 0.6
(a) Ru-Pt (b) Ru-Ru
Without methanol
Ru is metallic with Pt and Runeighbors at low V Pt/Ru @ 2.67 A& Pt @ 2.84 A
Ru oxidizes to completely above375 mV such that all metal dis-tances increase or disappear O @1.95 A & 1.99 A
With methanol
Ru is more metallic with Pt and Runeighbors at all V Pt/Ru @ 2.62 A& Pt @ 2.79 A
Ru has one low Z neighbor at allpotentials (C @ 1.90 A ); a secondabove 175 mV, O @ 2.06 A
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 35 / 37
Fitting results
-0.2 0 0.2 0.4 0.6
Applied Potential [V vs Ag/AgCl]
2.5
2.6
2.7
2.8
2.9
3
3.1
R [Å
]
-0.2 0 0.2 0.4 0.6
(a) Ru-Pt (b) Ru-Ru
Without methanol
Ru is metallic with Pt and Runeighbors at low V Pt/Ru @ 2.67 A& Pt @ 2.84 A
Ru oxidizes to completely above375 mV such that all metal dis-tances increase or disappear O @1.95 A & 1.99 A
With methanol
Ru is more metallic with Pt and Runeighbors at all V Pt/Ru @ 2.62 A& Pt @ 2.79 A
Ru has one low Z neighbor at allpotentials (C @ 1.90 A ); a secondabove 175 mV, O @ 2.06 A
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 35 / 37
Fitting results
-0.2 0 0.2 0.4 0.6
Applied Potential [V vs Ag/AgCl]
2.5
2.6
2.7
2.8
2.9
3
3.1
R [Å
]
-0.2 0 0.2 0.4 0.6
(a) Ru-Pt (b) Ru-Ru
Without methanol
Ru is metallic with Pt and Runeighbors at low V Pt/Ru @ 2.67 A& Pt @ 2.84 A
Ru oxidizes to completely above375 mV such that all metal dis-tances increase or disappear O @1.95 A & 1.99 A
With methanol
Ru is more metallic with Pt and Runeighbors at all V Pt/Ru @ 2.62 A& Pt @ 2.79 A
Ru has one low Z neighbor at allpotentials (C @ 1.90 A ); a secondabove 175 mV, O @ 2.06 A
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 35 / 37
Fitting results
1.9
2.0
2.1
R [Å
]
-0.2 0 0.2 0.4 0.6
Applied Potential [V vs. Ag/AgCl]
1
2
3
4
5
# of
Nei
ghbo
rs
(a)
(b)
Without methanol
Ru is metallic with Pt and Runeighbors at low V Pt/Ru @ 2.67 A& Pt @ 2.84 A
Ru oxidizes to completely above375 mV such that all metal dis-tances increase or disappear O @1.95 A & 1.99 A
With methanol
Ru is more metallic with Pt and Runeighbors at all V Pt/Ru @ 2.62 A& Pt @ 2.79 A
Ru has one low Z neighbor at allpotentials (C @ 1.90 A ); a secondabove 175 mV, O @ 2.06 A
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 35 / 37
Fitting results
1.9
2.0
2.1
R [Å
]
-0.2 0 0.2 0.4 0.6
Applied Potential [V vs. Ag/AgCl]
1
2
3
4
5
# of
Nei
ghbo
rs
(a)
(b)
Without methanol
Ru is metallic with Pt and Runeighbors at low V Pt/Ru @ 2.67 A& Pt @ 2.84 A
Ru oxidizes to completely above375 mV such that all metal dis-tances increase or disappear O @1.95 A & 1.99 A
With methanol
Ru is more metallic with Pt and Runeighbors at all V Pt/Ru @ 2.62 A& Pt @ 2.79 A
Ru has one low Z neighbor at allpotentials (C @ 1.90 A ); a secondabove 175 mV, O @ 2.06 A
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 35 / 37
Bi-functional mechanism
H+H+H+H+
H+
H+
H H
H
O
C
HO
C
H
O
Ru
O
C
Pt Pt Pt 2 Pt
Pt Pt Pt 1 Pt 1
x-rays
EXAFS
1 2
3
4
4e-
4
2e-
O C O
C. Pelliccione et al., “In situ Ru K-Edge x-ray absorption spectroscopy study of methanol oxidationmechanisms on model submonolayer Ru on Pt nanoparticle electrocatalyst” J. Phys. Chem. C 117,18904 (2013).
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 36 / 37
Principal collaborators - Thank you!
Pt/Ru core-shell• Christopher Pelliccione – IIT (Ph.D. student)
• John Katsoudas – IIT (MRCAT staff)
• Elena Timofeeva – Argonne, Energy Systems
Pt/Ru anode catalyst• Stanislav Stoupin – IIT (Ph.D. Student)
• Soma Chattopadhyay – IIT (MRCAT staff)
• Harry Rodriguez – UPR (Ph.D. student)
PtNi cathode catalyst• Qingying Jia – IIT (Ph.D. Student)
• Eugene Smotkin – Northeastern Univ.
• Emily Lewis – Northeastern Univ. (M.S. Student)
Supported by the Department of Energy
Illinois Institute of Technology IIT Chemistry Colloquium October 30, 2013 37 / 37