Presentation at the 10th European Symposium on Electrochemical Engineering, Sardinia, Italy  September 28, 2014 to October 02, 2014 Authors: Nejc Hodnik1,2, Marjan Bele2, Stanko Hocevar2 1) Max-Planck-Institut für Eisenforschung GmbH, Max-Planck Str. 1, 40237 Düsseldorf Germany 2) National Institute of Chemistry, Hajdrihova 19, 1000 Ljubljana, Slovenia http://www.sciencedirect.com/science/article/pii/S1388248112003256 also read: The Role of Water-Surface Interactions of Platinum Based Catalysts in Electrochemical Methanol Oxidation https://www.researchgate.net/profile/Nejc_Hodnik/publication/266146059_The_Role_of_Water-Surface_Interactions_of_Platinum_Based_Catalysts_in_Electrochemical_Methanol_Oxidation/links/542866b40cf26120b7b567df.pdf

1. The role of adsorptive properties of
platinum based catalysts in
electrochemical methanol oxidation
Nejc Hodnik1,2
, Marjan Bele2
, Stanko Hocevar2
1) Max-Planck-Institut für Eisenforschung GmbH, Max-Planck Str. 1, 40237 Düsseldorf
Germany
2) National Institute of Chemistry, Hajdrihova 19, 1000 Ljubljana, Slovenia
n.hodnik@mpie.de
10th
European Symposium on Electrochemical Engineering, Sardinia, Italy
September 28, 2014 to October 02, 2014
National Institute
of Chemistry
Slovenia

2. National Institute
of Chemistry
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Outline:
- the electrical double layer (ions and water interaction and PZC)
- CO oxidation, O2 reduction and methanol oxidation reactions
- new concept of interpretation of MOR
- new MOR catalyst
10th
European Symposium on Electrochemical Engineering, Sardinia, Italy
September 28, 2014 to October 02, 2014

3. National Institute
of Chemistry
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C+
A-
C+
C+
A-
A-
A-
A-C+
C+
C+
C+
C+
A-
A-
C+
C+
A-
A-
A-
The electrical double layer – ions interaction
Metal surface
Electrolite water
solution
10th
European Symposium on Electrochemical Engineering, Sardinia, Italy
September 28, 2014 to October 02, 2014

4. National Institute
of Chemistry
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+- - --- + +++
A- A-
A-
A-
A-
A-
A-
A-
C+
C+
C+
C+
C+
C+
C+
C+
C+
C+
A-
C+
C+
A-
A-
A-
A-
C+
A-
The electrical double layer – ions interaction
Ions get attracted to the surface.
Electric charge
Potential
10th
European Symposium on Electrochemical Engineering, Sardinia, Italy
September 28, 2014 to October 02, 2014

5. National Institute
of Chemistry
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The electrical double layer – water interaction
0 0 000 0 0 000
10th
European Symposium on Electrochemical Engineering, Sardinia, Italy
September 28, 2014 to October 02, 2014

6. National Institute
of Chemistry
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+- - --- + +++
Water interacts with oxygen;
oxygen-down arrangement.
Water interacts with hydrogen;
oxygen-up arrangement.
Water
molecule
dipole
orientation.
The electrical double layer – water interaction
10th
European Symposium on Electrochemical Engineering, Sardinia, Italy
September 28, 2014 to October 02, 2014

7. National Institute
of Chemistry
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C+
A-
C+
C+
A-
A-
A-
A-C+
C+
C+
C+
C+
A-
A-
C+
C+
A-
A-
A-
A-
A-
A-
C+
C+
C+
C+
A-
A-
0 0 000
The electrical double layer – “realistic” picture
Specific Adsorption
of Anions
C+C+Σ δ− + Σ δ+ = 0
PZTC
PZC + chemically bonded species
PZC
- - --- 0 0 000
Water molecules and ions interaction with surface is the weakest at PZTC.
10th
European Symposium on Electrochemical Engineering, Sardinia, Italy
September 28, 2014 to October 02, 2014

8. National Institute
of Chemistry
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C+
A-
C+
C+
A-
A-
A-
A-C+
C+
C+
C+
C+
A-
A-
C+
C+
A-
A-
A-
A-
A-
A-
C+
C+
C+
C+
A-
A-
0 0 000
The electrical double layer – reaction
Specific Adsorption
of Anions
C+C+Σ δ− + Σ δ+ = 0
This has a profound effect on the rate of electrochemical reactions:
1. It blocks the active sites for the adsorption of the reactant.
2. It acts as co-catalyst (OH formation from water).
3. It can alter the reactant adsorption energy.
- - --- 0 0 000
10th
European Symposium on Electrochemical Engineering, Sardinia, Italy
September 28, 2014 to October 02, 2014

9. National Institute
of Chemistry
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C+
A-
C+
C+
A-
A-
A-
A-C+
C+
C+
C+
C+
A-
A-
C+
C+
A-
A-
A-
A-
A-
A-
C+
C+
C+
C+
A-
A-
Adsorption is an ion or solvent replacement reaction.
C+C+
0 0 000
A-
- - --- 0 0 000
The electrical double layer – reaction
10th
European Symposium on Electrochemical Engineering, Sardinia, Italy
September 28, 2014 to October 02, 2014

10. National Institute
of Chemistry
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C+
A-
C+
C+
A-
A-
A-
A-C+
C+
C+
C+
C+
A-
A-
C+
C+
A-
A-
A-
A-
A-
A-
C+
C+
C+
C+
A-
A-
Adsorption is an ion or solvent replacement reaction.
C+C+
0 0 000
A-
- - --- 0 0 000
The electrical double layer – reaction
10th
European Symposium on Electrochemical Engineering, Sardinia, Italy
September 28, 2014 to October 02, 2014

11. National Institute
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Karl Mayrhofer, PhD thesis, Vienna University of Technology, (2005).
Langmuir–Hinshelwood Mechanism:
Begins with Eley−Rideal Mechanism:
M–CO + H2O → M + CO2 + 2H+
- strongly absorbing molecule
- it can be used as an indicator (probe) for OHad formation
CO: carbon monoxide oxidation

12. National Institute
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CO: carbon monoxide oxidation
- strongly absorbing molecule
- it can be used as an indicator (probe) for OHad formation
0,0 0,2 0,4 0,6 0,8 1,0 1,2
-0,0015
-0,0012
-0,0009
-0,0006
-0,0003
0,0000
0,0003
0,0006
I / A
U / V vs. RHE
CO
0,0 0,2 0,4 0,6 0,8 1,0 1,2
0,0
0,2
0,4
0,6
0,8
1,0
Θ
U / V vs. RHE
ΘCO
Pt poly.
CO + OHad CO2 + H+
+ e-
H2O OHad + H+
+ e-

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ORR: oxygen reduction reaction
- at high potentials the coverage of anions
1-ΘAad increases so much that the oxygen
can not find any space to adsorb
Pt poly.
- It can be used as an indicator for high anion-surface attraction
- Or it can be used as an indicator for high anion coverage (ΘAad )
D. Strmčnik, Nat Chem 2 (2010) 880–885
0,0 0,2 0,4 0,6 0,8 1,0 1,2
-0,0015
-0,0012
-0,0009
-0,0006
-0,0003
0,0000
0,0003
0,0006
I/A
U / V vs. RHE
ORR
CO
MOR

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MOR: methanol oxidation reaction
Pt poly.
- It is highly influenced by the surface coverage and the
ability of surface to oxidize intermediate CO
- weakly absorbing molecule
0,0 0,2 0,4 0,6 0,8 1,0 1,2
-0,0015
-0,0012
-0,0009
-0,0006
-0,0003
0,0000
0,0003
0,0006
I/A
U / V vs. RHE
MOR
10th
European Symposium on Electrochemical Engineering, Sardinia, Italy
September 28, 2014 to October 02, 2014

15. National Institute
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MOR: methanol oxidation reaction
Pt poly.
0,0 0,2 0,4 0,6 0,8 1,0 1,2
-0,0015
-0,0012
-0,0009
-0,0006
-0,0003
0,0000
0,0003
0,0006
I/A
U / V vs. RHE
CO
MOR
Dietmar Gerteisen, Journal of Power Sources 195 (2010) 6719
CO oxidation starts
- It is highly influenced by the surface coverage and the
ability of surface to oxidize intermediate CO
- weakly absorbing molecule

16. National Institute
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MOR: methanol oxidation reaction
Pt poly.
0,0 0,2 0,4 0,6 0,8 1,0 1,2
-0,0015
-0,0012
-0,0009
-0,0006
-0,0003
0,0000
0,0003
0,0006
I/A
U / V vs. RHE
CO
MOR
W. Vielstich, in: E. Julio Calvo (Ed.), Interfacial Kinetics and Mass
Transport, Vol. 2, Wiley-VCH, Weinheim, (2003) 466–511.
CO oxidation starts
Dietmar Gerteisen, Journal of Power Sources 195 (2010) 6719
- It is highly influenced by the surface coverage and the
ability of surface to oxidize intermediate CO
- weakly absorbing molecule

17. National Institute
of Chemistry
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MOR: methanol oxidation reaction
0,0 0,2 0,4 0,6 0,8 1,0 1,2
-0,0015
-0,0012
-0,0009
-0,0006
-0,0003
0,0000
0,0003
0,0006
I/A
U / V vs. RHE
ORR
CO
MOR
Pt poly.
O2 reduction stops
- It is highly influenced by the surface coverage and the
ability of surface to oxidize intermediate CO
- weakly absorbing molecule
D. Strmčnik, Nat Chem 2 (2010) 880–885

18. National Institute
of Chemistry
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MOR: methanol oxidation reaction
0,0 0,2 0,4 0,6 0,8 1,0 1,2
-0,0015
-0,0012
-0,0009
-0,0006
-0,0003
0,0000
0,0003
0,0006
I/A
U / V vs. RHE
ORR
CO
MOR
Pt poly.
MOR starts and stops
at this potentials
D. Strmčnik, Nat Chem 2 (2010) 880–885
W. Vielstich, in: E. Julio Calvo (Ed.), Interfacial Kinetics and Mass
Transport, Vol. 2, Wiley-VCH, Weinheim, (2003) 466–511.

19. National Institute
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Like aperture!
Pt poly.
0,0 0,2 0,4 0,6 0,8 1,0 1,2
0,0
0,2
0,4
0,6
0,8
1,0
U / V vs. RHE
Θ
ΘOH
10th
European Symposium on Electrochemical Engineering, Sardinia, Italy
September 28, 2014 to October 02, 2014

20. 0,0 0,2 0,4 0,6 0,8 1,0 1,2
0,0
0,2
0,4
0,6
0,8
1,0
U / V vs. RHE
Θ
ΘOH
National Institute
of Chemistry
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Like aperture!
Pt poly.
(1-ΘOH-ΘAad)
10th
European Symposium on Electrochemical Engineering, Sardinia, Italy
September 28, 2014 to October 02, 2014

21. 0,0 0,2 0,4 0,6 0,8 1,0 1,2
0,0
0,2
0,4
0,6
0,8
1,0
Θ
U / V vs. RHE
ΘCO
National Institute
of Chemistry
Slovenia
Like aperture!
0,0 0,2 0,4 0,6 0,8 1,0 1,2
-0,0015
-0,0012
-0,0009
-0,0006
-0,0003
0,0000
0,0003
0,0006
I/A
U / V vs. RHE
CO
Pt poly.
(1-ΘCO)
10th
European Symposium on Electrochemical Engineering, Sardinia, Italy
September 28, 2014 to October 02, 2014

22. 0,0 0,2 0,4 0,6 0,8 1,0 1,2
0,0
0,2
0,4
0,6
0,8
1,0
Θ
U / V vs. RHE
ΘCO
National Institute
of Chemistry
Slovenia
Like aperture!
Pt poly.
0,0 0,2 0,4 0,6 0,8 1,0 1,2
-0,0015
-0,0012
-0,0009
-0,0006
-0,0003
0,0000
0,0003
0,0006
I/A
U / V vs. RHE
CO
(1-ΘCO)
10th
European Symposium on Electrochemical Engineering, Sardinia, Italy
September 28, 2014 to October 02, 2014

23. (1-ΘCO)
(1-ΘOH-ΘAad)
National Institute
of Chemistry
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potential
Like aperture!
10th
European Symposium on Electrochemical Engineering, Sardinia, Italy
September 28, 2014 to October 02, 2014

24. (1-ΘCO)
(1-ΘOH-ΘAad)
National Institute
of Chemistry
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potential
Like aperture!
= (1-ΘCO-ΘOH-ΘAad)
+
10th
European Symposium on Electrochemical Engineering, Sardinia, Italy
September 28, 2014 to October 02, 2014

25. (1-ΘCO)
(1-ΘOH-ΘAad)
National Institute
of Chemistry
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potential
Like aperture!
= (1-ΘCO-ΘOH-ΘAad)
(1-ΘCO-ΘOH-ΘAad)
+
=
10th
European Symposium on Electrochemical Engineering, Sardinia, Italy
September 28, 2014 to October 02, 2014

26. National Institute
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Surface coverage 1-Θ
0,0 0,2 0,4 0,6 0,8 1,0 1,2
0,0
0,2
0,4
0,6
0,8
1,0
Θ
U / V vs. RHE
ΘCO
ΘOH
Pt poly.
10th
European Symposium on Electrochemical Engineering, Sardinia, Italy
September 28, 2014 to October 02, 2014

27. National Institute
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Surface coverage 1-Θ
0,0 0,2 0,4 0,6 0,8 1,0 1,2
0,0
0,2
0,4
0,6
0,8
1,0
Θ
U / V vs. RHE
ΘCO
ΘOH
1-(ΘCO
+ΘOH
)
Pt poly.
10th
European Symposium on Electrochemical Engineering, Sardinia, Italy
September 28, 2014 to October 02, 2014

28. National Institute
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Surface coverage 1-Θ
0,0 0,2 0,4 0,6 0,8 1,0 1,2
0,0
0,2
0,4
0,6
0,8
1,0
Θ
U / V vs. RHE
ΘCO
ΘOH
1-(ΘCO
+ΘOH
)
MOR
Pt poly.
10th
European Symposium on Electrochemical Engineering, Sardinia, Italy
September 28, 2014 to October 02, 2014

29. National Institute
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The electric double layer has been modified
by changing the adsorption properties of
electrode instead of electrolyte !
Pt/C, PtCu/C, PtCo, PtRu
Real catalyst?
10th
European Symposium on Electrochemical Engineering, Sardinia, Italy
September 28, 2014 to October 02, 2014

30. 0,0 0,2 0,4 0,6 0,8 1,0 1,2
-7
-6
-5
-4
-3
-2
-1
0
1
Pt/C
PtCu/C
PtCo/C
U vs. RHE / V
Currentdensity/mA/cm
2
geo
PtRu/C
0,0 0,2 0,4 0,6 0,8 1,0 1,2
0,00000
0,00005
0,00010
0,00015
PtRu/C PtNi/C
Pt/C
PtCo/C
PtCu/C
CurrentdensityA/cm
2
Pt
U vs. RHE / V
National Institute
of Chemistry
Slovenia
Real catalyst?

31. 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 1,1
0
1
2
3
4
5
6
U/ V vs. RHE
PtCo/CPtCo/C
PtRu/C
PtCu/C
Pt/C
I/mA/cm
2
Pt
0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 1,1
0,0
0,2
0,4
0,6
0,8
U / V vs. RHE
Θ
Pt/C
PtRu/C
PtCo/C
PtNi/C
PtCu/C
0,0 0,2 0,4 0,6 0,8 1,0 1,2
-7
-6
-5
-4
-3
-2
-1
0
1
Pt/C
PtCu/C
PtCo/C
U vs. RHE / V
Currentdensity/mA/cm
2
geo
PtRu/C
0,0 0,2 0,4 0,6 0,8 1,0 1,2
0,00000
0,00005
0,00010
0,00015
PtRu/C PtNi/C
Pt/C
PtCo/C
PtCu/C
CurrentdensityA/cm
2
Pt
U vs. RHE / V
National Institute
of Chemistry
Slovenia
Real catalyst?

32. National Institute
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Real catalyst?

33. National Institute
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Dietmar Gerteisen, Journal of Power Sources 195 (2010) 6719–6731
- at low potentials MOR rate is governed by ability of surface to
produce OH and oxidise (remove) CO.
Real new catalyst!

34. National Institute
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Real new catalyst!

35. National Institute
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Real new catalyst!
Ru PtCu

36. 0,0 0,2 0,4 0,6 0,8 1,0 1,2
-7
-6
-5
-4
-3
-2
-1
0
1
PtCu+Ru/C PtCu/C
U vs. RHE / V
Currentdensity/mA/cm
2
geo
0,0 0,2 0,4 0,6 0,8 1,0 1,2
0,00000
0,00005
0,00010
0,00015
PtCu+Ru/C
PtCu/C
CurrentdensityA/cm
2
Pt
U vs. RHE / V
National Institute
of Chemistry
Slovenia
Real new catalyst!

37. 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 1,1
0
1
2
3
4
5
6
U / V vs. RHE
PtCu+Ru/C
PtCu/C
I/mA/cm
2
Pt
0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 1,1
0,0
0,2
0,4
0,6
0,8
U / V vs. RHE
Θ
PtCu+Ru/C
PtCu/C
0,0 0,2 0,4 0,6 0,8 1,0 1,2
-7
-6
-5
-4
-3
-2
-1
0
1
PtCu+Ru/C PtCu/C
U vs. RHE / V
Currentdensity/mA/cm
2
geo
0,0 0,2 0,4 0,6 0,8 1,0 1,2
0,00000
0,00005
0,00010
0,00015
PtCu+Ru/C
PtCu/C
CurrentdensityA/cm
2
Pt
U vs. RHE / V
National Institute
of Chemistry
Slovenia
Real new catalyst!

38. Thank you for your attention!
National Institute
of Chemistry
Slovenia
nejc.hodnik@ki.si
38
Presented work has been published in the following article:
Nejc Hodnik, Marjan Bele, Stanko Hočevar, New Pt-skin electrocatalysts for
oxygen reduction and methanol oxidation reactions, Electrochemistry
Communications, 23 (2012) 125–128
Extended version is yet to be published.

39. National Institute
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N2O: nitrous oxide reduction reaction
reduction of nitrous oxide:
M + N2O → M–O + N2
M–O + H+
+e → M–OH
M–OH + H+
+e → M + H2O
- weakly absorbing molecule
- at the potencial of the weakest interaction
of supporting electrolyte with surface the
current density is the highest
- it can be used as an indicator (probe) for
PZTC
PZTC
0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7
-0,16
-0,14
-0,12
-0,10
-0,08
-0,06
-0,04
-0,02
0,00
Currentdensity/mA/cm
2
Pt
PtCu/C
U / V

40. National Institute
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0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7
-0,16
-0,14
-0,12
-0,10
-0,08
-0,06
-0,04
-0,02
0,00
Currentdensity/mA/cm
2
Pt
PtCu/C
U / V
N2O: nitrous oxide reduction reaction
- indirect evidence that the surface coverage governs the ORR
- the higher the PZTC, the later the surface coverage of anions will block the ORR

41. National Institute
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0.35 0.30 0.25 0.20 0.15 0.10
0.85
0.90
0.95
1.00
1.05
X
X
X
X
X
X
PtCo/C
PtNi/C
PtCu/C
Pt/C
PtCu+Ru/C
U@0.02mA/cm
2
/V
PZTC vs. RHE / V
PtRu/C
0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7
-0,16
-0,14
-0,12
-0,10
-0,08
-0,06
-0,04
-0,02
0,00
PtNi/C
PtCo/C
PtCu+Ru/C
PtCu/C
PtRu/C
Pt/C
U / V
N2O: nitrous oxide reduction reaction
- indirect evidence that the surface coverage governs the ORR
- the higher the PZTC, the later the surface coverage of anions will block the ORR

42. National Institute
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)exp()exp(21
RT
Gg
RT
FE
AnFKcK ad
O
∆
−−=
β
0,0 0,2 0,4 0,6 0,8 1,0 1,2
-0,0015
-0,0012
-0,0009
-0,0006
-0,0003
0,0000
0,0003
0,0006
I/A
U / V vs. RHE
ORR
ORR: oxygen reduction reaction
x
AadOH ΘΘKi )1(1 −−=
Pt poly.

43. National Institute
of Chemistry
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)exp()exp(21
RT
Gg
RT
FE
AnFKcK ad
O
∆
−−=
β
x
AadOH ΘΘKi )1(1 −−=
0,0 0,2 0,4 0,6 0,8 1,0 1,2
-0,0015
-0,0012
-0,0009
-0,0006
-0,0003
0,0000
0,0003
0,0006
I/A
U / V vs. RHE
ORR
CO
x
COΘKi )1(2 −=
ORR CO
Pt poly.

44. National Institute
of Chemistry
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)exp()exp(21
RT
Gg
RT
FE
AnFKcK ad
O
∆
−−=
β
0,0 0,2 0,4 0,6 0,8 1,0 1,2
-0,0015
-0,0012
-0,0009
-0,0006
-0,0003
0,0000
0,0003
0,0006
I/A
U / V vs. RHE
ORR
CO
MOR
“MOR”:
x
AadOHCOmeth ΘΘΘAnFKci )1( −−−=
+
=
x
AadOH ΘΘKi )1(1 −−= x
COΘKi )1(2 −=
COORR
Currents measured on polycrystalline Pt for ORR, CO stripping (current multiplied by 10), and MOR (0.01 M) in 0.1 M HClO4
Pt poly.

46. 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 1,1
0
1
2
3
4
5
6
U / V vs. RHE
PtCo/CPtCo/C
PtNi/C
PtRu/C
PtCu+Ru/C
PtCu/C
Pt/C
I/mA/cm
2
Pt
0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 1,1
0,0
0,2
0,4
0,6
0,8
U / V vs. RHE
Θ
Pt/C
PtRu/C
PtCu+Ru/C
PtCo/C
PtNi/C
PtCu/C
0.0 0.2 0.4 0.6 0.8 1.0 1.2
-7
-6
-5
-4
-3
-2
-1
0
1
PtCu+Ru/C
Pt/C
PtCu/C
PtNi/C
PtCo/C
U vs. RHE / V
Currentdensity/mA/cm
2
geo
PtRu/C
0.0 0.2 0.4 0.6 0.8 1.0 1.2
0.00000
0.00005
0.00010
0.00015
PtRu/C
PtCu+Ru/C
PtNi/C
Pt/C
PtCo/C
PtCu/C
CurrentdensityA/cm
2
Pt
U vs. RHE / V
National Institute
of Chemistry
Slovenia