Elementary mechanisms in electrocatalysis: Revisiting the ORR tafel slope

We use microkinetic modeling to demonstrate that deviations from ideal Tafel kinetics, which assume a linear relationship between overpotential and log-current, are an inherent property of multi-step heterogeneous electrocatalytic reactions. We show that in general, deviations from ideal Tafel behavior can often be attributed to a simultaneous increase in the rate of the rate-limiting elementary step and a change in the number of available active sites on the electrode as overpotential is induced. Our analysis shows that in the oxygen reduction reaction (ORR) on Pt electrodes, which exhibits nonlinear Tafel behavior, changing electrode potential affects not only the rate-limiting step (the initial electron transfer to molecular oxygen), but also the concentration of surface intermediates—mainly OH and H 2 O. Based on comparison of measured and predicted changes in Tafel slope (as well as pH dependence), we show that alternative interpretations of the non-ideal Tafel behavior of ORR on Pt, such as changes in rate-limiting step or adsorbate repulsion effects, are inconsistent with the observed ORR kinetics.

[1]  Allen J. Bard,et al.  Electrochemical Methods: Fundamentals and Applications , 1980 .

[2]  J. Nørskov,et al.  On the Compensation Effect in Heterogeneous Catalysis , 2003 .

[3]  A. Damjanović,et al.  Electrode kinetics of oxygen reduction on oxide-free platinum electrodes☆ , 1967 .

[4]  Peter Faguy,et al.  An in Situ Infrared Study on the Effect of pH on Anion Adsorption at Pt(111) Electrodes from Acid Sulfate Solutions , 1996 .

[5]  H. Gasteiger,et al.  Temperature‐Dependent Methanol Electro‐Oxidation on Well‐Characterized Pt‐Ru Alloys , 1994 .

[6]  Philip N. Ross,et al.  Improved Oxygen Reduction Activity on Pt3Ni(111) via Increased Surface Site Availability , 2007, Science.

[7]  S.Lj Gojković,et al.  Kinetic study of methanol oxidation on carbon-supported PtRu electrocatalyst , 2003 .

[8]  P. Ross,et al.  Surface science studies of model fuel cell electrocatalysts , 2002 .

[9]  Z. Nagy,et al.  Symmetry factor and transfer coefficient. A source of confusion in electrode kinetics , 1973 .

[10]  A. Wokaun,et al.  Oxygen reduction on high surface area Pt-based alloy catalysts in comparison to well defined smooth bulk alloy electrodes , 2002 .

[11]  J. X. Wang,et al.  Kinetic Analysis of Oxygen Reduction on Pt(111) in Acid Solutions: Intrinsic Kinetic Parameters and Anion Adsorption Effects , 2004 .

[12]  N. Alonso‐Vante,et al.  Novel low-temperature synthesis of semiconducting transition metal chalcogenide electrocatalyst for multielectron charge transfer: molecular oxygen reduction , 1994 .

[13]  Bockris Jo'm.  Modern Aspects of Electrode Kinetics , 1954 .

[14]  V. Radmilović,et al.  Oxygen Reduction on Carbon-Supported Pt−Ni and Pt−Co Alloy Catalysts , 2002 .

[15]  Junliang Zhang,et al.  Catalytic Activity−d-Band Center Correlation for the O2 Reduction Reaction on Platinum in Alkaline Solutions , 2007 .

[16]  M. Salmeron,et al.  Molecular structure of water at interfaces: wetting at the nanometer scale. , 2006, Chemical reviews.

[17]  S. Haq,et al.  Hydrogen bonding in mixed OH+H2O overlayers on Pt(111). , 2004, Physical review letters.

[18]  Junliang Zhang,et al.  Double-trap kinetic equation for the oxygen reduction reaction on Pt(111) in acidic media. , 2007, The journal of physical chemistry. A.

[19]  Analysis of simple kinetic models in heterogeneous catalysis , 2004 .

[20]  D. Tryk,et al.  In situ ATR-FTIR study of oxygen reduction at the Pt/Nafion interface. , 2010, Physical chemistry chemical physics : PCCP.

[21]  N. Marković,et al.  Surface Composition Effects in Electrocatalysis: Kinetics of Oxygen Reduction on Well-Defined Pt3Ni and Pt3Co Alloy Surfaces , 2002 .

[22]  R. Parsons.  General equations for the kinetics of electrode processes , 1951 .

[23]  H. Gasteiger,et al.  Activity benchmarks and requirements for Pt, Pt-alloy, and non-Pt oxygen reduction catalysts for PEMFCs , 2005 .

[24]  Junliang Zhang,et al.  Intrinsic kinetic equation for oxygen reduction reaction in acidic media: the double Tafel slope and fuel cell applications. , 2008, Faraday discussions.

[25]  Yu Morimoto,et al.  First principles based mean field model for oxygen reduction reaction. , 2011, Physical chemistry chemical physics : PCCP.

[26]  N. Marković,et al.  Temperature dependent surface electrochemistry on Pt single crystals in alkaline electrolyte: Part 3: The oxygen reduction reaction , 2002 .

[27]  Stewart K. Reed,et al.  Water at an electrochemical interface--a simulation study. , 2008, Faraday discussions.

[28]  Ping Liu,et al.  Superoxide anion is the intermediate in the oxygen reduction reaction on platinum electrodes. , 2006, Journal of the American Chemical Society.

[29]  Ernest Yeager,et al.  Temperature dependence of the Tafel slope for oxygen reduction on platinum in concentrated phosphoric acid , 1993 .

[30]  M. Scheffler,et al.  On the Accuracy of DFT for Describing Hydrogen Bonds: Dependence on the Bond Directionality , 2004 .

[31]  P. Feibelman.  Partial Dissociation of Water on Ru(0001) , 2002, Science.

[32]  V. Stamenkovic,et al.  Enhanced electrocatalysis of the oxygen reduction reaction based on patterning of platinum surfaces with cyanide. , 2010, Nature chemistry.

[33]  Hubert A. Gasteiger,et al.  Kinetics of oxygen reduction on Pt(hkl) electrodes : Implications for the crystallite size effect with supported Pt electrocatalysts , 1997 .

[34]  Jens K Nørskov,et al.  Changing the activity of electrocatalysts for oxygen reduction by tuning the surface electronic structure. , 2006, Angewandte Chemie.

[35]  A S Bondarenko,et al.  Alloys of platinum and early transition metals as oxygen reduction electrocatalysts. , 2009, Nature chemistry.

[36]  Bongjin Simon Mun,et al.  Trends in electrocatalysis on extended and nanoscale Pt-bimetallic alloy surfaces. , 2007, Nature materials.

[37]  Sanjeev Mukerjee,et al.  Role of Structural and Electronic Properties of Pt and Pt Alloys on Electrocatalysis of Oxygen Reduction An In Situ XANES and EXAFS Investigation , 1995 .

[38]  Mahlon Wilson,et al.  Scientific aspects of polymer electrolyte fuel cell durability and degradation. , 2007, Chemical reviews.

[39]  Egill Skúlason,et al.  The oxygen reduction reaction mechanism on Pt(111) from density functional theory calculations , 2010 .

[40]  A. Damjanović,et al.  Different views regarding the kinetics and mechanisms of oxygen reduction at Pt and Pd electrodes , 1987 .

[41]  P. Stoltze.  Surface science as the basis for the understanding of the catalytic synthesis of ammonia , 1987 .

[42]  A. Damjanović,et al.  Reaction intermediates as a controlling factor in the kinetics and mechanism of oxygen reduction at platinum electrodes , 1981 .

[43]  S. Mukerjee,et al.  Oxygen Reduction Kinetics in Low and Medium Temperature Acid Environment: Correlation of Water Activation and Surface Properties in Supported Pt and Pt Alloy Electrocatalysts , 2004 .

[44]  H. Jónsson,et al.  Origin of the Overpotential for Oxygen Reduction at a Fuel-Cell Cathode. , 2004, The journal of physical chemistry. B.

[45]  H. Gasteiger,et al.  Oxygen reduction on platinum low-index single-crystal surfaces in sulfuric acid solution. Rotating ring - Pt(hkl) disk studies , 1995 .

[46]  P. Ross,et al.  Oxygen reduction on silver low-index single-crystal surfaces in alkaline solution: rotating ring disk(Ag(hkl)) studies. , 2006, The journal of physical chemistry. B.