H2 and H2/CO oxidation mechanism on Pt/C, Ru/C and Pt–Ru/C electrocatalysts

The oxidation kinetics of H2 and H2 + 100 ppm CO were investigated on Pt, Ru and Pt–Ru electrocatalysts supported on a high-surface area carbon powder. The atomic ratios of Pt to Ru were 3, 1 and 0.33. XRD, TEM, EDS and XPS were used to characterize the electrocatalysts. When alloyed with ruthenium, a decrease in mean particle size and a modification of the platinum electronic structure were identified. Impedance measurements in H2SO4, at open circuit potential, indicated different mechanisms for hydrogen oxidation on Pt/C (Tafel–Volmer path) and Pt–Ru/C (Heyrowsky–Volmer path). These mechanisms also occur in the presence of CO. Best performances, both in H2 and H2 + CO, were achieved by the catalyst with the ratio Pt/Ru = 1. This is due to a compromise between the number of free sites and the presence of adsorbed water on the catalyst. For CO tolerance, an intrinsic mechanism not involving CO electroxidation was proposed. This mechanism derives from changes in the electronic structure of platinum when alloyed with ruthenium.

[1]  Alfred B. Anderson,et al.  Systematic Theoretical Study of Alloys of Platinum for Enhanced Methanol Fuel Cell Performance , 1996 .

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

[3]  G. Wertheim,et al.  Unit Charge on Supported Gold Clusters in Photoemission Final State , 1983 .

[4]  E. Kay,et al.  Core binding energies for clusters deposited on different insulating substrates: esca spectra and theoretical electronic structure studies , 1985 .

[5]  J. Beery,et al.  An electrochemical, ellipsometric, and surface science investigation of the PtRu bulk alloy surface , 1989 .

[6]  J. Rodríguez,et al.  Physical and chemical properties of bimetallic surfaces , 1996 .

[7]  S. Mukerjee,et al.  In Situ X‐Ray Absorption Studies of a Pt‐Ru Electrocatalyst , 1995 .

[8]  P. Stonehart,et al.  Effect of poisons on kinetic parameters for platinum electrocatalyst sites , 1972 .

[9]  G. Wertheim,et al.  Photoemission from surface-atom core levels, surface densities of states, and metal-atom clusters: A unified picture , 1983 .

[10]  Volkmar M. Schmidt,et al.  Electrochemical surface reactions of intermediates formed in the oxidative ethanol adsorption on porous Pt and PtRu , 1999 .

[11]  H. Gasteiger,et al.  H2 and CO Electrooxidation on Well-Characterized Pt, Ru, and Pt-Ru. 1. Rotating Disk Electrode Studies of the Pure Gases Including Temperature Effects , 1995 .

[12]  E. Passalacqua,et al.  Influence of the PTFE content in the diffusion layer of low-Pt loading electrodes for polymer electrolyte fuel cells , 1998 .

[13]  Volkmar M. Schmidt,et al.  Performance Data of a Proton Exchange Membrane Fuel Cell Using H 2 / CO as Fuel Gas , 1996 .

[14]  G. Squadrito,et al.  Improvement in the diffusion characteristics of low Pt-loaded electrodes for PEFCs , 1999 .

[15]  Masahiro Watanabe,et al.  Electrocatalysis by ad-atoms: Part II. Enhancement of the oxidation of methanol on platinum by ruthenium ad-atoms , 1975 .

[16]  K. Wandelt,et al.  Surface and electrochemical characterization of electrodeposited PtRu alloys , 1995 .

[17]  E. Passalacqua,et al.  Influence of Nafion loading in the catalyst layer of gas-diffusion electrodes for PEFC , 1999 .

[18]  A. Shukla,et al.  An X-ray photoelectron spectroscopic study on the effect of Ru and Sn additions to platinised carbons , 1999 .

[19]  R. Behm,et al.  CO adsorption and oxidation on bimetallic Pt/Ru(0001) surfaces: a combined STM and TPD/TPR study , 1998 .

[20]  B. Beden,et al.  The electrooxidation of CO: a test reaction in electrocatalysis , 1990 .

[21]  E. Kay,et al.  Reply to the comment by DiCenzo and Wertheim on “core binding energies for clusters⋯” , 1987 .

[22]  Hubert A. Gasteiger,et al.  Carbon monoxide electrooxidation on well-characterized platinum-ruthenium alloys , 1994 .

[23]  Shimshon Gottesfeld,et al.  A New Approach to the Problem of Carbon Monoxide Poisoning in Fuel Cells Operating at Low Temperatures , 1988 .

[24]  F. Albert Cotton,et al.  Advanced Inorganic Chemistry , 1999 .

[25]  H. Gasteiger,et al.  Rotating Disk Electrode Measurements on the CO Tolerance of a High‐Surface Area Pt/Vulcan Carbon Fuel Cell Catalyst , 1999 .