Investigation of the electro-oxidation of CO on Pt-based carbon supported catalysts (Pt75Sn25/C, Pt65Ru35/C and Pt/C) by electrochemical impedance spectroscopy

In spite of the abundant literature on carbon monoxide (CO) oxidation on Pt-based catalysts several aspects of the reaction remain obscure, particularly on actual materials used in low temperature fuel cells. Electrochemical impedance spectroscopy (EIS) is a powerful technique for the investigation of complex electrochemical reactions and can elucidate important aspects of such an important reaction in electrochemical energy conversion, namely, the oxidation of CO on Pt surfaces with different properties. This work describes an EIS study of the carbon monoxide electrochemical oxidation on three fuel cell catalysts, Pt75Sn25/C, Pt65Ru35/C and Pt/C. Impedance results in CO saturated 0.5 M H2SO4 solution were analyzed by a kinetic model containing one adsorbed intermediate, which allowed to extract successfully important kinetic parameters such as the charge-transfer resistance, the coverage resistance, the coverage relaxation time and the interfacial double layer capacitance as functions of the electrode potential. The relationship among the kinetic parameters is also discussed. Furthermore, EIS measurements in CO-free solution were also carried out in order to get information on the formation of the oxygen source available at the surface to oxidize adsorbed CO.