The Beneficial Role of the Cometals Pd and Au in the Carbon-Supported PtPdAu Catalyst Toward Promoting Ethanol Oxidation Kinetics in Alkaline Fuel Cells: Temperature Effect and Reaction Mechanism

Abstract

Electrochemical investigations have been carried out to study the oxidation kinetics of ethanol in alkaline solution on carbon-supported ternary alloy catalysts Pt–Pd–Au within the temperature range of 20–80 °C. To derive a better understanding of the contribution of each of the metallic components toward the catalytic oxidation of ethanol, some of the investigations were extended to the individual noble metals for comparison, however, at a single temperature (20 °C). The individual metals could barely show their catalytic efficiency toward ethanol oxidations when compared to the alloyed catalyst. The ternary catalyst exhibited much lower values and a larger temperature dependence of onset potential for ethanol oxidation. With the rise of potential, the apparent activation energy (Ea(app)) for ethanol oxidation on the Pt/C electrode increased, whereas a decreasing trend was observed with the Pt30Pd38Au32/C electrode. It was suggested that the Pt30Pd38Au32/C electrode bears an excellent tolerance toward ethanolic residues, for the temperature range studied. In correlation with the results obtained from the above study, attempts were made to elucidate the oxidation reaction mechanism, and this further evoked interest in extending the work to the estimation of products formed during oxidation of ethanol within the same temperature range through ion chromatographic analysis. The pronounced increase in the quantity of oxidation products, such as acetate and carbonate, obtained over the ternary catalyst as compared to single Pt, substantiates the kinetic enhancement of ethanol oxidation, attributable to the cometal partnership between Pd and Au when incorporated in the Pt matrix. In summary, the multimetallic nanocrystallites can not only show their capability of extracting the best possible number of electrons from the alcohol fuel in alkaline solutions, harnessing more energy, but also, at the same time, bring down the cost of the catalyst material by reducing the Pt content to a considerable extent.