(Invited) Pt/Metal Oxide/Ti and Pt/Metal Oxide/Carbon Composite Films for Ethanol Oxidation

Abstract

Metal oxides such as RuO2 and SnO2 can promote the oxidation of organic fuels at Pt nanoparticles in a number of ways. These include changing the d-band level of the Pt via electron transfer (electronic effect) and providing surface –OH functionality for the oxidation of adsorbed CO (bifunctional effect) [1]. Carbon black coated with a mixture of Ru and Sn oxides has been shown to increase the activity of Pt for ethanol oxidation without a significant loss of selectivity for its complete oxidation to CO2 [2].Here we report on the use of various mixed metal oxide composites prepared by thermal decomposition of metal acetylacetonate complexes (M(acac)n). Oxide layers were deposited onto Ti foil and high surface area carbon electrodes, and drop coated with preformed Pt nanoparticles. Cyclic voltammetry in H2SO4(aq) and polarization experiments in a proton exchange membrane cell were used to study the co-catalytic effects of the oxide layers. The use of acetylacetonate precursors provides a versatile method for screening libraries of oxide supported catalysts, as well as the production and screening of electrodes for fuel cells.Initially, decomposition of Ru(acac)3 and Sn(acac)2 and their mixtures on Ti foil electrodes was investigated. These experiments reproduced the effects previously observed with oxide layers deposited on glassy carbon from KRuO4 and SnCl4 [3]. Deposits formed from both complexes increased the activity for ethanol oxidation of Pt nanoparticles drop coated onto their surfaces, while use of mixtures produced a strong synergistic effect. Deposits formed by thermal decomposition of a variety of other acac complexes, including Ga(acac)3, Zr(acac)4, and In(acac)3, also increased the activity of Pt nanoparticles for ethanol oxidation.Mixed Ru+Sn oxides were also produced by thermal decomposition of Ru(acac)3 and Sn(acac)2 on carbon black, in order to better characterize the oxide deposits and produce catalysts that could be used in fuel cells. X-ray diffraction and energy dispersive X-ray spectrometry confirmed the presence of a mixed oxide. Preformed Pt nanoparticles were adsorbed onto the oxide coated carbon, supported on carbon fiber paper, and the resulting electrodes were evaluated for ethanol oxidation in a proton exchange membrane cell at 80 °C. Acknowledgments: This work was supported by the Natural Sciences and Engineering Research Council of Canada and Memorial University.[1] G.M. Alvarenga, H.M. Villullas, Current Opinion in Electrochemistry, 2017, 4, 39-44[2] D.D. James, R.B. Moghaddam, B. Chen, P.G. Pickup, Journal of the Electrochemical Society, 2018, 165, F215-F219[3] R. B. Moghaddam and P. G. Pickup, Electrochim. Acta, 2012, 65, 210– 215