Ethanol electrooxidation on Pt-Sn and Pt-Sn-W bulk alloys

Abstract

A oxidação de etanol foi estudada sobre eletrodos Pt-Sn e Pt-Sn-W preparados em forno a arco elétrico. Diferentes técnicas eletroquímicas, tais como voltametria cíclica e cronoamperometria foram utilizadas para avaliar a atividade catalítica desses materiais. O processo de eletro-oxidação também foi investigado in situ por espectroscopia de reflectância na região do infravermelho para determinar intermediários adsorvidos e produtos da reação. Os resultados experimentais indicaram que as ligas Pt-Sn e Pt-Sn-W são capaz de oxidar etanol principalmente para acetaldeído e ácido acético. CO adsorvido também foi detectado, demonstrando a viabilidade do rompimento da ligação C-C na molécula de etanol durante o processo de oxidação. Adicionalmente, o CO adsorvido foi oxidado a CO 2 . Esse produto de reação foi claramente detectado por SNIFTIRS. O catalisador Pt-Sn-W mostrou um melhor desempenho eletroquímico em relação ao Pt-Sn e este, por sua vez, é melhor do que Pt pura.Ethanol oxidation has been studied on Pt-Sn and Pt-Sn-W electrodes prepared in an arc-melting furnace. Different electrochemical techniques like cyclic voltammetry and chronoamperometry were used to evaluate the catalytic activity of these materials. The electro-oxidation process was also investigated by in situ infrared reflectance spectroscopy in order to determine adsorbed intermediates and reaction products. Experimental results indicated that Pt-Sn and Pt-Sn-W alloys are able to oxidize ethanol mainly to acetaldehyde and acetic acid. Adsorbed CO was also detected, demonstrating the viability of splitting the C-C bond in the ethanol molecule during the oxidation process. The adsorbed CO was further oxidized to CO 2 .This reaction product was clearly detected by SNIFTIRS. Pt-Sn-W catalyst showed a better electrochemical performance than Pt-Sn that, in it turn, is better than Pt-alone.Keywords: ethanol oxidation, direct ethanol fuel cell, platinum-tin, platinum-tin-tungsten, in situ Infrared Reflectance Spectroscopy IntroductionEthanol is a molecule of considerable interest because of its importance and potential use as renewable fuel (can be obtained from sugar cane for example) for fuel cells applications.1-4 Among the various alcohols which can be used as alternative fuel, ethanol is the most promising one because it is a safer molecule comparatively to methanol. As a liquid, it is easy to store and handle when comparing to hydrogen. Moreover, ethanol has a high theoretical energy (8 kWh kg -1 against 6.1 kWh kg -1 for methanol and 33 kWh kg -1 for pure hydrogen without storage). 5,6 Ethanol main disadvantage comes from its molecular structure with a carbon containing a primary alcohol function and a methyl group. This characteristic induces a hard conversion of ethanol into carbon dioxide due to the difficult to break the C-C bond and promote the complete oxidation of the methyl group with Pt as electrocatalyst. [7][8][9] Several studies on the ethanol electrooxidation focused mainly to identify adsorbed intermediates showed the presence of carbo...

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