Formaldehyde yields from methanol electrochemical oxidation on platinum and supported catalysts

Abstract

The formation of formaldehyde during methanol electrochemical oxidation is being measured with a fluorescence assay in order to assess the importance of formaldehyde as a reaction intermediate and source of efficiency loss in direct methanol fuel cells. Initial studies have focused on the oxidation of methanol on polycrystalline platinum. The formaldehyde yields approached 30% of the total electrolysis charge at 0.2-0.3 V (vs. a KCI saturated Ag/AgCI reference electrode) for methanol concentrations between 15 mM and 0.3 M in 0.1 M perchloric acid. The formaldehyde yields were lower at more positive potentials, as other oxidation pathways became dominant. However, the rate of formaldehyde production increased up to 0.5 V. These initial studies have demonstrated that formaldehyde, which is often not detectable with modern in situ spectroelectrochemical analysis techniques, can be produced in significant amounts during methanol electrochemical oxidation.

More recent work has focused on the formation of formaldehyde during methanol electrochemical oxidation on supported platinum and platinumruthenium catalysts. Solid, polycrystalline platinum-ruthenium alloys have been considered. Other catalysts studied have been suspended in Nafion and supported on glassy carbon. Methanol oxidation on the catalysts has resulted in low formaldehyde yields, below 2% at all potentials studied. The low formaldehyde yields, which result from more complete methanol oxidation, are believed to arise from the ability of partial oxidation products to be transported to an array of active catalyst sites dispersed within the three dimensional Nafion film network. Efforts to eliminate these volume effects through techniques such as electrochemical depositions of catalyst crystallites by reduction of transition metal salts onto solid, glassy carbon electrodes; direct metal nanoparticle deposition onto solid, glassy carbon electrodes using a hydrogen tube furnace; and "sticky" carbon methods for metal/wax/carbon type electrodes have been under investigation.