Electro-Oxidation of Formaldehyde on Thermally Prepared RuO₂ and Other Noble Metal Oxides

Abstract

The electro-oxidation of formaldehyde has been investigated at thermally prepared noble metal oxides, especially RuO2, in aqueous solution. Studies were carried out on thin layers of oxide supported on Ta or Ti, and on thin, Teflon-bonded oxide layers attached to a glassy carbon rotating disk electrode. The catalytic activity of RuO2 for HCHO oxidation was considerably greater than that of IrO2 and Rh2O3. At RuO2, formaldehyde was observed to undergo oxidation to formate at potentials from ca. 0.75–1.25V vs. reference hydrogen electrode (RHE), and to carbonate at higher potentials. The results suggest that HCHO (and HCOOH) oxidation is mediated by higher valent states of the oxide metal ions electro-generated at the electrode surface. Values of 10−3 cm s−1 (geometric electrode area based) and 10−6 cm s−1 (real area based) were estimated for the heterogeneous rate constant for HCHO oxidation at RuO2. The activity for HCHO oxidation is correlated with the catalytic activity of the oxides for the oxygen gas evolution reaction. © 1989, The Electrochemical Society, Inc. All rights reserved.