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, Teflonbonded 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 Rh203. 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 electrogenerated at the electrode surface. Values of I0 -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 RuO,.. The activity for HCHO oxidation is correlated with the catalytic activity of the oxides for the oxygen gas evolution reaction.Formaldehyde is an important reducing agent used in electroless metal deposition, where an electrochemical type mechanism involving anodic oxidation of the HCHO along with cathodic reduction of the metal ion is considered to be involved (1, 2). Further, formaldehyde belongs to the group of C1 compounds, which also includes methanol and formic acid, which is the subject of considerable attention in electrochemical energy conversion research (3). The electro-oxidation of formaldehyde has been the subject of a number of investigations at metallic electrodes (4-6). In alkaline solution, formate has been generally found to be the product of HCHO oxidation, and the evolution of H2 gas derived from the HCHO may also be observed during the oxidation reaction depending on the nature of the catalyst and the experimental conditions (4, 7). In a number of instances it has been observed that metals which are catalytically active for HCHO oxidation exhibit significantly less activity when anodic oxides are formed on their surfaces, e.g., Au (8). On the other hand, the oxidation of certain organic molecules, including HCHO, at Ni is observed only in the presence of an anodic oxide layer in which the Ni species are oxidized beyond the Ni(II) state (9, 10). This suggests that certain metal oxides should exhibit catalytic activity for the electro-oxidation of HCHO.The class of noble metal oxides merits attention as potential electrocatalysts for organic oxidation reactions in view of the high catalytic activity possessed by certain members of this class, e.g., RuQ, for the C12 and 02 generation reactions (11,12). Benzaldehyde has been shown to undergo electro-oxidation at RuO2 (13). There appear to be no reports in the literature of studies of HCHO oxidation at oxide electrodes. In this paper, a study of HCHO oxidation at a number of thermally prepared noble metal oxides, principally RuQ, is described. ExperimentalSome of the oxide electrodes used in this work were prepared essentially according to the stand...

Cyclic voltammetric behaviour of dimensionally stable anodes in the presence of C1 - C3 aldehydes

“…The cyclic voltammetry measurements were carried out in in 0.5 mol dm -3 H 2 SO 4 using a potentiostat (EG&G/PAR model 273). The potentials in this study are referred to the Hg/Hg 2 SO 4 /SO 4 2-(MSE) reference electrode. Acetaldehyde (CH 3 CHO > 99%) and propionaldehyde (CH 3 CH 2 CHO > 98%) were obtained from Merck and used without further purification.…”

“…4 The majority of the work has been done with the corresponding alcohols -methanol, 5 ethanol, 6,7 as examples. Burke and Murphy described the oxidation of methanol at RuO 2 electrodes and suggested that oxidation occurred via interaction with an OH ads species at the electrode surface.…”

Mechanistic Studies and Sensitive Determination of Norepinephrine at a Nafion/Lead-Ruthenium Oxide Pyrochlore Chemically Modified Electrode

“…The i k,L value was found to be 10.9 mA and the k h can thus be calculated as 7.99610 À4 cm=s. Similar k h value was reported for the Ru IV=VI mediated formaldehyde oxidation reaction on a thermally prepared RuO 2 electrode [33]. The order of reaction was measured by an indirect RDE electrochemical method under the reaction condition of the mixedactivation-diffusion control [18,38].…”

Synthesis of nanocrystalline RuO2(60%)-SnO2(40%) powders by amorphous citrate route

“…The catalytic and electrocatalytic activity strongly depend on particle size, size distribution and specific surface area of the powder, which in turn are governed by the technique used for the oxide preparation [1][2][3][4] . Traditionally, the active oxide coatings are usually prepared at about 450 ℃ by thermal decomposition of metal chloride and alkoxide coatings painted onto titanium substrates [5,6] .…”