Oxidation of formaldehyde, methanol, formic acid and glucose at ac heated cylindrical Pt microelectrodes

The oxidation of formaldehyde, methanol, formic acid and glucose on Pt was studied at increased temperatures under non-isothermal conditions by cyclic voltammetry. The platinum electrode (25 mu m diameter wire) was heated continuously with a high frequency ac (100 kHz) during de polarization (see also Ref. 1 [T. Zerihun, P. Grundler, J. Electroanal. Chem., 404 (1996) 243.]). The heating power employed determines the temperature attained at the electrode surface (up to ca. 79 degrees C in the present experiments). The catalytic activity of the platinum electrode (99.9% Pt) without ac heating was observed to be particularly low. On the other hand, markedly increased oxidation current signals of the organic substances were obtained at a heated electrode. Apparently, the self-poisoning effect of platinum, which is common in the oxidation of small organic molecules and glucose, decreases with increasing reaction temperature. The overall oxidation reaction will thus be enhanced at raised temperatures. The oxidation reactions of the small organic molecules also occur at increasingly lower potentials with increasing temperatures. This may be due to the decrease of the overvoltage for the formation of adsorbed OH (a reactive species involved in the oxidation of the organic substances) on Pt. Additional experiments performed in thermostated systems are also presented for the purposes of comparison. (C) 1998 Elsevier Science S.A.