THE ELECTROCATALYTIC PROPERTIES OF THE OXIDES OF NOBLE-METALS IN THE ELECTROOXIDATION OF SOME ORGANIC-MOLECULES

The electro-oxidation of organic compounds on gold and silver electrod es can occur either in a potential range more negative than that where the metal oxides are formed or within the more positive range where t he surface is covered by oxides. Oxidation of methanol on gold electro des proceeds in the potential range where the electrode is not covered with oxide and only at the slowest scan speed used (0.1 mV s(-1)). At the same scan rate the Au(110) orientation as well as the Au(111) ori entation favor the catalytic activation of the anodic electro-oxidatio n of methanol in the region of oxide formation. Oxidation of malic aci d on a gold electrode proceeds only in the region where the electrode is covered by gold oxide. On a glassy carbon electrode modified by sil ver, reactivation of the formaldehyde anodic oxidation is observed in the region where the electrode is covered by silver oxide. On the bulk silver electrode and on the glassy carbon electrode modified by silve r, alcohols such as methanol, ethylene glycol and glycerol are oxidize d only in the region where the electrodes are covered by silver oxide. On such electrodes the observed anodic currents increase in the seque nce: methanol < ethylene glycol < glycerol, and in the same sequence t he corresponding peaks occur at more negative potentials. (C) 1997 Els evier Science S.A.