The electrocatalytic properties of the oxides of noble metals in the electro-oxidation of some organic molecules

The electro-oxidation of organic compounds on gold and silver electrodes can occur either in a potential range more negative than that where the metal oxides are formed or within the more positive range where the surface is covered by oxides. Oxidation of methanol on gold electrodes 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) orientation favor the catalytic activation of the anodic electro-oxidation of methanol in the region of oxide formation. Oxidation of malic acid on a gold electrode proceeds only in the region where the electrode is covered by gold oxide. On a glassy carbon electrode modified by silver, 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 silver, alcohols such as methanol, ethylene glycol and glycerol are oxidized only in the region where the electrodes are covered by silver oxide. On such electrodes the observed anodic currents increase in the sequence: methanol < ethylene glycol < glycerol, and in the same sequence the corresponding peaks occur at more negative potentials. (C) 1997 Elsevier Science S.A.