Adsorbed states and the kinetics of electrooxidation of phenols on metal oxides
Abstract
We discuss the role of adsorbed states in determining the kinetics of electrochemical oxidation of substituted phenols on various metal oxide surfaces. On antimony-doped tin oxide (SnO2,-Sb) electrodes, oxidation of both p-methoxyphenol (PMP) and p-nitrophenol (PNP) follow Langmuir-Hinshelwood kinetics; at high concentrations of phenol in solution, the oxidation rates are controlled by surface processes. In general, anodic oxidation of PMP and PNP on SnO2-Sb electrodes leads to complete mineralization to CO2. Under surface saturation conditions, however, oxidation of PNP occurs to a lower extent due to the encumbered formation of OH surface species required for complete oxidation. The role of adsorbed states is further illustrated examining the effects of competing adsorption of p-chlorophenol (PCP) and PNP on bismuth- doped lead oxide (PbO2-Bi) electrodes. It is shown that due to stronger adsorption, the presence of PNP inhibits the oxidation of PCP.
