Effect of adsorbed layers on the anodic oxidation of simple organic compounds. Part 2.—Role of adsorbed HCOOH species

The anodic oxidation of 0.1 M HCOOH on smooth Pt electrodes in 1 M H2SO4 at 40°C has been examined. An adsorbed material with a high coverage θorganic accumulates on the electrode over a wide potential range. The rate of adsorption is not limited by mass transport. A maximum coverage, θorganic= 0.73, is indicated at +0.30 V, and this falls to zero by 0.65 V (RHE). This material poisons the main HCOOH → CO2 reaction at all potentials. The main oxidation process at ⩽0.45 V (RHE) proceeds via an adsorbed intermediate which has not been isolated on the surface. Electron transfer is the rate-limiting step. At 0.55⩽E⩽0.75 V (RHE), adsorption of the intermediate is rate limiting and this is followed by fast electron transfer. The role of θorganic in inhibiting the main oxidation process is discussed. A possible electroactive solution species is suggested.