Effect of adsorbed layers on the anodic oxidation of simple organic compounds. Part 1.—Time variations during the oxidation of HCOOH and effect of added Cl–

Abstract

The deterioration of currents with time (time effects) during the oxidation of 0.1 M HCOOH on Pt electrodes in 1 M H₂SO₄ at 40°C has been examined. The effect of added Cl^– on the HCOOH oxidation rate at 0.65 and 0.75 V (RHE) has been studied. HCOOH oxidation currents have been measured at 0.75 V (RHE) as a function of HCOOH purity. The current decays with time; results indicate that this decay is, to a large extent, due to an anionic type impurity in the solution. This impurity is present at very low levels and the behaviour is similar to that with a solution containing 5 × 10^–7 M Cl^–. Like Cl^–, the impurity is desorbed from the electrode at potentials below 0.30 V (RHE). Results are reported for HCOOH oxidation at 0.65 and 0.75 V (RHE) as a function of Cl^– concentration (up to 2 × 10^–5 M Cl^–). The reaction is extensively inhibited by increased addition of Cl^– as a direct consequence of Cl^– adsorption on the electrode. The observations imply that the electroactive species in HCOOH oxidation at these potentials is HCOO^–.