Steady State Kinetic Study of the Formic Acid Electrooxidation Reaction on Iridium in a Flow Cell

Abstract

The formic acid electrooxidation reaction was evaluated on an iridium electrode at room temperature in 0.5 M HCOOH + 0.5 M H2SO4 solution, using a flow cell. Chronoamperometric experiments allowed establishing the dependence of the electrocatalytic activity on potential, which reaches a maximum around 0.55 V. The open circuit chronopotentiometric transient was also measured. Moreover, the voltammetric stripping profile was also obtained at each analysed potential, enabling the evaluation of the presence of adsorbed carbon monoxide (COad) on the electrode surface through its electrooxidation charge. It was found that it is high at low potentials, and then it decays vanishing at 0.5 V. From the analysis of the results obtained, it was concluded that COad is originated from the spontaneous dissociative adsorption of HCOOH, producing the inhibition of reaction sites at low potentials. Meanwhile the water discharge generates adsorbed hydroxil (OHad), which inhibits the reaction at high potentials. A reaction mechanism was proposed and discussed, and the Ir electrocatalytic activity was compared with those of platinum, palladium and rhodium, evaluated under similar experimental conditions.