Kinetics and mechanism of “reduced CO₂” electrooxidation on electrodispersed platinum in different acid solutions

Abstract

The electrooxidation of “reduced CO₂” electroadsorbates on electrodispersed platinum electrodes has been investigated in 0.05 M HClO₄, 1 M HClO4, 0.5 M H₂SO₄ and 1 M H₃PO₄ at 25° C through voltammetry and potential step techniques. The overall reaction comprises three distinguishable processes, namely a first order triggering process, and two second order surface processes. The latter are influenced remarkably by the solution composition (anions). The second order reaction mechanism involves two distinguishable “ reduced CO₂” electroadsorbates which react independently with the OH species formed from H₂O electrooxidation on the bare platinum sites as the reaction proceeds. An interaction term has to be included in the rate equations to account for the experimental results. The mechanistic interpretation accounts for the values of the number of electrons per site ranging from 1 to 2.