Electrocatalysis of the oxygen reduction at a polarised interface between two immiscible electrolyte solutions by electrochemically generated Pt particles

Abstract

We present first evidence and evaluation of electrocatalysis of the interfacial oxygen reduction at the polarised water∣1,2-dichloroethane (DCE) interface by in situ deposited Pt particles. The electrochemical process involves the reduction of oxygen in the aqueous phase by decamethylferrocene (DCMFc) as an electron donor in DCE, and is investigated in a broad range of interfacial potential differences and the aqueous solution pH (3–10). The Pt particles are deposited at the interface by reducing ammonium tetrachloroplatinate in the aqueous phase by the same organic-phase electron donor. It is shown that the diffusion equations for an irreversible interfacial oxygen reduction coupled with the reversible partition of oxygen between the aqueous and DCE phase can be solved by using the convolution principle. Convolution analysis of voltammograms makes it possible to consider the stoichiometry of the overall electron transfer reaction, and to infer kinetic data (Tafel plots). This analysis indicates that: (a) the catalytic oxygen reduction proceeds as a four-electron transfer reaction; (b) the rate of the oxygen reduction by DCMFc increases by more than one order of magnitude in the presence of the interfacial Pt particles; (c) the rate-determining step is the first electron uptake not including the concerted proton transfer; and (d) a transition from the normal ( α = 0.26–0.39) to the activationless ( α < 0.1) region occurs, which is probably associated with a high overpotential for the rate-determining step.