Mechanism and simulation of electrochemical current oscillations observed in the H2O2-reduction reaction on platinum electrodes in acidic solutions

Mechanisms of electrochemical current oscillations of two types, named oscillation A and B, both observed for the H2O2-reduction reaction on Pt electrodes in acidic solutions, have been studied experimentally and by mathematical simulation. Oscillation A appears in a potential region just before hydrogen evolution, while oscillation B appears in a region of hydrogen evolution. A phase diagram we obtained has shown that oscillations A and B appear in limited ranges of the H+ and H2O2 concentrations and their ratio. The oscillation period for oscillation A increases with decreasing H2O2 concentration and negative shift of the electrode potential, mainly determined by the current density in the low-current state. Mathematical simulation by taking account of all plausible interfacial reactions (H2O2 reduction, hydrogen adsorption, and hydrogen evolution) reproduces the essential features of oscillation A, but does not reproduce oscillation B. It is shown that a positive feedback mechanism works in sudden transitions between the high- and low-current states for oscillation A.