Faradaic impedance studies of the autocatalytic reduction of H2O2 on Ag electrodes in HClO4

Recently, it was shown that the reduction of hydrogen peroxide on silver in perchloric acid proceeds in two parallel paths. The normal reduction is ob served at an overpotential of -1.5 V whereas a second reduction reaction oc curs at a significantly lower overpotential at -1.0 V. The second reaction involves the unstable intermediate OHad, which also acts as a catalyst. Hen ce, the second reaction has been proposed to be an autocatalytic one. In th is paper we present electrochemical impedance spectra together with numeric al simulations for the faradaic impedance in the autocatalytic region based on previously suggested kinetic rate laws. It will be shown that the exper imental data fit well with the results of the theoretical calculations, thu s strongly supporting the autocatalytic mechanism.