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Free keywords:
Electrochemical Impedance Spectroscopy (EIS); X-ray Photoelectron Spectroscopy (XPS); hydrogen peroxide; autocatalytic reduction; negative differential resistance (NDR)
Abstract:
Recently, it was shown that the hydrogen peroxide (H2O2) reduction on silver in perchloric acid (HClO4) proceeds in two parallel paths. The normal reduction is observed at an overpotential of â??1.5 V, whereas a second reduction reaction occurs at a significantly lower overpotential at â??1.0 V. The second reaction involves the unstable intermediate OHad, which also acts as a catalyst. Hence, the second reaction has been proposed to be an autocatalytic one. This autocatalytic reaction is deactivated after a certain time that depends on the rotation speed of the electrode. It can be recovered if the electrode is negatively polarized. In this thesis work, ex-situ XPS measurements on emersed Ag(111) electrodes were conducted. The analysis leads to the conclusion that the deactivation is caused by a small amount of chloride contamination. Electrochemical impedance spectra are presented together with numerical simulations for the faradaic impedance in the autocatalytic region based on previously suggested kinetic rate laws. The experimental data fit well with the results of the theoretical calculations, which strongly supports the autocatalytic mechanism.
