Control of the Period of an Electrochemical Oscillation by Atomic- or Nanometer-Scale Modifications and Structural Changes of Electrode Surfaces in a System of H 2 O 2 Reduction at Pt Electrodes

The influences of electrode-surface modifications and structural changes on an electrochemical oscillation of a negative differential resistance (NDR) type, observed for H 2 O 2 reduction on Pt electrodes in acidic solutions, and previously called oscillation A, were investigated. For Pt electrodes coated with a submonolayer amount of Ru atoms, the oscillation period became shorter than that for naked Pt, whereas for Pt coated with a submonolayer amount of iodine atoms, the period became longer. For naked Pt immersed in solutions containing a small amount of Cu 2+ , Ru 3+ , and AuCl 4 , the oscillation period became shorter with time, whereas it became longer in solutions containing Ag + . For Pt-layer electrodes with island structure, formed by vacuum deposition on single-crystal p-Si wafers, the oscillation period became longer with the increasing size of the islands. Such modulations of the oscillation period were all explained by considering three types of electrode surfaces, a surface (such as naked Pt) on which the H 2 O 2 reduction occurs oscillatorily, a surface (such as a Ru-covered part) on which it occurs steadily, and a surface (such as an iodine-covered part) on which no H 2 O 2 reduction occurs. Mathematical simulation showed that the oscillation period was determined by the ratios of the areas of these surfaces, which were mixed at the electrode surface on atomic or nanometer scales.

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