Electrochemical beaviour of the solid ionic conductor Ag<inf>7</inf>I<inf>4</inf>PO<inf>4</inf>

Abstract

Electrochemical investigation of the solid superionic conductor Ag7I4PO4 (0.8 AgI + 0.2 Ag3PO4) at room temperature and at 40°C were performed by means of cyclic voltammetry, cyclic chronoamperometry and cyclic chronocoulometry, normal pulse polarography and ac polarography. It was shown that the Ag+ ↔ Ag redox process on Pt and Ag working electrode occurs with a certain overvoltage, ie that for Ag+ → Ag+ oxidation and the return of Ag+ ions into the electrolyte a certain overvoltage is necessary. From the determined values of the exchange current one estimates the redox process as a rather fast one. The silver working electrode is electrochemically inactive, while only cathodically deposited silver is electrochemically active and can be oxidized to Ag+ ions. Chronoamperometry and chronocoulometry show that there is a certain difference in the behaviour of Pt and Ag working electrodes due to uneven passivating anodic processes. On the basis of measurements of faradaic and capacitance currents and their dependence on frequency, diagrams of complex impedance of the Pt/Ag7I4PO4 interface at various anodic and cathodic polarizations of the Pt electrode were plotted. The dependence of the serial capacity of the interface on the dc potential and temperature are discussed. © 1983.