Electrochemical impedance spectroscopy of the alkaline manganese dioxide electrode

Abstract

Two-probe electrochemical impedance spectroscopy measurements were carried out on the electrolytic manganese dioxide electrode in concentrated KOH electrolytes under a variety of experimental conditions. These included varying the electrode thickness and compaction pressure, electrolyte content and concentration, degree of manganese dioxide reduction and the presence of TiO₂ (anatase) as an additive. The overall electrode impedance was found to decrease when thin electrodes, prepared under high compaction pressures, with an excess of electrolyte, were used. The impedance of the EMD/electrolyte interface was also minimized when 5.0 M KOH was used as the electrolyte. This correlates with a maximum in electrolyte conductivity. The electrode impedance also increased as the degree of EMD reduction was increased, as was expected. Under these experimental conditions the electrode impedance increased in the presence of TiO₂ (anatase), which has negative implications for its commercial use. This conclusion was reached despite the differences in experimental conditions between this work and in commercial applications. An equivalent circuit was also derived and used as an aid in interpreting the impedance data.