Chapter 3 Reactions at Metal Oxide Electrodes

Abstract

Publisher Summary This chapter focuses on the reactions at metal-oxide electrodes. Reactions at oxide electrodes have attracted the attention of electrochemists for both fundamental and technological reasons. The semiconducting properties of many oxides, for example, can be advantageously used to test current theories on electron transfer at electrochemical interfaces. Unlike a metal, where the number density of carriers is fairly constant and the energy can be varied over a wide range by means of the electrode potential, in the case of semiconducting oxides, the number of electrical carriers on the surface may be varied over a narrow energy range, although the span of available energies is more limited. Metallic oxides are employed, often as coatings or thin films, as electrode materials for a range of electrocatalytic reactions, such as oxygen evolution and reduction, chlorine evolution, and organic electrosynthesis. The ideal oxide electrode for a fundamental kinetic study is an oxide single crystal, where the surface exposed to the electrolyte is well defined geometrically, chemically, and morphologically. Oxide materials that are attractive because of their catalytic activity are often employed in the form of finely divided powders of considerable surface area. An oxide electrode in equilibrium with the aqueous solution is a multicomponent system with metal, oxygen, and hydrogen ions in both places. Metal oxides that undergo proton-insertion reactions find extensive application in batteries and are currently being investigated as potential electrochromic materials. The oxygen electrode is of major importance to energy conversion, storage, and conservation.