ELECTROCATALYSIS OF THE OXYGEN REACTION ON THE MULTICOMPONENT OXIDES OF TRANSITION METALS

The review presents the current state of research on oxides of transition metals as electrocatalysts for the both reactions of oxygen reduction and evolution, which are of key importance ones for electrochemical devices of alternative energy: metal-air rechargeable batteries and fuel cells with an oxygen electrode. The review includes the consideration of the thermodynamic, electronic and adsorption conditions for activation of the molecular oxygen by oxide surface, as well as the advantages of the oxide surfaces as catalysts in the alkaline electrolytes. The influence of the chemical composition and structural features of oxides of transition elements on the adsorption and chemisorption of water and oxygen, the formation of ionic forms at adsorption and the main factors, which influence on transfer of electrons, protons and oxygen, are considered. Synthesis of double and other multicomponent oxides and the usage of cationic doping expands the possibilities of forming the necessary properties of the electrocatalysts: porosity, thickness of hydrated layers, electronic and ionic conductivity, proton and electron-donor (acceptor) properties in a optimal combination. The oxide should have a metal with variable valence, and even better if there are two ones. Such oxides can be various structures based on Co2O3, MnO2, Ni2O3, Mn3O4, Fe2O3, and others. A qualitative leap in improving the performance of catalysts for electrode reactions with oxygen was made possible by the synthesis of nanoparticles, as well as nanocomposites with metallic and carbon materials. The some characteristics of the electroca­talytic activity of promising oxide electrocata­lysts, mainly, multicomponent ones, as well as the results of studies of oxide composites with carbon nanomaterials, are presented. Several of the most well-known oxide structures (spinel, perovskite, pyrochlor) are currently being studied as the most promising matrices for the efficient transfer of charge, oxygen, and metal ions. All of them are multicomponent. The most active non-platinum bifunctional catalysts for oxygen reactions concluded to be cobaltites with spinel structure. Nanocomposites based on cobalt and cobalt-manganese spinel are the most promising materials for use in alkaline rechargeable batteries, both in terms of cost and in terms of electrocatalytic activity as well as in terms of corrosion resistance.