aqueous and non-aqueous solutions electrical conductivity electrochemical synthesis heterovalent substitution hydrogen peroxide interaction non-stoichiometric fluorides scientific school sol-gel synthesis calcium calcium chloride catalytic activity catalytic decomposition cerium chlorides of sodium cobalt and manganese oxides complex oxide compositions electrochemistry electroche­mis­try electrode reactions electrolytes electrolytic dissociation electroreduction eutectic melt fluoride-conducting solid electrolytes manganese molten mixture molten salts molybdenum carbides oxides of cobalt