Self-discharge and potential recovery phenomena at thermally and electrochemically prepared RuO2 supercapacitor electrodes

Films of ruthenium oxide (RuO2) exhibit large, almost constant capacitance, over a potential range of similar to 1.4 V in aqueous acid solutions. This behaviour has led to their development as supercapacitor materials giving many Farads per gram. Applications of electrochemical capacitors require minimum self-discharge rates. In the present paper, the self-discharge kinetics of charged RuO2 electrodes are studied and a remarkable phenomenon of successive potential recovery after sequential discharge transients is reported. The self-discharge and potential-recovery behaviour is analysed in terms of a process of diffusion of oxidation state involving proton and electron hopping, treated in a model of the RuO? film structure having three regions between which redistribution of oxidation states in the oxide film takes place on self-discharge and recovery. (C) 1997 Elsevier Science Ltd.