Effect of Nonstoichiometry of Nickel Oxides on Their Supercapacitor Behavior

摘要

How electrochemical capacitance is affected by the non-stoichiometric properties of nickel oxide (NiO_x films is reported. Nonstoichiometric NiO, thin-film electrodes were prepared for use in a supercapacitor by reactive radio-frequency (rf) sputtering of a nickel metal target. The oxygen partial pressure in the sputtering gas was systematically varied to fabricate various nonstoichiometric NiO_x films. As the oxygen partial pressure increased in the sputtering gas, hole concentration increased from 4.7 X 10~(16) to 1.0 X 10~(18) cm~3while the specific capacitance of the NiO_x films decreased from 148 to 80 F/g. A mechanism to explain the relationship between the specific capacitance and nonstoichiometry is proposed. The specific capacitance values of these NiO_x films are determined by the number of Ni~(2+) states that can be oxidized to Ni~(3+) as a result of the double injection of OH~- ions and holes.