RuO2/Co3O4 thin films prepared by spray pyrolysis technique for supercapacitors

RuO2/Co3O4 thin films with different RuO2 content were successfully prepared on fluorine-doped tin oxide coated glass plate substrates by spray pyrolysis method, and their capacitive behavior was investigated. Electrochemical property was performed by cyclic voltammetry, constant current charge/discharge, and electrochemical impedance spectra. The capacitive performance of RuO2/Co3O4 thin films with different RuO2 content corresponded to a contribution from a main pseudocapacitance and an additional electric double-layer capacitance. The specific capacitance of pure Co3O4, 15.5%, 35.6%, and 62.3% RuO2 composites at the current density of 0.2 A g(-1) were 394 +/- 8, 453 +/- 9, 520 +/- 10, and 690 +/- 14 F g(-1), respectively; 62.3% RuO2 composite presented the highest specific capacitance value at various current densities, whereas 35.6% RuO2 composite exhibited not only the largest specific capacitance contribution from RuO2 (C (sp) (RuO2)) at the current density of 0.5, 1.0, 1.5, and 2.0 A g(-1) but also the highest specific capacitance retention ratio (46.3 +/- 2.8%) at the current density ranging from 0.2 to 2.0 A g(-1). Electrochemical impedance spectra showed that the contact resistance dropped gradually with the decrease of RuO2 content, and the charge-transfer resistance (R (ct)) increased gradually with the decrease of RuO2 content.