Size-dependent capacitance of NiO nanoparticles synthesized with cathodic contact glow discharge electrolysis

NiO nanoparticles of 70, 91 and 107 nm average diameter are synthesized by cathodic contact glow discharge electrolysis at 30, 36 and 42 VDC respectively, in 2 M H2SO4 + 0.5 M ethanol + 2.5 mg ml−1 of PVP, and are investigated for electrochemical energy storage. From the cyclic voltammetry and galvanostatic charge-discharge measurements in 1 M KOH, it was found that a maximum specific capacitance of 218 F g−1 is achieved with the 70 nm NiO nanoparticles at 2.7 A g−1. Larger nanoparticles of 91 and 107 nm diameter exhibit specific capacitances of 106 and 63 F g−1, respectively, suggesting a size-dependent capacitive performance enhanced with decreasing particles size.