Capacitive Behavior of Porous Nickel Oxide/Hydroxide Electrodes with Interconnected Nanoflakes Synthesized by Anodic Electrodeposition

Nanostructured nickel hydroxides are galvanostatically deposited onto a stainless steel substrate by a plating bath of nickel sulfate, sodium acetate, and sodium sulfate at room temperature. The anodically deposited nickel hydroxide electrodes are highly porous and composed of interconnected nanoflakes about in thickness. Pore size of the deposited electrode increases with decreasing the depositing current density. X-ray diffraction patterns show that the deposited nickel hydroxide converts into nickel oxide at annealing temperature above . Annealing temperature influences both the electrical resistance and the grain size of the electrode and, consequently, determines the capacitive behavior of the electrode investigated by cyclic voltammetry in KOH aqueous solution. An optimal annealing temperature of is obtained in terms of the electrode's specific capacitance. An electrode with larger pores deposited at lower current density has a higher specific capacitance because larger pores facilitate the ion diffusion rate. An electrode with smaller pore size deposited at higher current density exhibits more kinetically reversible behaviors, resulting in a better high-rate capability.