Cathode glow discharge electrolysis synthesis of flower-like β-Ni(OH)2 microsphere for high-performance supercapacitor

Abstract

Nanoscale β-Ni(OH)2 is considered to be one of the most promising electrode material for supercapacitors because of its low cost, long cycle life and high theoretical capacitance. However, its preparation often involves either high temperatures or the use of complicated alkaline system, water-soluble precursors and surfactants, which greatly restrict its development. In this paper, a 3D flower-like β-Ni(OH)2 microsphere was successfully fabricated at 500 V discharge voltage in NaCl electrolyte solution with adding a certain amount of CH3COONa as stabilizer via cathode glow discharge electrolysis (CGDE) plasma, in which Pt needle and Ni foil were acted as cathode and anode, respectively. The results of FT-IR, XRD, Raman and XPS demonstrated that the hexagonal phase β-Ni(OH)2 with structural defects is produced during the CGDE process. Morphological analysis by SEM, TEM and AFM revealed that β-Ni(OH)2 exhibits a 3D flower-like microsphere with a diameter of about 1–3 μm, which is assembled by dozens of ∼3.0 nm thick nanosheets. The specific surface area and average pore-size of the flower-like β-Ni(OH)2 microspheres are 184.9 m2 g−1 and 17.8 nm, respectively. A possible formation mechanism is proposed on the basis of Ostwald ripening. β-Ni(OH)2 exhibits a high specific capacitance of 1818 F g−1 at 3 A g−1 and good capacity retention of 85 % after 1000 charge–discharge cycles at current density of 5 A g−1. 3D flower-like β-Ni(OH)2 microsphere can be used as a highly promising candidate for the supercapacitor electrodes.