Snow crystal-like structure of NiSe as a binder-free electrode for high-performance hybrid supercapacitor

Snow crystal-like nickel selenide grown on nickel foam substrate was synthesized using a binder-free and one-step solvothermal approach. The effect of the reaction time of the synthesized material on its morphology and electrochemical performance was thoroughly investigated. Experimental results demonstrated that the optimum reaction time was 24 h giving a unique morphology and excellent electrochemical energy-storage behavior. The snow crystal-like NiSe exhibited a high specific capacity of 763.5 C g−1 at 1.5 A g−1 along with a good rate capability, while 83% of its initial specific capacity remained after 3000 cycles. More importantly, a hybrid asymmetric supercapacitor was assembled with a binder-free snow crystal-like nickel selenide as a positive electrode and activated carbon as a negative electrode. It showed remarkable energy-storage characteristics, with a specific energy of 32.04 Wh kg−1 at a specific power of 1112.44 W kg−1 and a capacity loss of 0.05% after 10,000 cycles. Such excellent electrochemical performance evidently proves that snow crystal-like nickel selenide is a promising candidate electrode material for energy-storage applications.