Ni(OH)2 Nanoflakes Supported on 3D Ni3Se2 Nanowire Array as Highly Efficient Electrodes for Asymmetric Supercapacitor and Ni/MH Battery

Porous Ni(OH)₂ nanoflakes are directly grown on the surface of nickel foam supported Ni₃ Se₂ nanowire arrays using an in situ growth procedure to form 3D Ni₃ Se₂ @Ni(OH)₂ hybrid material. Owing to good conductivity of Ni₃ Se₂ , high specific capacitance of Ni(OH)₂ and its unique architecture, the obtained Ni₃ Se₂ @Ni(OH)₂ exhibits a high specific capacitance of 1689 µAh cm^-2 (281.5 mAh g^-1 ) at a discharge current of 3 mA cm^-2 and a superior rate capability. Both the high energy density of 59.47 Wh kg^-1 at a power density of 100.54 W kg^-1 and remarkable cycling stability with only a 16.4% capacity loss after 10 000 cycles are demonstrated in an asymmetric supercapacitor cell comprising Ni₃ Se₂ @Ni(OH)₂ as a positive electrode and activated carbon as a negative electrode. Furthermore, the cell achieved a high energy density of 50.9 Wh L^-1 at a power density of 83.62 W L^-1 in combination with an extraordinary coulombic efficiency of 97% and an energy efficiency of 88.36% at 5 mA cm^-2 when activated carbon is replaced by metal hydride from a commercial NiMH battery. Excellent electrochemical performance indicates that Ni₃ Se₂ @Ni(OH)₂ composite can become a promising electrode material for energy storage applications.