Flower-like nickel hydroxide@tea leaf-derived biochar composite for high-performance supercapacitor application

Renewable and sustainable high-performance energy storage devices are desirable to fulfill the demands of next-generation power sources. In this study, we report a flower-like nickel hydroxide/spent tea leaf-derived biochar (NiNF@TBC) composite for high-performance supercapacitor application. The tea leaf-derived biochar (TBC) with a specific surface area of 1340 m² g^-1 is used as the Ni(OH)₂ support to fabricate NiNF@TBC composites. The highly porous and hierarchical structure of the as-synthesized NiNF@TBC composite facilitates the electrolyte ion and electron diffusion and transport more readily. As a result, the decrease in diffusion path and the increase in conductivity of NiNF@TBC for energy storage applications. The NiNF@TBC electrode shows excellent electrochemical properties with a specific capacitance of 945 F g^-1 at 1 A g^-1 in a three-electrode cell and high stability of 95% after 10,000 cycles. Moreover, the symmetric supercapacitor fabricated with NiNF@TBC delivers a specific capacitance of 163 F g^-1 in 1 M Na₂SO₄ solution. The Ragone plot of the symmetric device exhibits energy density in the range of 19 - 58 Wh kg^-1 with power density in the scale of 826 - 6321 W kg^-1. An excellent long-term cyclic stability of 94% is obtained after 10,000 charge-discharge cycles. Such an excellent performance has demonstrated the feasibility of utilizing agricultural wastes as green carbon sources, which can combine with various metal hydroxides to produce hybrid nanomaterials as a highly potential electrode material for green sustainable supercapacitor applications.