In this work, flower-like Ni(OH) 2 microspheres decorated on biomass-derived porous carbons (Ni/PC) were fabricated via a facile two-step approach for high performance supercapacitor. The as-prepared Ni/PC offered an outstanding specific capacitance of 1960 F g À 1 at 1 A g À 1 current density. The Ni/PC electrode showed well capacitance retention of 85 % after 5000 cycles in alkaline electrolyte. In addition, the home-assembled Ni-0.3/PC//activated carbon solid-state asymmetric device exhibited 40 Wh kg À 1 high-energy density at 800 W kg À 1 power density with superior cycle stability. The superior electro-chemical performances can be attributed to two aspects that the large surface of Ni/PC exposes more active sites for rapid faradic reactions, and the incorporation of N/S-doped PC accelerates the charge transfer efficiency and improves electrical conductivity. This study provides an efficient and convenient method for the preparation of electrochemical materials combining transition metal hydroxides and biomass carbon, which can be used as electrode materials for energy storage and energy conversion.

Biomass-derived carbon-based supercapacitors offer a promising sustainable energy storage strategy for addressing global energy and environmental challenges. Herein, we report the synthesis of a graphene-like porous carbon by co-pyrolysis of lotus pollen and ammonium nitrate. During the co-pyrolysis process, ammonium nitrate could release a large amount of heat, etch the carbon skeleton, reduce the pyrolysis temperature, and create hierarchically porous carbon networks with rich N doping. The hierarchically N-doped porous structure has an ultra-large specific surface area (3106 m 2 g À 1 ) and an adapted interconnected porous structure, provides highways for charge and mass transfer, leading to a specific capacitance as high as 373.7 F g À 1 at 0.5 A g À 1 current density. The symmetric solid-state supercapacitor device exhibits a specific energy density of 53.5 Wh kg À 1 at a power density of 640 W kg À 1 .