Natural Biomass-Derived Hierarchical Porous Carbon Synthesized by an in Situ Hard Template Coupled with NaOH Activation for Ultrahigh Rate Supercapacitors

An in situ hard template strategy coupled with NaOH activation is proposed to prepare hierarchical porous carbons with high surface area from biomass for high-performance supercapacitors. The preparation of the carbon includes the sol–gel process of lotus seed shell and sodium phytate, followed by carbonization and NaOH activation. The soluble sodium phytate is pyrolyzed to nano-Na5P3O10 during carbonization and then reacts with NaOH to convert to nano-Na2CO3 and nano-Na3PO4 particles, which are encapsulated in the carbon matrix as the in situ hard templates and leave large mesopores/macropores after being removed in the subsequent washing treatment. Combined with the micropores created by NaOH activation, the as-prepared carbons possess developed hierarchical pores with a large surface area of 3188 m2 g–1 and a pore volume of 3.2 cm3 g–1. Furthermore, the carbons are rich in the heteroatoms of O, N, and P originated from the biomass precursors and sodium phytate. As a result, the biomass-derived hierarchical porous carbon exhibits high capacitance (286 F g–1 at 0.5 A g–1), great rate performance (241 F g–1 at 200 A g–1), and excellent cycle stability in 6 M KOH electrolyte. Outstanding electrochemical performances are also achieved in 3 M H2SO4 electrolyte. Thus, the biomass-derived carbon with hierarchical porous structure and outstanding performance is considered as a promising electrode material for high-rate and high-energy density supercapacitors, and the strategy based on the in situ template method opens a new door for the preparation of hierarchical porous carbons with high surface area from biomass precursors.