Bioinspired in situ self-catalyzing strategy towards graphene nanosheets with hierarchical structure derived from biomass for advanced supercapacitors

Highlights: • Ultra-high quality O/N co-doped graphene with high surface area is derived from biomass. • Intrinsic Ca-containing species in biomass transfers into CaO during pyrolysis process. • The imbedded CaO functions as template and catalyst to generate hierarchical porous graphene. • KOH effectively facilitated the graphene formation and enhanced the porosity. • Biomass-based graphene exhibits excellent supercapacitive performance. Ultrahigh-quality graphene with structural hierarchy has been successfully fabricated through a novel and effective bioinspired in situ self-catalyzing strategy with camphor leaves as a renewable carbon source. The intrinsic Ca-containing species in biomass transfers into CaO via the intermediate of CaCO₃ during the pyrolysis process, and the finally imbedded CaO functions as in situ hard template and catalyst to generate hierarchical structure and construct the graphitic structure. The utilization of KOH effectively facilitated the graphene formation and enhanced the porosity of the carbon materials. The resultant graphene possesses many advantages for supercapacitor application, including large surface area, hierarchical porosity (crosslinked micro/meso/macroporous vacancies), well-organized graphene layers and favorable dually co-doping of O/N, thereby contributing to rapid charge transportation on the electrode/electrolyte interface, fast diffusion of electrolyte ions and high conductivity. When directly used as supercapacitor electrode (without the mixture of any conductive agent), as-produced graphene exhibited a specific capacitance of 397F/g at a current density of 1.0 A/g with a high rate retention of 74% from 1 to 20 A/g in a three-electrode system with 6 M KOH aqueous electrolyte. The high-quality graphene prepared from biomass via a readily scalable method opened up new vision towards high performance applications in energy storage and conversion.