Inorganic salt-induced synthesis of lignin derived hierarchical porous carbon with self-embedded quantum dots and ultrahigh mesoporosity for supercapacitors

Abstract

Inorganic salts are able to simultaneously control the microstructure and composition of biomass carbon materials; however, researchers always pay attention to the microstructure but ignore the composition. In this study, lignin derived hierarchical porous carbons (LHPCs) with embedded carbon quantum dots (CQDs) and a high mesopore ratio were synthesized by a salt template-assisted method, followed by activation. ZnCl₂/KCl salt was introduced into the hydrothermal process, which acted as a pore padding agent and temperature-conducting medium. As a consequence, the pore structure was optimized, and at the same time the CQDs were protected from re-aggregation, resulting in plentiful accessible storage sites and excellent ion migration ability and stability. Eventually, an integral conductive network was formed, which significantly enhanced the transfer kinetics and capacitance effect. Thus, LHPCs exhibited an ultrahigh meso-porosity of 90.17% and a superior specific capacitance of 458.7 F g⁻¹. After 10 000 cycles, they also displayed excellent cycling stability with 103% capacitance retention at a current density of 20 A g⁻¹. This method provides a simple and efficient strategy to prepare hierarchical porous carbon for high performance supercapacitors.