Exploring the effects of different pretreatment methods on the properties of materials is of great significance for the effective utilization of waste biomass to produce high value-added porous carbon. Herein, the waste eucalyptus bark was used as a low-cost biomass resource to produce a series of biomass porous carbons (BPCs) for supercapacitor electrode materials. The effects of different pretreatment methods on the physicochemical structure and supercapacitor performance of BPCs obtained by KOH were investigated systematically. It was found that the BPCs prepared from different methods had certain differences in morphology, phase structure, porous properties and surface chemical properties, which resulted in a significant influence on supercapacitor performance. The hydrothermal pretreatment was conducive to form 3D honeycomb-like architectures with a hierarchical pore structure in the KOH activation process, which resulted in an excellent cycling stability. The pyrolysis pretreatment was beneficial to improve the graphitization degree of porous carbons and produce more micropores and oxygen-containing functional groups, which presented a lower equivalent series resistance and higher specific capacitance with poor rate behavior and cycling stability. Among them, the PBPC-600 electrode possessed a marvelous specific capacitance of 349.4 F g⁻¹ at 0.5 A g⁻¹, displaying great application potential as an electrode material for supercapacitors. Moreover, to meet the portable requirement, the PBPC-600 based symmetric quasi-solid-state supercapacitor was assembled, which achieved a remarkable energy density as high as 15.0 W h kg⁻¹ at a power density of 160.0 W kg⁻¹.

A novel mesoporous g-C ₃ N ₄ loaded with biomass porous carbon was synthesized by molten salt assisted thermal polycondensation, and the formation of hollow tubular structure increased the specific surface area.