Hierarchical porous carbon materials derived from waste lentinus edodes by a hybrid hydrothermal and molten salt process for supercapacitor applications

Biomass-derived carbons with hierarchical porous structures are widely considered as one of the most promising electrodes for supercapacitor. In this work, we present a facile approach to synthesize hierarchical porous carbon materials from waste lentinus edodes. It exhibits that the duration of the hydrothermal treatment process strongly affects the pore size distribution of the prepared carbon materials. Many narrow pores are formed during the hydrothermal process; these preformed pores are vital for the formation of micropores and development of larger mesopores in the following molten salt activation process. The as-obtained HM-24, synthesized by hydrothermally treated for 24 h and subsequently activated in molten Na 2 CO 3 -K 2 CO 3 for 1 h, possesses high specific surface area of 1144 m 2  g −1 and developed hierarchical micro- and mesoporous structures. Moreover, oxygen- and nitrogen-containing functional groups are detected at the carbon surface. When evaluated as an electrode in a three-electrode system with 1 M H 2 SO 4 electrolyte, the as-prepared HM-24 exhibits a high specific capacitance of 389 F g −1 at 0.2 A g −1 and a good rate capacity with capacitance remaining 174 F g −1 at 20 A g −1 . Furthermore, the assembled symmetric supercapacitor delivers a high specific capacitance of 329 F g −1 at 0.2 A g −1 , excellent energy density of 45.69 Wh kg −1 and good cycling stability which retains 90.3% of the initial capacitance at 5 A g −1 after 10,000 cycles.