High-performance solid-state supercapacitor based on sustainable synthesis of meso-macro porous carbon derived from hemp fibres via CO2 activation

• Single-step, low temperature carbonization and CO 2 physical activation of meso-macroporous carbon for high performance solid-state supercapacitor. • Interconnected meso-to-macroporous nature is obtained. • Highest specific capacitance of 475 Fg -1 in 1 Ag -1 in PVA-KOH hydrogel as gel electrolyte is obtianed. • Solid-state symmetric supercapacitor device delivered excellent capacitance retention of 85% with an extended potential window of 2V for 10,000 cycles. Most porous carbons have been prepared using KOH, ZnCl 2 as activating agents via chemical activation process, where toxic chemicals, elevated temperature and multi-stage preparation are involved. Herein, we report synthesis of porous carbon from hemp fibre (HFPC) via single step, low temperature carbonization followed by CO 2 physical activation for high-performance solid state supercapacitor application in a PVA-KOH hydrogel as gel electrolyte. Detailed characterization and optimization studies based on varying the duration (hours) of activation yields HFPC-30 material that comprises of interconnected carbon network of meso and macro pores with a high specific surface area of 1060 m 2 g −1 . This enables rapid ion transfer and efficient electrode- electrolyte interaction and HFPC-30 exhibit an excellent half-cell specific capacitance of ~600 Fg −1 at 1 Ag −1 . The assembled symmetric supercapacitor device with HFPC-30 delivers a full-cell specific capacitance of ~457 Fg −1 in PVA-KOH hydrogel as gel electrolyte. A maximum specific energy of 25.3 Whkg −1 at ~4320 Wkg −1 specific power is obtained, which is very high compared to other reported carbon materials. Further, the assembled supercapacitor device works until 2V delivering a capacitance retention of ~85% after 10,000 cycles. Thus, biomass derived porous carbon material in a hydrogel electrolyte presents a novel strategy for developing highly promising sustainable electrodes for high energy, solid state supercapacitor applications.