Sustainably transforming biomass waste into porous carbon by a hydrothermal-activation strategy for high-performance hybrid supercapacitors

Chinese medicine residues (CMRs) are the major waste from pharmaceutical industry with a huge annual output, which could be upcycled into one promising alternative for producing solid carbon materials. However, direct transforming CMRs into engineered biochar needs additional pre-drying treatment, which is one energy-intensive process, mainly owing to high moisture content of CMRs. Therefore, we developed a hydrothermal carbonization (HTC)-chemical activation strategy to produce porous carbon from CMRs. The HTC simplifies the processes of both pre-drying treatment and pyrolysis into one step for obtaining carbon precursor. Moreover, the porous carbon produced by HTC-activation strategy has more developed pore structure and capacitive properties than that produced by the traditional pyrolysis-activation strategy. The resultant sample HCPC-R3-800 exhibits a high capacitance of 357 F g⁻¹ and 90.3% capacitance retention after 10,000 cycles. This work provides one promising and practical approach for effectively transforming CMRs into engineered biochar for zinc ion hybrid supercapacitors, which is beneficial to simultaneously achieving sustainable biomass management and circular carbon economy.