Dual potassium salts-assisted lyophilization of natural fibres for high-yield synthesis of one-dimensional carbon microtubes for supercapacitor and oxygen reduction reaction
One-dimensional kapok fibre-derived carbon microtubes (KCMT) were synthesized by the dual potassium salts-assisted lyophilization of biochar. The optimal KCMT not only possesses the well-developed porous, microtubular architecture with large specific surface area but also presents the high production yield (55.3%) owing to the moderate effect of molten potassium salts. The optimum material manifests excellent capacitive performance, including large mass specific capacitance (380.1 F g–1 in the alkaline electrolyte), high energy density (25.0 Wh kg–1 in the neutral electrolyte) and good cycling stability (capacitance retention of 90.1% after 8000 cycles). This synthetic strategy can be extended to the preparation of analogous CMT made from other natural fibres exemplified by poplar catkin and cotton wool. Further, the metal-free carbon-based electrocatalyst obtained by the post nitrogen doping of KCMT exhibits high catalytic activity towards the oxygen reduction reaction (ORR). Our synthetic approaches have substantiated good prospects for microtubular carbon-based materials of electrochemical energy-related technologies.