Biocarbon with large specific surface area and tunable pore structure from binary molten salt templating for supercapacitor applications

•A binary ZnCl2-CaCl2 molten salt system was applied to fabricate porous biocarbon.•Large specific surface area and well-balanced micro/mesopores were achieved.•The pore size distribution could be controlled to avoid excessive pore fusion.•The assembled supercapacitors showed notable rate capability at high current density.