Abstract: N/B co-doped porous carbon materials (NBPCs) are regarded as an ideal cathode material for Zn-ion hybrid supercapacitors (ZHSCs). As a capacitive cathode material, the improvement of specific surface area (SSA) and pore structure can efficiently enhance the capacity and rate capability of NBPCs. However, the B atom doping progress will patch up the defect and pore of NBPCs, thereby impeding the further expansion of the SSA area and porous structure. This paper designs a new route for high-efficiency fabrication of NBPCs with high SSA and rich pore structure, employing biomass waste as the carbon source and a novel deep eutectic solvent (DES) as the activation agent. The obtained NBPCs process superior SSA (2270 m² g^-1) and abundant pore structure with rich B, N-doping level. Notably, an interesting occupied effect of doped B atoms on the N-doped carbon network can be identified, which optimizes the proportion of N-contained surface functional groups, leading to the enhancement of conductivity and capacity in NBPCs. Together with the large SSA, high B, N-doping level, an appropriate proportion of N-contained surface groups, and hierarchical porous structure, the NBPC-3 sample exhibits excellent electrochemical performance as cathode materials for ZHSCs, with an energy density of 139.46 W h kg^-1.

Key words: Zn-ion hybrid supercapacitors, N/B co-doped carbon, Deep eutectic solvents, Hierarchically porous structure