Preparation of crab-shell-based N, O co-doped graded porous carbon for supercapacitors using the confined nanospace deposition method

Biomass-based carbon materials with hierarchical porous structures have attracted attention for their ability to provide more channels and shorten ion transport paths. Here, we developed a simple method based on confined nanospace deposition. During high-temperature treatment, the mesoporous silica layer wrapped around the outside of the crab shells acted as a closed nanospace and effectively suppressed the severe deformation of the crab shell structure by shrinking inward. The prepared carbon material has a layered porous structure with abundant and stable N and O co-doping (N 7.32%, O 3.69%). The specific capacitance of the three-electrode system was 134.3 F/g at a current density of 0.5 A/g in a 6 mol/L KOH electrolyte, and the assembled aqueous symmetric supercapacitors exhibited an excellent cycling stability of 98.81% even after 5000 cycles. Graphical abstract