In Situ, Nitrogen-Doped Porous Carbon Derived from Mixed Biomass as Ultra-High-Performance Supercapacitor.

How to address the destruction of the porous structure caused by elemental doping in biochar derived from biomass is still challenging. In this work, the in-situ nitrogen-doped porous carbons (ABPCs) were synthesized for supercapacitor electrode applications through pre-carbonization and activation processes using nitrogen-rich pigskin and broccoli. Detailed characterization of ABPCs revealed that the best simple ABPC-4 exhibited a super high specific surface area (3030.2-3147.0 m² g^-1) and plentiful nitrogen (1.35-2.38 wt%) and oxygen content (10.08-15.35 wt%), which provided more active sites and improved the conductivity and electrochemical activity of the material. Remarkably, ABPC-4 showed an outstanding specific capacitance of 473.03 F g^-1 at 1 A g^-1. After 10,000 cycles, its capacitance retention decreased by only 4.92% at a current density of 10 A g^-1 in 6 M KOH. The assembled symmetric supercapacitor ABPC-4//ABPC-4 achieved a power density of 161.85 W kg^-1 at the maximum energy density of 17.51 Wh kg^-1 and maintained an energy density of 6.71 Wh kg^-1 when the power density increased to 3221.13 W kg^-1. This study provides a mixed doping approach to achieve multi-element doping, offering a promising way to apply supercapacitors using mixed biomass.