Jujube shell-derived organic/inorganic nitrogen-doped porous carbon: electrochemical properties and contribution of nitrogen-doped forms to ion adsorption and storage

Biomass-derived nitrogen-doped porous carbon was prepared using jujube shell as the precursor through a two-step process involving activation and nitrogen-doping. Different nitrogen sources, organic-N and inorganic-N, were employed to modulate the nitrogen-doping forms, aiming to analyze the influence of various nitrogen-doping forms on the electrochemical energy storage performance. The nitrogen-doped porous carbon exhibited abundant pores and a smooth surface. Remarkably, organic nitrogen-doping significantly enhanced the electrical conductivity, while inorganic nitrogen-doping showed an adverse effect. In a three-electrode system, MN-DPC, ON-DPC, and IN-DPC achieved specific capacitances of 155.6 F/g, 147.0 F/g, and 137.0 F/g at 1 A/g, respectively. This represented increases of 37.7%, 30.1%, and 21.2%, respectively, compared to Free-N. Even at a high current density of 15 A/g, these materials maintained notable rate performance. Moreover, ON-DPC demonstrated excellent electrochemical energy storage performance with a symmetric capacitor achieving a power density of 5188 W/kg and an energy density of 7.0 Wh/kg. Density functional theory was conducted to assess mutual adsorption energy and charge distribution. Negative adsorption energy contributed to thermodynamic behavior, Oxided-N, Pyridinic-N, and Pyrrolic-N enhanced the adsorption energy for K⁺. Conversely, Graphitic-N weakened the adsorption energy. The improved adsorption energy facilitated the capture and storage, thereby enhancing electrochemical cycling stability.