N/o-co-doped porous carbon supercapacitor electrode material from sunflower discs via potassium citrate green activation strategy

In the current study, nitrogen and oxygen (N/O)-co-doped porous carbon for supercapacitors was successfully synthesized from sunflower discs through activation modification with potassium citrate and urea. Material characterization and electrochemical performance testing in three-electrode and two-electrode systems demonstrated that the porous carbon (SDU-900), prepared under activation conditions at 900 \(^{\circ }\) C exhibited an interconnected pore structure and excellent electrochemical properties. In a three-electrode system (6 M KOH as the electrolyte, current density of 0.5 A/g), SDU-900 demonstrated a high specific capacitance of 294.2 F/g. Moreover, the symmetric device based on SDU-900 exhibits an excellent energy density of 20.05 Wh/kg at a power density of 495 W/kg. After 15,000 galvanostatic charge–discharge (GCD) cycles at 5 A/g, the initial specific capacitance was retained at 93.89%, indicating remarkable cycling stability. Notably, the activation process utilized sunflower discs discarded from agricultural production as precursors, replacing the highly corrosive alkali activators with potassium citrate, a benign salt. This approach provides an environmentally friendly method for synthesizing porous carbon for supercapacitor applications.