Microwave-modulated graded porous carbon for supercapacitors: Pore size matching and operating voltage expansion

Optimizing the pore structure and its interaction with the electrolytes was vital for enhancing the performance of supercapacitors based on the electrical double layer mechanism. In this study, graded porous carbon material (STP) with outstanding properties was prepared by adjusting the activation temperature and KOH dosage in the microwave pyrolysis process of sargassum thunbergii. The results demonstrated that better electrochemical performance was obtained when 1 M NaNO₃ was used as electrolyte and STP-800-3 was employed as electrode material, attributed to its excellent specific surface area (SSA) of 2011.8 m² g^-1, high micropore ratio, and the optimal matching degree between micropore size and electrolyte ion diameter. Moreover, the operating voltage window was expanded to 2.0 V in supercapacitors assembled with 6 M NaNO₃ high-concentration electrolyte. Simultaneously, the symmetric supercapacitors exhibited a remarkable specific capacitance of 290.0 F g^-1, a high energy density of 39.0 W h kg^-1, and outstanding capacity retention at 70.9% after 10,000 charge/discharge cycles based on 6 M NaNO₃ electrolyte. Consequently, the results provided valuable technical support and theoretical basis to foster progress of novel and high-performance supercapacitors.