Nitrogen-enriched activated carbons via dual N-doping processes: Electrode material for high gravimetric- and volumetric-performance supercapacitor

N/O co-doped activated carbons are prepared via a hydrothermal synthesis (HTS) using glucose and egg solution (egg white + egg yolk) as precursors, followed by an ammonia activation. Controlling the egg amount for the HTS processing and the ammonia concentration for activation, we tailor the N and O contents in the ACs and achieve a N amount of 6.44 at.%. The comprehensive electrochemical performances of the symmetrical supercapacitors (SCs) prepared with the N/O co-doped ACs are investigated with 1 M H₂SO₄ as electrolyte and show positive dependence on the N amount. The SCs with the ACs of the highest N amount possess a gravimetric capacitance of 364 F/g and a volumetric capacitance of 276 F/cm³ as well as good rate performances of 72 % in the capacitance retention at 10 A/g and remarkable cycling stability of ~95 % after 10,000 GCD cycles at 5 A/g. The positive effects on the intrinsic electrochemical properties of the ACs are further confirmed by an optimized specific capacitance per surface area of 0.28 F/m² and a highest nominal diffusion coefficient of 0.146 × 10⁻⁶ cm²/s which are achieved by the ACs with highest amount of N contents.