Distinguished Roles of Nitrogen‐Doped Sp² and Sp³ Hybridized Carbon on Extraordinary Supercapacitance in Acidic Aqueous Electrolyte

Abstract The acidic aqueous supercapacitors have been found to deliver appealing capacitive properties due to fast ion diffusion caused by the applied smallest size of hydrion. However, their practical applications are largely inhibited by the narrow electrochemical stability window of water (1.23 V). Herein, A nitrogen‐enriched porous carbon materials (RNOPCs) is reported, consisting of varied nitrogen doping bonded on sp² and sp³ carbon sites, which are capable of stimulating a wider potential window up to 1.4 V and thus resulting in a great enhancement of capacitive performance in aqueous acidic electrolytes. Together with the improved electrical conductivity and preferable hydrion diffusion, RNOPCs exhibit an ultrahigh volumetric capacitance (1084 F cm⁻³) in 0.5 M H₂SO₄. Besides, a fully packed RNOPCs‐based symmetrical supercapacitor can deliver a high gravimetric and volumetric energy density of 31.8 Wh Kg⁻¹ and 54.3 Wh L⁻¹ respectively, approaching those of lead acid batteries (25–35 Wh Kg⁻¹). The first‐principles calculations reveal that the lone pair electrons of the doped nitrogen can be delocalized on its neighboring carbon atoms, improving charge uptakes and overpotentials. Such facile and scale‐up production of carbon‐based supercapacitors can bridge the gap of energy density between traditional supercapacitors and batteries in aqueous electrolytes.