Carbon cathode with heteroatom doping and ultrahigh surface area enabling enhanced capacitive behavior for potassium-ion hybrid capacitors

Potassium-ion hybrid capacitors (PIHCs) are widely regarded as highly promising energy storage devices, due to their exceptional energy density, impressive power density, and abundant potassium resources. Unfortunately, restricted by the inherent capacitive storage mechanism, the carbon cathodes possess a much lower specific capacity than battery-type anodes. Therefore, designing high-performance carbon cathodes is extremely urgent for the development of PIHCs. Herein, N, O co-doped porous carbon (NOPC) was fabricated through the NaCl hard template method and combined KOH/melamine chemical activation technique, displaying the characteristics of abundant N/O content (4.7 at%/16.9 at%), ultrahigh specific surface area (3092 m²·g^?1) and hierarchical pore network. The designed NOPC cathode delivers a high specific capacity (164.4 mAh·g^?1 at 0.05 A·g^?1) and superior cyclability (95.1% retention ratio at 2 A·g^?1 over 2500 cycles). Notably, the adjustable ratio of micropores to mesopores facilitates the achievement of the optimal balance between capacity and rate capability. Moreover, the pseudocapacitance can be further augmented through the incorporation of N/O functional groups. As expected, the graphite//NOPC based PIHC possesses a high energy density of 113 Wh·kg^?1 at 747 W·kg^?1 and excellent capacity retention of 84.4% after 4000 cycles at 1.0 A·g^?1. This work introduces a novel strategy for designing carbon cathodes that enhances the electrochemical performance of PIHCs.