Hierarchical porous carbon with optimized mesopore structure and nitrogen doping for supercapacitor electrodes

Heteroatom-doped porous carbons with optimized pore structure have become attractive as supercapacitor electrodes. In this work, hierarchical porous carbon possessing optimized mesopore structure and nitrogen doping (NHPC) was prepared by carbonizing the mixtures of potassium humate and manganous nitrate (Mn(NO3)2). The NHPC exhibits similar specific surface area, while significantly higher mesopore ratio with narrow pore size distribution compared with hierarchical porous carbon without the Mn(NO3)2 (HPC), which benefit ion storage and transfer in the corresponding electrodes. Moreover, the NHPC shows higher nitrogen content of (3.89 at.%) than HPC (1.99 at.%), leading to enhanced wettability and pseudo-capacitance effect. Based on these optimized characteristics, even with an ultrahigh mass loading of 13.56 mg cm−2, NHPC demonstrates improved gravimetric capacitance of 258 F g−1 and areal capacitance of 23.1 μF cm−2 at 0.046 A g−1 (18.9% and 12.1% higher than HPC, respectively), as well as significantly enhanced rate capability. Moreover, NHPC exhibits excellent cycling stability with 93.6% capacitance retention after 10,000 cycles at a current density of 2.32 A g−1. This work provides a facile and low-cost strategy for preparing the nitrogen-doped hierarchical porous carbon for practical supercapacitor application.