Nanoarchitectonics of activated carbon with high electrochemical performance via boron/nitrogen co-doping

In the field of carbon materials, introducing heteroatoms is a key strategy for enhancing pseudocapacitance in supercapacitors. Boron (B) and nitrogen (N) are suitable doping elements due to their atomic structural characteristics. However, the process of heteroatom doping may provoke carbon framework restructuring or micropore blockage, disrupting the original hierarchical porous structure. Meanwhile, excessive doping alters the electronic structure, reduces graphitization, and introduces defects, thereby suppressing carrier mobility. This study successfully synthesized B/N co-doped activated carbon materials using alga-based activated carbon as the precursor and ammonium pentaborate octahydrate as the dual B/N source via hydrothermal activation. The effects of doping ratios on the material's pore structure, surface chemical state, and electrochemical performance were systematically investigated. The results indicate that the degree of heteroatom incorporation exhibits a positive correlation with the doping ratio, but a saturation effect is observed. When the mass ratio of activated carbon to ammonium pentaborate octahydrate reaches 1:30, the B and N contents in the modified activated carbon attain 2.50% and 3.25%, respectively. Further increasing the doping ratio causes the elemental contents to plateau, indicating that the doping process has approached its limit. This doping ratio significantly optimized the modified activated carbon's pore structure: achieving a specific surface area of 2616.2 m2·g−1 and a total pore volume of 1.41 cm3·g−1. The synergistic distribution of micropores and mesopores formed a hierarchical pore network conducive to rapid ion transport. As a supercapacitor electrode material, BNAC_1/30 exhibits a specific capacitance of 322.0 F·g−1 at a current density of 0.1 A·g−1, with outstanding rate performance maintaining 268 F·g−1 even at 5 A·g−1. After 5000 charge-discharge cycles, the capacitance retention reached 94.43%, demonstrating excellent stability. The performance enhancement is primarily attributed to the rational micro/mesoporous structure facilitating ion transport and the pseudocapacitive synergistic effect introduced by B/N co-doping. This work proposes a synergistic design strategy of “heteroatom doping-pore structure optimization” achieved by regulating the doping ratio, providing an effective pathway for developing high-performance carbon electrode materials based on biomass.