Boron and Nitrogen Co-Doped Coal-Based Activated Carbon as Cathode Material for High-Performance Aqueous Zinc-Ion Hybrid Capacitors
Aqueous zinc-ion capacitors (ZICs) are promising energy storage systems due to their high specific capacity and superior reliability. Heteroatom-doped carbon materials have been shown to substantially increase the capacitance of ZICs, yet the underlying mechanisms remain poorly understood. In this work, coal-based activated carbon was functionalized with both boron (B) and nitrogen (N) to serve as the cathode material in ZICs. The optimized material, designated CAC-120, exhibits a high specific capacity of 371.4 mAh g−1 at 1 A g−1 and retains 74% of its initial capacity after 10,000 cycles. Electrochemical analysis and density functional theory (DFT) calculations reveal that pyridinic N plays a crucial role in enhancing Zn2+ storage, demonstrating superior electrochemical reversibility. Furthermore, an assembled aqueous ZIC using the CAC-120 cathode achieves a high reversible capacity of 90.8 mAh g−1 at 0.2 A g−1 and exceptional long-term stability over 17,000 cycles. This work provides valuable insight into the design of high-capacity and ultrafast pseudocapacitive carbon cathodes for ZICs, highlighting the synergistic effects of pore structure engineering and heteroatom doping.