The doping of coal-based activated carbon with both B and N for use as the cathode of high performance aqueous zinc-ion hybrid capacitors

Aqueous zinc-ion capacitors (ZICs) have significant potential as energy storage systems because of their high specific capacity and superior reliability. Heteroatom-doped carbon materials were known to substantially increase the capacitance of ZICs, however the mechanism remains poorly understood. Coal-based activated carbon was functionalized with B and N to serve as the cathode material in ZICs. This modification gave the material a high specific capacity of 371.4 mAh g−1 at 1 A g−1 and it retained 74% of its initial capacity after 10 000 cycles. Experimental results and density functional theory calculations revealed that pyridinic N plays a crucial role in increasing Zn2+ storage, demonstrating superior electrochemical reversibility. This work gives valuable insight into the design of high-capacity and ultrafast pseudocapacitive carbon cathodes for ZICs.