N/S co-doped interconnected hierarchical porous carbon cathode for zinc-ion hybrid capacitors with high energy density

Porous carbon materials (PCMs) are regarded as one of the most promising cathode materials for zinc-ion hybrid capacitors (ZIHCs) because of their low cost and abundant resource. Nevertheless, it is still a major challenge to enhance the energy density of PCMs-based ZIHCs. Herein, N/S co-doped interconnected hierarchical porous carbons (NS–IHPCs) are prepared from coal tar pitch (CTP) via a MgO@ZIF-8 double-template, in situ activation and N/S doping strategy to tune the microstructure and chemical composition. The as-prepared NS-IHPC1.5 features high specific surface area of 1273 m2 g−1, hierarchical pore structure and suitable heteroatom doping. Consequently, as a cathode, the NS-IHPC1.5-based ZIHC exhibits a high energy density of 125.3 Wh kg−1 at 134.5 W kg−1 and still remains 85.3 Wh kg−1 at 14096.1 W kg−1. The calculation results of density functional theory (DFT) demonstrate that the combination of pyrrole nitrogen and ortho-oxidized sulfur in samples achieves more negative Zn2+ adsorption energy. Correspondingly, the high capacity (166.5 mAh g−1 at 0.2 A g−1) and long cycle stability (94.0 % capacitance retention at 5 A g−1 after 20,000 cycles) are achieved for NS-IHPC1.5. This work offers a reliable way for synthesizing remarkable cathode materials from coal chemical by-products for energy storage. •N/S co-doped interconnect hierarchical porous carbons (NS–IHPCs) are obtained.•NS-IHPCs are synthesized by double-template coupled with in situ activation strategy.•NS-IHPCs feature 3D architecture with hierarchical pores and tunable N/S species.•DFT results show N-6 and S–O render NS-HIPC more negative Zn2+ adsorption energy.•NS-HIPC1.5 capacitor achieves high energy density of 125.3 Wh kg−1 at 134.5 W kg−1.