Heteroatom-doped hierarchical porous carbon materials demonstrate significant promise for energy storage applications. In this paper, nitrogen-doped hierarchical porous carbon (NPC) materials were synthesized by one-step carbonization process using agar as the carbon precursor, urea as the nitrogen precursor, and KHCO₃ as the activating agent. Owing to the combined influence of substantial nitrogen and oxygen functional groups, interconnected hierarchical porous structure and large specific surface area, the NPC-600 electrode delivers a high specific capacitance of 450 F g⁻¹ and remarkable cyclic stability. Moreover, the NPC-600//NPC-600 symmetrical supercapacitor delivers an energy density of 29.41 Wh kg⁻¹ and good cyclic performance. More interestingly, a zinc ion hybrid capacitor (ZIHC) constructed with NPC-600 as the positive electrode achieves a capacitance of 368.78 F g⁻¹ (163.9 mAh g⁻¹), an energy density reaching 120.75 Wh kg⁻¹ and superior cyclic characteristics. The research affords a straightforward way for fabricating heteroatom-doped porous carbon as electrode for supercapacitor and ZIHCs.

Zinc-ion hybrid capacitors (ZHCs) combine the merits of zinc ion batteries and supercapacitors, have attracted increasing attention due to cost-effectiveness, improved safety, high energy/power densities, long-term electrochemical stability, and ease of assembling. As one type of promising electrode material for ZHCs, MXene-based materials have drawn wide research because of their adjustable layer spacing, excellent physical and chemical properties, high conductivity and good electrochemical stability. In recent years, massive research on improving the energy density and cycle stability of ZHCs, and the modification and optimization of MXene have provided a new way to enhance the performance of ZHCs. In this paper, we briefly introduce the basic information about MXene, review several preparation methods of MXene, and emphasis on the modification and utilization of MXene in the cathodes, anodes and electrolyte of ZHCs. In addition, the utilization of MXene in ZHCs separators is also displayed. Eventually, the promising future and challenges of MXene-based materials for ZHCs applications are outlined.

Supercapacitors (SCs) are considered promising energy storge systems because of their outstanding power density, fast charge and discharge rate and long-term cycling stability. The exploitation of cheap and efficient electrode materials is the key to improve the performance of supercapacitors. As the battery-type materials, transition metal phosphides (TMPs) possess high theoretical specific capacity, good electrical conductivity and superior structural stability, which have been extensively studied to be electrode materials for supercapacitors. In this review, we summarize the up-to-date progress on TMPs materials from diversified synthetic methods, diverse nanostructures and several prominent TMPs and their composites in application of supercapacitors. In the end, we also propose the remaining challenges toward the rational discovery and synthesis of high-performance TMP electrodes materials for energy storage.