Large-scale multirole Zn(II) programmed synthesis of ultrathin hierarchically porous carbon nanosheets

ZIF-derived carbon structures are considered as desired electrode materials for supercapacitors due to their high surface area, high conductivity, and porous structure. However, the most reported ratio of 2-methylimidazole and Zn(II) is 4:1 to 20:1, which limits commercial applications due to the increasing cost. In this paper, a multirole Zn(II)-assisted method is presented from Zn(II) solution, ZnO, ZnO/ZIF-8 core-shell nanostructure, to 3D hierarchical micro-meso-macroporous carbon structures with a 1:1 ratio of 2-methylimidazole and Zn(II). The hierarchically porous carbon has a high surface area of 1800 m² g⁻¹ due to the synergistic effect of multirole Zn(II). The unique carbon-based half-cell delivers the specific capacitances of 377 and 221 F g⁻¹ at the current densities of 1.0 and 50 A g⁻¹, respectively. As a 2.5 V symmetrical supercapacitor, the device reveals a high double-layer capacitance of 24.4 F g⁻¹, a power density of 62.5 kW kg⁻¹, and more than 85.8% capacitance can be retained over 10000 cycles at 10 A g⁻¹. More importantly, the low-cost hierarchically porous carbon could be easily produced on a large scale and almost all chemicals can be reused in the sustainable method.