Nano-MgO Templated Three-Dimensional Hierarchically Porous Carbon Nanosheets with Tunable Porosity for High-Rate Supercapacitors

Rapid ion transport and charge-transfer kinetics are essential for promoting the rate capability and power density of supercapacitors. Hierarchically porous carbons featuring three-dimensionally interconnected microstructures have emerged as highly promising materials for high-rate supercapacitors. Herein, we propose a cost-effective approach for synthesizing hierarchically porous carbon nanosheets featuring a distinctive three-dimensional microstructure using honey as a sustainable carbon source and nanosized MgO as a hard template and green activating agent. By means of the synergistic effect of self-chemical bubbling and MgO templates, the resultant materials exhibited a three-dimensional crosslinked microstructure, well-interconnected hierarchical porosity, large surface area, a high proportion of micropores, and tunable micro-meso-macroporosity. Benefiting from its structural merits, the resultant hierarchically porous carbon exhibited a superior capacitive behavior, especially an excellent rate capability. The optimal material can deliver a satisfactory capacitance of 359 F g–1 at 0.5 A g–1 and superb rate performance. The assembled symmetric capacitors delivered a satisfactory energy density of 12.7 Wh kg–1 at a power density of 450 W kg–1 in Na2SO4 electrolyte. Importantly, this strategy provides great promise for rationally engineering three-dimensional hierarchically porous carbons for high-rate supercapacitors in the future.