Boosting supercapacitor and capacitive deionization performance of hierarchically porous carbon by polar surface and structural engineering

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Heteroatom doped hierarchically porous carbon materials are considered as promising candidates for high performance capacitive deionization and supercapacitor applications. However, the development of carbons simultaneously having both a reasonable polar surface and a hierarchically porous structure via a flexible synthetic strategy is critical but still a great challenge. Herein, a facile and effective strategy is presented for the preparation of N and P dual-doped hierarchically porous carbon networks by one-pot carbonization of a rationally designed precursor that was built using a metal–organic gel with a zinc ion metallic cluster and nitrogen/phosphorus chelate ligands. Due to the abundant exposed polar surface groups and the highly developed interconnected macro-/meso-/microporous structure, the optimal sample delivers a high specific capacitance of 373 F g−1 at a current density of 1 A g−1 and retains 270 F g−1 at 100 A g−1 with a capacitive retention of 72.3%. Furthermore, the symmetric supercapacitors assembled in aqueous and PVA/KOH solid electrolytes exhibit excellent energy outputs of 38.5 and 7.5 W h kg−1, respectively. For capacitive deionization, the sample displays a superior salt adsorption capacity of 7.7, 10.3 and 18.1 mg g−1 in NaCl solution with an initial concentration of 250 mg L−1 at applied voltages of 1, 1.2 and 1.4 V, respectively. Additionally, kinetics studies and density functional theory simulations reveal that N/P dual-doping not only reliably introduces pseudocapacitance, but also greatly enhances the chemisorption of Na and Cl, resulting in a remarkable electrochemical performance. This work provides a new insight into the relationship between polar surface/structural engineering and the capacitive performance of the designed materials.