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

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.