Green synthesis of high N-doped hierarchical porous carbon nanogranules with ultra-high specific surface area and porosity for capacitive deionization.

[Display omitted] • A sustainable and facile self-activation strategy is proposed to synthesize high N-doped hierarchical porous carbon (HNHPC) for CDI. • The synthesized HNHPC PUA possesses ultrahigh specific surface area (3280.16 m2/g), splendid pore volume (2.49 cm3/g), large mesopore ratio (57.83%) and high N content (6.4%). • The small hierarchical porous carbon nanogranlue structure of HNHPC PUA helps to expose more accessible and extra active sites, accelerating the ions insertion and extraction from the micropores. • The HNHPC PUA delivered a splendid desalination capacity of 24.86 mg/g and good cycling stability. High N-doped hierarchical porous carbon (HNHPC) with ultrahigh BET surface area (S BET) and pore volume (V pore) has attracted great attention in capacitive deionization (CDI) due to the copious active sites. However, the traditional methods often adopt strong corrosive activators and fail to achieve high N-doping, which are harmful for its practical application. Herein, we develop a sustainable CO(NH 2) 2 -C 6 H 5 O 7 (NH 4) 3 -co-assisted C 6 H 5 K 3 O 7 (U-A-co-assisted P) self-activation strategy to prepare ultrahigh S BET and V pore HNHPCs for CDI desalination. Compared to the single P self-activation and U/A-assisted P self-activation, HNHPC PUA acquired via U-A-co-assisted P self-activation possesses ultrahigh S BET (3280.16 m2/g), splendid V pore (2.49 cm3/g), high V meso /V pore (57.83%) and high N-doping (6.40%). Its small hierarchical porous carbon nanogranlue structure helps to expose more accessible S BET and extra active sites, accelerating the ions insertion and extraction from the micropores. The resultant HNHPC PUA delivers a high specific capacitance of 203.9F/g. In the assembled CDI setup, HNHPC PUA exhibits a superior salt adsorption capacity (SAC) of 24.86 mg/g, a rapid salt adsorption rate (SAR) of 8.29 mg/g/min and reaches 88.7% SAC retention after 50 cycles in 500 mg/L NaCl at 1.2 V, suggesting good application potential. Overall, this work provides new insight into rapidly preparing ultrahigh S BET and V pore HNHPCs for energy and environmental applications. [ABSTRACT FROM AUTHOR]