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

High N-doped hierarchical porous carbon (HNHPC) with ultrahigh BET surface area (SBET) and pore volume (Vpore) 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(NH2)2-C6H5O7(NH4)3-co-assisted C6H5K3O7 (U-A-co-assisted P) self-activation strategy to prepare ultrahigh SBET and Vpore HNHPCs for CDI desalination. Compared to the single P self-activation and U/A-assisted P self-activation, HNHPCPUA acquired via U-A-co-assisted P self-activation possesses ultrahigh SBET (3280.16 m2/g), splendid Vpore (2.49 cm3/g), high Vmeso/Vpore (57.83%) and high N-doping (6.40%). Its small hierarchical porous carbon nanogranlue structure helps to expose more accessible SBET and extra active sites, accelerating the ions insertion and extraction from the micropores. The resultant HNHPCPUA delivers a high specific capacitance of 203.9F/g. In the assembled CDI setup, HNHPCPUA 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 SBET and Vpore HNHPCs for energy and environmental applications.