Green double organic salt activation strategy for one-step synthesis of N-doped 3D hierarchical porous carbon for capacitive deionization

• 3D N-doped hierarchical porous carbons (3DNHPC) are prepared in a green strategy. • Tertiary porous structure and surface-exposed active sites accelerate ion insertion. • Superior desalination capacity and rapid desalination rate are achieved. • Ultrahigh water recovery and productivity are acquired. Exploiting a sustainable and effective strategy for fabricating 3D N-doped hierarchical porous carbon (3DNHPC) for capacitive deionization (CDI) is a huge challenge for desalination. The traditional methods often adopt expensive precursors, complex routes and strong corrosive activators that are harmful for its practical application. Herein, a novel green double organic salt activation strategy is developed that utilizes lotus stem (LS) with a regular 3D macroarray structure to acquire 3DNHPC x . Different from single C 6 H 5 K 3 O 7 or Na 2 EDTA activation, 3DNHPC x obtained under double organic salt co-activation exhibits a suitable micro-meso-macro porous structure with a high BET surface area (S BET ) of 2256.2 m 2 /g, a large pore volume of 1.02 cm 3 /g, a remarkable mesoporous volume of 0.41 cm 3 /g and 1.31% N content. Its unique tertiary pore structure and copious surface-exposed active sites facilitate the ions rapid insertion and extraction from the micropores. The assembled CDI cells achieve a superior salt removal capability of 25.36 mg/g as well as a splendid volumetric adsorption capacity (VAC) of 6.21 mg/cm 3 and an ultrafast average salt removal rate of 7.84 mg/g/min. Meanwhile, 3DNHPC 11 maintain 89.4% adsorption capacity after 50 cycles. Besides, 3DNHPC 11 obtains a high water recovery (WR) of 82.2% and high productivity of 290 g NaCl /g C /(h m 2 ) or 108.1 g NaCl /cm 3 C /(h m 2 ). This work sheds light on one way to design economical and eco-friendly 3DNHPCs for high-performance CDI desalination.