Porous nitrogen-doped MXene-based electrodes for capacitive deionization

A facile and novel process is proposed and demonstrated to fabricate highly-porous nitrogen-doped MXene sheets (N–Ti3C2Tx) with great promise for seawater desalination. The nitrogen-doping is used to form a framework with open pore structures (total pore volume of 0.84 cm3 g−1) and high specific surface area (368.8 m2 g−1), simultaneously to hinder the restacking of MXenes layers and to improve electrical conductivity. The processed N–Ti3C2Tx shows promising volumetric capacitance (514 F cm−3) and represents tremendous electrochemical stability maintaining 99.75% of the initial volumetric capacitance after 2,000 cycles in 1 M sodium chloride electrolyte. We showed that nitrogen-doped MXene sheet is a high-potential electrode material for capacitive deionization (CDI) application, which outperforms all the recently reported materials by considering a combination of two efficient characteristics: electroadsorption rate and capacitance. The N–Ti3C2Tx shows stable performance over 24 CDI cycles with an average salt adsorption capacity of 117 ± 4.7 mg cm−3 (43.5 ± 1.7 mg g−1) in 5,000 mg/L NaCl solution (applied voltage of 1.2 V).