Amorphous FePO4-anchored three-dimensional macro-porous Ti3C2Tx for superior capacitive deionization and sodium-ion selectivity

Faradaic capacitive deionization (CDI), which exploits pseudo-capacitive electrodes, is an appealing water-purification candidate from low-salinity desalinated water due to its fast Faradaic electro-sorption and ion intercalations. However, current Faradaic CDI faces the challenge in low salt adsorption capacity and poor selective sodium-ion (Na⁺) applicability. Herein, amorphous ferric phosphate (FePO₄)-anchored on three-dimensional macro-porous Ti₃C₂T_x network (3D FePO₄@Ti₃C₂T_x) electrode is proposed without scarifying Ti₃C₂T_x electronic conductivity, wherein sodium-ion captured FePO₄ provided abundant Na⁺ adsorption site for enhancing desalination capacity and Na⁺ selectivity. Simultaneously, highly-interconnected channels accelerated electron/ion transport to enable effective Na⁺ intercalation in electro-sorption. Accordingly, the assembled FePO₄@Ti₃C₂T_x//activated carbon (AC) asymmetric CDI device delivered a typical Na⁺-intercalated behavior with high desalination capacity of 65 mg g⁻¹, in which electric current generation could power a blue light-emitting diode (LED) screen. Importantly, the asymmetric CDI device enabled an evident Na⁺ selectivity over the Al³⁺ with high separator factor up to 6.3 in binary mixture feed of Na⁺ and Al³⁺. This study offers a new idea to achieve high desalination performance and sodium-ion selectivity via 3D framework supported ions-capture structure in seawater desalination.