Extraordinary dual-ion electrochemical deionization capacity and energy efficiency enabled by coupling of Na3Fe2(PO4)3 and NiVAl layered double hydroxide electrodes

Abstract

Electrochemical deionization is an emerging desalination technique with great promise for production of fresh water, but its widespread application is still hindered by the low desalination capacity of the conventional carbonaceous electrodes. Herein, we constructed a novel dual-ion electrochemical deionization (DEDI) system using two types of faradaic material that accommodate specifically Cl⁻ and Na⁺ as the electrodes, i.e. NiVAl trimetallic layered double hydroxides as the anode and a Na super ionic conductor Na₃Fe₂(PO₄)₃ as the cathode, to remove NaCl from saline water. Both faradaic materials were incorporated with a carbon support to prevent aggregation of the active materials as well as to enhance the electrical conductivity. The DEDI system allowed a high operation voltage due to the large gap of the redox potential between the two faradaic materials, and thus delivered an extraordinary NaCl adsorption capacity of 105.5 mg g⁻¹ at 1.6 V. It also exhibited excellent cycling stability, with the adsorption capacity even increased by 148.3% after 100 cycles of charge and discharge. Furthermore, the excellent electrical conductivity, good electrochemical stability and high voltage endow the system with a high efficiency for energy recovery, with 56.2% of the energy consumed for deionization recoverable during discharging.