Na3V2(PO4)3@C as Faradaic Electrodes in Capacitive Deionization for High-Performance Desalination.

Abstract

Among various desalination technologies, capacitive deionization (CDI) has rapidly developed because of its low energy consumption and environmental compatibility, among other factors. Traditional CDI stores ions within the electric double layers (EDLs) in the nanopores of the carbon electrode, but carbon anode oxidation, the co-ion expulsion effect, and a low salt adsorption capacity (SAC) block its further application. Herein, the Faradaic-based electrode is proposed to overcome the above limitations, offering an ultrahigh adsorption capacity and a rapid removal rate. In this paper, the open framework structure Na3V2(PO4)3@C is applied for the first time as a novel Faradaic electrode in the hybrid capacitive deionization (HCDI) system. During the adsorption and desorption process, sodium ions are intercalated/deintercalated through the crystal structure of Na3V2(PO4)3@C while chloride ions are physically trapped or released by the AC electrode. Different concentrations of feedwater are investigated, and a high SAC of 137.20 mg NaCl g-1 NVP@C and low energy consumption of 2.157 kg-NaCl kWh-1 are observed at a constant voltage of 1.0 V, a concentration of 100 mM, and a flow rate of 15 mL min-1. The outstanding performance of the Na3V2(PO4)3@C Faradaic electrode demonstrates that it is a promising material for desalination and that HCDI offers great future potential.