Three-dimensional titanium mesh-based flow electrode capacitive deionization for salt separation and enrichment in high salinity water

Abstract

Flow electrode capacitive deionization (FCDI) is a highly promising desalination technique known for its exceptional electrosorption capacity, making it suitable for efficient salt separation in high salinity water. However, the unsatisfactory charge transfer process between the flow electrode and current collector severely curtails the salt separation and enrichment performance of the FCDI device. To address this issue, three-dimensional titanium mesh (3D-TM) was proposed as a novel current collector for FCDI device, which significantly amplifies the charge transfer area and exhibits excellent salt separation performance. The 3D-TM current collector promotes the electron transfer, charge percolation, and ion migration processes through the electroconvection generated by the turbulence effect on the flow electrode. In the specific case of the 20-mesh 3D-TM, which is composed of 12 stacking layers of titanium mesh, the remarkable average salt removal rate and charge efficiency were achieved 5.06 μmol cm−2 min−1 and 92.9 % under an appropriate applied voltage of 2.0 V, respectively. Dramatically, the desalination performance maintained above 76.4 % over 100 desalination cycles at 2.0 V, demonstrating the exceptional cyclic stability of the 3D-TM FCDI cell. In the seawater desalination, the 3D-TM FCDI cell exhibited an impressive salt removal efficiency of 97.5 % (from 34.2 g L−1 to 0.84 g L−1) for 1 L East China seawater at 2.0 V for 24 h. For lithium-ion enrichment, the FCDI continuous desalting system achieved an astonishing concentration of 17.3 g L−1 for Li+ ions enrichment from an initial concentration of 1.30 g L−1, obtaining the average salt treating rate of 23.6 g m−2h−1 and charge efficiency of 80.0 %. Moreover, the lithium-sodium ions and lithium-magnesium ions enrichments were both conducted, yielding an enriched concentration of 10.4 g L−1 and 7.30 g L−1 for Li+ ions, respectively. These findings highlight the enormous potential of FCDI technology in industrial engineering applications, further establishing it as a highly viable solution.