Cobalt and nickel ferrites based capacitive deionization electrode materials for water desalination applications

Capacitive deionization (CDI) is an emerging technology for water desalination and is based on electrosorption of ions onto surfaces of electrically charged electrodes. The CDI electrode materials play a significant role in determining the process efficiency. In this study, pure and mixed nickel-cobalt ferrites Co_xNi_1-xFe₂O₄ (x = 0.0, 0.3, 0.5, 0.7 and 1.0) were synthesized using the sol-gel auto-combustion method and investigated as novel CDI electrode materials. The purity, structure, and morphology of the synthesized ferrite nanoparticles were analyzed by various techniques. The electrochemical performance of the synthesized materials was investigated, and the results showed that the mixed ferrite Co_0.5Ni_0.5Fe₂O₄ electrode possessed the highest specific capacitance of 255 F/g at a scan rate of 10 mV/s. The electrodes were used to treat 250 mg/L NaCl solution in a CDI cell at 1.2 V and a feed flow rate of 10 mL/min. Under optimized experimental conditions, the highest specific salt adsorption capacity was 21.84 mg/g, corresponding to 23.43% of NaCl removal efficiency. These electrodes were highly stable and easily regenerable with less than 5% loss in electrosorption capacity for six adsorption/desorption cycles. The recyclability, stability, and enhanced electrochemical performance of the fabricated electrodes establish cobalt-nickel ferrites as a promising material for use in CDI desalination application.