Understanding the Enhanced Capacitive Desalination Performance of Spherical ZnCo₂O₄ Electrode

Abstract In this work, the spinel ZnCo₂O₄ (ZCO) prepared by a simple strategy is employed for capacitive deionization (CDI) towards enhanced desalination performance. The ZCO reveals typical spherical structure that is beneficial in providing 3D tunnels for ions diffusion. On the basis of electrochemical measurements, the ZCO electrode possesses specific capacitance of 307.9 F g⁻¹ in 1 m NaCl solution at the scan rate of 1 mV s⁻¹. Remarkably, the equivalent series resistance and the Warburg impedance of ZCO electrode is only 0.54 and 0.66 Ω, respectively. Such low resistivity is conducive to improve the efficiency of charge transfer and the driven energy utilization. Regarding the desalination, the ZCO electrode illuminates the salt removal capacity of 39.4 mg g⁻¹ in 2000 µS cm⁻¹ NaCl solution at 1.2 V. Under the same experimental conditions, the ZCO electrode demonstrates a high desalination capacity of 73.39 mg g⁻¹ with charge efficiency of 76.8% at a constant current of 10 mA g⁻¹. Moreover, the preferential removal of Na⁺, K⁺, and Mg²⁺ enabled by ZCO electrode is investigated, suggesting the radius of hydration ions plays a significant role. Beyond that, the analysis on the morphology, crystal phase, and valance state of ZCO electrode at different desalination/salination state are explored to propose the possible desalination mechanism.