Zinc Spinel Ferrite Nanoparticles as a Pseudocapacitive Electrode with Ultrahigh Desalination Capacity and Long-Term Stability

The hybrid capacitive deionization (HCDI) configuration is a significant branch of CDI for desalinating brackish water to address the worldwide freshwater shortage. Apart from traditional carbon-based electrodes, new inexpensive electrode materials with a high desalination capacity are pivotal in the large-scale application of capacitive deionization technology. In this study, a novel zinc spinel ferrite (ZFO) nanoparticle electrode was fabricated and applied for the first time in CDI. The electrode achieved ultrahigh desalination capacity and long-term stability without any modifications, such as carbon coating. The desalination capacity reached 136.6 mg of NaCl/g of ZFO under optimized conditions with a current density of 30 mA/g, a voltage range of -1.4 to 1.4 V, and an initial concentration of 100 mM. Moreover, the CDI system is stable for 200 cycles over a duration of more than 10 days. The excellent long-cycle performance reveals that ZFO is a competitive material for CDI in the future. The consumption of the bench-scale CDI system is also estimated ($0.33/g of NaCl), which is obviously decreased as a result of the simple synthesis and high capacity. Therefore, zinc spinel ferrite electrodes are appealing for actual desalination applications, which highlights pseudocapacitive materials for future CDI application.