Unravelling the enhanced capacitive desalination behavior of nanoneedle-like NiFe2O4

In this work, the nanoneedle-like NiFe 2 O 4 (NFO) has been prepared by a template method and post annealing process for capacitive deionization (CDI) with enhanced performance. Owing to the unique structure, the nanoneedle-like NFO provides large accessible surface area, which benefits to offer abundant electroactive sites for electrosorption. Meanwhile, the salty ions diffusion and electron exchange are promoted by needle-like structure. Further, it is found that the NFO annealed at 450 °C (NFO-450) demonstrate the high crystallinity, rich mesopores and exceptional electrochemical properties. As electrode for CDI, the NFO-450 has manifested the high desalting capacity of 1.62 mmol/g when the effective loading mass of both electrodes is 23.6 mg. Interestingly, the desalting capacity realizes the linear correlation with the mass of NFO electrode ranging from 23.6 to 45.8 mg. The mechanism analysis stands out that the Na + are captured by NFO, accompanied by the reduction of Ni 3+ to Ni 2+ in the 1 st cycle. Afterwards, the Na + can be electrostatically removed by the NFO//AC system.