Highly Efficient Capacitive Deionization Enabled by NiCo₄MnO_8.5 Electrodes

The shortage of fresh water resources is one of the major challenges facing this planet. Capacitive deionization (CDI) techniques that are deemed to be highly efficient and require low capital cost have attracted widespread attention in the last few decades. In this work, the cubic ternary metal oxides NiCo₄MnO_8.5 (Ni-Co-Mn-O) are synthesized by facile hydrothermal method for enhanced symmetrical CDI. Electrochemical measurements illustrate that the Ni-Co-Mn-O possesses low internal resistance and ion diffusion impedance. As a result, the salt removal capacity of the Ni-Co-Mn-O electrode increases from 26.84 to 65.61 mg g^-1 by varying the voltage from 0.8 to 1.4 V in 1.0 × 10^-2 m NaCl solution, while the charge efficiency stabilizes at ≈80%. After 20 cycles, the capacitance retained is 64.27%, which is due to the irreversibility of Co²⁺/Co³⁺ and Mn²⁺/Mn³⁺ and the release of Ni³⁺ from the Ni-Co-Mn-O electrode after long desalination/salination cycles.