Dual redox centers in MnCo2O4 nanorod cathode for highly efficient capacitive deionization

Abstract

Capacitive deionization (CDI) technology via faradic electrodes with active redox pairs has achieved tremendous success in desalination. However, the inner collaborative mechanisms of multi-redox centers in electrodes are rarely deep-analyzed. Thus, this work intensively investigated the inner enhanced mechanisms of multi-redox centers, starting from the dual-redox-based MnCo₂O₄ nanorod (MCO-NR) cathode in capacitive desalination. The electrochemical tests indicated a surface capacitive ratio of MCO-NR as high as 86 % when the scan rate was 100 mV s⁻¹. Multi-dimensional CDI tests demonstrated that the highest capacity of MCO-NR could reach 61.78 mg g⁻¹, with four theory models elaborating the electrosorption kinetics and maximum desalination capability. The refined ex-situ XPS measurements, carefully designed comparative experiments, and DFT calculations were used to analyze the Na⁺ (de)intercalation characteristics, the inner enhanced electrosorption mechanisms of dual redox centers, and the effects that the Mn redox center exerts on the MnCo₂O₄ structure. These results showed the superiority of dual- or multi-redox-center-based faradic capacitive desalination, providing a new perspective for designing high-property faradic electrode materials.