Novel mesoporous Co₃O₄-Sb₂O₃-SnO₂ active material in high-performance capacitive deionization

Capacitive deionization (CDI), as an emerging eco-friendly electrochemical brackish water deionization technology, has widely benefited from carbon/metal oxide composite electrodes. However, this technique still requires further development of the electrode materials to tackle the ion removal capacity/rate issues. In the present work, we introduce a novel active carbon (AC)/Co₃O₄-Sb₂O₃-SnO₂ active material for hybrid electrode capacitive deionization (HECDI) systems. The structure and morphology of the developed electrodes were determined using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Brunauer-Emmett-Teller (BET)/Barrett-Joyner-Halenda (BJH) techniques, as well as Fourier-transform infrared (FT-IR) spectroscopy. The electrochemical properties were also investigated by cyclic voltammetry (CV) and impedance spectroscopy (EIS). The CDI active materials AC/Co₃O₄ and AC/Co₃O₄-Sb₂O₃-SnO₂ showed a high specific capacity of 96 and 124 F g^-1 at the scan rate of 10 mV s^-1, respectively. In addition, the newly-developed electrode AC/Co₃O₄-Sb₂O₃-SnO₂ showed high capacity retention of 97.2% after 2000 cycles at 100 mV s^-1. Moreover, the electrode displayed excellent CDI performance with an ion removal capacity of 52 mg g^-1 at the applied voltage of 1.6 V and in a solution of potable water with initial electrical conductivity of 950 μs cm^-1. The electrode displayed a high ion removal rate of 7.1 mg g^-1 min^-1 with an excellent desalination-regeneration capability while retaining about 99.5% of its ion removal capacity even after 100 CDI cycles.