Exceptional long-term stability of titanium oxynitride nanoparticles as non-carbon-based electrodes for aerated saline water capacitive deionization

Abstract

Carbon-based capacitive deionization (CDI) electrodes suffer from long-lasting stability challenges due to sets of parasitic side reactions, including the high oxidation rate of the electrodes during the desalination process. Consequently, it is essential to identify, design, and fabricate novel electrodes that overcome such challenges to achieve robust and high desalination performance. This work reports on the fabrication and utilization of titanium oxynitride (TixOyNz) nanoparticles as stable non‑carbon-electrodes for capacitive deionization. The oxynitride nanoparticles were synthesized via a simple template-free approach and fully characterized using XRD, XPS, Raman, SEM, and BET techniques. Moreover, the fabricated electrodes were electrochemically evaluated via cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) techniques. The electrode exhibited a pseudocapacitance behavior with a specific capacitance of 150 F/g. A symmetric configuration CDI setup was constructed, enabling the investigation of the effect of different flow rates and voltages. Remarkably, the TixOyNz CDI cell revealed a salt adsorption capacity (SAC) of up to 56.6 mg/g with fast adsorption kinetics. Moreover, the electrodes retained ~100% of its initial SAC even after 1960 cycles over 110 days of continuous testing. Furthermore, several post- characterization techniques such as XPS, XRD, FTIR, and potential of zero charge have been deeply studied and analyzed to unravel the observed exceptional stability of the tested electrodes.