Photochemical Protection of Reactive Sites on Defective TiO2–x Surface for Electrochemical Water Treatment

The electrode is the key in electrochemical process for water and wastewater treatment. Many nonstoichiometric metal oxides are active electrode materials but have poor stability under strong anodic polarization due to their susceptible nature of the oxygen vacancies on surface and subsurface as defective reactive sites. In this work, a novel photochemical protecting strategy is proposed to stabilize the defective reactive sites on the TiO2- x surface and subsurface for long-term anodic oxidation of pollutants. With this strategy, a novel photoassisted electrochemical system at low anodic bias is further constructed. Such a system exhibits a high protecting capacity at a low operation cost for electrochemical degradation of bisphenol A (BPA), a typical persistent organic pollutant. Its excellent photochemical protecting capacity is found to be mainly attributed to the mild non-band-gap excitation pathways on the defective TiO2- x electrode under both visible-light irradiation and moderate anodic polarization. Under real sunlight irradiation, a 20 run cyclic test for BPA degradation demonstrates the excellent performance and stability of the constructed system at low bias without significant oxygen evolution. Our work provides a new opportunity to utilize the defective and reactive TiO2- x for efficient, stable, and cost-effective electrochemical water treatment with the aid of its photo- and electrochemical bifunctional properties.