A self-biased water at a TiO2–water interface for light-to-electricity conversion

Interfacial water plays a crucial role in charge transfer and energy conversion at the semiconductor–liquid junction. Here, we firstly demonstrate that TiO 2 with varied crystal phases generates a region of particle-free and negatively charged water at the TiO 2 –water interface without light. Upon irradiation, a mixed-phase TiO 2 electrode (anatase: rutile ≈ 7:3) paired with FTO generated a stable photovoltage of 0.32 V in deionized water without any added redox couples. This photovoltage correlates with surface hydrophilicity as well as crystal-phase composition, revealing a previously overlooked interplay between TiO 2 and interfacial water. These experimental findings not only provide new insights into photoinduced charge dynamics and self-cleaning mechanism at the TiO 2 –water interface, but also suggest an alternative pathway for light-to-electrochemical energy conversion directly from water.