Photothermal Catalytic Water Splitting at Diverse Two-Phase Interfaces Based on Cu–TiO₂

Wasted high-temperature water from power plants or industrial boilers for photothermal catalytic water splitting reactions may be used to produce solar fuel and provide high-temperature heat to achieve solar-energy cascade utilization. Cu-modified TiO2 was used for the overall photothermal catalytic water splitting reaction, resulting in a hydrogen–oxygen ratio of approximately 2:1. The liquid–solid interface reaction yield was up to 10 times that of the gas–solid interface at the same reaction temperature. With the Cu modification, the photoresponse was improved, the energy barrier of the rate-determining step was reduced, and the water splitting reaction was promoted. As the copper content increased, Cu elements changed from a low valence state to an oxidized state. Moreover, the effect of temperature on the reaction was also explored. Increasing the temperature reduced the energy barrier of the rate-determining step and reduced the charge-transfer resistance, which explains the positive correlation between the hydrogen yield and temperature.