Photoelectrolysis of TiO₂ is highly localized and the selectivity is affected by the light

On the way to sustainable prosperity for future generations, photoelectrochemistry is becoming a key area for energy conversion and the environmentally friendly generation of chemical resources because it combines the advantages of electrochemical and photochemical processes. Highly active catalyst materials with excellent selectivity towards the desired reaction are certainly required for efficient processes. Understanding the underlying processes, including detailed in situ information, facilitates the design and development of catalyst materials. In this work, we utilize the scanning photoelectrochemical microscopy for the spatially resolved in situ investigation of the electrochemical and photoelectrochemical evolution of hydrogen, oxygen, reactive oxygen species, and chlorine for energy conversion. Herein, we demonstrate that the activity and the selectivity of the TiO₂ photoelectrocatalyst are highly localized despite their apparently uniform composition based on regular morphological characterization. Furthermore, the results suggest that the illumination dramatically changes the selectivity in electrolysis reactions, which is demonstrated on the competing oxygen- and chlorine- evolution reaction. Consequently, this leads to the critical implication that the activity and selectivity should not be considered uniform per se, especially under the illumination. This implies that light might be used for controlling the selectivity in electrolysis reactions. Such discovery shall dramatically impact the optimization of photoelectrocatalysts in general.