Degradation Mechanisms of Rutile‐Type TiO ₂ Photoanodes during Photoelectrochemical Water Splitting

ABSTRACT TiO ₂ is widely applied as a photoanode material for the oxygen evolution reaction (OER), as well as for corrosion protection. However, its stability during photoelectrochemical (PEC) processes is still under debate. Here, we systematically investigate the effect of illumination, electrode potential, and electrolyte pH on the stability of rutile‐type TiO ₂ nanowires during PEC OER. We provide operando insights into the photostability of TiO ₂ , quantifying the photodissolution to identify degradation mechanisms in acidic and alkaline electrolytes. The structural evolution of TiO ₂ nanowires is correlated with their photodissolution as well as local pH changes during OER. Based on these findings, we propose a model that links the pH‐dependent degradation of PEC performance with dissolution processes, thereby establishing a comprehensive understanding of the durabilities of TiO ₂ photoanodes in different electrolyte environments. Overall, this work identifies and rationalizes the PEC stability boundaries of TiO ₂ , which is key for its practical application in photo/electro‐catalysis and as a corrosion protection layer.