Long-Term Stability of Light-Induced Ti³⁺ Defects in TiO₂ Nanotubes for Amplified Photoelectrochemical Water Splitting

This study shows that the simple approach of keeping anodic TiO2 nanotubes at 70 degrees C in ethanol for 1 h results in improved photoelectrochemical water splitting activity due to initiation of crystallization in the material amplified by the light-induced formation of a Ti3+-V-o states under UV 365 nm illumination. For the first time, the light-induced Ti3+-V-o states are generated when oxygen is present in the reaction solution and are stable when in contact with air (oxygen) for a long time (two months). We confirmed here that the amorphous or nearly amorphous structure of titania supports the survival of Ti3+ species in contact with oxygen. It is also shown that the ethanol treatment substantially improves the morphology of the titania nanotube arrays, specifically, less surface cracking and surface purification from C- and F-based contamination from the electrolyte used for anodizing.