Disentangling the Impact of Morphology on the Photoelectrochemical\nPerformance of Nanostructured Anodic TiO<sub>2</sub>: A Systematic\nStudy of Anodization Potential at Constant Oxide Thickness

Understanding\nthe photoelectrochemical water oxidation performance\nof highly textured semiconductors requires systematic studies capable\nof revealing relevant correlations among the synthetic methods used,\nthe resulting morphologies, and their relationship to activity. Here,\nwe carry out a systematic study on anodized TiO<sub>2</sub> to understand\nthe impact of anodization potential on the transition from a nanoporous\nto a nanoring morphology and its influence on the semiconductor properties\nand photoassisted water oxidation. We demonstrate that the applied\nanodizing potential has a profound impact on the material properties,\nin particular, the morphology of the top layer as well as the size\nand shape of nanotubes. The anodized substrates produced at higher\npotentials possess superior photoelectrochemical properties, which\nare ensured by a hierarchical nanoporous-nanoring morphology, high\ndonor density, and a more positive flat band potential. We further\nconfirmed the generation of oxygen at the anodic TiO<sub>2</sub> under\nwhite light irradiation through scanning electrochemical microscopy\n(SECM). This work introduces a methodology to systematically synthesize\nand characterize the features of hybrid semiconductor materials toward\nmaterials with improved photoelectrochemical properties for renewable\nenergy technologies.