Disentangling the impact of morphology on the photoelectrochemical performance of nanostructured anodic $TiO_2$ : a systematic study of anodization potential at constant oxide thickness

Understanding the photoelectrochemical water oxidation performance ofhighly textured semiconductors requires systematic studies capable of revealing relevantcorrelations among the synthetic methods used, the resulting morphologies, and theirrelationship to activity. Here, we carry out a systematic study on anodized $TiO_{2}$ tounderstand the impact of anodization potential on the transition from a nanoporous to ananoring morphology and its influence on the semiconductor properties and photoassistedwater oxidation. We demonstrate that the applied anodizing potential has a profoundimpact on the material properties, in particular, the morphology of the top layer as well asthe size and shape of nanotubes. The anodized substrates produced at higher potentialspossess superior photoelectrochemical properties, which are ensured by a hierarchicalnanoporous-nanoring morphology, high donor density, and a more positive flat bandpotential. We further confirmed the generation of oxygen at the anodic $TiO_{2}$ under whitelight irradiation through scanning electrochemical microscopy (SECM). This work introduces a methodology to systematicallysynthesize and characterize the features of hybrid semiconductor materials toward materials with improved photoelectrochemicalproperties for renewable energy technologies.