Microscopic investigation of hematite (alpha-Fe2O3) photoelectrodes for water splitting

Photoelectrochemical materials promise a green hydrogen generation, and, among them, transition metal oxides attracted interest during the past decades for their potential production efficiency. However, each major candidate is facing issues related to either energetic structure, charge carriers properties or degradation. These properties can be tuned with proper modifications of the deposition processes, but more improvements are essential for sufficient performances. For this thesis, we developed two setups for microscopic investigation of oxides: an in operando Atomic Force Microscope (AFM) system coupled with LED light and an in situ Scanning Photocurrent Microscope (SPCM) based on a focused laser light. Hematite (alpha-Fe2O3), an extensively studied PEC material characterized by limiting charge transport problems, was taken as a test case for the development of the two setups. After them, we used the two developed setups to measure microscopic properties of hematite. Using the AFM, it was possible to measure photelectrochemical strain induced by photoproduced polarons at the semiconductor surface, both in distilled water and in phosphate-buffered saline (PBS). The change in modulated height of hematite surface upon illumination was between 3 and 6 $pm$, compatible with DFT estimations found in literature. Instead, the SPCM setup successfully mapped the photelectrochemical current of hematite electrodes, with a maximal resolution of 3 micrometers. On the other hand, it should be noted that potential oxygen gas production as a byproduct of the PEC current was not detected on the material surface, likely due to the dissolution of oxygen molecules in the liquid. These results give insights about the potential of these techniques for the investigation of photelectrochemical systems.