Investigation on Photocorrosion of TiO₂ during The Photoelectrochemical Process by In-Situ ICP-MS Characterization

With the growing environmental deterioration and ever-increasing energy demand, exploring a renewable and clean energy for human development has been regarded as a promising research subject. Hydrogen is one of the most desirable energy carriers because of its abundance, high energy density and only byproduct of water. A breakthrough was made by Fujishima and Honda in 1972, who founded that hydrogen could be generated from water splitting on a TiO₂ photoelectrode under UV light. However, the energy conversion efficiency of TiO₂ semiconductor for photo(electro)catalytic process is relatively low owing to their fast recombination of electron–hole pairs and its large bandgap (3-3.2 eV). Fortunately, various methods are designed to improve the performance of photo(electro)catalyst which is closely associated with its nanostructure.<br/>TiO₂ is considered to be quite stable since its redox potential has been calculated to be more positive/negative relative to the water oxidation/reduction potential, which means that photogenerated charge carriers participate in driving the desired redox potential rather than oxidizing or reducing semiconductor photoelectrodes. Nevertheless, the real photocorrosion (decomposition or degradation) depends on specific kinetic parameters such as illumination intensity, electrolyte property, radiation adsorption, charge transport and mass transport. We use inductively coupled plasma mass spectrometry (ICP-MS) to reveal the dissolution products of TiO₂ photoelectrode during PEC water splitting. It is unveiled that TiO₂ photoanode experiences photocorrosion from its oxidation with photogenerated holes. We demonstrate how the atomic scale structure of TiO₂ correlates with its PEC performance and photocorrosion process to enable a better understanding of the complex structure-activity-stability relationship in photoelectrocatalysis. ICP-MS analysis under solar water splitting conditions reveals the chemical instabilities that are not predicted from thermodynamic considerations of stable solid oxide phases represented by the Pourbaix diagram. Our investigation of photochemical corrosion pathway of TiO₂ thin film proves the competition between water splitting and semiconductor oxidation experimentally.