Towards stable solar water-splitting devices: elucidating the degradation kinetics in metal oxides-based photoelectrochemical devices

Advanced economies, including European Union, have recently adopted or will soon announce hydrogen (H2) strategies targeting the broader goal of 'sector integration'. These strategies present a clear shift in global politics towards a net-zero approach in which H2 will play a major role to help decarbonize hard-to-electrify sectors. At present, however, industrial H2 is mainly produced by steam reforming of methane, which requires substantial hydrocarbon inputs and generates CO2 emissions. Photoelectrochemical (PEC) devices constitute one of the most challenging yet promising H2 production technologies, and can potentially achieve sustainable development of H2 energy in the future. However, until now, the investigation of environmentally friendly PEC systems for H2 production has been mainly focused on improving the solar-to-hydrogen (STH) efficiency while their stability and in particular the causes behind degradation, are less investigated. However, as scientists and engineers, it is important to develop new technologies in which the overall performances are taken into account, to pave the way for their commercial application. In RainDrop I tackle this issue, aiming to investigate the underlying causes of degradations of state-of-the-art metal oxides photoelectrodes and of their passivation layers, using a holistic approach that foresees the use of novel advanced methods based on in-situ and operando techniques. A wide range of spectroscopic and surface probe techniques will be used to develop a deeper understanding of the interplay between kinetics and energetics of the devices, and in particular how the dynamics and degradation processes are reciprocally influenced. Through iterative design the key factors of the degradation mechanisms will be identified and general materials design guidelines will be proposed to improve the stability of MOx-based PEC systems. Ultimately, an optimized MOx-PEC device will be assembled for obtaining a stable solar H2 generation.