Solar fuel production by semiconductor photoelectrochemical water splitting entails the convertion of water by solar radiation into a storable clean fuel. Various materials have been investigated for obtaining an efficient and stable photoelectrodes, including silicon, various oxides, and III-V compounds. Oxides are stable in aqueous evironments but suffer from the low efficiency due to their wide bandgaps. Silicon and III-V compundes have bandgaps well-suited to absorbing a large portion of the solar spectrum, but their stability in aqueous electrolyte are very poor. Thus, metal-oxide-semiconductor (MOS) architecture has been proposed for photoelectrochemical solar fuel production.
In a typical MOS photoelectrodes, oxide layer protects the semiconductor substrates from corrosion, while maintains the facile transport of photo-generated carriers from semiconductor to metal catalysts. Here is a trade-off between efficiency and stability. A thin oxide layer would allow facile electron/hole transport but the long-term stability will be problematic. A thick oxide layer provides high stability while the efficiency would be affected. So, in this work, to address this issue, several strategies were investigated to engineering the oxide layer to obtain an efficient photoelectrode with high stability.