| Solar hydrogen is one ideal energy source to replace fossil fuel, as it is sustainable and environmentally friendly. Solar hydrogen can be generated in a number of ways. Photoelectrochemical (PEC) water splitting is one of the most promising methods for solar-to-chemical energy conversion. In this research project, metal oxide-based photocatalysts, especially hematite (alpha-Fe 2O3) and cupric oxide (CuO), were investigated for use as electrodes in PEC water splitting for solar hydrogen production.;In our research project of hematite-based electrodes, we started with the incorporation of transition metal, particularly titanium (Ti), in hematite thin films to modify the valence and conduction band edges of hematite. We found that Ti impurities improve the electron conductivity of hematite and consequently lead to significantly enhanced photocurrents. We further investigated the Ti and Mg co-alloyed hematite. In this case, Ti is the donor and Mg is the acceptor in hematite. The co-alloying approach enhanced the solubility of Mg and Ti, which led to reduced electron effective mass and therefore increased electron mobility. Also, co-alloying tunes the carrier density and therefore allows the optimization of electrical conductivity. The densities of charged defects were found to be reduced, and therefore carrier recombinations were reduced. As a result, the Ti and Mg co-alloyed hematite thin films exhibited much improved performance in PEC water splitting as compared to pure hematite thin films.;For the study of cupric oxide-based electrodes, we first investigated the possibility of reducing the electrode corrosion of cupric oxide in aqueous solutions by incorporating Ti as an electrode corrosion inhibitor. We found that Ti alloying can enhance the stability of cupric oxide in base solutions at the cost of reducing its crystallinity and optical absorption, and consequently lowering its photon-to-electron conversion efficiency. In order to balance the stability and the generated photocurrent, we developed a two-layer structure in which a thin layer of Cu-Ti-O was deposited on bare CuO thin film as a protective layer. Our experimental results indicated that this two-layer structure has an ideal thickness for the protection layer and is suitable for high-performance and long-term application for PEC water splitting. |
