Metal oxide nanomaterials for solar hydrogen generation from photoelectrochemical water splitting

This review focuses on recent developments in the study of hydrogen generation from water splitting using photoelectrochemical (PEC) cells based on metal oxide (MO) nanomaterials. The emphasis is on the unique properties of MO nanostructures and their advantages as well as limitations for PEC solar hydrogen generation. While abundant and stable, metal oxide nanomaterials tend to have weak visible light absorption that limits their use for solar energy conversion. In addition, MO nanomaterials tend to exhibit a high density of trap states or defect sites that limit their overall efficiency. Different strategies have been developed to enhance visible light absorption (e.g., doping, dye, or quantum dot sensitization and band structure engineering using composite structures) as well as to enhance transport by reducing the density of trap states via surface modification, improving crystallinity, or using 1D structures. In some cases, combining different strategies has led to strong synergistic effects. Recent studies point to the importance and promise of engineering electronic band structure for improving PEC performance of MO nanostructures for hydrogen generation and other potential applications.