Recent progress on photocatalytic and photoelectrochemical water splitting under visible light irradiation

Photocatalytic and photoelectrochemical (PEC) water splitting using semiconductor materials has attracted considerable interest due to its potential to cleanly produce H₂ from water by utilizing abundant solar light. Since Fujishima and Honda used a TiO₂ photoanode in 1972 to split water, researchers have been attempting to develop water-splitting systems that can efficiently use visible light (which accounts for almost half of the solar spectrum on the Earth's surface) in order to realize efficient conversion of solar light. In this report, we review recent progress in this field by focusing on strategies that utilize visible light. Such strategies include two-step photoexcitation systems that were inspired by photosynthesis in nature, band engineering for producing novel photocatalysts that have both a high visible light absorption and suitable energy levels for water splitting, the development of new cocatalysts for efficient H₂ or O₂ production, fabrication of efficient photoelectrodes based on visible-light-responsive semiconductors, and the construction of tandem-type PEC water-splitting systems.