Nanoclusters for photoelectrochemical water splitting: Bridging the photosensitizer and carrier transporter

Increasing global environmental deterioration is becoming a serious concern, leading to an exponential increase in scientific interest in renewable energy as an alternative to replace fossil fuels. Photoelectrochemical (PEC) water splitting, which directly converts sunlight into hydrogen fuel, offers a promising renewable energy technology. Semiconductors, used as photoelectrodes, provide the most feasible method for converting solar energy into electrical energy and chemical fuels. Unfortunately, most of the common semiconductors used in PEC water splitting have wide bandgaps, which greatly restrict the utilization efficiency of sunlight. To promote the solar-to-hydrogen (STH) efficiency of PEC water splitting, atomically precise clusters with regular crystal structures have been introduced in the PEC systems. In this review, the recent advances in nanoclusters for PEC water splitting, including metal clusters, polyoxometalates, semiconductor clusters, and carbon clusters, are summarized. At last, major challenges and outlook for the development of clusters for PEC water splitting are provided.