Non-oxide semiconductors for artificial photosynthesis: Progress on photoelectrochemical water splitting and carbon dioxide reduction

Among various artificial photosynthesis routes, photoelectrochemical (PEC) hydrogen (H2) production via water splitting and hydrocarbon generation via carbon dioxide (CO2) reduction are particularly intriguing for achieving a sustainable society. A simpler and potentially economical device design for PEC cells, as compared with those containing photovoltaic cells, is using semiconductor–liquid junction (SCLJ) based photoelectrodes to assemble a photoanode–photocathode tandem cell. The SCLJs form immediately upon semiconductor films immersing into electrolytes, which are then used to separate photogenerated electron–hole pairs and drive corresponding redox chemistry. To engineering these SCLJ-based photoanode–photocathode tandem PEC devices to achieving considerable solar energy conversion efficiencies, the key step is to identify suitable semiconductor materials, the core component in most solar energy conversion systems. In addition, applying effective strategies to modify these semiconductors are needed, as they cannot simultaneously meet all the requirements of efficient light absorption, charge separation and extraction, surface reaction, and operational stability at the same time. This article provides a review on promising non-oxide semiconductors for PEC conversion of solar energy into chemical fuels. The efforts to increase charge transport and separation, to accelerate the charge transfer kinetics across various interfaces, and to engender long-term durability of these non-oxide photoelectrodes are emphasized. As screening, evaluation and optimization have led to substantial improvement in both PEC performance and operational durability, non-oxide semiconductors will provide new opportunities, in addition to classical metal oxide semiconductors, to realize efficient and cost-effective PEC solar fuel production.