Recent Progress on Photoelectrochemical Valorizations: A Review of Reactions, Catalyst Design, and Future Prospects

Photoelectrochemical (PEC) cells have been considered a promising technology for converting solar energy into chemical energy. However, the solar-to-hydrogen (STH) conversion efficiency and cost-effectiveness of PEC water splitting are significantly limited by the sluggish oxygen evolution reaction (OER) kinetics and the poor economic of the produced oxygen gas, hindering the practical commercialization of PEC energy conversions. In recent years, PEC valorizations including alternative OER and HER reactions have attracted considerable attention. PEC valorizations not only improve STH efficiency but also enhances the overall economic benefits of PEC conversions. Thereby, this review briefly summarizes the basic mechanisms several typical types of PEC value-added reactions, including nitrogen reduction, nitrogen oxide reduction, ammonia oxidation, urea oxidation, and alcohol oxidation reactions. Subsequently, the design and optimization strategies of photoelectrode materials applied to these PEC value-added reactions are specifically analyzed. Finally, the current development, future prospects, and challenges toward commercial-scale applications are discussed.