Photocatalytic Water Splitting for Hydrogen Production

Photocatalytic water splitting to produce hydrogen is one of the most promising technologies to solve energy and environmental problems and realize the effective conversion and storage of solar energy. And the development of it has attracted more and more attention with the proposed target of peaking carbon dioxide emissions before 2030 and achieving carbon neutrality before 2060. After decades of unremitting efforts, this "Holy Grail" reaction has made many important research progresses. This article will review the basic concepts, activity test methods and precautions, types of photocatalytic reactions and means of measurement for efficiency. The development of photocatalytic materials including inorganic semiconductor including oxide, (oxy)nitride, sulfur oxides, oxyhalide, sulfide and solid solutions, sensitized photocatalytic materials, polymer, metal-organic framework materials, etc. are introduced. The important research progresses from the perspective of basic processes and key scientific issues such as light absorption, photo-generated charge separation and surface catalytic reaction of photocatalytic water splitting to produce hydrogen are summarized. The strategies for improving the charge separation such as construction of heterojunction, and the reduction/oxidation cocatalyst for promoting the surface catalysis are introduced. The research progress of hydrogen production by photocatalytic overall water splitting (OWS) using one-step or two-steps photo-excitation system is also summarized in details. For the one-step system, the different materials and the strategies of realizing OWS are introduced. Moreover, for two-step system, the types of electron transfer medium, the exploration of materials and the inhibition of competing reaction are mainly discussed. Finally, the challenges and potential development directions of photocatalytic water splitting to produce hydrogen are analyzed and prospected. It is hoped that through the brief introduction of this review, young scientific and technical personnel who have just been engaged in this research will have a clear understanding of some basic concepts, operating specifications, research progresses and current status in the field of photocatalytic water splitting.