Hydrogen Evolution by Molecular Photocatalysis

• Published in: Springer Handbook of Inorganic Photochemistry pp. 1381 - 1395
• Main Authors: Fukuzumi, Shunichi, Lee, Yong-Min, Nam, Wonwoo
• Format: Book Chapter
• Language: English
• Published: Cham Springer International Publishing 2022
• Series: Springer Handbooks
• Subjects: Electron transfer; Hydrogen evolution; Metal-hydride complex; Photocatalysis; Reaction mechanism
• ISBN: 3030637123; 9783030637125
• ISSN: 2522-8692; 2522-8706
• DOI: 10.1007/978-3-030-63713-2_46

This chapter focuses on photocatalytic mechanisms of hydrogen (H2) evolution to clarify how photons are converted to two electrons that are required for H2 production from two protons. A two-electron-reduced metal complex is produced via disproportionation of the one-electron-reduced species of a metal complex produced via photoinduced electron transfer, leading to H2 evolution. A one-photon two-electron process is made possible in photocatalytic H2 evolution by combination of thermal and photoinduced electron transfer. Photoexcitation of 9-mesityl-10-methylacridinium ion (Acr+–Mes) with NADH that is a hydride (two-electrons and a proton) donor resulted in the reduction of two equivalents of Acr+–Mes to produce two equivalents of Acr•-Mes that reduce protons to produce H2 in the presence of an H2 evolution catalyst. Acr+-Mes can also be applied to photocatalytic generation of H2, accompanied by dehydrogenative oxygenation of an alkene and selective C(sp2)-H amination of arenes. A one-photon two-electron process is also made possible by a bimolecular reaction of the excited state of a metal-hydride complex with the ground state complex to produce H2.