Efficient Photogeneration of Hydrogen Boosted by Long-Lived Dye-Modified Ir(III) Photosensitizers and Polyoxometalate Catalyst

Abstract

Developing efficient catalysts and photosensitizers is crucial for the construction of effective photocatalytic H2-evolving systems. Here, we report the facile preparation of Coumarin-modified Ir(III) complexes (PS-2 and PS-3) and their utilization as chromophores to drive favorable photocatalytic H2 evolution using Ni-substituted polyoxometalate (Ni3PW10) catalyst and triethanolamine (TEOA) as an electron donor. Compared with the commercially available unmodified Ir(III) complex (PS-1), both PS-2 and PS-3 displayed intensive absorption in the range of 400-550 nm with ϵmax of 110,620 and 91,430 M-1 cm-1, respectively. Varying the substitutes on the bipyridine ligand affected their physicochemical properties and the corresponding photocatalytic activity dramatically. Under photocatalytic conditions, the quantity of H2 molecules generated by PS-2- and PS-3-containing systems were 13.1 and 2.1 times, respectively, that of the PS-1-containing system. When PS-2 was used as a photosensitizer, the highest turnover number (TON) of 19,739 was obtained versus Ni3PW10 catalyst. Various spectroscopic and computational studies have revealed that factors such as strong and broad visible-light-absorbing ability, long-lived triplet state, suitable redox potential, opposed by using polyoxometalate (POM) catalyst, and large highest occupied molecular orbital (HOMO)- lowest unoccupied molecular orbital (LUMO) gap of PS-2 attributed to drastically enhanced photocatalytic activity.