Highly Efficient Visible‐Light‐Induced Photocatalytic Hydrogen Production via Water Splitting using FeCl3‐Based Ionic Liquids as Homogeneous Photocatalysts

Abstract The ionic liquid (IL) 1‐octyl‐3‐methylimidazolium bromide/FeCl 3 [OMIM]Br/FeCl 3 was prepared with three molar ratios of [OMIM]Br/FeCl 3 (0.5 : 1, 1 : 1, and 2 : 1), and fully characterized through 1 H and 13 C NMR, Fourier‐transform IR, and Raman spectroscopic techniques. The optical properties of the prepared [OMIM]Br/FeCl 3 ILs were revealed via diffuse reflectance and photoluminescence spectra. The photocatalytic activity of [OMIM]Br/FeCl 3 ILs as homogenous photocatalysts were investigated towards hydrogen generation from methanol/water mixtures under visible light irradiation. The FeCl 3 ‐based IL with [OMIM]Br/FeCl 3 molar ratio of 1 : 1 exhibited the highest visible light photocatalytic activity with a hydrogen productivity of 243.2 mmol h −1 g −1 and a hydrogen purity of 95.5 %; such a high hydrogen yield and purity was reported for the first time. It was proposed that [OMIM] Br acted as an electron acceptor, which delayed the electron‐hole pair recombination of FeCl 3 . Also, [OMIM] Br could capture the produced carbon dioxide that is released with hydrogen gas. Additionally, [OMIM] Br/FeCl 3 could be reused six times with nearly the same photocatalytic activity. These outstanding credits in terms of hydrogen generation rate and purity plus the economic feasibility, through several cycles of reuse, could certify such an IL as a promising photocatalyst for employment in water splitting. This paper suggests ways forward for research to develop the use of ILs as efficient and effective photocatalysts for hydrogen generation via water splitting.