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

The ionic liquid (IL) 1‐octyl‐3‐methylimidazolium bromide/FeCl3 [OMIM]Br/FeCl3 was prepared with three molar ratios of [OMIM]Br/FeCl3 (0.5 : 1, 1 : 1, and 2 : 1), and fully characterized through 1H and 13C NMR, Fourier‐transform IR, and Raman spectroscopic techniques. The optical properties of the prepared [OMIM]Br/FeCl3 ILs were revealed via diffuse reflectance and photoluminescence spectra. The photocatalytic activity of [OMIM]Br/FeCl3 ILs as homogenous photocatalysts were investigated towards hydrogen generation from methanol/water mixtures under visible light irradiation. The FeCl3‐based IL with [OMIM]Br/FeCl3 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 FeCl3. Also, [OMIM] Br could capture the produced carbon dioxide that is released with hydrogen gas. Additionally, [OMIM] Br/FeCl3 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. IL photocatalyst: The first use of [OMIM]Br/FeCl3 ionic liquid as a visible light homogenous photocatalyst in water splitting is reported, exhibiting a narrow bandgap energy (2.0 eV), achieving a high H2 yield (243.2 mmol h−1g−1), and purity (95 %). In addition, the photocatalyst shows a good recycling performance over six consecutive runs.