Photocatalytic H₂ Evolution from Water–Methanol System by Anisotropic InFeO₃(ZnO)_m Oxides without Cocatalyst in Visible Light

InFeO3(ZnO)m series of oxides are found to give unprecedented H2 evolution from water-methanol mixtures without using any cocatalysts. This family of compounds has an anisotropically layered structure in which Zn/FeOn polyhedra are sandwiched between InO6 octahedral layers. Local structure characterization by X-ray absorption spectroscopy reveals that Zn coordination changes from pentacoordinated to tetrahedral geometry across the series, whereas Fe geometry remains trigonal bipyramidal in all the compounds. This peculiar structure is conducive for a spatial separation of photogenerated charges reducing recombination losses. Band gap energies calculated from absorption spectra indicate potential visible light activity, and this may be due to the orbital mixing of Fe 3d and O 2p as revealed by pre-edge features of X-ray absorption spectra. Band positions are also advantageously placed for a visible light H2 generation and is indeed found to be the case in methanol-assisted water splitting with standardized hydrogen evolution of ∼19.5 mmol g(-1) h(-1) for all the catalysts.