Fe 1Γx Cr x ) 2 O 3 Sulfite a b s t r a c t The hydrogen photo-evolution was successfully achieved in aqueous (Fe 1Γx Cr x ) 2 O 3 suspensions (0 x 1). The solid solution has been prepared by incipient wetness impregnation and characterized by X-ray diffraction, BET, transport properties and photo-electrochemistry. The oxides crystallize in the corundum structure, they exhibit ntype conductivity with activation energy of w0.1 eV and the conduction occurs via adiabatic polaron hops. The characterization of the band edges has been studied by the Mott Schottky plots. The onset potential of the photo-current is w0.2 V cathodic with respect to the flat band potential, implying a small existence of surface states within the gap region. The absorption of visible light promotes electrons into (Fe 1Γx Cr x ) 2 O 3 -CB with a potential (wΓ0.5 V SCE ) sufficient to reduce water into hydrogen. As expected, the quantum yield increases with decreasing the electro affinity through the substitution of iron by the more electropositive chromium which increases the band bending at the interface and favours the charge separation.
The generated photo-voltage was sufficient to promote simultaneously H 2 O reduction and SO 3 2Γ oxidation in the energetically downhill reaction (H 2 O ΓΎ SO 3 2Γ / H 2 ΓΎ SO 4 2Γ , DG ΒΌ Γ17.68 kJ mol Γ1 ). The best activity occurs over Fe 1.2 Cr 0.8 O 3 in SO 3 2Γ (0.1 M) solution with H 2 liberation rate of 21.7 mmol g Γ1 min Γ1 and a quantum yield 0.06% under polychromatic light. Over time, a pronounced deceleration occurs, due to the competitive reduction of the end product S 2 O 6 2Γ .