Characterization of new heterosystem CuFeO2/SnO2 application to visible-light induced hydrogen evolution

Photo-assisted H-2 evolution has been realized over the new heterosystem CuFeO2/SnO2 without any noble metal and was studied in connection with some physical parameters. The delafossite CuFeO2 has been prepared by thermal decomposition from various salts. The polarity of generated voltage is positive indicating that the materials exhibit p-type conductivity whereas the electroneutrality is achieved by oxygen insertion. The plot of the logarithm (conductivity) vs. T (1) gives average activation energy of 0.12 eV. CuFeO2 is a narrow band gap semiconductor with an optical gap of 1.32 eV. The oxide was characterized photoelectrochemically; its conduction band (-1.09 V-RHE) is located below that of SnO2 (-0.86 V-RHE) at pH similar to 13.5 itself more negative than the H2O/H-2 level leading to a thermodynamically favorable H-2 evolution under visible irradiation. The sensitizer CuFeO2, working as an electron pump, is stable towards photocorrosion by hole consumption reactions involving the reducing agents X2- (=S2O32 and SO32-). The photoactivity was dependent the precursor and the best performance (0.026 ml h (1) mg(-1)) was obtained in S2O32- (pH similar to 13.5) over CuFeO2 synthesized from nitrate with a mass ratio (CuFeO2/SnO2) equal to unity. A quantum yield of 0.5% was obtained under polychromatic light. H-2 liberation S2O32- occurs concomitantly with the oxidation of S2O32- to dithionate and sulfate. The tendency towards saturation, in a closed system, is mainly ascribed to the competitive reduction of the end product S2O62-. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.