Hydrogen photoproduction over new catalyst CuLaO2

Excellent quality CuLaO2 has been synthesized through solid reaction in evacuated silica tubes and the delafossite structure was refined in the space group R3¯m. The oxide is thermally stable up to ∼200 °C, above ∼610 °C it converts irreversibly to CuLa2O4. The conduction band (−1.99 Vsce) lies below H2O/H2 level leading to a thermodynamically favorable H2-photoevolution with concomitant oxidation of X2− (=S2− or SO32−). The surface platinization improved the activity by increasing the rate constants of X2− oxidation. The redox kinetic is relatively fast with SO32− whereas the electrochemical system S2−/Pt behaves irreversibly and where the polarization is mainly of activation. The charge carriers move in a narrow conduction band made up primarily of Cu 3d orbitals. The rate determining step is the supply of electrons at the interface because of their low electron mobility. The system is optimized with respect to some physical parameters and the best photoactivity (47 ml g−1 h−1) was obtained with SO32− at pH ∼8. In a closed reactor, the oxidized species namely S2O62− and Sn2− tend to stop the H2 formation because of their competitive reductions with H2O. Moreover, the formation of Sn2− leads to a less transparent electrolyte that permits fewer photons to reach the crystallites.