Hydrogen evolution under visible light over the heterojunctionp-CuO/n-ZnO prepared by impregnation method

Abstract

The semiconducting properties of the heterojunction CuO/ZnO, synthesized by impregnation method from nitrates, are studied for the first time to assess its feasibility for the hydrogen production under visible light, an issue of energy concern. CuO exhibits a direct optical transition at 1.33 eV, due to Cu2+: 3d orbital splitting in octahedral site, and possesses a chemical stability in the pH range (4–14). The Mott–Schottky plot in (Na2SO4, 0.1 M) medium indicates p-type conduction with a flat band potential of 0.70 VSCE and a holes density of 1.35 × 1017 cm−3. As application, hydrogen evolution upon visible light is demonstrated on the heterojunction ×%CuO/ZnO (x = 5, 10 and 20 wt.%). The best performance occurs at pH ~12 with an evolution rate of 4.8 cm3 min−1 (g catalyst)−1 and a quantum yield of 0.12%. The improved activity is attributed to the potential of the conduction band of CuO (−1.34 VSCE), more negative than that of ZnO, the latter acts as electrons bridge to water molecules. The presence of SO32− reduces the recombination process, thus resulting in more H2 evolution. Copyright © 2015 John Wiley & Sons, Ltd.