Hydrogen evolution under visible light over the heterojunction p‐CuO/n‐ZnO prepared by impregnation method

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 V_SCE 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 V_SCE), more negative than that of ZnO, the latter acts as electrons bridge to water molecules. The presence of SO₃^2? reduces the recombination process, thus resulting in more H₂ evolution. Copyright © 2015 John Wiley & Sons, Ltd.