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

Summary 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 Cu 2+ : 3 d orbital splitting in octahedral site, and possesses a chemical stability in the pH range (4–14). The Mott–Schottky plot in (Na 2 SO 4 , 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 × 10 17  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 cm 3  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 SO 3 2− reduces the recombination process, thus resulting in more H 2 evolution. Copyright © 2015 John Wiley & Sons, Ltd.