Photoassisted hydrogen production under visible light over NiO/ZnO hetero-system

Visible light driven water reduction is successfully achieved over the novel hetero-system NiO/ZnO. The capacitance measurement (C−2–V) of NiO exhibits a positive slope, characteristic of n type conductivity, from which a flat band potential of −0.80 VSCE and a density of 1.41 × 1018 cm−3 are obtained. The correlation of the energy levels indicates that the photo electrons react with adsorbed H2O molecules via ZnO interfacial mechanism. Two NiO compositions (4% and 10%) onto ZnO support are prepared by the impregnation technique. The electrons generated upon visible light in the conduction band of NiO, anchored uniformly on ZnO, diffuse to the interface for achieving the water reduction. NiO is photoelectrochemically stable by hole consumption reactions involving S2O32- as sacrificial agent. The best performance is obtained in basic media on NiO (4%) with an evolution rate of 435 μmol h−1 (mg catalyst)−1 and a quantum efficiency of 0.3%. The hetero-system has the thermodynamically force to drive the uphill reaction (S2O32-+H2O+2OH-→2SO32-+2H2,ΔGf∘=101.04kJmol-1).

► Visible light driven hydrogen evolution is achieved over the hetero-system NiO/ZnO.
► NiO/ZnO shows a good activity and stability for hydrogen evolution.
► The improved activity is due to adherence of NiO, prepared in situ by impregnation.