Enhanced surface electron transfer by fabricating a core/shell Ni@NiO cluster on TiO2 and its role on high efficient hydrogen generation under visible light irradiation

A Ni@NiO core/shell cluster was fabricated on TiO2 surface (Ni@NiO/TiO2) and its roles on surface electron transfer and the enhancement on hydrogen evolution under visible light irradiation were investigated. For a comparison, the Ni/TiO2 and NiO/TiO2 catalysts were fabricated, respectively. By photosensitization using Eosin Y as an antenna molecule, (1.6 wt%)Ni@NiO/TiO2 exhibited the highest activity (364.1 μmol h−1) in comparison with (1.6 wt%)Ni/TiO2 and (1.6 wt%)NiO/TiO2 and the corresponding apparent quantum efficiency reached 28.6% at 460 nm. The photoluminescence spectra and photoelectrochemical characterization results confirmed that the Ni@NiO core/shell structure could promote the photogenerated electrons transferring from TiO2 conduction band to Ni@NiO clusters, resulting in the quicker separation of electron–hole pairs. In addition, part of NiO shell can be reduced into metallic Ni during the photoreaction and vice versa. Cyclic voltammogram characterization verified that the transformation between Ni and NiO was a dynamic balance process, which can not only provide reacting channels for electrons and protons but also ensure the photocatalytic hydrogen evolution proceeding continuously. This study discloses structure-dependent effect of non-noble metal cocatalyst on semiconductor photocatalysts in photocatalytic water reduction, and gives an insight into designing high-efficient non-noble metal/semiconductor hybrid photocatalysts.