Oxygen-vacancy-anchoring NixOy loading towards efficient hydrogen evolution via photo-thermal coupling reaction

Abstract

Oxygen vacancy (VO) is a significant component in defect engineering. The present work reports the anchoring effects of initial VO for further loading modifications and the reducing capacity of photo-induced VO for pure water splitting. Herein, we propose Ni-loaded Cu-doped TiO2 (NCT) materials by successive doping and loading. The continuously added Ni ions should accumulate around the VOs and gradually grow into complete nickel oxide crystals, achieving a higher average valence state of the Ni species. NiO crystals can be detected on a 0.5% NCT sample, while the structure of Ni2O3 has been confirmed with a higher nickel mass ratio. Moreover, the introduction of nickel oxide effectively improves the photochemical and electrochemical performance by the interface charge separation, finally reaching an H2 yield of 30.6 μmol/g-cat on 0.5% NCT for VO-based photo-thermal coupling reaction, which consists of VO generation in photo and VO consumption in thermal environment. In situ infrared spectroscopy further indicated that the presence of high valence state nickel oxide hindered the H2 formation but effectively promoted the conventional oxidizing reaction, with an H2 yield of 20.6 mmol/g-cat in a methanol–water reaction on the 2.0% NCT material. In summary, VO controls the morphological structure of Ni loading and produces diverse effects for reactions with dissimilar mechanisms, which provides a novel way to design modifications for promoting various chemical reactions.