Morphological optimized CeO2 and Cu-doped CeO2 nanocrystals for hydrogen production by solar photo-thermochemical water splitting based on surface photoinduced oxygen vacancies

Photo-thermochemical (PTC) reaction produces hydrogen by water splitting through the consumption of surface photoinduced oxygen vacancies (VOs). In this study, CeO2 and Cu-doped-CeO2 were synthesized with typical different morphologies of nanorods and nanospheres and different crystallite sizes. These factors, i.e. microstructure, crystalline size and Cu doping were proven to influence the physical properties and photoresponse performance of CeO2 which affected the generation of surface photoinduced VOs and their reactions of hydrogen production in PTC. Cu-doped CeO2 nanospheres with smaller crystallite size demonstrated the best catalytic activity with the largest H2 yield of 18.4 μmol g-1h−1. The electron paramagnetic resonance and Ultraviolet–visible diffuse reflection spectroscopy analysis showed that the VOs generation of nanospheres was strengthened compared to nanorods when the physical characteristics were similar. The positive correlation between the change in physical properties and yield supports its importance in VOs consumption in the thermochemical process. The smaller crystallite size of the nanospheres exhibited better porous properties and specific surface area, which facilitated thermochemical reaction. The doping significantly reduces the band gap of the sample, enhances the light absorption capacity and significantly increases the H2 yield of CeO2.