Abstract
In this study, we report the successful synthesis of solid solution (SS) cerium bismuth oxide (CBO) photocatalysts via a facile combustion method using urea as starting materials at different calcination temperatures (300–900°C). The prepared CBO exhibited a nanocrystalline fluorite structure with a direct band gap of 3.02 eV, enabling efficient visible light driven photocatalytic water splitting. Under natural solar irradiation, the optimized CBO achieved excellent H2 and O2 evolution rates of 776.3 μmol g-1 and 388.2 μmol g-1 respectively. A high hydrogen evolution rate of 766.3 μ mol g-1 was also obtained under artificial sunlight using methanol as a sacrificial agent. Detailed characterization confirmed the partial conversion of Ce4+ to Ce3+ species and the formation of oxygen vacancies through electron hopping within the solid-solution matrix. These oxygen defects significantly enhance charge separation, carrier migration and surface reaction kinetics. The optimized defect concentration improves electronic structure, charge transport, and photocatalytic active sites. The superior hydrogen generation performance is attributed to the combined effects of high crystallinity, porous architecture, defect-rich surface, suitable band alignment, and efficient charge transfer pathways. This study provides valuable insights into the role of oxygen vacancy engineering in solid solution (SS) photocatalysts for sustainable solar hydrogen production.