Advanced CeO2-Based Heterojunctions: Aspects of Structure–Function Relationships for Sustainable CO2 Conversion and H2 Production

The rising global energy demand and climate crisis have intensified the need for sustainable technologies to mitigate carbon emissions while enabling renewable energy conversion. Photocatalysis, particularly using solar energy, has emerged as a promising green solution for hydrogen production and CO2 reduction. Among various semiconductor photocatalysts, cerium oxide (CeO2) has garnered considerable interest due to its favourable properties, including strong redox capability, high oxygen storage capacity, chemical stability, and earth abundance. However, intrinsic drawbacks such as a wide band gap, limited visible-light absorption, and rapid charge recombination restrict its standalone performance. This review comprehensively examines recent advancements in CeO2-based photocatalysts, focusing on structural modifications and the formation of heterojunctions, including S-scheme, Type II, and Z-scheme architectures, that enhance charge separation and retain redox potential. Fabrication strategies are broadly classified into bottom-up and top-down methodologies, with particular emphasis on techniques such as sol–gel, hydrothermal, and co-precipitation methods, which are comprehensively discussed for their effectiveness in optimizing morphology and surface activity. Furthermore, the integration of CeO2 with advanced materials (e.g. g-C3N4, Ti3C2, Metal–organic frameworks (MOFs)) and defect engineering approaches is highlighted for improving photocatalytic efficiency under solar irradiation. Promising applications in photocatalytic reduction of CO2 to value-added chemicals and solar-driven catalytic hydrogen evolution are explored. The review also outlines current challenges, such as poor selectivity, low photostability, and scalability, and provides future perspectives on rational design, real-world testing, and eco-friendly fabrication routes to accelerate the deployment of CeO2-based photocatalytic systems.