Halide perovskites have emerged as a class of most promising and cost-effective semiconductor materials for next generation photoluminescent, electroluminescent and photovoltaic devices.

Environmental degradation due to the carbon emissions from burning fossil fuels has triggered the need for sustainable and renewable energy. Hydrogen has the potential to meet the global energy requirement due to its high energy density; moreover, it is also clean burning. Photoelectrochemical (PEC) water splitting is a method that generates hydrogen from water by using solar radiation. Despite the advantages of PEC water splitting, its applications are limited by poor efficiency due to the recombination of charge carriers, high overpotential, and sluggish reaction kinetics. The synergistic effect of using different strategies with cocatalyst decoration is promising to enhance efficiency and stability. Transition metal-based cocatalysts are known to improve PEC efficiency by reducing the barrier to charge transfer. Recent developments in novel cocatalyst design have led to significant advances in the fundamental understanding of improved reaction kinetics and the mechanism of hydrogen evolution. To highlight key important advances in the understanding of surface reactions, this review provides a detailed outline of very recent reports on novel PEC system design engineering with cocatalysts. More importantly, the role of cocatalysts in surface passivation and photovoltage, and photocurrent enhancement are highlighted. Finally, some challenges and potential opportunities for designing efficient cocatalysts are discussed.

A series of NiO/CeO₂ catalysts were prepared by using the combustion method and characterized by using XRD, N₂-physisorption, TEM, UV-visible, Raman, XPS, ICP-OES and H₂-TPR. Typical results indicated the NiO/CeO₂ had a better performance than CeO₂ for CO oxidation and 15 wt% NiO/CeO₂ is active and stable, whereas catalysts with a higher NiO content of 20 and 30 wt% deactivated at 130 °C onwards. The high activity and excellent stability of 15% NiO/CeO₂ catalysts can be ascribed to their high oxygen vacancy, high dispersion of NiO and strong metal–support interaction that leads to synergy between NiO and CeO₂.

Carbon dioxide (CO₂) decomposition has drawn significant interest over the years due to its global warming potential.