Polyoxometalate photocatalysts: solar-driven activation of small molecules for energy conversion and greenhouse gas valorization.

The efficient transformation of small molecules including CO, HO, CH, and N, critical to energy systems and environmental sustainability is fundamental to addressing global energy challenges and advancing a sustainable future. Key technologies driving this progress include photocatalytic CO reduction reaction (CORR), overall water splitting (OWS), direct selective methane conversion (DSMC), and nitrogen fixation reaction (NFR). The development of advanced photocatalysts is essential to accelerate sluggish reaction kinetics and improve the selectivity. Polyoxometalates (POMs), as a unique class of multi-electron transfer catalysts, have attracted considerable interest due to their tunable geometric and electronic structures, excellent redox properties, reversible electron storage capacity and stability. Their capacity to extend light absorption into the visible spectrum and offer specific active sites significantly enhances their potential for photocatalytic oxidation and reduction reactions. This review summarizes recent progress in utilizing POM-based materials for CORR, OWS, DSMC and NFR. Significant advancements in enhancing photocatalytic selectivity and activity have been achieved by managing charge generation and recombination, engineering band structures and active sites, and optimizing reaction parameters. The advantages, challenges, strategies and outlooks of POM-based materials for improving photocatalytic performance are discussed.