Polyoxometalate-based materials: Quasi-homogeneous single-atom catalysts with atomic precision structures

Polyoxometalates (POMs) are early transition metal oxide clusters with diverse structures and extensive functions. Due to the excellent redox property and stability, POM clusters can serve as ligands and supports to construct single-atom catalysts (SACs) with atomic precision structures, where the coordination state and loading amount of active sites can be controlled precisely. The metal-substituted POM clusters are also promising candidates as sub-nanometer building blocks, where neoteric morphologies and enhanced catalytic properties have been obtained in these cluster-based assemblies. Moreover, the POM-based single-atom catalysts display advantages of both heterogeneous and homogeneous catalysts, contributed by their excellent solubility and reusability. This perspective involves recent progress of polyoxometalate-based single-atom catalysts, including the synthesis and applications of metal-substituted POM clusters, as well as the cluster-based assemblies as single-atom catalysts. The future research directions and challenges are also expounded, which may provide comprehensive understanding and novel insights to the cluster-based single-atom catalysts.