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Atomically dispersed transition metals confined with nitrogen on a carbon support has demonstrated great electrocatalytic performance, but an extremely low concentration of metal atoms (usually below 1.5%) is necessary to avoid aggregation through sintering which limits mass activity. Here, a salt‐template method to fabricate densely populated, monodispersed cobalt atoms on a nitrogen‐doped graphene‐like carbon support is reported, and achieving a dramatically higher site fraction of Co atoms (≈15.3%) in the catalyst and demonstrating excellent electrocatalytic activity for both the oxygen reduction reaction and oxygen evolution reaction. The atomic dispersion and high site fraction of Co provide a large electrochemically active surface area of ≈105.6 m2 g−1, leading to very high mass activity for ORR (≈12.164 A mgCo−1 at 0.8 V vs reversible hydrogen electrode), almost 10.5 times higher than that of the state‐of‐the‐art benchmark Pt/C catalyst (1.156 A mgPt−1 under similar conditions). It also demonstrates an outstanding mass activity for OER (0.278 A mgCo−1). The Zn‐air battery based on this bifunctional catalyst exhibits high energy density of 945 Wh kgZn−1 as well as remarkable stability. In addition, both density functional theory based simulations and experimental measurements suggest that the CoN4 sites on the carbon matrix are the most active sites for the bifunctional oxygen electrocatalytic activity.

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In the recent years, polyoxometalate (POM) encapsulated metal–organic framework (MOF) composites have attracted much attention in photocatalysis. Both POMs and MOFs have been attracting immense attention in this area. Furthermore, in order to promote charge transfer and separation between POMs and MOFs, theoretical and experimental analysis can be applied to match their energy levels; however, their individual applications are hindered by several defects, such as poor visible-light utilization efficiency. The combination of MOFs and POMs can benefit from the virtues of both POMs and MOFs while avoiding the drawbacks of them. Notably, MOFs with high specific surface area and long-range ordered structure ensure a uniform distribution of POMs, which cannot only prevent the self-aggregation of POMs but also allow the exposure of more active sites for catalysis. POM@MOF composites have been identified as promising materials for photocatalysis because of their diverse unique advantages, such as ultrahigh porosity, large specific surface area, and excellent electron redox transformation. In this work, we present an overview of the developments in POM@MOF composite-based catalysts for visible light induced photocatalysis. The strategies employed for the preparation of POM@MOF composites are summarized and discussed with a particular focus on the stability of such materials. The representative works on photocatalytic water splitting, CO2 reduction, degradation of pollutants, and selective oxidation of organics are highlighted. Special attention is paid to the synergistic effects between the MOF and POM that result in an enhanced performance. Besides, the stability and reusability of these materials are also discussed. Also, the unsolved problems and development opportunities of POM@MOF composites in the field of photocatalysis are proposed.

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