Rational design of efficient, sustainable and low-cost hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) bifunctional catalysts within the scope of feasibility is of great significance for realizing rapid output water splitting. Here, we used a simple coprecipitation method to prepare Keggin-type polyoxometalate (POM) nanoscale particles coated with coreshell-type metal-organic framework (MOF) derived Co-NC (Co-NC-POM). Thanks to synergy effect, abundant active sites, unique structure and defects, the as-synthesized Co-NC-POM hybrids exhibit excellent eletrocatalytic performance both for HER and OER. Moreover, it can act as bifunctional electrocatalysts for overall water splitting, exhibiting a low voltage of 1.60 V and an excellently stability up to 24 h at a current density of 10 mA cm À 2 . It shows competitive performance against the same type of advanced bifunctional catalysts currently reported and thus is expected to among the most efficient non-precious metal catalysts to drive the water splitting device.

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In recent years, single-atom catalysts (SACs) have received a significant amount of attention due to their high atomic utilization, low cost, high reaction activity, and selectivity for multiple catalytic reactions. Unfortunately, the high surface free energy of single atoms leads them easily migrated and aggregated. Therefore, support materials play an important role in the preparation and catalytic performance of SACs. Aiming at understanding the relationship between support materials and the catalytic performance of SACs, the support effects in SACs are introduced and reviewed herein. Moreover, special emphasis is placed on exploring the influence of the type and structure of supports on SAC catalytic performance through advanced characterization and theoretical research. Future research directions for support materials are also proposed, providing some insight into the design of SACs with high efficiency and high loading.