Atomic clusters typically exhibit distinctive electronic structures and physicochemical properties. However, as the size decreases, their ability to adsorb and dissociate water also diminishes, thereby affecting chemical reactions involving water molecules. Enhancing the adsorption and dissociation capabilities of atomic clusters towards water molecules and elucidating the mechanisms underlying their performance enhancement have become important research directions. Herein, employing the carrier-anchored strategy, Ru-O-Ru atomic clusters were prepared and displayed excellent activity and durability in the hydrogen evolution reaction. Specifically, the Ru-O-Ru atomic clusters exhibited only 86 mV overpotential at 100 mA·cm^-2 and superior membrane-electrode-assembly activity than commercial Ru/C catalyst. Synchrotron radiation-based Fourier transform infrared spectroscopic measurements revealed that the modification of oxygen in Ru-O-Ru units promoted the reorientation of water molecules from a H-up orientation to H-down, therefore, enhanced the formation of strong hydrogen-bond network of interfacial water on the surface of Ru-O-Ru clusters, leading to enhanced adsorption and dissociation of water and accelerated Volmer step. Those findings provide a potential strategy and deep insights for the development of atomic clusters in electrocatalysts.

Single-atom catalysts (SACs) have shown unexpected catalytic activity due to their unique electronic structure and coordination environment. Nonetheless, the synthesis of an atomically precise low-coordination single-atom catalyst remains a grand challenge. Herein, we report a coordinately unsaturated Ni-N₃ single-atom electrocatalyst using a metal-organic framework (MOF) derived N-C support with abundant exposed N for excellent electrochemical CO₂ reduction. The obtained Ni-N₃/NC active site exhibited highly efficient CO₂-to-CO conversion with a Faradaic efficiency of 94.6% at the current density of 100 mA/cm². In situ X-ray absorption spectroscopy (XAS) measurement suggested that the Ni atomic center with unsaturated coordination had the lower initial chemical state and higher charge transfer ability. In situ Fourier transform infrared (FT-IR) and theoretical calculation results revealed that the unsaturated catalytically active center could facilitate activation of CO₂ and thus heighten CO₂ electroreduction activity. These findings provided insights into the rational design of definitive coordination structure of SACs for boosting activity and selectivity.