Single‐Nickel‐Atom‐Stabilized Positively Charged Sub‐Nanometric Ruthenium Clusters for Efficient Reduction of Low‐Concentration Nitrate to Ammonia

ABSTRACT Sub‐nanometric metal clusters, featuring highly exposed active sites and tunable electronic structures, exhibit exceptional activity toward diverse electrocatalytic reactions. However, their high surface energies often induce detachment or aggregation of clusters, leading to deactivation during prolonged electrolysis. Here, we report a robust strategy for stabilizing Ru clusters by leveraging single‐atomic Ni as an electron bridge through Ru−Ni−N 4 interfacial metal coordination. It is demonstrated that the Ni bridges‐induced strong metal‐support interaction effectively suppresses the detachment and aggregation of Ru clusters, enabling long‐term stability of 500 h at a high current density of 1000 mA cm −2 for the electrochemical nitrate reduction reaction (NO 3 − RR). Furthermore, the electron transfer from Ru clusters to Ni bridges induces the generation of positively charged Ru δ+ sites. Both operando electrochemical spectroscopic characterizations and theoretical calculations reveal that the Ru δ+ sites can provide a favorable local reaction environment with high nitrate enrichment and low water content. Simultaneously, they reduce the energy barrier for the nitrate reduction reaction (NO 3 − RR) while increasing that for the hydrogen evolution reaction (HER). This dual effect significantly enhances the NO 3 − RR while suppressing the HER under low‐concentration nitrate conditions (2000 ppm).