Nitrogen chemisorption is a prerequisite for efficient ammonia synthesis under ambient conditions, but promoting this process remains a significant challenge. Here, by loading yttrium clusters onto a single-atom support, an electronic promoting effect is triggered to successfully eliminate the nitrogen chemisorption barrier and achieve highly efficient ammonia synthesis. Density functional theory calculations reveal that yttrium clusters with abundant electron orbitals can provide considerable electrons and greatly promote electron backdonation to the N₂ antibonding orbitals, making the chemisorption process exothermic. Moreover, according to the “hot atom” mechanism, the energy released during exothermic N₂ chemisorption would benefit subsequent N₂ cleavage and hydrogenation, thereby dramatically reducing the energy barrier of the overall process. As expected, the proof-of-concept catalyst achieves a prominent NH₃ yield rate of 48.1 μg·h⁻¹·mg⁻¹ at −0.2 V versus the reversible hydrogen electrode, with a Faradaic efficiency of up to 69.7%. This strategy overcomes one of the most serious obstacles for electrochemical ammonia synthesis, and provides a promising method for the development of catalysts with high catalytic activity and selectivity.