Symmetry-Breaking p-Block Antimony Single Atoms Trigger N-Bridged Titanium Sites for Electrocatalytic Nitrogen Reduction with High Efficiency

The electrochemical nitrogen reduction reaction (eNRR) under mild conditions emerges as a promising approach to produce ammonia (NH₃) compared to the typical Haber-Bosch process. Herein, we design an asymmetrically coordinated p-block antimony single-atom catalyst immobilized on nitrogen-doped Ti₃C₂T_x (Sb SA/N-Ti₃C₂T_x) for eNRR, which exhibits ultrahigh NH₃ yield (108.3 μg h^-1 mg_cat^-1) and excellent Faradaic efficiency (41.2%) at -0.3 V vs RHE. Complementary in situ spectroscopies with theoretical calculations reveal that the nitrogen-bridged two titanium atoms triggered by an adjacent asymmetrical Sb-N₁C₂ moiety act as the active sites for facilitating the protonation of the rate-determining step from *N₂ to *N₂H and the kinetic conversion of key intermediates during eNRR. Moreover, the introduction of Sb-N₁C₂ promotes the formation of oxygen vacancies to expose more titanium sites. This work presents a strategy for single-atom-decorated ultrathin two-dimensional materials with the aim of simultaneously enhancing NH₃ yield and Faradaic efficiency for electrocatalytic nitrogen reduction.