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 (NH 3 ) compared to the typical Haber-Bosch process. Herein, we design an asymmetrically coordinated p -block antimony single-atom catalyst immobilized on nitrogen-doped Ti 3 C 2 T x (Sb SA/N-Ti 3 C 2 T x ) for eNRR, which exhibits ultrahigh NH 3 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-N 1 C 2 moiety act as the active sites for facilitating the protonation of the rate-determining step from *N 2 to *N 2 H and the kinetic conversion of key intermediates during eNRR. Moreover, the introduction of Sb-N 1 C 2 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 NH 3 yield and Faradaic efficiency for electrocatalytic nitrogen reduction.