Single‐Atomic Ruthenium Active Sites on Ti 3 C 2 MXene with Oxygen‐Terminated Surface Synchronize Enhanced Activity and Selectivity for Electrocatalytic Nitrogen Reduction to Ammonia

Abstract Downsizing the catalyst to atom scale offers an effective way to maximize the atom utilization efficiency for electrocatalytic nitrogen reduction reaction (NRR). Herein, single‐atomic ruthenium (Ru) anchored on a chemically activated Ti 3 C 2 with O‐terminated groups (Ti 3 C 2 O) was designed to catalyze the NRR process. The catalyst achieved a superior activity and selectivity with ammonia yield rate of 27.56 μg h −1 mg −1 and faradaic efficiency of 23.3 % at a low potential of −0.20 V versus the reversible hydrogen electrode. According to the atomic resolution images from aberration‐corrected scanning transmission electron microscopy, Ru sites on Ti 3 C 2 O achieved good dispersion on atomic scale. X‐ray photoelectron spectroscopy analysis further demonstrated that the O‐termination groups were successfully activated. Density functional theory calculations combined with experiments revealed that single Ru sites binding to four oxygen were the main reaction centers that permitted the hydrogenation of *NNH 2 to *NHNH 2 in a novel distal/alternating hybrid path while reducing the energy barrier of the potential‐limiting step to 0.78 eV from 0.96 eV in the distal path alone or 1.18 eV in the alternating path alone, thereby significantly promoting the NRR dynamics.