Single-Atomic Ruthenium Active Sites on Ti3C2 MXene with Oxygen-Terminated Surface Synchronize Enhanced Activity and Selectivity for Electrocatalytic Nitrogen Reduction to Ammonia.

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) is designed to catalyze the NRR process . The catalyst achieves 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 achieve well dispersion in atomic scale. X-ray photoelectron spectroscopy (XPS) analysis further demonstrates that the O-termination groups are successfully activated. Density functional theory calculations combined with experiments reveal that single Ru sites binding to four oxygen are the main reaction centers that permit the hydrogenation of *NNH 2 to *NHNH 2 in a novel distal/alternating hybrid path with reducing the energy barrier of the potential-limiting step to 0.78 eV from 0.96 eV in distal path alone or 1.18 eV in alternating path alone , thereby significantly promoting the NRR dynamics.