Modulation of Cu Electronic Structure to Accelerate the Conversion of Key Intermediates for Electrocatalytic Ammonia Synthesis

Electrochemical nitrate reduction (NO3RR) is primarily hampered by high energy barriers associated with the rate-determining step (RDS), which involves the conversion of *NO3 to *NO2, and the selectivity-determining step (SDS) from *NO to *NHO. Herein, we exhibit a molecular catalyst, Cu(I)-phen-SCN, where the S of the SCN ligand has the highest polarizability and lowest electronegativity compared to C or N. The optimized electronic structure of the catalyst effectively reduces the energy barrier of RDS and SDS simultaneously. In situ impedance and infrared spectroscopy revealed that Cu(I)-phen-SCN exhibits the fastest early reaction kinetics, deeply reducing *NO3 to generate *NO intermediates at an extremely low potential (+0.2 V vs RHE). As a result, the resulting catalyst can achieve ammonia synthesis with Faradaic efficiency and N-selectivity close to ∼100% and ammonia yields as high as 241.20 ± 10.82 mg h–1 mgcat–1. In situ X-ray absorption spectroscopy (XAS) and attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) measurements have shown that Cu(I)-phen-SCN is maintained in a dynamically stable state throughout the electrochemical processes, exhibiting excellent catalytic durability. This work proposes a new method to lower the energy barrier in nitrate-based ammonia synthesis reactions, providing an effective strategy to improve the efficiency of ammonia synthesis.