Atomically Dispersed Zinc(I) Active Sites to Accelerate Nitrogen Reduction Kinetics for Ammonia Electrosynthesis

Abstract

Developing highly active and stable nitrogen reduction reaction (NRR) catalysts for NH₃ electrosynthesis remains challenging. Herein, an unusual NRR electrocatalyst is reported with a single Zn(I) site supported on hollow porous N-doped carbon nanofibers (Zn¹ N-C). The Zn¹ N-C nanofibers exhibit an outstanding NRR activity with a high NH₃ yield rate of ≈16.1 µg NH₃ h^-1 mg_cat ^-1 at -0.3 V and Faradaic efficiency (FE) of 11.8% in alkaline media, surpassing other previously reported carbon-based NRR electrocatalysts with transition metals atomically dispersed and nitrogen coordinated (TM-N_x ) sites. ¹⁵ N₂ isotope labeling experiments confirm that the feeding nitrogen gas is the only nitrogen source in the production of NH₃ . Structural characterization reveals that atomically dispersed Zn(I) sites with Zn-N₄ moieties are likely the active sites, and the nearby graphitic N site synergistically facilitates the NRR process. In situ attenuated total reflectance-Fourier transform infrared measurement and theoretical calculation elucidate that the formation of initial *NNH intermediate is the rate-limiting step during the NH₃ production. The graphitic N atoms adjacent to the tetracoordinate Zn-N₄ moieties could significantly lower the energy barrier for this step to accelerate hydrogenation kinetics duing the NRR.