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

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 ((ZnN)-N-1-C). The (ZnN)-N-1-C nanofibers exhibit an outstanding NRR activity with a high NH3 yield rate of approximate to 16.1 mu g 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. N-15(2) 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-N-4 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-N-4 moieties could significantly lower the energy barrier for this step to accelerate hydrogenation kinetics duing the NRR.

Automated summary

This study reports a novel NRR electrocatalyst with a single Zn(I) site supported on hollow porous N-doped carbon nanofibers, exhibiting outstanding NRR activity in alkaline media for high NH3 yield rate. The atomically dispersed Zn(I) sites are likely the active sites, and the nearby graphitic N site facilitates the NRR process. In-situ measurements and theoretical calculations reveal that the formation of initial *NNH intermediate is the rate-limiting step, and the graphitic N atoms adjacent to Zn-N-4 moieties lower the energy barrier to accelerate hydrogenation kinetics during NRR.