Electron distribution tuning of fluorine-doped carbon for ammonia electrosynthesis

Abstract

The electrochemical N₂ reduction reaction (N₂RR), as a key reaction to realize the electrosynthesis of ammonia under ambient conditions, is significantly inhibited by the low efficiency of electrocatalysts. In this study, we report the improvement of the N₂RR efficiency using a nonmetal, fluorine-doped carbon. The fluorine doping enables the tuning of the electron distribution of carbon, which provides positively charged carbon sites that are prone to adsorb N₂ than H⁺ under acidic aqueous conditions. Density-functional theory calculations indicate that the N₂ molecule is adsorbed on the two contrapuntal carbon atoms in the form of a side-on pattern, and the pathway of N₂ turning to NH₃ has the lowest energy barrier. The fluorine-doped carbon exhibits better N₂RR performance than the undoped carbon, with a peak ammonia production rate (6.9 μg h⁻¹ cm⁻²) and a corresponding high faradaic efficiency (12.1%) at −0.55 V versus the reversible hydrogen electrode (RHE). Our work shows the attractive features of developing doped carbon materials as nonmetal N₂RR electrocatalysts.