A Highly Efficient Metal-Free Electrocatalyst of F-Doped Porous Carbon toward N₂ Electroreduction.

Abstract

N₂ electroreduction into NH₃ represents an attractive prospect for N₂ utilization. Nevertheless, this process suffers from low Faraday efficiency (FE) and yield rate for NH₃ . In this work, a highly efficient metal-free catalyst is developed by introducing F atoms into a 3D porous carbon framework (F-doped carbon) toward N₂ electroreduction. At -0.2 V versus reversible hydrogen electrode (RHE), the F-doped carbon achieves the highest FE of 54.8% for NH₃ , which is 3.0 times as high as that (18.3%) of pristine carbon frameworks. Notably, at -0.3 V versus RHE, the yield rate of F-doped carbon for NH₃ reaches 197.7 µg_NH3 mg^-1 _cat. h^-1 . Such a value is more than one order of magnitude higher than those of other metal-free electrocatalysts under the near-ambient conditions for NH₃ product to date. Mechanistic studies reveal that the improved performance in N₂ electroreduction for F-doped carbon originates from the enhanced binding strength of N₂ and the facilitated dissociation of N₂ into *N₂ H. F bonding to C atom creates a Lewis acid site due to the different electronegativity between the F and C atoms. As such, the repulsive interaction between the Lewis acid site and proton H suppresses the activity of H₂ evolution reaction, thus enhancing the selectivity of N₂ electroreduction into NH₃ .