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 µgNH3 mg−1cat. 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 *N2H. 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.

Active Site Engineering in Porous Electrocatalysts

“…Considering Lewis acidity of H + ion (or a proton), Liu et al introduced F atoms into 3D porous carbon framework to generate Lewis acidic sites in the material, via electron modulation, that can repel a proton and limit its binding on the material. [ 106 ] NH 3 temperature‐programmed desorption (NH 3 ‐TPD) proved the presence of a much higher density of Lewis acidic sites in the F‐doped carbon than in the pristine carbon. DFT calculations revealed that F‐containing graphene model possessed a higher energy barrier for H 2 evolution as well as a lower energy barrier for N 2 adsorption and dissociation than the F‐free counterpart.…”

Carbon‐based anode materials for potassium‐ion batteries: From material, mechanism to performance

“…Meanwhile, the electronic structure of the local carbon skeleton would have a significant change in the potassium storage behavior. The F dopants are usually successfully doped into carbon skeleton by direct heat treatment of F‐containing precursors, such as polyvinylidene fluoride (PVDF) and poly‐tetrafluoroethylene (PTFE), or posttreatment of HF etching 71,72 . NH 4 F, through mixing with the carbon sources and further pyrolyzing the mixture under inert atmosphere, was also found to be an effective F dopant 73 …”

Glycerine-based synthesis of a highly efficient Fe2O3 electrocatalyst for N2 fixation

“…6,7 To realize a green and sustainable strategy for N 2 xation, electrochemical reduction of N 2 has recently attracted much attention, being an environmentally friendly route involving mild conditions. [8][9][10] To date, a number of catalysts have been developed for the NRR, including noble metals, [11][12][13] transition metals, 14,15 metalfree materials, [16][17][18] metal-C composite materials [19][20][21] and Au-Fe 3 O 4 . 22 These catalysts have demonstrated potential applications in the NRR with improved FE and NH 3 yield.…”