Over 56.55% Faradaic efficiency of ambient ammonia synthesis enabled by positively shifting the reaction potential

Abstract

Ambient electrochemical N2 reduction is emerging as a highly promising alternative to the Haber–Bosch process but is typically hampered by a high reaction barrier and competing hydrogen evolution, leading to an extremely low Faradaic efficiency. Here, we demonstrate that under ambient conditions, a single-atom catalyst, iron on nitrogen-doped carbon, could positively shift the ammonia synthesis process to an onset potential of 0.193 V, enabling a dramatically enhanced Faradaic efficiency of 56.55%. The only doublet coupling representing 15NH4+ in an isotopic labeling experiment confirms reliable NH3 production data. Molecular dynamics simulations suggest efficient N2 access to the single-atom iron with only a small energy barrier, which benefits preferential N2 adsorption instead of H adsorption via a strong exothermic process, as further confirmed by first-principle calculations. The released energy helps promote the following process and the reaction bottleneck, which is widely considered to be the first hydrogenation step, is successfully overcome.

Recent Advanced Materials for Electrochemical and Photoelectrochemical Synthesis of Ammonia from Dinitrogen: One Step Closer to a Sustainable Energy Future

“…d) NH 3 Faradaic efficiencies and mass‐normalized yield rates at each given potential of N–C. Reproduced with permission . Copyright 2019, Nature Publishing Group.…”

“…In addition to precious metal Ru, Fe SACs have also been developed and explored. In 2019, Wang et al investigated Fe SACs dispersed on N‐doped carbon (Fe SA NC) with an NH 3 yield of 7.48 µg mg −1 h −1 and a desirably high FE of 56.55% at 0 V versus RHE in a 0.1 m KOH solution (Figure c) . The outstanding performance of Fe SA NC was attributed to a combination effect of NRR promotion and HER suppression.…”

Overcoming Chemical Inertness under Ambient Conditions: A Critical View on Recent Developments in Ammonia Synthesis via Electrochemical N2 Reduction by Asking Five Questions

“…For example, Mengfan Wang et al. reported the synthesis of Fe SACs supported on N‐doped carbons as NRR catalysts . Interestingly, the NRR onset potential can be shifted to 0.193 V (Figure a), which effectively inhibits HER and enhances the FE of NH 3 production to 56.55 % as well (Figure b) with 0.1 M KOH as electrolyte.…”

Atomic Modulation, Structural Design, and Systematic Optimization for Efficient Electrochemical Nitrogen Reduction

“…Single atom Ru coordinated by N gave a very high NH 3 yield of 120.9 µg mg −1 h −1 . The single atom Fe–N–C electrocatalyst exhibited a more positive onset potential for NRR as compared to N–C owing to the strong adsorption of dinitrogen (Figure b) . The abundance of sharp edges and corners in the gold nanocages provided more valence‐unsatisfied surface atoms for fast NRR with a high Faradaic efficiency of 30.2% (Figure c) .…”

“…b) Linear sweep voltammograms of Fe SA –N–C and N–C in Ar‐saturated (dashed line) or N 2 ‐saturated (solid line) KOH solution. Reproduced with permission . Copyright 2019, Nature Publishing Group.…”