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

Abstract

Ambient electrochemical N-2 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 (NH4+)-N-15 in an isotopic labeling experiment confirms reliable NH3 production data. Molecular dynamics simulations suggest efficient N-2 access to the single-atom iron with only a small energy barrier, which benefits preferential N-2 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.