Li+-ion bound crown ether functionalization enables dual promotion of dynamics and thermodynamics for ambient ammonia synthesis

Abstract

Electrosynthesis of ammonia from the reduction of nitrogen is still confronted with the limited supply of gas reactant in dynamics as well as high activation barrier in thermodynamics. Unfortunately, despite tremendous efforts devoted to electrocatalysts themselves, they still fail to tackle the above two challenges simultaneously. Herein, we employ a heterogeneous catalyst adlayer—composed of crown ethers associated with Li⁺ ions—to achieve the dual promotion of dynamics and thermodynamics for ambient ammonia synthesis. Dynamically, the bound Li⁺ ions interact with the strong quadrupole moment of nitrogen, and trigger considerable reactant flux toward the catalyst. Thermodynamically, Li⁺ associated with the oxygen of crown ether achieves a higher density of states at the Fermi level for the catalyst, enabling effortless electron transfer from the catalysts to nitrogen and thus greatly reducing the activation barrier. As expected, the proof-of-concept system achieves an ammonia yield rate of 168.5 μg h⁻¹ mg⁻¹ and a Faradaic efficiency of 75.3% at −0.3 V vs. RHE. This system-level approach opens up pathways for tackling the two key challenges that have limited the field of ammonia synthesis.