Modulating the Leverage Relationship in Nitrogen Fixation Through Hydrogen-Bond-Regulated Proton Transfer

Abstract

In the electrochemical nitrogen reduction reaction (NRR), a leverage relationship exists between NH<inf>3</inf>-producing activity and selectivity because of the competing hydrogen evolution reaction (HER), which means that high activity with strong protons adsorption causes low product selectivity. Herein, we design a novel metal-organic hydrogen bonding framework (MOHBF) material to modulate this leverage relationship by a hydrogen-bond-regulated proton transfer pathway. The MOHBF material was composited with reduced graphene oxide (rGO) to form a Ni-N<inf>2</inf>O<inf>2</inf> molecular catalyst (Ni-N<inf>2</inf>O<inf>2</inf>/rGO). The unique structure of O atoms in Ni-O-C and N-O-H could form hydrogen bonds with H<inf>2</inf>O molecules to interfere with protons being directly adsorbed onto Ni active sites, thus regulating the proton transfer mechanism and slowing the HER kinetics, thereby modulating the leverage relationship. Moreover, this catalyst has abundant Ni-single-atom sites enriched with Ni-N/O coordination, conducive to the adsorption and activation of N<inf>2</inf>. The Ni-N<inf>2</inf>O<inf>2</inf>/rGO exhibits simultaneously enhanced activity and selectivity of NH<inf>3</inf> production with a maximum NH<inf>3</inf> yield rate of 209.7 μg h⁻¹ mg<inf>cat.</inf>⁻¹ and a Faradaic efficiency of 45.7 %, outperforming other reported single-atom NRR catalysts.