Building of sub-monolayer MoS2-x structure to circumvent the scaling relations in N2-to-NH3 electrocatalysis

• A peculiar sub-monolayer MoS 2-x structure was synthesized. • The unique sub-monolayer MoS 2-x leads to excellent electrochemical NRR performance. • The compressive strain effects were described by AC-STEM and computational simulations. • The circumvention of the scaling relations contributes to the ultralow overpotential. Finding catalysts and mechanisms for efficient electroreduction of N 2 into NH 3 remains of great challenge, due to the limitation of the scaling relations and competing HER. Here we report that N 2 can be dissociated and dynamically hydrogenized on a peculiar sub-monolayer MoS 2-x structure. Different with conventional surface-binding paradigms of the reaction intermediates, such a dynamic surface-binding paradigm can selectively stabilize the nitrogen intermediates and enable the circumvention of the inherent scaling relations in electrocatalysis of N 2 to NH 3 . Atomic resolution AC-STEM and DFT calculations confirm the atomic arrangement and a ∼3% compressive strain in the large area of in-plane S-vacancies of sub-monolayer MoS 2-x structure. Further experimental and theoretical results demonstrate that the as-designed surface tune their catalytic properties through adjusting their surface-binding to nitrogen intermediates with tunable nitrogen affinity, leading to outstanding electrocatalytic NRR performance at ultra-low overpotential (−0.2 V. vs . RHE).