Targeted Modulation of Competitive Active Sites toward Nitrogen Fixation via Sulfur Vacancy Engineering Over MoS2

Electrocatalytic nitrogen reduction reaction (NRR) offers an environmentally benign and sustainable alternative for NH3 synthesis. However, developing NRR electrocatalysts with both high activity and selectivity remains a significant challenge. Guided by the density functional theory (DFT) calculations and further verified by the experiment, a modulated MoS2 with well‐controlled S vacancies (MoS2‐Vs) is prepared as an excellent electrocatalyst for NRR, where both the activity and selectivity of NRR mightily rely on the S‐vacancy concentration. The optimized catalyst (MoS2‐7H) in a suitable S‐vacancy concentration (17.5%) is empowered with an excellent NRR activity (NH3 yield rate: 66.74 µg h−1 mg−1 at −0.6 V) and selectivity (Faradic efficiency (FE): 14.68% at −0.5 V). Further mechanistic study reveals that the NRR performance is powerfully concentration‐dependent since its activity is enhanced due to the S‐vacancy‐strengthened N2 adsorption and reduced reaction energy barrier. Simultaneously, its selectivity is synchronously improved by the steadily enhanced NRR activity and inversely suppressed hydrogen evolution reaction through limiting H2 desorption kinetics, which sets it markedly apart from other reported defective MoS2‐based catalysts. By the S‐vacancy gradient modulation, the nitrogen reduction reaction (NRR) selectivity exhibits strong gradient dependent, which can be enhanced through regulating the competitive adsorption and the reaction energy barrier between NRR and hydrogen evolution reaction. As a result, the region from 12.5% to 18.75% S‐vacancy concentration can be identified as the “NRR favor window” that can satisfactorily address the tradeoff between NRR activity and selectivity.