Unveiling the competitive behavior by the orientated regulation of S-vacancy over MoS2 for highly effective N2 fixation.

• FL-MoS 2 -20 with V s gradient (16.3%) was prepared by a chemical etching strategy. • The high V s density can effectively boost N 2 adsorption and reduce E b for NRR. • The HER activity shows a "roller-coaster" type with the increased V s density. • Regulating the asynchronous evolution of NRR and HER results in a high selectivity. • FL-MoS 2 -20 rendered a high NH 3 yield rate (92.95 µg h −1 mg −1) and FE (20.80 %). The electrochemical N 2 reduction reaction (NRR) renders great potential for sustainable ammonia generation but still suffers from serious challenges, which limit the effective enhancement of catalytic performances. Herein, we skillfully utilize the asynchronous NRR and hydrogen evolution reaction (HER) activities as a function of S-vacancy (V s) concentrations to enhance the NRR activity but sacrifice the HER activity, thus achieving the tradeoff between activity and selectivity towards the NRR. Inspired by the theoretical guidance, the optimized catalyst (FL-MoS 2 -20) with a suitable V s concentration (16.30 %) renders a high NH 3 yield rate of 92.95 ± 2.10 µg h −1 mg −1 and a Faradic efficiency (FE) of 20.80 ± 0.18 %, exceeding virtually all previously published MoS 2 -based NRR catalysts and the overwhelming majority of state-of-the-art NRR catalysts. This work broadens the potential of vacancy engineering to manage the competitive reaction on a single active site and enlightens the catalyst design in the NRR field and beyond. [ABSTRACT FROM AUTHOR]