Electrochemical nitrogen reduction (NRR) is a clean, facile, and sustainable approach towards ammonia (NH 3 ) production at ambient conditions. However, the inert nature of nitrogen and competitive hydrogen evolution reaction (HER) command it towards sluggish kinetics and poor selectivity. Inspired by the metal-sulfur (M-S) linkages in the nitrogenase enzyme, here we show a surface modification strategy to modulate the electronic structure and improve the N 2 availability on the catalytic surface, which suppresses the HER and synergistically improved the rate of NH 3 production. Thus, ruthenium nanocrystals anchored on reduced graphene oxide (Ru/rGO) are modified with different aliphatic thiols to achieve M-S linkages. A high faradaic efficiency (11%) with an improved NH 3 yield (50 µg h -1 mg -1 ) is achieved at -0.1 V vs RHE in acidic conditions by using dodecanethiol. DFT calculations reveal intermediate N 2 adsorption and desorption of the product is achieved by electronic structure modification along with the suppression of the HER by surface modification. The modified catalyst exerts excellent stability and recyclability for NH 3 production, as confirmed by rigorous control experiments including the 15 N isotope labeling experiments.