Increasing the activity of the nitrogen reduction reaction while slowing the detrimental hydrogen evolution reaction is a key challenge in current electrocatalysis to provide a sustainable route to ammonia. Recently, nanoparticles in ionic liquid (IL) environments have been found to boost the selectivity of electrochemical synthesis of ammonia from dinitrogen at room temperature. Here, we use for the first time a fully atomistic representation of metal–IL interfaces at the density functional theory level to understand experimental evidence, with particular focus on the rate and selectivity determining formation of N2H intermediates compared to hydrogen evolution. We find that decorating the metal surface with fluorinated ILs creates specific H-bond interactions between Ru–N2H and IL anions, stabilizing this intermediate and thus driving the selectivity of the electrochemical process.