Li-mediated NH3 synthesis process suffers from low energy efficiency due to the need for extremely reducing plaUng potenUal of Li (~-3.04 V vs SHE) and, idenUfying an alternaUve mediator is highly desired. Several criteria for a successful mediator of NH3 electrosynthesis have been idenUfied previously including: (i) spontaneous formaUon of a nitride in the presence of N2; (ii) stability of a vacancy in the surface nitride; (iii) rapid acUvaUon of N2 at a surface vacancy of the nitride in the SEI; (iv) facile diffusion of N in the bulk nitride; and (v) solubility of salts of the mediator in nonaqueous electrolyte. Here, we argue that criteria (iv), facile diffusion of N in the bulk nitride, may not be necessary: although a surface nitride must form, only a few layers are necessary to achieve the desired effect given the 'near-sightedness' of metals with respect to distant perturbaUons. Figure below shows a theoreUcal descriptor for criteria (ii), surface nitride vacancy stability, and (iii), facile acUvaUon of N2 at a surface vacancy of the nitride in the SEI. The y-axis of Figure corresponds to the energy required to move a bulk vacancy to the surface (or, equivalently, the energy required to move a surface N to fill a bulk vacancy), i.e., following the approach of Nørskov and Cargnello 28 ,