First, Ca is electrodeposited on a substrate by dissolving Ca salt in a non-aqueous solvent (Calcium ElectrodeposiUon, Eq. 3) and applying a strongly reducing bias on the cathode. The electrodeposited Ca metal reacts spontaneously with N2 (either dissolved or gaseous in a GDE setup) to form Ca3N2 (Calcium NitridaUon, Eq. 4). Following formaUon of calcium nitride, a sequence of coupled proton-electron transfer steps (Eqs. 5-7) forms ammonia adsorbed to calcium nitride (Calcium Nitride Protolysis). Finally, NH3 desorbs, forming a surface nitrogen vacancy in the calcium nitride (Eq. 8). Given the stability of this surface nitride shown in Figure , we hypothesize that it is filled by N2 dissociaUon (facile at room temperature), thereby compleUng the catalyUc cycle. Ca metal and nitride can also serve as a catalyst for hydrogen evoluUon to form H2, an undesired side reacUon (Calcium Protolysis). We note that this proposed mechanism is slightly different than those appearing in recent works for the analogous Li-mediated NH3 synthesis process , which has been proposed to involve concomitant dissoluUon of Li to form Li + . Although the precise mechanism is sUll poorly understood and likely depends strongly on specific details of the experimental protocal in use (e.g., dynamic potenUal control, electrolyte and salt choice, N2 pressure, and others), we hypothesize here that concomitant dissoluUon cannot occur under the strongly reducing condiUons typically used, as the corrosion sub-reacUon will be endergonic. In this LeYer, we provide a proof of concept for the Ca-mediated NH3 synthesis.