We invesUgate other possible mediators, such as Ca, Mg, and Sr, to acUvate N2 and form NH3. Among them, Ca is a candidate material for N2 acUvaUon and electrochemical NH3 synthesis as the standard reducUon potenUal of Ca (-2.87 V vs. SHE) is close to Li (-3.04 V vs. SHE). The formaUon of Ca3N2 is favorable by the reacUon of N2 and Ca as the free energy of the formaUon of Ca3N2 is -4 eV. Also, Ca has excellent N2 absorpUon energy (~-1.8 eV) and a reasonable N2 diffusion barrier (~0.5 eV) on orders similar to Li; hence, Ca-mediated NH3 synthesis is worth invesUgaUng. We hypothesize that Ca-mediated NH3 synthesis occurs in a process analogous to Li-mediated NH3 synthesis, i.e., based on the following reacUon scheme: