What Metals Should Be Used to Mediate Electrosynthesis of Ammonia From Nitrogen and Hydrogen?

Recently, metal-mediated electrochemical conversion of nitrogen and hydrogen to ammonia (M-eNRR) has been attracting intense research attention as a promising route for ammonia synthesis under ambient conditions, offering the prospect of a sustainable, energy-efficient and environmentally friendly pathway for ammonia production. However, what metals should be used to mediate M-eNRR remains unanswered. This work provides an extensive comparison of the energy consumption in the classical Haber Bosch (H-B) process and the M-eNRRs. The results indicate that, when employing lithium and calcium, metals popularly used to mediate the M-eNRRs, the energy consumption is more than 10 times that of the H-B process even assuming a 100% Faradaic efficiency and zero overpotentials. A further analysis of other metals in the periodic table reveals that only some heavy metals, including In, Tl, Co, Ni, Ga, Mo, Sn, Pb, Fe, W, Ge, Re, Bi, Cu, Po, Tc, Ru, Rh, Ag, Hg, Pd, Ir, Pt and Au, can potentially con-sume less energy than that of the H-B process. This work should provide insights for future development of M-eNRR that may have the opportunity to replace the H-B process on a large scale.