Sodium-mediated redox cascade for electrochemical ammonia synthesis

Artificial ammonia synthesis is vital to modern life; however, the Haber-Bosch process, by which most ammonia is synthesized, is capital and carbon intensive. Zero-valent-metal-mediated ammonia synthesis is a promising alternative but requires a metal that is both a strong reductant and forms a stable nitride. Only a small number of metals, like lithium, can satisfy these constraints. Therefore, we developed an electrochemical paradigm enabling the use of different reductants by orthogonalizing the roles of the zero-valent metal between sodium metal and a Ti active site. These components are cheaper than lithium by two orders of magnitude. Using a sodium-naphthalene-titanium cascade, we achieved a rate of 475 nmol cm⁻² s⁻¹ and a Faradaic efficiency of 24% and found that the reaction rate depends primarily on current density.