Enzyme-Inspired Molecular Design Unlocks Efficient and Selective Ammonia Electrosynthesis From Nitrate in Water

Ammonia is a vital feedstock and emerging carbon-free energy carrier, yet its industrial synthesis via Haber-Bosch process remains highly energy- and carbon-intensive. Electrochemical nitrate reduction (eNO₃RR) offers a sustainable alternative; however, achieving high selectivity via this pathway necessitates efficient proton management at the catalytic site. Here, we report a family of cobaloxime complexes (C1-C14) incorporating diverse outer coordination sphere (OCS) functionalities that act as enzyme-inspired proton relays. These electrocatalysts enable complete 8e^-/10H⁺ conversion of nitrate ( ${\mathrm{NO}}_3^{-}$ ) exclusively to ammonium ( ${\mathrm{NH}}_4^{+}$ ) under near-neutral aqueous conditions, with the adenosine-functionalized derivative (C13) achieving a rate of 22.5 mmol.cm^-2.hr^-1. mmol_cat ^{- 1} with ∼83% Faradaic efficiency. Mechanistic studies combining in situ Raman spectroscopy, isotopic labelling, 2D NMR, and buffer-dependent kinetics reveal a stepwise nitrate-to-ammonia conversion via metal-bound intermediates, directed by cooperative intra- and intermolecular proton relays. The catalysts operate homogeneously, without electrode deposition or molecular structure decomposition, during eNO₃RR. These results establish OCS engineering as a powerful strategy for functionally mimicking enzymatic architectures in selective ammonia electrosynthesis via a sustainable eNO₃RR pathway.