Electrocatalytic Reduction of Dinitrogen to Ammonia with Water as Proton and Electron Donor Catalyzed by a Combination of a Tri-ironoxotungstate and an Alkali Metal Cation

[Image: see text] The electrification of ammonia synthesis is a key target for its decentralization and lowering impact on atmospheric CO(2) concentrations. The lithium metal electrochemical reduction of nitrogen to ammonia using alcohols as proton/electron donors is an important advance, but requires rather negative potentials, and anhydrous conditions. Organometallic electrocatalysts using redox mediators have also been reported. Water as a proton and electron donor has not been demonstrated in these reactions. Here a N(2) to NH(3) electrocatalytic reduction using an inorganic molecular catalyst, a tri-iron substituted polyoxotungstate, {SiFe(3)W(9)}, is presented. The catalyst requires the presence of Li(+) or Na(+) cations as promoters through their binding to {SiFe(3)W(9)}. Experimental NMR, CV and UV–vis measurements, and MD simulations and DFT calculations show that the alkali metal cation enables the decrease of the redox potential of {SiFe(3)W(9)} allowing the activation of N(2). Controlled potential electrolysis with highly purified (14)N(2) and (15)N(2) ruled out formation of NH(3) from contaminants. Importantly, using Na(+) cations and polyethylene glycol as solvent, the anodic oxidation of water can be used as a proton and electron donor for the formation of NH(3). In an undivided cell electrolyzer under 1 bar N(2), rates of NH(3) formation of 1.15 nmol sec(–1) cm(–2), faradaic efficiencies of ∼25%, 5.1 equiv of NH(3) per equivalent of {SiFe(3)W(9)} in 10 h, and a TOF of 64 s(–1) were obtained. The future development of suitable high surface area cathodes and well solubilized N(2) and the use of H(2)O as the reducing agent are important keys to the future deployment of an electrocatalytic ammonia synthesis.