Nature of the First Electron Transfer in Electrochemical Ammonia Activation in a Nonaqueous Medium

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Decreasing costs of renewable sources of electricity will increase the viability of electrochemical processes in chemical manufacturing. To this end, improved understanding of electrochemical N–H bond activation is essential to develop electrochemical routes for producing nitrogen-containing chemicals. In this work, we investigate electrochemical ammonia activation in acetonitrile, a prototypical nonaqueous solvent for electro-organic syntheses. Nonaqueous environments are desirable for electro-organic syntheses due to large electrochemical stability windows and high solubility for organic products. We find that ammonia oxidation in acetonitrile proceeds through an outer-sphere mechanism involving an initial electron transfer as the rate-determining step, likely producing an ammonia radical cation. Density functional theory calculations explain a low transfer coefficient and suggest possible subsequent reaction steps. Structural factors involved in lowering of the transfer coefficient provide insights that are applicable to a wider range of small-molecule activation chemistries.