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

Abstract

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.