Chemical and Electrocatalytic Ammonia Oxidation by Ferrocene

Recognizing the potential of ammonia to serve as a carbon-free fuel, we describe an electrocatalytic system for the oxidation of ammonia based on ferrocene (Cp2Fe), an inexpensive, robust catalyst utilizing Earth-abundant iron. Ferrocenium (Cp2Fe+), the 1-electron oxidized form of ferrocene, cleanly oxidizes ammonia to generate nitrogen gas (N2) and protons captured by excess ammonia as NH4+ with electrons reducing ferrocenium to ferrocene. This process occurs under electrocatalytic conditions to generate N2 with sustained current. Simple modification of ferrocene through sulfonation allows for solubility in liquid ammonia to enable electrocatalysis in highly concentrated, energy dense solutions of ammonia. Kinetic and computational analysis provides mechanistic insight into the oxidation of ammonia by ferrocenium.