Electrochemical ammonia oxidation with a homogeneous molecular redox mediator

Abstract

Ammonia (NH3) is a promising carbon-free energy carrier due to its high energy density and hydrogen storage capacity. Its utilization in energy systems relies on the ammonia oxidation reaction (AOR), which is critical for direct ammonia fuel cells (DAFCs) and hydrogen production. Herein, we explore a robust and inexpensive ferrocene-based molecular electrochemical mediator, N-pyridylferrocenecarboxamide (Fcpy), for AOR. The Fcpy-mediated AOR exhibits the N2 faradaic efficiency (FE) of 94.7%, along with the concomitant production of H2 (FE = 87.3%). Mechanistic studies reveal the crucial role of H-bonding through the pyridyl moiety of Fcpy in facilitating N–H bond activation. Computational analysis further corroborates the observed reaction pathways, providing deeper insights. This work highlights the potential of molecular catalysts to advance ammonia oxidation and underscores their role in sustainable energy systems.