Characterization of Aqueous Iron Anode Passivation

Metallic iron is an attractive anode material for aqueous batteries due to its mild voltage, low cost, and non-toxicity. However, cycling-induced passivation precludes it from being widely used, especially when cycled beyond Fe (II). Oxidation to Fe (III) leads to irreversible formation of resistive phases, yet the mechanism by which these phases form is poorly understood. In this talk, the evolution of the phase and morphology of this passivation layer is investigated. Iron oxides in the passivation layer are characterized by Raman spectroscopy and conductive AFM, while morphology evolution is studied by SEM and in-situ electrochemical AFM.<br/>Uniquely, this work combines in situ characterization with iron thin films, allowing the growth of oxide phases to be deconvoluted from particle morphology. This enables characterization of individual particles and gives enhanced understanding of their growth mechanisms. Understanding the phase transformations of iron oxides in aqueous batteries provides insights into the Fe (II)/(III) conversion and will aid the engineering of iron anodes to achieve increased capacity and cyclability.