Redox cycling of iron/iron oxide has many potential applications for gas-phase reactions and electrochemical devices, including intermediate temperature (550-800°C) iron-air batteries [1,2]. The major limitation to such technologies is the pulverization and sintering of the iron substrate with repeated phase transformation-induced volume changes and consequent mechanical stresses.

By alloying the redox-active Fe, a variety of new behaviors emerge that can be used to extend the lifetime of the material overall. By observing the microstructure of different alloys in the reduced state, the oxidized state, or in between we can better understand how the alloying element influences the microstructure and how microstructural evolution impacts the architecture of the sample as a whole. For instance, we have found that in the presence of a redox-inactive, Fe-soluble metal such as Ni or Co, the reduction reaction is accelerated and pores formed during cycling sinter close much more readily than in the pure Fe foam [3,4,5]. Current work focuses on the influence of different architectures, such as ink-printing or bridging fibers, on the longevity of Fe foams.

Our characterization techniques include metallography, SEM, operando X-ray diffraction, and X-ray computed tomography.