Freeze-Cast Manufacturing of Stable Iron-Alloy Foams for Energy Conversion and Storage

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Freeze casting is a low-cost manufacturing technique for creating porous materials or foams. This award investigates freeze casting as a means to make iron-nickel, iron-cobalt, and iron-copper foams that help power batteries for storing energy on the electricity grid, or improve chemical looping technologies for capturing carbon dioxide emissions from power plants. By advancing the materials manufacturing for these applications, this project contributes to national energy security, climate action goals, and U.S. competitiveness in the advanced energy materials sector. The knowledge developed in freeze casting of porous materials also benefits other industrial sectors such as healthcare, via porous bone-replacement implants, and automotive and aerospace, via lightweight structures. One current limitation to using freeze-cast energy materials is that they degrade during use. To address this problem, this research investigates methods, such as adding an alloying element, to stabilize freeze-cast iron foams and increase their usable lifetime. The relationships between manufacturing parameters and materials performance lay the groundwork for optimization and commercialization of such freeze-cast alloys. This project actively promotes participation of women and underrepresented minorities in research and continues building interdisciplinary and international collaborations.In energy applications, such as high-temperature solid-oxide batteries or chemical looping combustion, iron-based redox materials rapidly degrade due to the repeated molar volume changes associated with oxidation/reduction reactions. The pore architecture of freeze-cast, lamellar foams is ideally suited to address this issue, as it provides space for each lamella to expand and contract freely, without constraints from neighboring lamellae. Nevertheless, mechanical degradation still occurs due to Kirkendall micropore formation from imbalanced diffusion fluxes and fracture/spallation of the oxide phase. Alloying iron foams with nickel, cobalt, or copper is investigated as a strategy to suppress the above degradation processes, by creating Ni-, Co- or Cu-rich ductile cores within the lamellae, and by making diffusional fluxes more balanced. In-situ synchrotron X-ray diffraction and nano-tomography are used to reveal the phase and microstructural evolution in these alloys during redox cycling. These in-situ studies are complemented by thermogravimetry, ex-situ redox cycling, and metallography studies. Lastly, CALPHAD, phase-field, and finite-element models are developed to help guide alloy and composition selection, with validation provided by experiment.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.