Effects of pore morphology on the cyclical oxidation/reduction of iron foams created via camphene-based freeze casting

Abstract

Solid-oxide iron-air batteries have potential for applications in large-scale energy storage systems, but their storage materials, iron and iron oxides, have limited cycle life due to powder sintering and choking of gas flow. To address this issue, Fe foams are synthesized with either equiaxed or directional dendritic pore structures by camphene-based freeze casting of Fe2O3 powders, followed by H2 reduction to Fe and sintering. For each pore architecture, Fe foams are created with three different initial porosities, ranging from 47 to 63 vol %, and are then cycled at 800 °C under alternating oxidation (via H2O) and reduction (via H2) conditions. The redox-cycled foams are examined by optical microscopy, scanning electron microscopy, and synchrotron X-ray tomography to assess the evolution of their porosity driven by the redox volume changes, sintering, and micropore formation via the Kirkendall effect. After 5 redox cycles, the Fe foams have lost the majority (39 ± 2 vol %) of their initial porosity.