Processing of Advanced Foam Scaffolds for Iron-Air Battery Applications

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The generation, storage, and local use of hydrogen to generate electric power via fuel cells are critical to reaching an electrical grid with low-to-zero carbon dioxide emissions, benefiting the U.S. economy and worldwide society. In recent years, iron oxide powder has attracted attention as an inexpensive, non-toxic option to store and create pure hydrogen through the iron-oxide reduction/oxidation ("redox") reaction. One of the main problems associated with this cyclical redox reaction is powder pulverization and subsequent agglomeration and consolidation. These effects drastically reduce the high surface areas needed for the reaction. Thus, maintaining stability, high surface area and high gas permeability in the powder bed after multiple redox cycles are the main challenges for this promising technology. This award supports research to develop a structure that takes advantage of novel processing approaches to create iron scaffolds which can maintain structural integrity, high permeability and high surface area during the redox cycles, thus enabling a novel, inexpensive and non-toxic iron-air battery for large scale use.In this research program, the investigators will directionally freeze an aqueous suspension of iron oxide nanopowders to create ice dendrites, which will push the particles into interdendritic space, thus creating a network of iron oxide powders walls. After hydrogen reduction, this network is sintered into a continuous scaffold with directionally aligned channels templating the original ice dendrites, surrounded by iron walls with high surface area and enough internal free space to achieve the microstructural stability needed to withstand multiple reduction/oxidation cycles without sintering or pulverization. The scaffold stability will be further improved by adding various materials to the iron oxide nanopowder suspension: (i) nickel oxide powders which are co-reduced to form iron-nickel solid solution walls with higher strength; (ii) space-holder powders such as strontium fluoride, which can be evaporated from the scaffold walls to generate further porosity within the walls and increase their surface area and the free volume to accommodate volume changes and (iii) inert reinforcements such as ceramic particles, which will strengthen and stiffen the scaffold walls. Mechanical testing will be used to examine relative structural degradation of samples after reduction/oxidation cycles, and x-ray tomography and finite element modeling will be used to map and examine 3-dimensional scaffold structure and stress distribution within its walls during the volumetric changes associated with the redox cycles.