Processing of Advanced Foam Scaffolds for Iron-Air Battery Applications

通过燃料电池生产、储存和就地使用氢气发电，对于实现二氧化碳排放量低至零的电网至关重要，从而造福美国经济和全球社会。近年来，氧化铁粉末作为一种廉价、无毒的选择，通过氧化铁还原/氧化反应储存和产生纯氢，引起了人们的关注。与这种循环氧化还原反应相关的主要问题之一是粉末粉化以及随后的团聚和固结。这些效应极大地减少了反应所需的高表面积。因此，在多次氧化还原循环后，保持粉末床层的稳定性、高比表面积和高气体渗透性是这项前景广阔的技术面临的主要挑战。该奖项支持研究开发一种结构，该结构利用新的加工方法来创建铁支架，该支架可以在氧化还原循环中保持结构完整性、高渗透性和高比表面积，从而使新型、廉价和无毒的铁空气电池能够大规模使用。在这项研究计划中，研究人员将定向冻结纳米氧化铁粉末的水悬浮液，以产生冰枝状结晶，从而将颗粒推入树枝间空间，从而形成氧化铁粉末壁的网络。氢还原后，这个网络被烧结成具有定向排列的通道的连续支架，模板是原始冰枝晶，由具有高比表面积和足够的内部自由空间的铁壁包围，以实现所需的微观结构稳定性，以承受多次还原/氧化循环，而不需要烧结或粉化。通过在纳米氧化铁悬浮液中添加各种材料，支架的稳定性将进一步提高：(I)氧化镍粉末，它们被共还原以形成强度更高的铁镍固溶体壁；(Ii)可从支架壁蒸发的空间持有者粉末，如氟化锶，它们可以在支架壁内产生进一步的孔洞，增加其表面积和自由体积，以适应体积变化；以及(Iii)惰性增强材料，如陶瓷颗粒，它将增强支架壁的强度。将使用力学测试来检查还原/氧化循环后样品的相对结构退化，并将使用X射线断层扫描和有限元建模来绘制和检查三维支架结构和在与氧化还原循环相关的体积变化期间其壁内的应力分布。

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.