Processing of Advanced Foam Scaffolds for Iron-Air Battery Applications

氢气的生产、储存和在当地的使用，通过燃料电池发电，对于实现低至零二氧化碳排放的电网至关重要，这将有利于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（“氧化还原”）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碎和随后的团聚和固结。这些效应大大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的稳定性、高表面积和高透气性是这项有前途的技术面临的主要挑战。该奖项支持研究开发一种结构，该结构利用新颖的加工方法来制造铁支架，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。在这个研究项目中，研究人员将定向冻结氧化铁纳米粉的水悬浮液，以形成冰枝晶，这将推动颗粒进入枝晶间空间，从而形成氧化铁粉末壁的网络。氢气还原后，该网络被烧结成一个连续的支架，其定向排列的通道模板化了原始的冰枝晶，并被具有高表面积和足够的内部自由空间的铁壁包围，以达到承受多次还原/氧化循环所需的微观结构稳定性，而无需烧结或粉碎。通过在氧化铁纳米粉悬浮液中加入不同的材料，可以进一步提高支架的稳定性：(1)氧化镍粉共还原形成强度更高的铁-镍固溶体壁；（二）可从支架壁上蒸发的氟化锶等空间保持粉末，可在支架壁上产生更多孔隙，并增加其表面积和自由体积，以适应体积变化；（三）惰性增强物，如陶瓷颗粒，可加强和加固支架壁。机械测试将用于检查样品在还原/氧化循环后的相对结构退化，x射线断层扫描和有限元建模将用于绘制和检查与氧化还原循环相关的体积变化过程中支架结构的三维结构和壁内的应力分布。

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.