Processing of Advanced Foam Scaffolds for Iron-Air Battery Applications

氢的产生、储存和本地使用，通过燃料电池发电，对于实现二氧化碳排放量低至零的电网至关重要，有利于美国经济和全球社会。近年来，氧化铁粉末作为通过氧化铁还原/氧化（“氧化还原”）反应来储存和产生纯氢的廉价、无毒选择而引起了关注。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附聚和固结。这些效应大大降低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中的稳定性、高表面积和高透气性是这种有前途的技术的主要挑战。该奖项支持研究开发一种结构，利用新的加工方法来创建铁支架，可以在氧化还原循环过程中保持结构完整性，高渗透性和高表面积，从而实现新型，廉价和无毒的铁-空气电池的大规模使用。在这项研究计划中，研究人员将定向冷冻氧化铁纳米粉末的水悬浮液以产生冰树枝状晶体，其将颗粒推入枝晶间空间，从而产生氧化铁粉末壁的网络。在氢还原之后，该网络被烧结成具有定向对准通道的连续支架，所述定向对准通道模板化原始冰枝晶，所述定向对准通道被具有高表面积和足够内部自由空间的铁壁包围，以实现经受多次还原/氧化循环所需的微观结构稳定性而不烧结或粉碎。通过向铁氧化物纳米粉末悬浮液中加入各种材料将进一步提高支架稳定性：（i）共还原以形成具有更高强度的铁-镍固溶体壁的氧化镍粉末;（ii）空间保持剂粉末如氟化锶，其可以从支架壁蒸发以在壁内产生进一步的孔隙并增加它们的表面积和自由体积以容纳体积变化和（iii）惰性增强物，如陶瓷颗粒，这将加强和覆盖支架壁。机械测试将用于检查还原/氧化循环后样品的相对结构降解，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期间其壁内的三维支架结构和应力分布。

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.