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The impact of the catalyst layer structure on phosphoric acid migration in HT-PEFC – An operando X-ray tomographic microscopy study
Journal of Electroanalytical Chemistry ( IF 4.5 ) Pub Date : 2020-02-01 , DOI: 10.1016/j.jelechem.2020.113832
J. Halter , N. Bevilacqua , R. Zeis , T.J. Schmidt , F.N. Büchi

Abstract Acid migration and loss at high current densities has previously been identified as an important degradation mechanism for phosphoric acid in high temperature polymer electrolyte fuel cells. In this process, the structure of the anode catalyst layer plays an important role for the acid migration mechanism. Therefore, the acid retaining capabilities of two significantly different catalyst layer structures were investigated by means of operando X-ray tomographic microscopy. In a commercial catalyst layer, with cracks with a mean width of 39 μm, ideal crack connectivity and no bottlenecks in the crack structure, phosphoric acid penetrates and traverses the catalyst layer and migrates to the GDL and gas channel. In contrast, an in-house catalyst layer retained phosphoric acid within itself. Although with lower mean crack size of only 20 μm, the different crack connectivity and accessibility, as determined by crack width and simulated mercury intrusion crack size analysis, were identified as main causes for better acid retaining capabilities. A fraction of over 95% of the crack-volume is protected by bottlenecks smaller than 20 μm. The present analysis is a guideline for engineering acid retaining catalyst layers structures for high temperature polymer electrolyte fuel cells.

中文翻译:

催化剂层结构对 HT-PEFC 中磷酸迁移的影响——原位 X 射线断层扫描显微镜研究

摘要 高电流密度下的酸迁移和损失先前已被确定为高温聚合物电解质燃料电池中磷酸的重要降解机制。在这个过程中,阳极催化剂层的结构对酸迁移机制起着重要作用。因此,通过操作 X 射线断层显微术研究了两种显着不同的催化剂层结构的酸保持能力。在商业催化剂层中,平均宽度为 39 μm 的裂纹、理想的裂纹连通性和裂纹结构中没有瓶颈,磷酸渗透并穿过催化剂层并迁移到 GDL 和气体通道。相比之下,内部催化剂层将磷酸保留在其内部。虽然平均裂纹尺寸较低,仅为 20 μm,由裂纹宽度和模拟压汞裂纹尺寸分析确定的不同裂纹连通性和可达性被确定为更好的酸保持能力的主要原因。超过 95% 的裂纹体积的一小部分受到小于 20 μm 的瓶颈的保护。本分析是设计用于高温聚合物电解质燃料电池的酸保持催化剂层结构的指南。
更新日期:2020-02-01
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