Effective catalyst layer design is vital for high-performing polymer electrolyte fuel cells. However, the desired catalyst layer structure may be compromised by operational degradation, causing performance decay. The present work investigates the multi-scale catalyst layer structure and properties across different stages of degradation, including liquid water distribution in an operating fuel cell. A correlative, multi-scale imaging workflow with a combined analysis by operando lab-based micro-X-ray computed tomography (XCT) and nano-XCT is developed for this purpose. From operando XCT results, the catalyst layer solid area fraction was found to gradually decrease by 25% with crack formation and severe localized corrosion accompanied by up to 50% thinning and significantly altered liquid water distribution. Localized degradation features such as nano-scale cracks and internal pore-size distribution changes were resolved using nano-XCT and tracked by 3+1D imaging at different stages of degradation. Porosity changes quantified by nano-XCT on the order of 40% from beginning-of-life to end-of-life with reduction in connected pore fraction were observed as well as increase in average pore size by 50%. The effect of changes at the nano-scale on diffusion properties were calculated and an empirical model is proposed for degraded catalyst layer structures where Knudsen effects are dominant.

中文翻译：

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燃料电池中催化剂层降解的相关X射线层析成像

有效的催化剂层设计对于高性能聚合物电解质燃料电池至关重要。但是，所需的催化剂层结构可能会因操作性能下降而受损，从而导致性能下降。本工作研究了降解不同阶段的多尺度催化剂层结构和性能，包括运行中的燃料电池中的液态水分布。为此，开发了相关的多尺度成像工作流程，并结合了基于操作实验室的微型X射线计算机断层扫描（XCT）和纳米XCT进行的分析。根据操作XCT结果，发现催化剂层固体面积分数随着裂缝的形成和严重的局部腐蚀而逐渐降低25％，伴随着高达50％的变薄和液体水分布的显着改变。使用nano-XCT解决了局部降解特征，例如纳米级裂纹和内部孔径分布变化，并在降解的不同阶段通过3 + 1D成像进行了跟踪。观察到通过纳米-XCT从寿命开始到寿命结束的40％数量级的孔隙率变化，连接孔隙率降低，并且平均孔径增加了50％。计算了纳米尺度上的变化对扩散性能的影响，并提出了以降解的催化剂层结构为主要参数的经验模型。观察到通过纳米XCT定量的孔隙率变化，从寿命开始到寿命终止，随着连接孔分数的降低，其变化为40％左右，并且平均孔径增加了50％。计算了纳米尺度上的变化对扩散性能的影响，并提出了以降解的催化剂层结构为主要参数的经验模型。观察到通过纳米-XCT从寿命开始到寿命结束的40％数量级的孔隙率变化，连接孔隙率降低，并且平均孔径增加了50％。计算了纳米尺度上的变化对扩散性能的影响，并提出了以降解的催化剂层结构为主要参数的经验模型。