X-ray photoelectron spectroscopy (XPS) is one of the most common techniques used to analyze the surface composition of catalysts and support materials used in polymer electrolyte membrane (PEM) fuel cells and electrolyzers, providing important insights for further improvement of their properties. Characterization of catalyst layers (CLs) is more challenging, which can be at least partially attributed to the instability of ionomer materials such as Nafion during measurements. This work explores the stability of Nafion during XPS measurements, illuminating and addressing Nafion degradation concerns. The extent of Nafion damage as a function of XPS instrumentation, measurement conditions, and sample properties was evaluated across multiple instruments. Results revealed that significant Nafion damage to the ion-conducting sulfonic acid species (>50% loss in sulfur signal) may occur in a relatively short time frame (tens of minutes) depending on the exact nature of the sample and XPS instrument. This motivated the development and validation of a multipoint XPS data acquisition protocol that minimizes Nafion damage, resulting in reliable data acquisition by avoiding significant artifacts from Nafion instability. The developed protocol was then used to analyze both thin film ionomer samples and Pt/C-based CLs. Comparison of PEM fuel cell CLs to Nafion thin films revealed several changes in Nafion spectral features attributed to charge transfer due to interaction with conductive catalyst and support species. This study provides a method to reliably characterize ionomer-containing samples, facilitating fundamental studies of the catalyst-ionomer interface and more applied investigations of structure-processing-performance correlations in PEM fuel cell and electrolyzer CLs.

中文翻译：

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含 Nafion 样品的 X 射线光电子能谱分析：陷阱、实验方案和对物理化学性质的看法


X 射线光电子能谱 (XPS) 是分析聚合物电解质膜 (PEM) 燃料电池和电解槽中使用的催化剂和支撑材料表面组成的最常用技术之一，为进一步改进其性能提供重要见解。催化剂层 (CL) 的表征更具挑战性，这至少部分归因于 Nafion 等离聚物材料在测量过程中的不稳定性。这项工作探索了 XPS 测量过程中 Nafion 的稳定性，阐明并解决了 Nafion 降解问题。通过多种仪器评估 Nafion 损伤程度与 XPS 仪器、测量条件和样品特性的函数关系。结果表明，根据样品和 XPS 仪器的确切性质，Nafion 对离子传导磺酸物质的显着损害（硫信号损失 >50%）可能会在相对较短的时间范围（数十分钟）内发生。这推动了多点 XPS 数据采集协议的开发和验证，该协议可最大限度地减少 Nafion 损坏，从而避免 Nafion 不稳定造成的重大伪影，从而实现可靠的数据采集。然后使用开发的方案来分析薄膜离聚物样品和基于 Pt/C 的 CL。 PEM 燃料电池 CL 与 Nafion 薄膜的比较揭示了 Nafion 光谱特征的一些变化，这些变化归因于由于与导电催化剂和载体物质的相互作用而导致的电荷转移。这项研究提供了一种可靠地表征含离聚物样品的方法，促进了催化剂-离聚物界面的基础研究以及质子交换膜燃料电池和电解槽CL中结构-加工-性能相关性的更多应用研究。