XPS characterization of a membrane electrode assembly from a proton exchange fuel cell

Importance of the Topic

The characterization of membrane electrode assemblies (MEAs) is critical for advancing proton exchange membrane fuel cell performance. Detecting and mapping trace platinum migration from catalyst layers into the Nafion electrolyte helps ensure long-term efficiency and durability in applications ranging from automotive propulsion to portable power units.

Study Objectives and Overview

The primary aim of this study was to apply high-resolution X-ray photoelectron spectroscopy (XPS) to a cross-sectioned MEA to quantify platinum distribution and assess any diffusion into the adjacent polymer electrolyte. By leveraging large-area imaging and depth information, the study sought to verify that catalyst integrity is maintained under operating conditions.

Methodology and Instrumentation

• Sample Preparation: Ultra-low angle microtomy (ULAM) was used to generate shallow cross sections several microns wide, exposing multilayer architecture of the MEA.
• XPS Analysis: Thermo Scientific Nexsa XPS system provided high sensitivity (detection limit ~0.5 at.%) and mapping capability.
• Data Processing: Principal component analysis and advanced spectral reconstruction within Avantage software reduced noise and enhanced signal-to-noise ratio for element and chemical state mapping.

Key Results and Discussion

• Elemental Mapping: High-resolution XPS maps revealed clear separation of cathode, Nafion, and anode regions, with no detectable platinum signal within the Nafion layer.
• Atomic Percent Line Scan: Quantitative line profiles across the cross section confirmed the absence of platinum above the detection limit in the polymer electrolyte.

Benefits and Practical Applications of the Method

By combining ULAM sample preparation with large-area XPS imaging and robust data analysis, this approach enables:

• Non-destructive, depth-resolved chemical characterization of complex layered assemblies.
• Reliable detection of sub-percent platinum to monitor catalyst stability.
• Guidance for optimizing manufacturing protocols to prevent performance loss in fuel cells.

Future Trends and Potential Applications

Advancements may include correlative microscopy combining XPS with electron or ion imaging for even finer spatial resolution. In situ or operando XPS under controlled humidity and temperature could track real-time catalyst degradation. The methodology is also transferable to other energy conversion materials such as electrolysis membranes and battery electrodes.

Conclusion

This study demonstrates that high-performance XPS, coupled with ULAM cross-sectioning and multivariate data analysis, effectively detects and rules out platinum migration into the Nafion electrolyte of MEAs. The protocol supports quality control and materials development for durable, high-efficiency fuel cells.

Reference

• Mack P., Nunney T. XPS characterization of a membrane electrode assembly from a proton exchange fuel cell. Thermo Fisher Scientific Application Note AN51933 (2018).