Assessing the Unique Degradation Mechanisms of Hydrocarbon-Based Membranes in Conventional MEA Design Using 4D in-Situ X-Ray Computed Tomography

The degradation of proton exchange membrane fuel cells (PEMFCs) stands as a critical determinant in evaluating the robustness of fuel cell systems, crucial for the commercial-scale transition to sustainable energy. For zero-emission vehicles, fuel cell stacks need to demonstrate lifespans exceeding 8,000 (light-duty vehicles) and 30,000 hours (heavy-duty vehicles)[1]. For achieving robust PEMFC systems at commercial scale, it is crucial to precisely understand the degradation pathways to effectively pinpoint and mitigate degradation issues. To achieve this, customized small-scale fuel cell fixtures are utilized for accelerated stress testing (AST) and X-ray computed tomography (XCT) in-situ and ex-situ visualization [2,3]. This approach enables comprehensive analysis of membrane electrode assembly (MEA) aging processes. Our group previously employed this approach to identify chemical, mechanical, and chemo-mechanical degradation mechanisms in commonly used perfluorosulfonic acid (PFSA) ionomer membranes[4,5]. In recent years, transitioning from PFSA membranes to hydrocarbon-based (HC) membranes in PEMFCs has gained significant attention. This shift eliminates fluorinated compounds typically found in PFSA membranes, aligning with sustainability goals, and reducing environmental impact. This transition signifies both technological advancement and innovation, driving forward the quest for efficient, cost-effective, and environmentally friendly energy solutions. Despite their promising characteristics, HC membranes are more susceptible to mechanical degradation than PFSA ones[6], presenting unique compatibility challenges due to their distinct chemical composition. Historically, PEMFC systems intentionally developed and optimized for PFSA may face performance issues and premature failure with HC membranes. This research therefore investigates the unique aspects of HC membrane degradation within a conventional fuel cell design with PFSA ionomer catalyst layers, using 4D in-situ XCT to understand chemo-mechanical degradation, enhancing fuel cell technology. Herein, ZEISS Xradia® 520 Versa micro XCT system was used to visualize samples. Repetitive scans were taken at room temperature in a dry state of the MEA. The first set of MEAs consisted of reinforced HC membranes (Pemion-PF1-HLF8-15-X) of 15 µm thickness, spray-coated with PFSA catalyst ink to form catalyst-coated membranes (CCMs), and assembled with gas diffusion layers (Freudenberg H14C15, 190 µm) featurin