Correlative X-ray Tomographic Imaging of Catalyst Layer Degradation in Fuel Cells

Abstract

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.

Stability of Platinum‐Group‐Metal‐Based Electrocatalysts in Proton Exchange Membrane Fuel Cells

“…From operando XCT results, the catalyst layer solid area fraction gradually decreases by 25% with cracks' formation and severe localized corrosion accompanied by up to 50% thinning and significantly altered liquid water distribution. [169] As an alternative ex situ technique that could be more adaptive and simulative to real operating conditions, the identicallocation TEM (IL-TEM) utilizes the specially designed TEM grid as the secondary electrode substrate by loading PGM-based catalysts, which can be mounted to the electrode. This technique, with a lower cost and a higher flexibility than the E-chem STEM, can be used to observe the structural evolution of the catalyst by investigating the same region and the same NP of interest during the whole stability/durability test, as shown in Figure 10a.…”

“…From operando XCT results, the catalyst layer solid area fraction gradually decreases by 25% with cracks’ formation and severe localized corrosion accompanied by up to 50% thinning and significantly altered liquid water distribution. [ 169 ]…”

Enhanced Water Management in PEMFCs: Perforated Catalyst Layer and Microporous Layers

“…The MPL creates close contact with the CL and reduces the water accumulation at the interface between the electrode layer and GDL‐S/MPL . The porosity and pore interconnectivity of the electrodes and MPL/GDL, which can be influenced by the choice and composition of materials and/or by addition of pore formers, determine the effective pathways for the two‐phase flow transport. Neutron imaging has been used as a state‐of‐the‐art technique for visualizing liquid water in operating PEMFCs with a high special resolution .…”

Unraveling Structural Details in Ga-Pd SCALMS Systems Using Correlative Nano-CT, 360° Electron Tomography and Analytical TEM

“…These methods are usually historically realized at synchrotron facilities [25,26]. However, with the development and transfer of synchrotron optics to lab instruments in recent years, micro-CT and nano-CT can be performed in the lab with amazingly comparable performance, except for the X-ray source brilliance [27][28][29][30][31][32][33][34]. State-of-the-art lab nano-CT instruments like the ZEISS Xradia 810 Ultra typically offer several imaging modalities.…”