Current state-of-the-art fuel cell designs exhibit heterogeneity, e.g., in wettability and pore size distributions in gas diffusion layers (GDLs) or land-channel patterns in flow fields. This inherent heterogeneity impacts liquid water transport and fuel cell performance and durability and needs accurate characterization to enable next-generation designs. Here, we reveal novel insights on how heterogeneity affects a) formation of pore-scale water pathways within GDLs, b) distribution of operando membrane hydration and morphology, and c) fundamental contact angle variation.

3-D pore-scale liquid water distribution within the cathode GDL was characterized via operando synchrotron X-ray tomography to capture the early appearance of liquid water pathways. Liquid water only partially fills certain GDL pores, which is attributed to heterogeneous pore sizes and wettability distribution. Liquid water is observed to preferentially flow along some GDL fibers, due to the hydrophilic nature of carbon fiber and the presence of pore-scale mixed wettability within the GDLs.

Operando spatiotemporal distributions of six interacting fuel cell components are resolved in high contrast using a novel combination of simultaneous neutron and X-ray tomography (NeXT) and advanced image processing, enabling the highest reported pairwise contrast between these materials (average and median pairwise contrast-to-noise ratio of 9.5). Signal and contrast are enhanced by up to 10 times and 48 times, respectively compared to single-modality imaging with conventional image processing. These drastic contrast enhancements reveal subtle variation in operando microstructural morphology of the catalyst coated membrane and liquid water distribution with respect to flow-field land-channel patterns in fuel cells. Quantitative analysis reveals that local heterogeneity in membrane hydration and interfacial properties are dependent upon operating conditions and geometry of flow-field lands and channels and interfaces such as GDL-gasket interface.

Bubble adhesion on a smooth surface is analyzed using a novel mechanics perspective to reveal the existence of a pinning force during thermodynamic non-equilibrium. A new definition proposed here extends the validity of Young and Young-Laplace equations to a wide range of experimentally observed contact angles and lends insights into the fundamental mechanism of contact angle evolution.