Water transport across membrane-electrode assemblies is one of the key factors in determining the performance of protonexchange membrane fuel cells (PEMFCs). In particular, the water saturation in the catalyst layers (CLs) is significantly related to the gas transport to the reaction sites and the ionic conductivity decided by water activity. Herein, to investigate the effect of CL structure on water transport, we compare the transport properties at various water saturation levels of two CLs, namely conventional CL and nanosized dense-structured (NSDS) CL. The two CLs were three-dimensionally reconstructed using focused ion beam-scanning electron microscopy tomography. Subsequently, the structural and transport properties were calculated based on the reconstructed CLs. The results show that the smaller pore size of the NSDS CL led to lower water permeability (a high water-retaining property) and lower saturation (water-flooding prevention). Thus, this provides insight into how the CLs could be used in the water management of PEMFCs to improve their performance.

Keywords: Micro/nano structure, Catalyst layer, Water imbibition, Reconstruction, Model.