Analysis of the MPL/GDL Interface: Impact of MPL Intrusion into the GDL Substrate
Anne Berger, Yen-Chun Chen, Jacqueline Gatzemeier, Thomas J. Schmidt, Félix N. Büchi, Hubert A. Gasteiger
Abstract
Interfaces are crucial for the water management in polymer electrolyte membrane fuel cells (PEMFCs). The introduction of a microporous layer (MPL) had a revolutionary effect on the water distribution by improving the interface between the catalyst layer and the gas diffusion layer substrate (GDL-S). Hence, it is vital to maximize the improvement by further characterizing and advancing the properties of the interfaces, in this case the MPL/GDL-S interface. This study aims at fabricating a GDL with an MPL that intrudes into the GDL-S, analyzing the impact on the GDL-S structure and on PEMFC performance. Mercury intrusion porosimetry (MIP) and ex situ X-ray tomography (XTM) show that the intrusion of the MPL into the hydrophobic GDL-S proceeds via the preferential filling of the GDL-S macropores, thereby reducing their size and volume fraction in the GDL-S. While an intruding MPL leads to a small performance increase under wet PEMFC operating conditions, this improvement could only be achieved by a careful management between the extent of MPL intrusion and the partial macropore blocking in the GDL-S. Furthermore, the impact of MPL intrusion on the liquid water saturation of the GDL was quantified by operando XTM. The results provide design guidelines for improved GDLs.