The oxygen and water transport through various microporous layers (MPLs) is investigated by fuel cell tests in a 5 cm 2 active area cell under differential-flow conditions, analyzing polarization curves, the associated high-frequency resistance, and the oxygen transport resistance extracted from limiting current density measurements. In this study, MPLs with two different carbon blacks are prepared and compared to a commercial material, all coated on the same GDL-substrate (Freudenberg); furthermore, perforated MPLs with large pores produced by a thermally decomposable polymeric pore former with a particle diameter of ≈30 μm are examined. The materials are characterized by mercury porosimetry, nitrogen adsorption and scanning electron microscopy. While at dry conditions (T cell = 80 • C, RH = 70%, p abs = 170 kPa) the performance of all materials is similar, at conditions of high water saturation (T cell = 50 • C, RH = 120%, p abs = 300 kPa), MPLs with larger pores or perforations exhibit a performance improvement due to a ≈30% reduction in oxygen transport resistance. The results indicate that liquid water is transported exclusively through these large pores, while the oxygen transport occurs in the small pores defined by the carbon black structure.

Microporous layers consisting of different ratios of acetylene black and carbon fibers with either a hydrophobic polytetrafluoroethylene (PTFE) or a hydrophilic perfluorosulfonic acid (PFSA) ionomer binder are investigated with regards to oxygen and water transport in PEMFCs. For that, the materials are characterized by scanning electron microscopy and mercury porosimetry, revealing an increase of porosity and pore sizes for an increasing carbon fiber content. MPLs, coated onto a commercial hydrophobized non-woven gas diffusion layer substrate, are examined in H 2 /air fuel cell tests under differential-flow conditions at various dry and humid operating conditions. For both hydrophobic and hydrophilic MPLs in the presence of significant amounts of liquid water in the diffusion layer substrate, the materials with larger pore sizes, i.e. higher carbon fiber contents, perform superior at 0.6 V and show the lowest oxygen transport resistance. However, at the same carbon composition, hydrophilic MPLs have a lower performance compared to the corresponding hydrophobic MPLs, which is explained by the capillary pressure barriers for different pore properties. At operating conditions relevant for automotive applications, a performance enhancement of 48% could be achieved for a purely carbon fiber based MPL compared to a commercial reference.

An empirical valence-bond (EVB) model is developed to describe the transfer of a proton from aqueous solution bulk to a metal electrode surface. The results of density functional calculations are used for parametrizing the model for a Pt(111) surface, which was chosen as a model system. Thereby, the metal surface is addressed in terms of the cluster model. The developed EVB model makes it possible to perform large-scale molecular dynamics (MD) simulations for a metal/electrolyte solution interface. Using MD we explore the proton transfer to a Pt(111) electrode surface with different negative surface charge densities. Preliminary conclusions are reported to elucidate some aspects of the proton transfer mechanism.