Novel Graphene Foam Microporous Layers for PEM Fuel Cells: Interfacial Characteristics and Comparative Performance

The microporous layer (MPL) provides many beneficial properties for performance improvement of H-2 PEM fuel cells, particularly with respect to water management and two-phase (gas/liquid) flow dynamics. However, the interface between the catalyst layer (CL) and MPL could be a source of additional overpotential losses due to poor electronic conductivity and/or mass transfer limitations. This is particularly important for low loading CLs which may suffer from spatial disconnect with the micro-scaled features of conventional MPLs. In an effort to better understand the factors influencing the MPL vertical bar CL interface, the conventional carbon MPL is comparatively studied with respect to three alternative layers: graphene foam, perforated graphitic sheet and perforated stainless steel. The graphene foam shows beneficial interfacial properties that contribute to electrode kinetic and ohmic improvements during polarization. This can be attributed to the graphene's ability to conform at local length scales due to its unique flake-like structure (achieved upon compression), an ability to intimately adhere to the CL and the layer's superior conductivity. Further investigation through single cell performance tests supports the application of the graphene foam as an MPL alternative. The results also highlight the interplay of various factors that influence the MPL vertical bar CL interface and ultimately the overall polarization performance, such as: morphology, conductivity, connectivity, compression and adhesive effects between layer components.