The microporous layer (MPL) is a key cathodic component in proton exchange membrane fuel cells owing to its beneficial influence on two-phase mass transfer. However, its performance is highly dependent on material properties such as morphology, porous structure, and electrical resistance. To improve water management and performance, electrochemically exfoliated graphene (EGN) microsheets are considered as an alternative to the conventional carbon black (CB) MPLs. The EGN-based MPLs decrease the kinetic overpotential and the Ohmic potential loss, whereas the addition of CB to form a composite EGN+CB MPL improves the mass-transport limiting current density drastically. This is reflected by increases of approximately 30 and 70 % in peak power densities at 100 % relative humidity (RH) compared with those for CB- and EGN-only MPLs, respectively. The composite EGN+CB MPL also retains the superior performance at a cathode RH of 20 %, whereas the CB MPL shows significant performance loss.

The microporous layer (MPL) provides many beneficial properties for performance improvement of H 2 PEM fuel cells, particularly with respect to water management and twophase (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‰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‰CL interface and ultimately the overall polarization performance, such as: morphology, conductivity, connectivity, compression and adhesive effects between layer components.

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