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A device and a method for direct measurement of the local contact pressures of gas diffusion layers (GDL) are presented. The new tool determines the spatially resolved contact pressure on the GDL side opposite to the flow-field/GDL interface which is relevant to good electrical contact between the GDL and the catalyst coated membrane (CCM) in a practical fuel cell setting. In a second step, using a fit function determined by separate two and four point resistance measurements, the method is extended to deliver spatially resolved contact resistance data. These experimental methods, in addition to shear-force measurements, are applied to a range of state-of-the-art GDL media. Whereas the shear-force measurements correlate well with data from recent work in the literature, the comparison of a non-woven and a paper based GDL with distinct differences in their shear moduli shows almost the same contact pressures underneath the flow field channel. This result indicates that shear-force data alone is of limited use for predicting contact pressure underneath flow field channels. In-situ current/voltage curves confirm the predictive power of a direct measurement of the contact pressure which highlights the importance for future GDL development and modeling activities.Contact resistances are a major source of performance losses in proton exchange membrane fuel cells (PEMFC). Two important trends in PEMFC technology, particularly for automotive applications, exacerbate this problem: On the one hand, modern bipolar plates (BPP) in automotive stacks exhibit wider and shallower channels due the use of hydro-formed metal sheets or embossed thin graphite foils. 1 On the other hand, demanding cost and performance targets drive membrane electrode assembly (MEA) manufacturers toward the use of advanced non-woven gas diffusion media which are typically less "stiff" in comparison to traditional papers. 2 The mechanical properties of the GDL material are the decisive factor for intrusion into the channels of bipolar plates. Intrusion may cause excessive pressure drops along the gas channels and influence the water drag-out. 3-5 The mechanical behavior of GDL is assumed to be strongly dependent on the base structure of the substrate. There are three different types of commonly used GDL structures such as woven, paper and non-woven material which differ strongly with respect to their mechanical properties. These differences are due to the characteristics of the production process. Woven and non-woven materials are mechanically bonded by weaving techniques or by hydro-entanglement, respectively, whereas a paper is chemically bonded by an additional resin. A woven material consists of ordered, endless fibers in contrast to the randomly orientated, short staple fibers which are used for non-woven and paper materials. Non-woven materials are preferable from a cost and handling perspective (roll-to-roll process), and they have been designed to exhibit superior performance.The other important property of gas diffusion media which is determine...

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