Polymer Additives for the Fabrication of Defect-Free Direct Membrane Fuel Cell Catalyst Layer Coatings

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Direct deposition of fuel cell catalyst layers onto membranes is an appealing fabrication approach by virtue of its lower contact resistance compared to traditional coatings onto a gas diffusion media. However, it remains a challenge to produce defect-free catalyst layers, especially in single layer coating processes relevant to roll-to-roll manufacturing (e.g., Mayer rod and doctor blade coating). While the membrane may swell by absorbing the solvents in the ink, the catalyst layer thickness could potentially induce cracks in the resulting electrode. The lack of uniformity and morphological defects that arise from these competing factors can lead to performance loss and early membrane electrode assembly failure. As a solution to these problems, we explored the impact of polymer additives on direct membrane coating (DMC) quality. Incorporation of additives to a pre-mixed catalyst ink enhanced fracture resistance and reduced propensity to swelling in rod-coated DMCs with Pt loadings of ~0.2 mgPt/cm2. Beginning-of-life performance in a 50 cm2 active area closely resembles plots reported for ultrasonic spray coated membranes. Accelerated stress tests and short stack degradation tests reveal that additives can mitigate defects without compromising the long-term durability of these electrodes.