Additionally, we explored the materials-process-performance relationships associated with R2R coating of PEMFC electrodes. Lab-scale fabrication of electrodes sequentially builds up the thickness of the electrode through spraying multiple layers of a dilute dispersion to create a homogenous electrode. In contrast, with gravure coating a concentrated dispersion is coated, forming a thick, wet film that dries to form the electrode. Using several electrochemical diagnostic techniques2,3and electron microscopy, we explored the foundational relationships between ink formulation, coating physics, drying conditions, and substrate to understand how parameters such as ionomer-to-carbon ratio, solvent blend, and diffusion media porosity influenced electrode morphology, concentration gradients of materials, and critical MEA performance parameters such as surface area, activity, and oxygen transport (Figure 1c).
Figure 1 (a) NREL’s roll-to-roll coating station, (b) illustration of the gravure coating processes, and (c) polarization curves and electrochemical impedance spectra comparing spray-coated and roll-to-roll coated electrodes.
Acknowledgements: This work was supported by the U.S. Department of Energy under Contract No. DE-AC36-08GO28308 with the National Renewable Energy Laboratory. Funding provided by U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Fuel Cell Technology Office, program manager Nancy Garland. S.A.M. would also like to thank Guido Bender and Brian Green for assistance with reactive impinging flow measurments.
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2. Thompson, E. L. & Baker, D. Proton Conduction on Ionomer-Free Pt Surfaces. ECS Trans. 41,709–720 (2011).