Roll-to-roll (R2R) coating is the most economical and highest throughput method for producing fuel cell electrodes. R2R coating encompasses many different methodologies to create uniform films on a moving web substrate (Figure 1a). One of the methodologies, gravure coating, uses rollers patterned with grooves or wells that fill with liquid, which is then transferred from the gravure roller to the substrate when the come into contact, creating a film (Figure 1b). Here, we present our work that utilized gravure coating to create highly uniform proton exchange membrane fuel cell electrodes on diffusion media. In addition to X-ray fluorescence, we utilized an in-line reactive impinging flow technique, developed by NREL, to characterize electrode uniformity.¹

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 techniques^2,3and 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.

1. Zenyuk, I. V., Englund, N., Bender, G., Weber, A. Z. & Ulsh, M. Reactive impinging-flow technique for polymer-electrolyte-fuel-cell electrode-defect detection. J. Power Sources 332,372–382 (2016).

2. Thompson, E. L. & Baker, D. Proton Conduction on Ionomer-Free Pt Surfaces. ECS Trans. 41,709–720 (2011).

3. Neyerlin, K. C. et al. New Insights from Electrochemical Diagnostics Pertaining to the High Current Density Performance of Pt-Based Catalysts. 230th ECS Meeting Abstracts (2016).