Development and Characterization of Microporous Layers on Porous Transport Layers for Proton Exchange Membrane Water Electrolyzers

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Porous transport layers (PTLs) serve many important functions for proton exchange membrane water electrolyzers. PTLs facilitate fluid transport towards and away from the anode catalyst layer, act as a mechanical support for the membrane, and provide electrical contact with the anode catalyst layer [1]. As a result, PTLs can greatly impact cell performance. However, while there has been an effort to improve similar gas diffusion layers in PEM fuel cells, there has not been a significant effort to optimize the overall form factor and design of PTLs for PEM water electrolyzers. One of the primary concerns about the current design of PEM water electrolyzer PTLs is how they interact with the anode catalyst layer. In order to ensure proper fluid transport through the PTL, there is significant porosity throughout the PTL including at the anode interface. The large porosity and particle sizes of the PTL can cause heterogeneous contact of the PTL and catalyst layer thus reducing the catalyst utilization. Therefore, high catalyst loadings are required to obtain acceptable performance and durability. One method to address this concern would be to develop a metal microporous layer (MPL) that can be integrated onto a PTL at the anode interface that can withstand the high potentials at the anode while maintaining sufficient fluid transport. The MPL is fabricated using smaller metal particle sizes compared to the bulk PTL, which results in smaller pores creating a more uniform surface. The uniform surface and small pore sizes of the MPL provide a much higher interfacial contact area at the anode interface compared to a traditional PTL and would allow for a more uniform contact pressure across the anode interface. Higher interfacial contact will improve catalyst utilization and facilitate the reduction in anode catalyst loading, leading to reductions in overall electrolyzer capital cost [2]. In this work, prototype PTLs with metal MPLs are developed and tuned for optimal PEM water electrolyzer cell performance. The prototype PTLs with MPLs are characterized to understand how specific properties (thickness, porosity, tortuosity, etc.) influence cell performance. Electrochemical testing shows that adding an MPL at the anode/PTL interface can allow for acceptable cell performance with 90% lower anode catalyst loading compared to when using a baseline PTL. References [1] X.-Z. Yuan, N. Shaigan, C. Song, M. Aujla, V. Neburchilov, J.T.H. Kwan, D. P. Wilkinson, A. Bazylak, K. Fatih. The porous transport layer in proton exchange membrane water electrolysis: perspectives on a complex component. Sustainable Energy & Fuels, 6, (2022), 1824-1853. [2] T. Schuler, J.M. Ciccone, B. Krentcher, F. Marone, C. Peter, T.J. Schmidt, F.N. Büchi. Hierarchically Structured Porous Transport Layers for Polymer Electrolyte Water Electrolysis. Advanced Energy Materials, 10, (2019), 1903216

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