Characterization of Porous Transport Electrodes in Proton Exchange Membrane Water Electrolyzers with Scanning Electron Microscopy and Micro X-ray Computed Tomography

Abstract

With the move towards commercialization of proton exchange membrane water electrolyzers (PEMWE’s), the integration of the porous transport layer (PTL) and the anode catalyst layer (CL) into the porous transport electrode (PTE) is of much interest. Specifically, it is important to understand how different CL fabrication routes and ink formulations affect the performance. In addition to electrochemical characterization, a visual understanding of all components and the CL/PTL interface is needed to identify most optimum fabrication conditions.Typically, the CL is deposited on the polymer membrane, and then integrated with PTL. Deposition of the CL onto PTL has certain advantages, but generally results in CL with variation in coverage and thickness. Depending on the catalyst loading, this can range from very thin layers on the order of several hundred nanometers, to thicker coatings on the order of tens to hundreds of microns. Typically, characterization techniques such as Scanning Electron Microscopy Electron combined with X-Ray Dispersive Spectroscopy (SEM-EDS), is used in correlation with performance testing for initial assessment of the coating heterogeneity. Top-down analysis and analysis of cross-sections are both commonly employed. Other SEM-based techniques are also used, including Focused Ion Beam (FIB) technique, which can provide information about internal structure. Micro X-ray Computed Tomography (XCT) is another powerful method for investigation of CLs and their integration with PTLs 1. Thinner CLs produced with low catalyst loadings are inherently more challenging to characterize and require multi-analytical approach.This work investigates a series of PTEs produced using a Meyer Rod method. Fabrication parameters such as rod size, ink formulations and catalyst loadings were varied resulting in changes in the quality of the CLs. SEM-EDS and synchrotron micro-XCT (at the Advanced Photon Source (APS) on beamline 2-BM) were used to assess CL distribution, homogeneity, and thickness. This talk will discuss both benefits and limitations of using micro-XCT on these materials and compare techniques to highlight the benefit of using multiple characterization techniques for analysis.Citations:(1) Leonard, E.; Shum, A. D.; Danilovic, N.; Capuano, C.; Ayers, K. E.; Pant, L. M.; Weber, A. Z.; Xiao, X.; Parkinson, D. Y.; Zenyuk, I. V. Interfacial Analysis of a PEM Electrolyzer Using X-Ray Computed Tomography. Sustain. Energy Fuels 2020, 4 (2), 921–931.