Microstructure Characterization of Iridium Oxide Catalyst for Polymer Electrolyte Membrane Water Electrolyzer Using X-Ray Scattering

Abstract

Polymer electrolyte membrane water electrolyzers (PEMWEs) are promising hydrogen production systems for fuel cell vehicles and industrial uses with virtually no greenhouse gas emissions when using renewable energy sources [1]. Unsupported iridium oxide (IrO2) is a typical oxygen evolution reaction (OER) catalyst utilized in the anode of the PEMWE [2]. The atomic and microstructure of the IrO2 catalysts and electrodes and interactions between and ionomer and catalyst can affect the ultimate performance of the PEMWE anode. These properties and phenomena may be controlled by the interactions of the ionomer in the catalyst-ionomer ink, by the effect of ink solvent composition on those interactions, and by the ink mixing and coating procedures. This presentation will study relationships between ink formulation, electrode morphology, and performance for the IrO2-based anode for low-temperature PEMWEs. These relationships have been explored using a ultra-small angle X-ray scattering (USAXS) combined with SAXS to elucidate the effects of coating parameters and defects on the membrane electrode assembly (MEA) performance and to determine particle size distributions and extent of agglomeration of IrO2 in inks and electrodes. The resulting electrodes have been characterized using X-ray nano-computed tomography (nano-CT) to determine the spatial distribution of pores, solids, and ionomer in standard electrodes and those with intentionally-produced coating defects. The effects of ionomer concentration, catalyst concentration, and solvent composition on the microstructure of the IrO2 catalyst inks and electrode will be correlated with the PEMWE performance. Acknowledgements This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies, Program Manager Nancy Garland.. This work was authored in Argonne National Laboratory, a U.S. Department of Energy (DOE) Office of Science laboratory operated for DOE by UChicago Argonne, LLC under contract no. DE-AC02-06CH11357. This work was also authored in part by Alliance for Sustainable Energy, LLC, the manager and operator of the National Renewable Energy Laboratory for the U.S. Department of Energy (DOE) under contract no. DE-AC36-08GO28308. This research used the resources of the Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.