Investigation of Surface Chemistry of Pemwes Iridium Oxide Catalyst Layers as a Function of Ink Aging Time

Abstract

Proton exchange membrane water electrolyzers (PEMWEs) are an advanced and effective solution to producing hydrogen from water for green hydrogen production. To improve PEMWEs operation, it is necessary to analyze the catalyst layer (CL) to better understand relationships between surface properties and processing, performance, and durability. However, understanding the CL composition, structure, and morphology at all relevant scales is difficult. X-ray photoelectron spectroscopy (XPS) is a surface-sensitive technique that is capable of measuring subtle differences in chemistry of a sample’s surface within top 3-10 nms. However, there are several challenges associated with limited information that has been reported in the literature thus far.This study focuses on investigating the CLs made with IrO2 catalysts using Mayer Bar coating method, one of the scalable fabrication routes. XPS analysis was conducted using a recently developed approach that mitigates issues with degradation of ionomer induced during X-ray exposure. First, XPS was used to probe variations between different areas of the CLs to assess spatial homogeneity to confirm good quality of the coatings. XPS was also employed to investigate CLs made with inks aged for different amount of time (0, 3, and 14 days), noting some differences in the surface chemistry. Results from this study will discuss the effect of ink age on surface composition at the catalyst-ionomer interface, as well as address specific challenges in fitting the O 1s and Ir 4f core level spectra which are inherently challenging to curve fit. This work motivates further studies investigating other aspects related to processing and fabrication as well as investigations of CLs stability.