(585f) Iridium/Ionomer Interfaces in Water Electrolyzers

Proton-exchange-membrane water electrolyzers (PEMWEs) are the state-of-the-art water electrolyzer technology, able to produce hydrogen from green electrons at high current densities and pressures. These devices are based on a membrane-electrode-assembly architecture, in which two catalyst layers (CLs) sandwich a PEM. The CLs are heterogeneous electrodes containing agglomerates of catalyst particles (typically iridium on the anode) coated with an ion-conducting polymer (ionomer). One of PEMWE’s key challenges is the sluggish kinetics of the oxygen evolution reaction on the anode. Importantly, this reaction is highly influenced by its reaction environment. Therefore, understanding how ionomer and iridium interact is crucial.

In this talk, we will explore how the type of Ir catalyst (metal, oxide, and hydroxide form) affects MEA performance. We gain insight into these performance differences by studying model thin films and inks. In solution, we probe aggregation behavior of ionomer and catalyst particles as well as binding strengths between the two via calorimetry. We then fabricate model substrates and deposit thin films of ionomer, and study the ionomer structure via x-ray scattering and water-uptake properties as a function of relative humidity and substrate type. We also gain chemical insights into the surface speciation as a function of water content via ambient-pressure x-ray photoelectron spectroscopy. In this way, we correlate macroscale device performance with nanoscale phenomena occurring at the iridium/ionomer interface.