Comparative Studies of Ir-Based PEM Electrolyzers Via Operando ‘Tender’ X-Ray AP-XPS

Abstract

Ir-based catalysts are considered the state-of-the-art cathode material for the oxygen evolution reaction (OER) in water splitting devices. However, large scale hydrogen production from such devices will require reduced Ir loadings and/or new materials due to factors such as Ir scarcity, cost and loss during electrolysis operation. In the hopes of enabling progress of rational design for OER catalysts, effective characterization of the electrode-liquid interface is crucial. Synchrotron-based X-ray Photoelectron Spectroscopy (XPS) offers a versatile way to obtain surface chemical and elemental characterization of these materials. The use of X-rays in the ‘tender’ regime (~2-6 keV) allows for deeper probing than the conventional ‘soft’ x-ray (< 2000 eV) set up that is common at synchrotrons and lab-based sources. The photoelectrons generated from tender x-rays have enough energy to penetrate tens of nanometers through low density components such as a layer of liquid or polymeric electrolyte. This opens the door to access the chemistry at the interface of liquid and ionomer electrolyte-electrocatalyst materials. With the use of a fully operational two-electrode system, we are able to study these membrane electrode assemblies under active water splitting conditions.My talk will highlight recent AP-XPS results on iridium-based polymer electrolyte membranes for water splitting. With application of elevated potential, we can correlate the iridium valency and surface species with the appearance of product traces in a mass spectrum. I will show trends within and between Ir catalyst types that lend to a better understanding of these OER cathodes. Figure 1