Synchrotron-based X-ray Photoelectron Spectroscopy (XPS) a is a versatile technique for surface chemical and elemental characterization of materials. Application of this technique to in situ studies was historically challenging in large part due to the attenuation of signal from interaction of photoelectrons with the surrounding environment. With the technological development of ambient pressure systems, we are now able to study catalysts in conditions that resemble their working environments. Further, the use of X-rays in the ‘tender’ regime (2-7 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 electrolyte-electrocatalyst materials.

We have built a fully operational two-electrode system for the study of PEM electrolyzers in working conditions. Water flows through the cell and the chamber is held at 100% humidity (20 Torr at 300 K) to yield a fully hydrated environment for our electrocatalyst. We are then able to run operando electrochemical measurements while acquiring XP spectra to elucidate the important physical and chemical processes taking place at the interface. My talk will highlight recent 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.