An Electrochemical Flow Cell for Operando XPS and NEXAFS Investigation of Solid-Liquid Interfaces

Suitable reaction cells are critical for operando near ambient pressure (NAP) soft X-ray photoelectron spectroscopy (XPS) and Near-edge X-ray absorption fine structure (NEXAFS) studies. They enable tracking the chemical state and structural properties of catalytically active materials under realistic reaction conditions, and thus allow a better understanding of charge transfer at the liquid-solid interface, activation of reactant molecules, and surface intermediate species. In order to facilitate such studies, we have developed a top-side illuminated operando spectro-electrochemical flow cell for synchrotron-based NAP-XPS and NEXAFS studies. Our modular design uses a non-metal (PEEK) body, and replaceable membranes which can be either of X-ray transparent silicon nitride (SiNx) or of water permeable polymer membrane materials (e.g., NafionTM). The design allows rapid sample exchange and simultaneous measurements of total electron yield (TEY), Auger electron yield (AEY) and fluorescence-yield (TFY). The developed system is highly modular and can be used in the laboratory or directly at the beamline for operando XPS/ X-ray absorption spectroscopy (XAS) investigations of surfaces and interfaces. We present examples to demonstrate the capabilities of the cell. These include an operando NEXAFS study of the Cu-redox chemistry using a SiNx membrane/Ti-Au/ Cu working electrode assembly (WEA) and a NAP-XPS and -NEXAFS study of water adsorption on a NafionTM polymer membrane based working electrode assembly (NafionTM/C/IrOx catalyst).