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/-NEXAFS studies. Our modular design uses a non-metal (PEEK) body, and replaceable membranes which can be either of x-ray transparent silicon nitride (SiN _x ) or of water permeable polymer membrane materials (e.g. Nafion ^TM ). The design allows rapid sample exchange and simultaneous measurements of total electron yield, Auger electron yield and fluorescence-yield. 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 investigations of surfaces and interfaces. We present examples to demonstrate the capabilities of the flow cell. These include an operando NEXAFS study of the Cu-redox chemistry using a SiN _x /Ti-Au/Cu working electrode assembly (WEA) and a NAP-XPS/-NEXAFS study of water adsorption on a Nafion ^TM polymer membrane based WEA (Nafion ^TM /C/IrO _x catalyst). More importantly, the spectro-electrochemical flow cell is available for user community of B07 beamlines at Diamond Light Source.