Design and Operation of a Versatile Operando Electrochemical X-ray Photoelectron Spectroscopy Platform for Aqueous Electrocatalysis.

Understanding electrocatalyst activation and degradation under realistic operating conditions requires operando spectroscopic techniques capable of probing solid-liquid interfaces with running electrochemistry. Here, we present the design and implementation of a versatile operando electrochemical X-ray Photoelectron Spectroscopy (XPS) platform compatible with aqueous environments and controlled current- or potential-driven operation. The modular cell architecture enables both conventional three-electrode half-cell measurements as well as a two-electrode setup for zero-gap proton-exchange membrane or anion-exchange membrane water electrolysis at high current densities. Key design considerations, including electrolyte management, membrane integration into the cell, gas handling, and X-ray access geometry, are discussed in detail. The platform allows investigation of catalyst oxidation, hydroxylation, reduction, and surface restructuring under realistic electrochemical conditions. Representative measurements demonstrate stable operation during high-current water electrolysis as well as flexibility for broader electrocatalytic studies. This protocol provides a practical framework for implementing operando XPS in electrochemical research laboratories and facilitates reproducible investigation of dynamic catalyst transformations at electrified interfaces.