Perspective—Outlook on Operando Photoelectron and Absorption Spectroscopy to Probe Catalysts at the Solid-Liquid Electrochemical Interface

Operando X-ray Photoelectron and Absorption Spectroscopy (XPS and XAS) using soft (up to 2 KeV) and tender (2–10 KeV) X-rays applied to study functional materials for energy conversion has gone through great development in the last years and several approaches to different cell designs combined with instrumentation development now allow successful characterization of electrode-electrolyte interfaces under working conditions. An overview of the current state and challenges are presented along with an outlook into the direction that future development should take, which we expect would allow us to expand and complete our understanding of the liquid-solid electrochemical interfaces.