X-ray photoelectron spectroscopy meets electrochemistry: From UHV to operando conditions

In this article the use of X-ray photoelectron spectroscopy (XPS) for the characterization of electrochemically relevant systems is examined. From its origins under ultra-high vacuum (UHV) conditions, followed by the instrumental development that gave birth to near ambient pressure XPS (NAP-XPS) setups. The electrochemical cells and sample stages that followed making possible measurements under operando conditions are described. After this, the power of operando XPS in the investigation of electrochemically relevant systems is depicted with two selected examples. Finally, the remaining challenges, the current and future development of NAP-XPS instrumentation toward higher pressures, faster measurements and combination with other techniques and its application to operando measurements are summarized.