Lab-based operando x-ray photoelectron spectroscopy for probing low-volatile liquids and their interfaces across a variety of electrosystems

Abstract

The understanding of fundamental processes in liquids and at the liquid/electrode interfaces of electrochemical systems is crucial for the development of new devices and technologies with higher efficiency and improved performance. However, it is generally difficult to isolate and study the component of interest in such complex systems. Additionally, ex situ analyses do not always reflect the same properties under operating conditions. Hence, operando characterization tools are required for observing related electrical and chemical processes directly at the places where and while they occur. Operando x-ray photoelectron spectroscopy (o-XPS) has been used, while the sample is imposed to DC/AC voltage stress, to record the binding energy shifts in and on liquids and their interfaces to extract local potentials, as well as many related properties specific to the application in a noncontact and chemically resolved fashion. The applications of o-XPS to low-volatile liquids shown in this review span well-defined studies of (1) electrochemical cells, (2) double-layer capacitors, and (3) electrowetting on dielectrics. The methodology and several applications selected from the authors’ recent publications are presented.