Understanding and controlling electronic properties at solid/liquid interfaces is crucial for optimizing catalytic materials, particularly in electro- and photo-catalytic processes. Accurate monitoring of changes in electronic properties, such as oxidation states and the formation of transient species, is essential for advancing our understanding of key chemical reactions.

Synchrotron radiation-based spectroscopies, including X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS), are among the most effective tools for in-situ and operando investigations. These techniques provide valuable insights into electron transfer processes and catalyst behavior under operational conditions, which are critical for developing more efficient and effective catalysts. The Beamline for Advanced Circular diCHroism (BACH) at the Elettra synchrotron facility in Trieste is leading the way in these investigations. BACH utilizes a multi-technique approach to explore a broad spectrum of material properties, including electronic, chemical, structural, and dynamic characteristics.

Recent innovations include the development of electrochemical cells (EC-cells) designed to isolate the liquid electrolyte from the vacuum environment necessary for soft X-ray measurements, featuring a transparent Si₃N₄ window or graphene membranes [1,2]. This setup, equipped with a three-electrode configuration, including an Ag/AgCl reference electrode, a platinum wire counter electrode, and a window serving as the working electrode where the catalytic material is deposited as a thin film, enables real-time collection of s-XAS data during electrochemical experiments. This configuration provides direct insights into the behavior of catalysts during electrochemical and photo-catalytic reactions [3]. The ability to perform cyclic voltammetry (CV), linear sweep voltammetry (LSV), and other electrochemical tests while simultaneously acquiring s-XAS data significantly enhances our understanding of electrochemical processes at solid/liquid interfaces. The flow EC-cell, provided with a liquid flow system, allows for the replacement of the electrolyte during the experiment, enabling the refreshment of the spent solution or adjustment of the solution’s pH as needed. Moreover, a static cell, consisting of a lithium anode and a thin-film cathode material deposited on the window, designed for easy assembly in a glove box, has been specifically developed for the study of rechargeable Li-ion batteries (LIBs).

This comprehensive approach is crucial for the development of new materials with improved activity, selectivity, and performance, which are essential for advancements in chemistry, materials science, and energy technology. Examples of promising Cu nanoparticle (NP) catalysts for CO and CO₂ reduction, investigated using in-operando s-XAS measurements, will be discussed. In particular, the in-situ electrodeposition of Cu NPs and their stability in an alkaline environment during CV and CO₂ reduction reactions will be presented.