Laboratory-based in situ and operando tricolor x-ray photoelectron spectroscopy.

Innovative approaches to study buried interfaces and heterogeneous interactions under reaction conditions are crucial for advancing energy and catalytic materials. Our near-ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) setup is equipped with a tricolor x-ray source, with Al Kα, Ag Lα, and Cr Kα excitation energies, enabling information depth-selective operando and in situ analysis of solid-liquid, solid-gas, and solid-solid interfaces. We present three case studies to demonstrate the systems' capabilities. First, we compare experimental depth profiling of a LaMnO/LaFeO/Nb:SrTiO multilayer with SESSA (simulation of electron spectra for surface analysis) simulations. Second, we examine the oxidation and reduction of FeO as a function of environment and temperature. Last, the Pt/liquid electrolyte interface is examined, revealing surface oxidation in the absence of bulk oxidation. As our results confirm, the unique combination of a NAP-XPS with the tricolor x-ray source empowers laboratory-based in situ and operando XPS characterization of advanced materials under reaction conditions in a wide range of applications.