Soft X-Ray Operando Characterization of Electrochemical Interfaces

Abstract

HIPPIE is a high-flux, high-resolution soft x-ray beamline at MAX IV Laboratory (Sweden) with a new dedicated experimental setup for operando studies of electrochemical interfaces.[1] Such experiments utilize the dip-and-pull method to form a thin liquid meniscus on the surface of the working electrode in a three-electrode cell with a liquid electrolyte solution. Both the liquid film itself and the electrode-electrolyte interface can then be probed using X-ray photoelectron spectroscopy (PES) whilst maintaining full electrochemical control. The technique can be used to probe oxidation state changes, chemical shifts, electronic structure and electrochemical potentials in-situ.In this talk we will discuss status of spectroelectrochemical PES using soft X-rays, discussing the merits of the various different approaches to cell design. We will present three case studies on the topics of molecular redox reactions, battery interfaces and metal corrosion, all of which can be studied using dip-and-pull.[2-4] We will primarily aim to provide an introduction to the dip-and-pull method for those interested in this genre of advanced operando characterization. We will additionally outline the experimental realities and challenges that any potential new user of the dip-and-pull method should be aware of before applying for beamtime to conduct an experiment.The three case studies were all measured at HIPPIE, where the beamline operates in the 250-2000 eV range, providing access to the L absorption edges of many transition metals and the K edges of light elements. The dip-and-pull PES experiments are realized with an ambient-pressure hemispherical electron analyzer allowing measurements in vapor pressures up to 25 mbar. Electrochemical cells can therefore use aqueous electrolyte solutions as well as some organic solvents, including many of those common in batteries. An argon/nitrogen atmosphere glove box can be attached to the measurement chamber such that air sensitive materials can be studied. Typically foils or thin films are used for the working electrode. This apparatus therefore provides one of the most flexible platforms for electrochemical studies using soft-X-ray spectroscopy.