Experimental and Computational Aspects of Electrochemical Reflection Anisotropy Spectroscopy: A Review

Abstract

Electrode/electrolyte interfaces play a crucial role in many electrochemical energy conversion and storage technologies. Hence, a deep understanding of the interfacial structure, energetic alignment and processes is of high relevance and has triggered the development of a number of in situ and operando techniques. One approach for gaining information about the change in surface chemistry and structure on an atomic scale is reflection anisotropy spectroscopy (RAS). This review presents and discusses the continuing effort to develop RAS as an in situ optical probe for solid‐liquid interfaces under applied potentials. Experimental and computational basic principles are presented and key challenges of electrochemical RAS are highlighted. Furthermore, we exemplarily demonstrate the potential of the method for spectroelectrochemistry, focusing on indium phosphide‐ and gold‐aqueous electrolyte interfaces as exemplary case studies, and outline research directions for battery systems.

The relevance of structural variability in the time-domain for computational reflection anisotropy spectroscopy at solid–liquid interfaces

“…The blue curve depicts the average spectrum of the MD simulation without water. observed data of the full electrochemical system [5,[8][9][10]. This, however, is likely to be a consequence of the limited system size as well as the absence of electrolyte ions.…”

“…This means that electrodes with anisotropic crystal surfaces can be investigated under operating conditions, allowing to relate particular features in a cyclic voltammogram to an in operando measured spectroscopic response. The observed spectra can then ideally be connected to particular structural modifications such as reconstructions or the adsorption of certain atoms and molecules on the surface [5,7]. Early electrochemical RAS studies used gold as electrode in aqueous electrolytes [8][9][10].…”

“…However, most experimental techniques applicable to solid-liquid interfaces under operando conditions are either restricted in structural or temporal resolution, which means that the availability of information on the atomistic scale under realistic electrochemical conditions is limited. Here, electrochemical reflection anisotropy spectroscopy (RAS) is an emerging optical method in the field, allowing for a non-destructive investigation of crystalline surfaces and interfaces providing insights in their atomistic structure [5].…”

In Situ Monitoring of the Al(110)‐[EMImCl] : AlCl3 Interface by Reflection Anisotropy Spectroscopy

“…In battery research, RAS has the potential to give insight into SEI formation, metal stripping/plating, as well as ion transport processes. In the working principle of RAS, linearly polarized light impinges at near‐normal incidence on a single‐crystalline surface [21,22] . The difference in reflectivity, Δ r , with respect to two orthogonal directions in the surface plane (x, y) is then measured and scaled with the mean reflectivity, r .…”

“…With such a technique, changes in surface structure and surface chemistry can be studied with a time resolution of about 10 ms. Furthermore, real‐time monitoring in an electrochemical environment is possible [22] . Since RAS is restricted to single crystals, the present study focuses on the evolution of Al(110) in the IL electrolyte.…”