Electrochemical reflection anisotropy spectroscopy reveals the reversible re-structuring of InP surfaces in contact with low-concentration electrolytes upon applied potentials, while higher concentrations induce non-reversibility.

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.

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