What X-Ray Absorption Spectroscopy Can Tell Us About the Active State of Earth-Abundant Electrocatalysts for the Oxygen Evolution Reaction.

Implementation of chemical energy storage for a sustainable energy supply requires the rational improvement of electrocatalyst materials, for which their nature under reaction conditions needs to be revealed. For a better understanding of earth-abundant metal oxides as electrocatalysts for the oxygen evolution reaction (OER), the combination of electrochemical (EC) methods and X-ray absorption spectroscopy (XAS) is very insightful, yet still holds untapped potential. Herein, we concisely introduce EC and XAS, providing the necessary framework to discuss changes that electrocatalytic materials undergo during preparation and storage, during immersion in an electrolyte, as well as during application of potentials, showing Mn oxides as examples. We conclude with a summary of how EC and XAS are currently combined to elucidate active states, as well as an outlook on opportunities to understand the mechanisms of electrocatalysis using combined operando EC-XAS experiments.