What X-ray absorption spectroscopy can tell us about the active state of earth-abundant electrocatalysts for the oxygen evolution reaction

TL;DR

This paper reviews how X-ray absorption spectroscopy combined with electrochemical methods can reveal the active states of earth-abundant metal oxide electrocatalysts for oxygen evolution, aiding rational catalyst design.

Contribution

It introduces the use of electrochemical and X-ray absorption spectroscopy techniques to understand active states of earth-abundant electrocatalysts, with manganese oxides as examples.

Findings

EC and XAS reveal catalyst changes during preparation and operation

Combined operando EC-XAS elucidates active states of catalysts

Framework aids future mechanistic studies of electrocatalysis

Abstract

Chemical energy storage is an attractive solution to secure a sustainable energy supply. It requires an electrocatalyst to be implemented efficiently. In order to rationally improve the electrocatalyst materials and thereby the reaction efficiency, one must reveal the nature of the electrocatalyst under reaction conditions, i.e., its active state. 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) has been very insightful and still holds untapped potential. Herein, we concisely introduce the basics of EC and XAS and provide the necessary framework to discuss changes that electrocatalytic materials undergo, presenting manganese oxides as examples. Such changes may occur during preparation and storage, during immersion in an electrolyte, as well as during application of potentials without or with catalytic reactions. We conclude with a concise summary of how EC and XAS are currently combined to elucidate the active state as well as an outlook on future opportunities to understand the mechanisms of electrocatalysis using combined operando EC-XAS experiments.