Judicious selection, validation, and use of reference electrodes for in situ and operando electrocatalysis studies

Abstract

The development and implementation of in situ and operando characterization techniques to understand electrocatalytic processes, establish structure-property-performance relationships, and elucidate properties of electrified interfaces aid in accelerating the discovery and design of new materials for sustainable energy technologies. The validity of operando characterization techniques is predicated on the ability to accurately and reliably control the electrochemical potential of the working electrode—factors dictated by the reference electrode. Because the utilization of an appropriate reference electrode is a prerequisite for reliable operando experiments, guidelines for the judicious selection, validation, and use of reference electrodes are necessary. In this review, we discuss existing knowledge and highlight examples of the use of reference electrodes (including quasi-reference electrodes), provide practical tips, and highlight challenges in the context of operando experiments in aqueous electrolytes. We discuss critical concepts (calibration, potential drift, and preparation) and prospective opportunities regarding the use of reference electrodes for operando characterization of electrocatalytic processes. Electrochemical technologies will be integral components of sustainable economies by storing renewable sources of energy (e.g., wind, solar, and hydro) or producing fuels, chemicals, and fertilizers from non-fossil-fuel feedstocks. Widespread deployment of electrochemical technologies relies on high-performance and inexpensive catalysts. The rational discovery and development of next-generation catalysts are predicated on a fundamental understanding of the catalytic mechanisms and properties that dictate performance. Operando characterization, a growing area of research, elucidates the understanding of catalyst properties “in action” (under operating conditions). The accuracy and reliability of operando studies are dictated by appropriate selection, validation, and use of reference electrodes. The impact on the scientific community will be operando experiments done with increased rigor, which will accelerate the development of advanced catalyst designs and sustainable technology development. The judicious selection, validation, and use of reference electrodes in the development and implementation of in situ and operando characterization techniques predicate gaining in-depth insight including a fundamental understanding of electrocatalytic processes, structure-property-performance relationships, and the properties of electrified interfaces. Accurate and reliable operando experiments facilitate acceleration in the discovery and design of new catalytic materials.