Abstract
Oxygen electrocatalysis involving the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) plays a vital role in cutting-edge energy conversion and storage technologies. In situ studies of the evolution of catalysts during oxygen electrocatalysis can provide important insights into their structure - activity relationships and stabilities under working conditions. Among the various in situ characterization tools available, in situ electron microscopy has the unique ability to perform structural and compositional analyzes with high spatial resolution. In this review, we present the latest developments in in situ and quasi-in situ electron microscopic techniques, including identical location electron microscopy, in situ liquid cell (scanning) transmission electron microscopy and in situ environmental transmission electron microscopy, and elaborate their applications in the ORR and OER. Our discussion centers on the degradation mechanism, structural evolution and structure - performance correlations of electrocatalysts. Finally, we summarize the earlier discussions and share our perspectives on the current challenges and future research directions of using in situ electron microscopy to explore oxygen electrocatalysis and related processes.
Highlights
The global demand for sustainable clean energy has continued to grow in recent decades[1]
The main techniques used for this purpose include identical location (IL)-electron microscopy and in situ liquid cell (LC)-(S)transmission electron microscopy (TEM), with in situ environmental TEM (ETEM) occasionally used for specific research objectives
Owing to its easy operation, ILelectron microscopy has been widely used to identify the structural changes in specific catalyst particles during the electrocatalytic process performed outside the electron microscope and is considered a quasi-in situ characterization technique
Summary
The global demand for sustainable clean energy has continued to grow in recent decades[1]. While IL-electron microscopy can provide high-resolution images of the initial and final states of a specimen, it is more desirable to observe the evolution of a specimen in its native states in real time during a dynamic process, such as an electrochemical reaction For this purpose, in situ LC-(S)TEM techniques have been developed and widely used in a variety of fields, including nanomaterial nucleation and growth, corrosion science, biomolecular structure studies, bubble dynamics, radiation effects and electrochemistry[36,71]. Beermann et al.[73] employed in situ electrochemical LC-(S)TEM to investigate the activation and degradation processes of carbon-supported PtNi (PtNi/C) alloy fuel-cell catalysts They observed several real-time phenomena, including carbon support and nanoparticle motion, nanoparticle coalescence, the growth of stringy particles and atomic redeposition under electrochemical conditions, in response to the potential sweeps and holds [Figure 7]. These in situ ETEM reports elucidate the interactions between H2O and the OER catalyst, as well as indicate that in addition to structural damage, the electron beam irradiation may produce other effects (e.g., induced potential), which must be carefully considered when interpreting the experimental data
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