Applications of in situ electron microscopy in oxygen electrocatalysis

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.

A review of recent developments for the in situ/operando characterization of nanoporous materials

“…These developments enhanced the energy resolution capabilities and especially the spatial resolution of TEM measurements. [71][72][73][74] As described above, most synthesized porous materials, such as zeolites, MOFs, and COFs, are polycrystalline with small crystallite sizes preventing the structure determination via single-crystal X-ray diffraction. [10][11][12] Even though structure solution from powder data is possible, overlapping reflections and large unit cells, as well as the often disordered nature of these porous materials are challenging.…”

“…77 With modern TEM instruments and mostly specially designed TEM sample holders, in situ and operando investigations are possible allowing the establishment of not only the bulk structure but also local structure-property relationships. 71,73,74,83,84 This setup can be combined with different in situ sample holders (e.g. heating or cooling) but the general gas pressure has to be kept low to maintain the high vacuum.…”

4D-STEM Ptychography for Electron-Beam-Sensitive Materials

“…Transmission electron microscopy (TEM) integrates diffraction, imaging, and spectroscopy and plays a vital role in material chemistry. − Modern electron microscopes equipped with spherical aberration correctors can probe the crystallographic, physical, and chemical properties of materials with a subangstrom spatial resolution. However, many materials are sensitive to electron beam irradiation, and their high-resolution TEM imaging has long been challenging due to electron-beam-induced structural damage. − Typical electron-beam-sensitive materials (or “beam-sensitive materials”) include materials with porous structures, organic components, or weak chemical bonds, such as metal–organic frameworks (MOFs), covalent–organic frameworks, organic–inorganic hybrid perovskites, and supramolecular crystals.…”

Insights into Heterogeneous Catalysts under Reaction Conditions by In Situ/Operando Electron Microscopy

“…The development of the environmental TEM (ETEM) has demonstrated the ability to capture the dynamic morphological changes at solid/gas or solid/liquid interfaces in real-time in catalytic reactions, including electrocatalysis in liquid media and heterogeneous catalysis in gas media. [8,11,14,[53][54][55] These catalytic or electrocatalytic reactions can be found in many technological fronts, including water-splitting electrolysis, fuel cells, lithium batteries, fuel conversion, and emission control systems. Some of the best catalysts are noble metals from the catalytic activity and selectivity perspectives but are worst from the cost perspective.…”

“…Despite an apparent lack of clarity in the literature in terms of in situ and operando TEM and related techniques, it is generally accepted that in situ or operando TEM directly or indirectly shows the ability to obtain the information related to the reaction conditions. [53,54,71,72,[85][86][87][88][89][90][91][92] Identical location TEM (IL-TEM) is a method that has attracted some interest in heterogeneous catalysis research in recent years. [93] While this technique may fall in between ex situ and in situ/operando modes, it is practically an ex-situ technique that allows imaging of the same sample area before and after catalysis experiment, to assess the changes in surface morphology.…”