environmental transmission-electron microscopy

In the development of nanomaterials for energy and environmental applications, a key role is played by environmental transmission-electron microscopy (ETEM). ETEM allows variations in the fine-grained structure of specimens to be observed in real time, in situ, and with high spatial resolution, under environments closely resembling the operating environments of actual catalytic materials—making it a powerful tool for identifying the causes of material degradation, for determining reaction mechanisms, and for analyzing other key phenomena1-4). In particular, recent years have witnessed intense interest in, and growing demand for, ETEM analysis of electrode catalysts under various gaseous atmospheres and high-temperature environments, for purposes such as enhancing the power-generation performance and durability of hydrogen cells and other fuel cells and improving the electrolysis performance of solid-oxide electrolysis cells (SOECs). In this article we focus on one particular choice of electrode catalyst for SOEC cathodes: perovskite oxides, which are known to exhibit high activity and good stability.
SOECs—high-temperature electrolytic systems that can use wind, solar, or other renewable energy sources to convert carbon dioxide (CO2) into reusable forms of energy such as carbon monoxide (CO) or hydrogen (H2)— offer great promise for CO2 capture, energy recycling, and other techniques for promoting carbon neutrality5). To improve CO2 electrolysis performance, a catalyst structure has been proposed in which copious quantities of metallic nanoparticles are dispersed over the perovskite surface; for such structures, understanding the mechanism through which metal nanoparticles form on the perovskite catalyst surface in the presence of redox reactions is an important prerequisite for increasing catalytic activity and controlling stability6). For this purpose, in this study we develop a technique for in-situ observation of specimen surfaces on sub-nanometer length scales via aberration-corrected secondary electron (SE) imaging with atomic resolution; we demonstrate the use of this technique by acquiring simultaneous high-resolution in-situ scanning TEM (STEM) and SE images of specimen surfaces and the internal specimen structure under gaseous atmospheres.
In this article, we first describe our measurement system—the Hitachi High-Tech HF5000 transmission electron microscope, featuring an automated aberration corrector and capable of high-resolution STEM/SEM observation at an accelerating voltage of 200 kV, and equipped with a microelectromechanical systems (MEMS)-based heated specimen holder —and then use this system to investigate an SOEC electrode catalyst. Because our technique uses STEM and SEM for environmental STEM observations, we refer to it as ESTEM.
This article is a revised version of content published in Nature Communications with our collaborators Professor Guoxiong Wang and Dr. Houfu Lv of the Dalian Institute of Chemical Physics (Lv, H. et al., Nature Communications, 12, 5665 (2021)); some figures from that publication are also reproduced here.