In situ Electrochemical TEM experiments on solid oxide electrolysis materials

Performance and structural degradation of materials have been among the major challenges in the commercialization of green energy technologies. Acquiring a full understanding of the changes in the electrochemical and structural properties of the components, in actual operating conditions, is therefore critical to be able to optimize them and secure a sustainable energy future.

In situ Transmission Electron Microscopy (TEM) and Electrochemical Impedance Spectroscopy (EIS) are two powerful and widely used tools in investigating the structural evolution and electrochemical performance, respectively, of energy materials. In this study, a method was developed where EIS was integrated with in situ TEM to get a full overview not only of the changes in the electrochemical response and structural properties of the materials in actual working conditions, but most importantly, to establish a direct relationship between them. The developed method was used to characterize electrospun nanofibers of popular solid oxide electrolysis cell (SOEC) components, particularly Ce_0.9Gd_0.1O_1.95-δ (CGO) and La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF).

To make the samples both TEM- and EIS- suitable, a commercial heating and biasing microelectromechanical system (MEMS) chip was used, wherein a single nanofiber was mounted on the latter. To carry this out, different approaches were explored and an attempt to optimize each was done. After careful consideration of the advantages and challenges associated with each approach, as well as the resources’ availability, the succeeding sample preparations were carried out using a micromanipulator inside a scanning electron microscope (SEM).

Using the developed method, which was carried out inside an Environmental TEM (ETEM), coupled EIS-TEM datasets were acquired in several sets of investigations to determine if the method works and to confirm its repeatability. Results from the coupled datasets revealed the significant influence of the structural evolution of the CGO nanofibers on its electrochemical response. Furthermore, results from parallel EIS measurements of LSCF nanofiber sheets acquired from the developed method and from a conventional electrochemical test rig showed similar activation energies. This confirmed the reliability of the results from the developed method.