Experimental Requirements for High‐Temperature Solid‐State Electrochemical TEM Experiments

Abstract

The ability to perform both electrochemical and structural/elemental characterization in the same experiment and at the nanoscale allows to directly link electrochemical performance to the material properties and their evolution over time and operating conditions. Such experiments can be important for the further development of solid oxide cells, solid‐state batteries, thermal electrical devices, and other solid‐state electrochemical devices. The experimental requirements for conducting solid‐state electrochemical TEM experiments in general, including sample preparation, electrochemical measurements, failure factors, and possibilities for optimization, are presented and discussed. Particularly, the methodology of performing reliable electrochemical impedance spectroscopy measurements in reactive gases and at elevated temperatures for both single materials and solid oxide cells is described. The presented results include impedance measurements of electronic conductors, an ionic conductor, and a mixed ionic and electronic conductor, all materials typically applied in solid oxide fuel and electrolysis cells. It is shown that how TEM and impedance spectroscopy can be synergically integrated to measure the transport and surface exchange properties of materials with nanoscale dimensions and to visualize their structural and elemental evolution via TEM/STEM imaging and spectroscopy.

Operando Electron Microscopy and Impedance Analysis of Solid Oxide Electrolysis and Fuel Cells

“…The YSZ electrolyte will contribute with a series of ionic transport resistance, R t . From separate operando TEM measurements of the Pt and STN current collectors, it was found that their contributions to R t are minimal compared to that of YSZ in the present gas environment. , In addition the electrical circuit on the MEMS chip, the TEM holder wires, and the cables connecting to the potentiostat influence the measurements with a shunt capacitance CPE shunt in parallel to the sample contribution. , …”

“…This particular "Z-cell" geometry was chosen for its demonstrated thermal cycling robustness, allowing multiple heating and cooling cycles without fracturing. 22 According to XRD characterization prior to mounting the cell on the chip, the CGO, YSZ, and STN are all cubic, show good crystallographic quality, and have highly (00l) oriented texture and c-axis oriented growth of the CGO and YSZ thin films on the STN substrate (Figure S1a). This preferential orientation is commonly observed in fluorite oxide grown on (001) perovskite substrates and is allowed by an in-plane 45°r otation of the YSZ and CGO cubic cell relative to the STN (illustrated in Figure S1b).…”

“…22,28 In addition the electrical circuit on the MEMS chip, the TEM holder wires, and the cables connecting to the potentiostat influence the measurements with a shunt capacitance CPE shunt in parallel to the sample contribution. 20,22 In macroscopic porous electrodes gas diffusion typically yields an additional contribution seen in EIS spectra. 34,35 For the present cell with small dense electrodes, however, contributions from mass transport are expected to be negligible.…”

“…In our recent work, it was proposed to extend the EIS-TEM concept to full model solid oxide cells. The experimental requirements were discussed, and different cell geometries were presented . Before applying the EIS-TEM methodology to analyze processes and dynamical changes in solid oxide cells, it is important to validate that reliable EIS measurements can be performed in the TEM for SOEC/SOFC model cells with nanoscale dimensions, and this was not achieved in previous work.…”

“…From separate operando TEM measurements of the Pt and STN current collectors, it was found that their contributions to R t are minimal compared to that of YSZ in the present gas environment. 22,28 In addition the electrical circuit on the MEMS chip, the TEM holder wires, and the cables connecting to the potentiostat influence the measurements with a shunt capacitance CPE shunt in parallel to the sample contribution. 20,22 In macroscopic porous electrodes gas diffusion typically yields an additional contribution seen in EIS spectra.…”