Electrochemical TEM experiments on solid oxide electrolysis cells

Session

Stream 1: EMAG - Energy and Energy Storage Materials

Authors

Zhongtao Ma (1), Kristian Mølhave (2), Christodoulos Chatzichristodoulou (1), Søren Simonsen (1)

Affiliations

1. Department of Energy Conversion and Storage, Technical University of Denmark
2. National Centre for Nano Fabrication and Characterization, Technical University of Denmark

Keywords

in situ; transmission electron microscopy (TEM); electrochemical impedance spectroscopy (EIS); solid oxide electrolysis cells (SOEC); gadolinium doped ceria (CGO); yttrium stabilized zirconia (YSZ)

Abstract text

In this work, in situ transmission electron microscopy (TEM) and in situ electrochemical impedance spectroscopy (EIS) are combined, to directly correlate structural and chemical evolution of the cell components with electrochemical properties of solid oxide electrolysis cells (SOEC).

Hydrogen production and application from electrolysis will play a vital role in future energy systems, such as the transportation and energy storage sector. Regarding electrolysis, solid oxide electrolysis cell (SOEC) technology has been reported as the most suitable option for wide-scale adoption [1]. Gadolinium doped ceria (CGO) with decent ionic conductivity is currently used as a barrier layer, and yttrium stabilized zirconia (YSZ) is used as the electrolyte in state-of-the-art SOEC [2][3]. However, degradation at the CGO-YSZ interface has a large contribution to the degradation of the electrolysis cell [4]. In order to improve the performance of the CGO-YSZ interface and optimize the CGO and YSZ themselves, we need to determine the relations of the electrochemical activity and structure/composition. 

In this work, in situ transmission electron microscopy (TEM) and in situ electrochemical impedance spectroscopy (EIS) are combined together, which allows the study of nanostructure development of cells at elevated temperature and electrode polarization conditions in a reactive gas environment.

An optimal procedure for handling, mounting, and conducting experiments with the model cells has been developed. A nano-sized symmetrical cell with CGO (electrode, 100 nm)-YSZ (electrolyte, 100 nm)-CGO (electrode, 100 nm) is synthesized by pulsed laser deposition (PLD), and followed by a focused ion beam (FIB) process. MEMS chips developed at DTU Nanolab and commercial MEMS chips are used to achieve the application of the electrical potentials and elevated temperatures. The electrochemical properties are evaluated as a function of different temperatures and gas compositions.

We can increase the electrical polarization while observing changes in crystal phases and morphology at the CGO-YSZ interface. For example, we can follow the oxidation state of cerium in CGO changing as a function of distance to the CGO-YSZ interface and as a function of applied bias. Possible new phase formation, element segregation, and some failure contributors like voids and cracks generated along the interface can also be determined. The goal of this project is not only to solve a specific scientific problem but also to provide a platform that can establish relations between nanostructures and electrochemical properties.

References

[1] Hauch, Anne, et al. "Recent advances in solid oxide cell technology for electrolysis." Science 370.6513 (2020).

[2] Ebbesen, Sune Dalgaard, et al. "High temperature electrolysis in alkaline cells, solid proton conducting cells, and solid oxide cells." Chemical reviews 114.21 (2014): 10697-10734.

[3] Garbayo, I., et al. "Full ceramic micro solid oxide fuel cells: towards more reliable MEMS power generators operating at high temperatures." Energy & Environmental Science 7.11 (2014): 3617-3629. 

[4] Tietz, F., et al. "Degradation phenomena in a solid oxide electrolysis cell after 9000 h of operation." Journal of Power Sources 223 (2013): 129-135.