Solid Oxide Electrolysis Cells: Microstructure and Degradation of the Ni/Yttria-Stabilized Zirconia Electrode

TLDR

Solid oxide fuel cells produced at Risø DTU were operated as electrolysis cells for steam by applying an external voltage. The authors discovered that the earlier reported passivation was due to glass sealing, and that long‑term electrolysis degradation was mainly caused by increasing polarization resistance at the hydrogen electrode, with significant microstructural changes occurring at high current density, temperature, and steam pressure, yet the electrode microstructure remained largely intact for extended operation.

Abstract

Solid oxide fuel cells produced at Risø DTU have been tested as solid oxide electrolysis cells for steam electrolysis by applying an external voltage. Varying the sealing on the hydrogen electrode side of the setup verifies that the previously reported passivation over the first few hundred hours of electrolysis testing was an effect of the applied glass sealing. Degradation of the cells during long-term galvanostatic electrolysis testing [, , ] was analyzed by impedance spectroscopy and the degradation was found mainly to be caused by increasing polarization resistance associated with the hydrogen electrode. A cell voltage degradation of was obtained. Postmortem analysis of cells tested at these conditions showed that the electrode microstructure could withstand at least of electrolysis testing, however, impurities were found in the hydrogen electrode of tested solid oxide electrolysis cells. Electrolysis testing at high current density, high temperature, and a high partial pressure of steam [, , ] was observed to lead to significant microstructural changes at the hydrogen electrode-electrolyte interface.