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

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 ͓850°C, −1/2 A/cm 2 , p͑H 2 O͒/p͑H 2 ͒ = 0.5/0.5͔ 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 2%/1000 h was obtained. Postmortem analysis of cells tested at these conditions showed that the electrode microstructure could withstand at least 1300 h 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 ͓−2 A/cm 2 , 950°C, p͑H 2 O͒ = 0.9 atm͔ was observed to lead to significant microstructural changes at the hydrogen electrode-electrolyte interface.

Ni/YSZ electrodes structures optimized for increased electrolysis performance and durability

“…The cells were heated (1 C/min) to 850 C for sealing and the NiO was reduced by leading 20 l/h of dry 9 % H2 in N2 to the fuel electrode for 2 hours followed by 1 hour of 20 l/h dry H2 to the fuel electrode while air was led to the oxygen electrode [21]. This reduction procedure was chosen to make the NiO reduction procedure similar to several previously reported SOEC test (e.g.…”

“…[32]. Blue squares in c) and d) highlight examples of lost Ni-Ni contact while red arrows highlights lost Ni-YSZ interface and red circles mark inclusions of silica-containing impurities in Ni [13,21].…”

Mechanism and Kinetics of Ni-Y2O3-ZrO2Hydrogen Electrode for Water Electrolysis Reactions in Solid Oxide Electrolysis Cells

“…43 However, H 2 O adsorption could occur on oxygen covered Ni surface at elevated temperatures. 44 Gorski et al studied the mechanism of H 2 O dissociation on YSZ surface using temperature-programmed desorption (TPD) spectroscopy and density functional theory (DFT) and showed that interaction of H 2 …”

WDX Studies on Ceramic Diffusion Barrier Layers of Metal Supported SOECs

“…Measurements on the substrate grains showed a distinct decrease in the Cr-content of up to 50 wt.-% due to Cr-loss compared with the virgin steel substrate (initial composition: Fe, 26Cr). The highest Ni concentration measured in the metal substrate is approximately 4 wt.-%, whereas the original ferritic steel alloy is altered at least partially into an austenitic structure [3]. This increases the coefficient of thermal expansion which can cause cracks in the substrate lowering the long-term stability and cell performance.…”

“…A porous cermet of Y 2 O 3 stabilised ZrO 2 (YSZ) and Ni is a commonly used material for the cathode in solid oxide electrolyser cells [1][2][3]. In metal supported cells (MSCs) from the German Aerospace Center (DLR) in Stuttgart, Germany [4], the Ni-cermet cathode material is directly deposited onto a porous metallic substrate of a Fe-Cr-Plansee alloy (oxide dispersive strengthened PM ODS-alloy) followed by the YSZelectrolyte and the Sr doped LaMnO 3 -anode (LSM) (Figure 1).…”