Relation Between Ni Particle Shape Change and Ni Migration in Ni–YSZ Electrodes – a Hypothesis

Mogensen, Mogens Bjerg; Hauch, Anne; Sun, Xiufu; Chen, Ming; Tao, Youkun; Ebbesen, Sune Dalgaard; Hansen, Kent Kammer; Hendriksen, Peter Vang

doi:10.1002/fuce.201600222

Cited by 126 publications

(142 citation statements)

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“…At the inlet of the tested cell, enrichment of Ni in the support layer just next to the active electrode is clearly visible, while at the outlet of the tested cell and in the reference cell, the Ni distribution is rather homogeneous. A more detailed discussion on the Ni migration can be found in [30]. Such phenomenon was however not found in the present test as confirmed by high resolution BSE images (not shown here).…”

Section: Discussionsupporting

confidence: 66%

“…It has been reported that kinetics for H 2 or CO oxidization are slightly faster than for H 2 O or CO 2 reduction [13,14]. At the Ni-YSZ electrode, beside loss of contact between Ni and Ni grain due to Ni agglomeration or Ni migration [19,20,28], nano ZrO 2 precipitation from Zr dissolved in the Ni bulk was observed [29,30]. In SOFC mode the process is highly exothermic, while in SOEC mode it is dependent on the operation voltage whether heat is produced or consumed in the electrolysis overall process (considering both reaction entropy changes and joule heat).…”

Section: Introductionmentioning

confidence: 97%

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Degradation in Solid Oxide Electrolysis Cells During Long Term Testing

et al. 2019

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In this work, we report a 4,400 h test of a state-of-the-art Ni-YSZ (yttria stabilized zirconia) electrode supported solid oxide electrolysis cell. The electrolysis test was carried out at 800°C, -1 A cm -2 with 10% H 2 + 90% H 2 O supplied to Ni-YSZ electrode compartment. Except for the first 250 h of fast initial degradation, the cell showed rather stable performance with a moderate degradation rate of around 25 mV per 1,000 h. The electrochemical impedance spectra (EIS) acquired during the test show that both serial resistance and electrode polarization resistance increased during the durability test. Further impedance analyzes show that both the LSCF (strontium and cobalt co-doped lanthanum ferrite)-CGO (gadolinium doped ceria) electrode and Ni-YSZ electrode degraded and the degradation was dominated by the Ni-YSZ electrode. Post mortem analysis on the Ni-YSZ electrode revealed loss of contact between Ni-Ni grains, Ni-YSZ grains and increased porosity inside the active layer. The microstructural changes were most severe at steam gas inlet and became less severe along the gas flow path. The present test results show that this type of cell can be used for early demonstration of solid oxide cell operation at electrolysis current densities around 1 A cm -2 .

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Section: Discussionsupporting

confidence: 66%

Section: Introductionmentioning

confidence: 97%

Degradation in Solid Oxide Electrolysis Cells During Long Term Testing

et al. 2019

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“…19, 26 The thickness of this layer is also increasing in the direction of the fuel inlet. In particular, at the fuel inlet the thickness of the layer is doubled.…”

Section: Resultsmentioning

confidence: 99%

Electrochemical Performance and Preliminary Post-Mortem Analysis of a Solid Oxide Cell Stack with 20,000 h of Operation

Fang

Frey

Menzler

et al. 2018

J. Electrochem. Soc.

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A long-term test with a two-layer solid oxide cell stack was carried out for more than 20,000 hours. The stack was mainly characterized in a furnace environment in electrolysis mode, with 50% humidification of H 2 at 800 • C. The endothermic operation was carried out with a current density of −0.5 Acm −2 and steam conversion rate of 50%. Electrolysis at lower temperatures (i.e., 700 • C and 750 • C) and fuel cell operation (with 0.5 Acm −2 and fuel utilization of 50%) at 800 • C were also carried out (<2000 h each) for comparison. The voltage and area specific resistance degradation rates were ∼0.6%/kh and 8.2%/kh after ∼18,460 hours of operation. In total, the stack was operated above 700 • C for more than 20,000 hours. Impedance measurement and analysis showed that the increase of ohmic resistance was the main degradation phenomenon, while electrode polarizations were kept nearly constant before a severe burning took place in one layer. Ni-depletion in fuel electrodes was confirmed during post-mortem analysis, which was assumed to be the major degradation mechanism observed. The stack performance and degradation analysis under different working conditions, as well as the results of preliminary post-mortem analysis will be presented. One of the critical challenges to the application and commercialization of solid oxide cell (SOC) technology is the long-term stability of complete systems, stacks and single components. Despite the fact that accelerating methods have long been under discussion, the time-consuming and costly endurance tests of stacks and cells under relevant conditions are still necessary for reliable degradation analyses and lifetime prediction. Compared to the tests with single cell or other stack and system component, the results of long-term degradation tests with stacks are quite limited. [1][2][3][4][5] Previous results have shown stable performance of stacks working in the temperature range of 700-800• C in SOFC mode. [6][7][8][9] Recently, a short stack achieved a 10 years lifetime, and remains in operation. 10 With proper protective coating, a voltage degradation rate of less than 0.3%/kh and lifetime of more than 40,000 h at 700• C is possible with current stack design and components. In contrast to the low degradation rate in SOFC mode, higher degradation rates of ∼0.6-1.5%/kh were observed with similar types of cells in the same stack design in SOEC mode, as described by Nguyen et al. 11 Therefore, the functionality and optimization potential of the cells and stacks, as well as their long-term degradation behavior and mechanisms in SOEC mode, needs to be further investigated. Amongst the stacks operated in SOEC mode, a two-layer stack was operated under different stationary conditions for more than 20,000 h. The stack performance was regularly monitored by open circuit voltage, voltage-current curves and impedance measurements. After cooling down, one third of the stack was embedded in resin for cross-section preparation, and the rest was disassembled for visual inspection. The prelim...

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“…Loss of percolation indicated the Nickel migration from the active layer to the support. Hence, it was also of interest to investigate the theory of Nickel migration . For this purpose, line scans were done through Cell‐C to check for the possibility of loss in Ni surface area due to migration.…”

Section: Resultsmentioning

confidence: 99%

“…For further information, please refer to Appendix‐B. This methodology gives an indication of the magnitude of the Ni migration from the active region to the fuel support .…”

Section: Resultsmentioning

confidence: 99%

Unwinding Entangled Degradation Mechanisms in Solid Oxide Electrolysis Cells Through Electrode Modifications and Impedance Analysis

Rao

Jensen²,

Sun

et al. 2019

Fuel Cells

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In the renewable energy scenario, energy storage is of essence. In this context, power‐to‐liquid (PtL) and power‐to‐gas (PtG) concepts have attracted large attention, where the use of solid oxide electrolysis cells (SOECs) has a huge potential, due to their high conversion efficiencies. However, performance and durability of these cells still need to be improved for a large‐scale commercialization of the SOEC technology. It is often difficult to identify the various loss and degradation mechanisms limiting the cell performance and durability. This paper contributes to this scientific discussion, by providing a careful analysis of the degradation mechanisms occurring in three different cells during long‐term H2O and CO2 co‐electrolysis, at 1,200 mV. Electrochemical impedance spectroscopy (EIS) is measured before, during and after the electrolysis operation, and is utilized to address the individual electrode degradation mechanisms and the development of leaks through the electrolyte. Moreover, the leak rates under open circuit voltage (OCV) measurements were compared. In addition, microstructural analysis of the electrodes and electrolytes is related to the electrochemical findings to contribute to the discussion on the interdependency of the degradation mechanisms.

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Relation Between Ni Particle Shape Change and Ni Migration in Ni–YSZ Electrodes – a Hypothesis

Cited by 126 publications

References 26 publications

Degradation in Solid Oxide Electrolysis Cells During Long Term Testing

Degradation in Solid Oxide Electrolysis Cells During Long Term Testing

Electrochemical Performance and Preliminary Post-Mortem Analysis of a Solid Oxide Cell Stack with 20,000 h of Operation

Unwinding Entangled Degradation Mechanisms in Solid Oxide Electrolysis Cells Through Electrode Modifications and Impedance Analysis

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