Stability and performance of tape cast anode supported electrolyte (ASE) cells.

Raphaël Ihringer, Jan Van Herle
European Solid Oxide Fuel Cell Forum, 2002
Article de conférence

Recent progress in our development of anode supported electrolyte (ASE) SOFcells is reported. The cells are fabricated by cocasting of aqueous slurries of NiO/YSZ and 8YSZ, followed by cofiring. A gradient cathode is deposited by screenprinting successive layers of LSM/YSZ composite and lanthanum cobaltite, followed by a 2nd firing step. Full cells show a final thickness of ? 0.25 mm, high flexibility and reasonable warpage. Proper anode current collection is crucial and obtained by cofiring an additional outer layer together with the substrate. Power density can reach 0.2 W/cm2 at 600°C with active cathodes (LSC, short-lived) and >1 W/cm2 at 810°C with the LSM cathode. Stability was tested during 2900 h, giving an average degradation of 3%/1000 h at 0.5 A/cm2 current density. Degradation can be delayed by short-time polarisation at higher current density: e.g. “reactivation” at 0.85 A/cm2 (30 min.) delayed degradation by 300 h.

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Raphaël Ihringer, Jan Van Herle
European Solid Oxide Fuel Cell Forum, 2002
Article de conférence

Résumé

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https://infoscience.epfl.ch/record/53441?ln=fr

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Modeling of Local Cell Degradation in Solid Oxide Fuel Cells: Cumulative Effect of Critical Operating Points

Nordahl Autissier, Stefan Diethelm, Antonin Faes, Daniel Favrat, Arata Nakajo, Jan Van Herle, Zacharie Wuillemin

A CFD model was developed to predict with accuracy the local electrochemical performance in an operating solid oxide fuel cell. A particular focus was given on the study of performance limitations and degradation sources caused by the design of the fuel cell, by the choice of materials and components, or by improper operating points. The model is used to understand typical degradation effects observed on stacks tested in collaboration with HTCeramix - SOFCpower. The model is able to predict several degradation effects caused by the use of compressive seal materials with remaining open porosity. Diffusion across seals is modeled, as well as the resulting parasitic combustion of air and fuel. The risk of local redox-cycling for the anode supported cell is evaluated locally, as well as an eventual local reduction of the cathode layers. The cracking of electrolyte caused by redox cycles is modeled locally, with increasing gas leakage at each cycle, allowing to model the cumulative effect of successive critical operating points. The results are compared with experiments, showing an overall good agreement.

European Fuel Cell Forum2008

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Dynamic behaviour of SOFC short stacks

Nordahl Autissier, Nicolas Badel, Raphaël Ihringer, Diego Larrain, Joseph Sfeir, Jan Van Herle

Electrical output behaviour obtained on solid oxide fuel cell stacks, based on planar anode supported cells (50 or 100 cm2 active area) and metallic interconnects, is reported. Stacks (1–12 cells) have been operated with cathode air and anode hydrogen flows between 750 and 800 ◦C operating temperature. At first polarisation, an activation phase (increase in power density) is typically observed, ascribed to the cathode but not clarified. Activation may extend over days or weeks. The materials are fairly resistant to thermal cycling. A 1-cell stack cycled five times in 4 days at heating/cooling rates of 100–300Kh−1, showed no accelerated degradation. In a 5-cell stack, open circuit voltage (OCV) of all cells remained constant after three full cycles (800–25 ◦C). Power output is little affected by air flow but markedly influenced by small fuel flow variation. Fuel utilisation reached 88% in one 5-cell stack test. Performance homogeneity between cells lay at ±4–8% for three different 5- or 6-cell stacks, but was poor for a 12-cell stack with respect to the border cells. Degradation of a 1-cell stack operated for 5500 h showed clear dependence on operating conditions (cell voltage, fuel conversion), believed to be related to anode reoxidation (Ni). A 6-cell stack (50 cm2 cells) delivering 100Wel at 790 ◦C (1kWel L−1 or 0.34Wcm−2) went through a fuel supply interruption and a thermal cycle, with one out of the six cells slightly underperforming after these events. This cell was eventually responsible (hot spot) for stack failure.

2006

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Poisoning effects of chlorine on a solid oxide cell operated in co-electrolysis

Stefan Diethelm, Guillaume Jeanmonod, Jan Van Herle

Although the effects of impurities on the Ni-YSZ electrode of a solid oxide cell in fuel cell operation have been studied, reports on their effects during electrolysis operation are limited. Here, short-term experiments at various current densities and a durability test (1400 h) are performed to investigate the effects of HCl on the Ni-YSZ electrode of a solid oxide electrolysis cell (SOEC) operated in co-electrolysis mode. Without current bias, exposure to 10 ppmv of HCl was tolerated whereas significant degradation was observed when the SOEC was exposed to 5 ppmv of HCl under polarization, mostly related to an increase of the resistance associated with the charge-transfer processes. Prolonged exposure to HCl revealed an initial steady degradation before an increase by a factor of >10 caused by polarization resistance increases, thereby emphasizing the importance of prolonged poisoning tests. Stopping the HCl supply and operating the SOEC in an HCl-free atmosphere allowed for voltage stabilization but no performance recovery was observed. An increased serial resistance indicates that the desorption of Cl can also be detrimental. A low-frequency pseudo-inductive hook appeared in the electrochemical impedance spectra, possibly related to the increase of the charge-transfer processes' resistance and indicating modification to the electrochemical pathways.

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