Long Term Tests of Ni-YSZ|YSZ|GDC|Pr0.6Sr0.4CoO3-δ in SOFC and SOEC Regimes

Thursday, 27 July 2017
Grand Ballroom East (The Diplomat Beach Resort)
G. Nurk (Institute of Chemistry, University of Tartu), F. Kukk (University of Tartu), R. Kanarbik, P. Möller, and E. Lust (Institute of Chemistry, University of Tartu)
Stability of electrochemical performance in time is one of the most important properties of SOFC/SOEC materials looking from the commercialization point of view. Long term characterization is resource consuming and therefore only commercially more interesting compositions are tested in time range of several thousand hours [1]. However, for better understanding of reasons and mechanisms of degradation processes alternative materials should also be tested in addition for the more attractive ones.

Pr0.6Sr0.4CoO3-δ (PSC) is an alternative material for widely used La0.6Sr0.4CoO3-δ with excellent activity as medium temperature SOFC cathode. However, so far there is lack of long-term test results for PSC. This study concentrates on the long term electrochemical characterization and microstructural post-test analysis of Ni-YSZ|YSZ|GDC|Pr0.6Sr0.4CoO3-δ 5 × 5 cm single cell, where YSZ is the yttria stabilized zirconia and GDC is the gadolinia doped ceria. Performance test conducted in SOFC mode at 650 °C and at cell potential 0.85 V was 17820 h long. Initial degradation of electrochemical performance was 2.6 % per 1000h. During second half of experiment degradation was only 1% per 1000h. Total power loss during test was 34.6 %. Moderate increase of total activation energy Etot at 0.8 V cell potential takes place (ΔEtot = 0.38 eV) and it increases from 0.57 eV to 0.95 eV. At 1V cell potential ΔEtot = 0.22eV, from 0.34 to 0.56 eV. Post mortem HR-SEM and TOF-SIMS analysis of tested cell has been performed and collected data show that minor structural changes caused by nickel coarsening in porous anode have been taken place. TOF-SIMS mappings of 5 × 5 cm electrode visualize the mobility of Sr from cathode into the electrolyte interface during electrode preparation. Some mobility of Si from gas-sealing glas to electrode as well as Cr deposition from Crofer 22APU current collector into electrode surface has been established.

[1] L. Blum, U. Packbier, I. C. Vinke, L.G. J. de Haart, Fuel Cells, 13 (4) 646-653