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The feasibility of long-term operation of SOFC is studied with a series of short stacks. Anode supported planar cells with 10 μm thick electrolyte cells were used in the studies. The cell dimension was 110 mm × 110 mm and 1 mm thick, the active area was 90 × 90 mm. A 1-cell stack with stainless steel current collector and gas distributor was demonstrated with pure hydrogen as fuel at 750 °C at 40 A (current density was 0.37 A/cm2)for nearly 4000 hours. The cell performed a rapid degradation in the initial hundred hours and then went relative stable until a power failure interrupted the test. Post tests showed both good structure and chemical stability of the electrolyte, electrodes and contact materials for the cell, but pin-holes can be found in the electrolyte. Metal current collector oxidation was limited both on air and fuel sides. These results revealed that the degradation might mainly cause by the pin-holes, which, judged from their morphology, were formed during the manufacture procedures. After improving the manufacture procedure and decreased the pin-hole amount, the cell shows an improved durability in the 1-cell. At operating temperature of 800 °C, the working voltage kept nearly a constant for over 400 hours at 400 mA/cm2 current density. Based on these works, a 10-cell external-manifold short stack was assembled and tested at 750 °C with hydrogen. For the initial 100 hours of the test, the degradation rate reduced greatly comparing with that of the pre-optimized cell. The comparison confirmed the deduction that the electrolyte pin-holes contribute most part for the degradation.

Solid Oxide Fuel Cells; Stack; Degradations; Long-Term Testing; Performance; Post Testing Analysis