Fabrication and characterization of SOC single repeating units: implementation of glass-ceramic sealants

Nowadays, there is an evident interest and demand of the industrial and domestic energy sectors to start the energy transition from fossil fuels-based energies to renewable sources. New and efficient clean power have to be implemented and Solid Oxide Fuel Cells (SOFC) are a suitable candidate to address this challenge. SOFC stacks are composed by several elements (cells, interconnects, endplates, sealants) that need to be optimized in order to maximize their performance. This work presents the implementation of glass-ceramic sealants in the setup used for large area SOFC cells, single repeating units (SRU) and stack tests at IREC. Two commercial sealants were studied, one produced by tape-casting (sealant 1) and another in form of powder (sealant 2) that was deposited by robocasting. As a first step the compatibility of these sealants with other materials involved in SRU/stack at IREC was tested. Both sealants showed excellent compatibility with all the interfaced counterparts: bare and coated Crofer22APU, bare and coated IC, anode of the cell, electrolyte of the cell. Large-area single cells and SRU were then tested in fuel cell mode performing polarization curves, electrochemical impedance spectroscopy and durability tests. Even though single cell characterization was not successful probably due to gas overpressure leading to important leakages, SRU characterization using with either sealant 1 or sealant 2 led to good results. In both cases, good OCV values were obtained, corresponding to limited leakages between the anode and cathode chambers and proves the effectivity of the tested glass-sealants. Polarization curves allowed to reach 0,3-0,4 A/cm2 at 0.7 V. Finally, a durability test of 800 h could be performed at 800ºC for the SRU made with robocasted sealant 2. Higher degradation rate was observed during the first 300 h (8,4 %) and then decreased to 3-4 %.