Performance of a glass-ceramic sealant in a SOFC short stack

Abstract

The development of sealants for solid oxide fuel cells (SOFCs) is a significant challenge as they must meet very restrictive requirements; they must withstand the severe environment of the SOFC (i.e., be resistant to oxidative and reducing gas environments) and be thermo-chemically and thermo-mechanically compatible with the materials to which they are in contact with. This work discusses the design and the operation of two SOFC short stacks (based on planar anode-supported cells) along with the performance of a glass ceramic sealant inside the stack.In particular, a joined Crofer22APU frame/glass-ceramic sealant/anode-supported-cell (ASC) was tested in two SOFC short stack configurations (referred to as “m1stack” and “m2stack” tests, respectively), in order to study the stability and the effectiveness of the glass-ceramic (boron and barium-free silica-based) sealant used in the experiment. The difference between the two stacks was the presence of a Mn1.5Co1.5O4 protective coating on the Crofer22APU frame prevent Cr poisoning of the cathode used in the m2stack. A full cell open circuit voltage was achieved during the experiments, indicating therefore that the glass ceramic sealant employed provided effective gas separation. The time-evolution of the cell voltage was investigated to evaluate eventual degradation caused by chromium poisoning at the cathode. The m2stack was operated at ∼0.3 A cm−2 and an FU (Fuel Utilisation) of 25% and no voltage degradation was observed for the duration of the galvanostatic experiment (350 h).Microstructural post-mortem analysis after the experiments (m1stack and m2stack) in the short stack configuration highlighted the excellent compatibility of the glass-ceramic sealant with Crofer22APU and YSZ, respectively, as well as the effectiveness of Mn1.5Co1.5O4 coating on Crofer22APU to prevent Cr poisoning of the cathode.