Experiments on metal-Glass-metal samples simulating the fuel inlet/outlet manifolds in SOFC stacks

The investigations performed on state-of-the-art SOFC stacks operated at various electrical load for several thousand hours have underlined the importance to better understand how the sealant materials evolve during the operation period. The opportunity to operate a stack and to have access to post-experiment samples is quite unique and opened the possibility to design and operate in a suitable rig samples replicating the metalglass-metal of a stack manifold. Samples prepared with the same materials and manufacturing method as for stacks have been aged at operating conditions of the fuel inlet and outlet for 500h under a polarization of 0.8V and a temperature of 700°C in dual atmosphere (i.e. air, fuel). The evolution of the glass properties has been followed in by Electrochemical Impedance Spectroscopy (EIS) with measurements performed at Open Circuit Voltage (OCV) and under polarization. EIS measurements allowed to monitor the behaviour of the investigated system during the ageing process. The bulk resistance of the glass was measured and related to the evolution of the microstructural features investigated by post experiment characterization on the cross-sections. The combination of different fuel stream composition and temperature resulted in a quite stronger evolution of the glass at the outlet.