The stack was mainly characterized in a furnace environment in electrolysis mode, with 50% humidified H2 at 800 °C. The endothermic electrolysis operation was carried out with a current density of -0.5 Acm-2 and steam conversion rate of 50%. Electrolysis at lower temperatures (i.e. 700 °C and 750 °C) and fuel cell operation (with 0.5 Acm-2 and fuel utilization of 50%.) at 800 °C were also carried out shortly (<2000 h each) for comparison. After altogether ~20,000 hours of operation, the voltage and ASR degradation rates during electrolysis at 800 °C (8000~20,000 h) are ~0.4%/1000h and 3%/1000h, respectively. Electrochemical impedance spectroscopy (EIS) and analysis of the distribution function of relaxation times (DRT) showed that the degradation was primarily due to the increase in ohmic resistance. An increasing polarization in fuel electrode in one of the layers was also observed during the last 2000 h of operation, most likely due to the increased leakage rate inside the stack.
The stack is planned to be operated for another 2000 h before post mortem analysis. Stack performance and degradation analysis under different working conditions, together with preliminary post analysis will be presented.