Performance and Degradation of Solid Oxide Electrolysis Cells in Stack
The stack was characterized in furnace environment in both fuel cell and electrolyser mode with 50% humidified H2 from 700 °C to 800 °C. At 800 °C, the area specific resistances (ASRs) were calculated to be 130 mΩcm² and 150 mΩcm² under fuel cell and electrolyser mode, respectively. Long-term electrolysis operation (endothermically) at 800 °C under constant current mode is being carried out with a current density of 0.5 Acm-2 and a steam conversion rate of 50% with 50% humidified H2. After 1500 h operation (status 09.12.2014), the stack showed an average voltage degradation rate of 0.7%/1000h. Electrical impedance spectroscopy (EIS) and analysis of distribution of relaxation time (DRT) showed that the degradation was mainly due to the increase of Ohmic resistance, and the electrode polarizations did not change with the chosen testing conditions. The stack is planned to be further operated at 700 °C after a 2000 h electrolysis period at 800 °C. The performance and degradation behavior of the stack at 700 °C and 800 °C will be analysed with the support of EIS and DRT.