Performance characterization of a solid oxide cell stack with chromium-based interconnects (CFY)

A 10-cell planar stack with solid oxide cells was tested in reversible operation: fuel cell and electrolysis mode. The stack consists of electrolyte supported cells (ESCs) based on Scandia doped Zirconia (∼165 μm thick), Chromium based interconnects (CFY) and H.C. Starck electrodes. Different temperature regimes have been tested and the results of the experiments are presented and discussed. The effects of different operating temperatures at various H2/H2O-ratios in steam electrolysis mode and various H2/H2O/CO2-ratios in co-electrolysis mode were studied and the operating limits determined. Finally an endurance test in co-electrolysis mode was conducted. Experiments were performed over a temperature range of 750-850 °C and current densities between 0 and 0.36 A/cm2. The results include temperature profiles in fuel cell mode and electrolysis performance at various temperatures, gas inlet compositions and inlet flow rates. In steam electrolysis best performance was achieved with a 20/80-H2/H2O-ratio, whereby a steam conversion rate of 92% and an electrolysis efficiency of 79% were obtained at the maximum current density of 0.36 A/cm2. Co-electrolysis tests were carried out up to current densities of 0.3 A/cm2 and H2/CO-ratios of 14.05, 6.43 and 2.82 were measured at the outlet. Using the inlet gas composition of H2/H2O/CO2 = 20/70/10, which is a typical outlet gas compositions for a small scale distributed hydrogen generation application, a steam conversion of 68% and an average H2/CO-ratio of 6.34 were achieved.