Pressurized operation of solid oxide electrolysis stacks: An experimental comparison of the performance of 10-layer stacks with fuel electrode and electrolyte supported cell concepts

Abstract

The electrochemical behavior of two different types of planar 10-layer solid oxide cell (SOC) stacks with having either fuel electrode supported cells or electrolyte supported cells, are examined under steam, co- and CO2 electrolysis at elevated pressures of up to 8 bar. Experiments with steady-state and dynamically recorded U(i)-characteristics are performed in order to evaluate the performances over a wide temperature range and for different operating conditions. Furthermore, the influence of the operating pressure is quantified via the temperature and pressure dependency of the related ASR values of each stack. Impedance analysis is conducted in order to investigate the major differences and the pressure effect on the specific process resistances during steam and CO2 electrolysis.In case of the stack with fuel electrode supported cells, the ASR is found to decrease significantly at elevated pressure leading to an overall performance gain, whereas the stack with electrolyte supported cells shows a minor pressure effect. An impedance study shows that the diffusion and activation resistances are significantly affected when conducting CO2 instead of H2O electrolysis for both stack concepts. Furthermore, the pressure sensitivity is found to be more dominant during CO2 electrolysis than during pure steam electrolysis operation.