Long term behaviour of solid oxide electrolyser (SOEC) stacks

Kurzfassung

The German funded project "Reversible Solid Oxide Cell" (RSOC) aims to demonstrate a reversible SOC system made by Sunfire GmbH (Dresden/Germany) in the industrial power-to-gas plant of Audi AG in Werlte (Germany). For the optimization of the RSOC system, a fundamental understanding of the stack behavior during reversible SOFC/SOEC long-term cycling is obligatory. Therefore, this paper presents the degradation results of a 30-cell stack of Sunfire GmbH with electrolyte supported cells operated for 9200 h and 337 SOFC/SOEC cycles with 70% fuel gas conversion. The stack showed a very good and homogeneous initial performance in both modes. During the following 8600 h of operation with 326 SOFC/SOEC cycles, very low degradation rates were measured. The degradation was dominated by the increase of the ohmic resistance. The resulting enhancement of the temperature gradients and the thermo-mechanical stresses inside the stack have led to progressive degradation after 9000 h of operation.