Performance maps of a MK352 CFY stack in steam- (H2O) and Co- (H2O/CO2) electrolysis operation show a difference in electric power demand of less than 5 %. This low additional power demand of Co-electrolysis together with the advantages of direct syngas production makes it promising for highly efficient integration within a process concept for the production of valuable hydrocarbons. The output syngas can be directly adjusted by choosing appropriate operating conditions for the SOEC to typical compositions used for reactions like Fischer-Tropsch synthesis. Based on this approach the operating conditions were set and durability tests with stacks (>1500 h) were conducted. The results raised several scientific questions which were answered by splitting the “black box” of the stack in separate parallel investigated experiments in the fields of cell tests, tests of interconnect materials, contact resistances, protective layer and glasses.
The surprising behavior of reversible degradation of the stacks was analyzed by single cell experiments and could be reduced by adjusting of operating conditions and resulted in a fine tuning of the electrode design. Nevertheless still an irreversible degradation of about 1%/1000 h was detected. Several material tests consolidated the common understanding of degradation phenomena and will be shown with comparison to the real stack tests. The results show the excellent suitability of the CFY stack for electrolysis applications and give an outlook on further improvements.
Figure: 30-cell MK352 stack for SOFC/SOEC and rSOC operation
