Systematic Lifetime Testing of Stacks in CO2 Electrolysis

Haldor Topsoe is commercializing a system for on-site CO generation (eCOs®) based on solid oxide electrolysis technology. The standard system is capable of producing CO at 99.5% purity, but can also be customized to produce CO at 99.999% purity. In this patented system, the electrochemical conversion of CO2 into CO is carried out in solid oxide stacks, each stack producing approximately 1.5 Nm3 CO/h. In contrast to SOFC operation, the performance of a stack operating in electrolysis mode is not exclusively determined by the area-specific resistance (ASR). While resistance determines the overall efficiency of the stack, other parameters, such as the purity of the produced gas, can be more critical in a commercial system.A systematic approach to screening and evaluating stack and cell-level improvements is presented. Several long-term tests were carried out for 2000 hours at a reference operating point and then intentionally stopped to evaluate the extent of degradation in stacks and to qualify/disqualify different design modifications. The described approach was used to significantly improve stack robustness and lifetime in CO2 electrolysis. Finally, some un-solved issues will be presented, in order to spur discussion on lifetime-limiting issues specific to electrolysis.