One of the main conditions for SOFC stacks' market entry is extremely low degradation rate. While stationary applications require cell and stack lifetime up to approximately 20 000 hours, stationary auxiliary power units demand more than 40 000 hours of service. This objective has been difficult to reach up to now except with very specific designs. Researchers initiated the EU-funded project DESIGN (Degradation signatures identification for stack operation diagnostics) to identify characteristic signatures of slow phenomena that, nevertheless, have a detrimental effect on both performance and durability of SOFC stacks in the long term. The ultimate aim was to provide a sound method to diagnose failures by appropriately processing data provided by a small number of sensors. Together with industrial partners of the GENIUS project, the researchers studied insidious phenomena that slowly accelerate the degradation of SOFC stacks. Their starting point was the influence of damaging operation conditions on stack subcomponents, including individual cells, single repeating units and small stacks. Extensive experimentation demonstrated that most cell and stack issues are related to the types of materials used and their quality. However, system dysfunctions also play a key role and were classified into impurities-induced effects and deviating operation conditions. The latter includes oxygen-to-carbon ratio at fault and high local fuel utilisation. A hazards and operability study allowed a systematic evaluation of stack dysfunctions and their consequences. Based on the results, researchers developed a test plan to simulate the anode re-oxidation by locally increased fuel utilisation – one of the most severe and frequent phenomena – and another two degradation mechanisms. In the last phase of DESIGN, these specific signatures characterising slow degradation phenomena at the local scale were extended for the diagnosis of full-size stacks with up to 64 cells and limited instrumentation. Importantly, reproducibility of the identified signatures was confirmed as well as their reliability as the basis for a diagnostic tool for commercial stacks. To implement the diagnostic tool, testing protocols and data have been shared with the DIAMOND project, which is a direct continuation of DESIGN. Diagnostic technology able to detect potential failures will have a significant impact on the lifetime of SOFC stacks and ultimately enable widespread market uptake of this promising technology.
Solid oxide fuel cell, electric power generation, diagnostic technology, degradation signatures, stack operation