Three-Dimensional Microstructural Analysis for the Characterization of Failure Mechanisms of a Novel SOEC

A novel Ni-GDC-cermet-supported intermediate temperature electrolysis cell that has been developed as promising candidate for hydrogen production with GDC as electrolyte, YSZ as electron-blocking layer and an additional GDC diffusion-blocking layer is characterized. Although this three-layer GDC-YSZ-GDC electrolyte enables improved performance compared to state-of-the-art YSZ electrolyte-based cells especially at lower operation temperatures, at temperatures below 750 °C and high electrolysis currents a voltage drop and subsequently crack formation in the three-layer electrolyte was observed in initial studies. Thus, in order to investigate the cause of this catastrophic cell failure a three-dimensional microstructural analysis of the cathode functional layer and electrolyte was conducted. Different methods were used to obtain detailed information on the microstructure and changes thereof. The methods used were FIB-SEM, X-ray computed tomography and laser confocal microscopy. By combining the results obtained from the different methods, a detailed understanding of the electrolyte/electrode microstructure was achieved. The analysis of a representative volume element via non-destructive X-ray computed tomography and FIB-SEM enabled the reconstruction of the microstructure and segmentation into a three-dimensional material distribution. Three-dimensional microstructures of cells before and after single-cell testing were analysed and compared. Additionally, laser confocal microscopy was used for a direct assessment of cracks and other defects. An overview of the advantages of the different characterization methods and findings will be given.