Quantifying morphological variability and operating evolution in SOFC anode microstructures

Abstract

Direct correlation of SOFC performance with electrode evolution requires compared electrodes to have quantifiably similar initial microstructures. Commercial SOFCs do not satisfy this requirement. Therefore, methods are explored to quantify morphological differences between many micro-scale sub-volumes taken from large meso-scale volumes of commercial anodes exposed to different operating conditions. Three microstructures were reconstructed in 3D using plasma-FIB SEM serial sectioning data (≈1002 μm2 in-plane and 6–9 μm in thickness, t) from two anodes exposed to different operating histories. 50 to 100 rectangular prism sub-volumes (122 μm2 x t μm) from each are compared using ANOVA methods. Variations in the local volume fractions and/or particles sizes render each of the three reconstructions statistically non-overlapping for many of their global averages, mesoscale distributions, and comparisons using ANOVA. However, the YSZ backbones are self-similar and scale adjusted electrodes are shown to have many comparable ANOVA sub-volumes, which allows for a quantification of relative microstructural changes in Ni/pore distributions. Ni coarsening and de-wetting of the YSZ phase are consistent with relative changes observed in the operated anode. Caution is nevertheless required in comparing commercial electrodes because spatial variations in the microstructural distributions are as significant as, or greater than, those from operation.