## 3 Results
### SEM and \(\mu\)-CT Analysis
#### 3.2.2 Thermal Treated Samples  
The SEM/EDX results of Cell 7 and Cell 8 are presented in Figure 6a,b. These samples were only subjected to thermal stress for a period of 100 and 1000 h, respectively, under dry conditions. The samples were contacted like the samples in regular electrochemical experiments. In the cathode and anode compartments, the respective gases (O\({}_{2}\) and dry H\({}_{2}\)) were flowing. Figure 4: Microstructure of Cell 6 which was only reduced and used as reference for comparison. Figure 5: (**a**) Typical \(\upmu\)-tomographic images of the cells used (**b**) resulting images of the element distribution and the pores (depending on the density of the material) and (**c**) a typical layer from the approximately 1000 in which the \(\upmu\)-CT image is divided in order to calculate the porosity in the total volume. Figure 6: Microstructure development in thermally treated cells at 850 \({}^{\circ}\)C in dry fuel conditions after (**a**) 100 h and (**b**) 1000 h and in thermally treated cells at 850 \({}^{\circ}\)C in humid fuel conditions after (**c**) 100 h and (**d**) 1000 h (delamination of (**d**) during sample preparation for SEM). All scale bars are 10 \(\upmu\)m.  
The color bar in Figure 6 shows the constituent elements of the anode. The grain size in Cell 7 ranges between approx. 1 \(\upmu\)m near the interface and approx. 8 \(\upmu\)m for some grains in the contact layer. The distribution of the elements Ni and Ce is homogeneous, but nickel coarsening of the grains, especially close to the surface, is observed after just 100 h of aging at 850 \({}^{\circ}\)C in a dry atmosphere. Pores are also found on the nickel particles. The grain size in Cell 8 ranges after 1000 h between approx. 1 \(\upmu\)m near the interface and approx. 10 \(\upmu\)m for some grains in the contact layer. An inhomogeneous distribution of the elements Ni and Ce over time is observed by comparing Cell 7 and Cell 8. Increased Ni coagulation is observed in the volume but especially on the surface of the anode. The micropores observed after 100 h (Cell 7) disappear when the nickel particles are compacted after 1000 h. A comparison with the reference Cell 6 clearly shows the differences in the microstructure after thermal treatment of 1000 h, with the nickel distribution suffering more than the GDC structure. This is reflected in the strong specific resistance increase on Cell 8 after 250 h, as the loss in contact points leads to a resistance increase. Images from the anode sections of both cells (not shown) were also used for microstructure analysis, and an initial value for the 2D porosity was calculated. The total porosity (open and closed) resulting from the \(\upmu\)-CT (not shown as the reader cannot extract any information from those pictures) is 31.45% for Cell 7. The 2D analysis presented based on SEM micrograph shows a slightly increased porosity for the contact layer of 33.8% and a porosity of 27.7% for the active layer. For Cell 8, the total porosity (open and closed) resulting from the \(\upmu\)-CT (not shown) is 36.08%. The 2D analysis results in a slightly increased porosity for the contact layer of 36.5% and a porosity of 31.04% for the active layer. SEM/EDX micrographs of Cell 9 and Cell 10 are presented in Figure 6c,d. These samples were subjected to thermal stress with humidified atmosphere in the anode compartment for a period of 100 and 1000 h, respectively. The samples were contacted like samples in regular electrochemical experiments. In the cathode and anode compartments, the respective gases (O\({}_{2}\) and humidified H\({}_{2}\) with 3% H\({}_{2}\)O) were flowing. The grain size in Cell 9 ranges after 100 h thermal treatment in humidified H\({}_{2}\) between approx. 1 \(\upmu\)m near the interface and approx. 10 \(\upmu\)m for some grains in the contact layer. A good and homogeneous distribution of the elements Ni, Gd, and Ce was found. The nickel distribution is visually almost the same as the reference Cell 6.