# GDC-Based Infiltrated Electrodes for Solid Oxide Electrolyzer Cells (SOECs)
## 3 Results and Discussion  
GDC loading by infiltration varies considerably when using water and ethanol as solvents. Figure 1 shows the GDC loading percentage vs. the number of infiltrations by using the GDCW and GDCE solutions. The infiltrated cathodes are named LSCM/GDCW and LSCM/GDCE. The target value corresponding to the 50 wt% of the YSZ/LSCM weight is 100%. By using the GDCE solution, the desired amount of GDC loading was reached with five infiltrations, while eight infiltrations were necessary for the GDCW solution. For each infiltration step, the same liquid volume was selected. Moreover, the difference in the wetting behavior of the electrode support at each infiltration step is noteworthy. In fact, the GDCE droplets almost immediately diffused all over the support surface, while the liquid-solid interaction between the support and GDCW was significantly lower, as the liquid droplets had to be gently deposited in different electrode sites to obtain a homogeneous distribution of the infiltrated volume. The GDCE infiltration process produced a constant rate loading, while the GDCW infiltration showed a strongly non-linear loading evolution. The linear trend in the case of the GDCE suggests that the superficial region of the sample is substantially unaltered by the sequence of the infiltration steps, whereas the parabolic behavior likely indicates the formation of some barriers that reduce the further loading. [PERSON] et al. observed that factors such as the volatility of the impregnating medium (solution) may affect the distribution of the impregnated phase, i.e., ethanol ensured a small blocking effect of the porous texture and, thus, a high specific surface area of the impregnated phase [33]. The LSCM/GDCW- and LSCM/GDCE-infiltrated cathodes with the same GDC amount were investigated by XRD analysis. Figure 2 shows the XRD pattern of the LSCM/GDCW infiltrated cell. The LSCM/GDCE cell exhibits an identical diffraction pattern and thus, for reasons of clarity, it is not reported. All peaks belong to the 8 YSZ (ICDD card n. 30-1468), GDC (ICDD card n. 75-161), and LSCM (ICDD card n. 86-1552) phases and no secondary phase has been revealed. Cerium and gadolinium mixed in the proper amount into the infiltrating solution formed a perfect homogeneous solid solution with a mild calcination step. The crystallographic parameter of cubic GDC was determined using UnitCell software [34]. The calculated value was 0.54177(1) nm in very good agreement with the theoretical value (0.5418 nm according to ICDD card n. 75-161), confirming the homogeneous dissolution of Gd\({}^{3+}\) cations in the fluorite lattice of ceria. The crystallite size was calculated using the Scherrer equation for the most intense peak, i.e., (111) at \(20=28.5^{\circ}\). The size was about 80 nm for both the LSCM/GDCW and LSCM/GDCE cathodes, meaning that no significant difference in the grain size was detectable for the two impregnation methods. Microstructural analyses of the cathode/electrolyte interface and cathode surface were performed. Figure 3 shows the SEM micrograph of a 30 \(\upmu\)m thick LSCM/GDCW cross section. A very good adhesion between cathode and electrolyte is reasonably revealed due to the presence of a thin YSZ screen-printed layer. The same features (not reported) were also revealed for the LSCM/GDCE cathode, indicating that no significant difference appears from the cross-section analysis. Figure 1: Weight gain of the lanthanum strontium chromium manganite/distilled water (LSCM/GDCW) and LSCM/pure ethanol (GDCE) electrodes as a function of the infiltration steps. Figure 2: XRD pattern of the LSCM/GDCW infiltrated electrode. Differently, from the top-view analysis, the LSCM/GDCE and LSCM/GDCW cathodes exhibit quite different morphologies, as shown in Figures 4 and 5. Figure 4: Top view micrographs (fully completed infiltration) of the LSCM/GDCE cathode at increasing magnifications (from **(A–C)**).