## 3 Results
### Electrochemical Performance of the Electrodes  
The following section examines the electrochemical behavior of La\({}_{0.6}\)Sr\({}_{0.4}\)FeO\({}_{3-8}\) (LSF) electrodes in contact with the LSGM electrolyte, with a focus on the impact of the sintering aids, sintering temperature of the electrode, and gas environment. This study compares two sintering aids: copper oxide, as a widely used sintering aid, and iron oxide, which closely aligns with the chemical composition of the electrode. As previously stated in the experimental section, this study did not vary the mass fraction of the sintering additive. Instead, electrodes were produced with only 3 wt.%, in accordance with the previously obtained data [59]. The designation of the electrodes is provided in Table 2. It should be noted that the production of a high-quality LSF electrode in the range of sintering temperatures 1000-1250 \({}^{\circ}\)C was not possible without the use of sintering aids. The electrode exhibited poor adhesion, crumbled, and did not conduct an electric current. Attempts to measure electrochemical performance were unsuccessful. In the studies of LSF electrodes with the sintering aids, it was demonstrated that the polarization resistance in air is significantly dependent on the sintering temperature (Figure 5a). Therefore, at a study temperature of 800 \({}^{\circ}\)C, the polarization resistance exhibited a four-fold variation as a function of the sintering temperature. The 1050-Cu sample exhibited the most favorable outcomes, with a value of approximately 0.25 \(\Omega\) cm\({}^{2}\), while the 1150-Cu sample demonstrated the least favorable outcomes, with a value of approximately 1 \(\Omega\) cm\({}^{2}\). The 1050-Fe electrode demonstrated intermediate-quality results, exhibiting a polarization resistance of approximately 0.45 \(\Omega\) cm\({}^{2}\) at 800 \({}^{\circ}\)C. It is noteworthy that the slope of the temperature dependence (activation energy) of the polarization resistance of electrodes with copper oxide and iron oxide addition was found to be relatively high, approximately 140 kJ/mol, and exhibited minimal dependence on the sintering temperature, suggesting the potential for these electrode materials in the high-temperature region. For a more detailed understanding of how the sintering temperature affects the electrode reaction mechanism, impedance spectra and DRT functions calculated from them were \begin{table}
\begin{tabular}{c c c c} \hline \hline \(\mathbf{\mathscr{N}}\)**\textbackslash{} of Sample** & **Sintering Temperature/\({}^{\circ}\)C** & **Sintering Aid** & **Designation** \\ \hline
1 & 1000 & 3 wt.\% CuO & 1000-Cu \\
2 & 1050 & 3 wt.\% CuO & 1050-Cu \\
3 & 1100 & 3 wt.\% CuO & 1100-Cu \\
4 & 1150 & 3 wt.\% CuO & 1150-Cu \\
5 & 1050 & 3 wt.\% Fe\({}_{2}\)O\({}_{3}\) & 1050-Fe \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Designation of La\({}_{0.6}\)Sr\({}_{0.4}\)FeO\({}_{3-8}\) electrodes with various sintering aids and sintering temperature. Figure 4: SEM images of chipped electrolyte samples. (**a-c**) LSGM; (**d-f**) LSGM + Fe\({}_{2}\)O\({}_{3}\). Sintering temperature 1350 \({}^{\circ}\)C (**a,d**); 1400 \({}^{\circ}\)C (**b,e**); 1450 \({}^{\circ}\)C (**c,f**). considered (Figure 5b and Figure 5c, respectively). For all investigated electrodes, the spectra are a single half-circle with no visual separation into semicircles. However, despite the visual similarity of the spectra, the obtained DRT functions differ significantly. Thus, the 1000-Cu sample is characterized by the presence of a split peak in the frequency range of 2-100 Hz. For electrodes 1050-Cu and 1100-Cu, the DRT functions register only one main peak with a frequency at the maximum of about 1 Hz. For these samples, minor peaks of very low intensity are also present; we do not consider them since the contribution of these stages to the polarization resistance is not significant. For 1150-Cu, two peaks are found, one of low intensity at 1 Hz and one with high intensity at 0.1 Hz.