# GDC-Based Infiltrated Electrodes for Solid Oxide Electrolyzer Cells (SOECs)
## 3 Results and Discussion
At very low frequencies, the impedance spectra of the two cells are quite different. All EIS measurements show at least two semicircles from which it is possible to get the intercept with the real axis at a low frequency and thus evaluate the R\({}_{\text{pol}}\) values. The LSCM/GDCE cell exhibits impedance \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{_LSCM/GDCE_} & \multicolumn{2}{c}{_LSCM/GDCW_} \\ \hline  & **R\({}_{\text{ohm}}\) [\(\Omega\)-cm\({}^{2}\)]** & **R\({}_{\text{pol}}\) [\(\Omega\)-cm\({}^{2}\)]** & **R\({}_{\text{ohm}}\) [\(\Omega\)-cm\({}^{2}\)]** & **R\({}_{\text{pol}}\) [\(\Omega\)-cm\({}^{2}\)]** \\ \hline
800 \({}^{\circ}\)C & 3.4 & 1.1 & 5.7 & 4.1 \\ \hline
750 \({}^{\circ}\)C & 4.9 & 1.9 & 8.3 & 11.4 \\ \hline
700 \({}^{\circ}\)C & 6.6 & 3.2 & 13.2 & 21.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: R\({}_{\text{ohm}}\) and R\({}_{\text{pol}}\) values of both cells operating in CO/CO\({}_{2}\) = 30/70 mixtures at different temperatures. Figure 6: Nyquist plots of the LSCM/GDCW and LSCM/GDCE cells working with CO/CO\({}_{2}\) at different temperatures. spectra comparable to the best performing literature data for similar cells [19; 27], while the LSCM/GDCW shows an incomplete Warburg-like behavior at low frequencies, indicating unrestricted diffusion phenomena. Thus, the CO\({}_{2}\) reduction process mostly occurs at the LSCM/GDCE porous cathode and it is related to the cathode microstructure made of well dispersed and interconnected GDC nanoparticles that increase the TPB sites for CO\({}_{2}\) reduction [19]. In order to compare the LSCM/GDCE performance with the state-of-art, the cell has been specifically tested at 900 \({}^{\circ}\)C. Figure 7 shows the Nyquist plot of the LSCM/GDCE cell operating with a CO/CO\({}_{2}\) = 30/70 mixture at 900 \({}^{\circ}\)C alongside the related fitted plot, obtained via software simulation by using the equivalent circuit reported in the inset. The Nyquist plot was fitted with an LR\({}_{1}\)(CPE\({}_{2}\)R\({}_{2}\))(CPE\({}_{3}\)R\({}_{3}\)) equivalent circuit, in which L is the inductance due to the wires of the instrument set up, R\({}_{1}\) is the high-frequency intersection of the plot with the real axis and represents the ohmic resistance (R\({}_{\rm{ohm}}\)) of the electrolyte and infiltrated cathode, R\({}_{2}\) is the polarization resistance obtained from the high-frequency (HF) arc and is related to the charge transfer process at the electrode/electrolyte interface, and R\({}_{3}\) is the polarization resistance from the low-frequency (LF) arc and is ascribable to non-charge transfer processes at the electrodes. The overall polarization resistance (R\({}_{2}\) + R\({}_{3}\)) value is 0.3 \(\Omega\)-cm\({}^{2}\), which is comparable to the best performing cathodes from literature. In fact, the conventional Ni-YSZ cathode in the same experimental conditions shows a polarization resistance value of 0.23 \(\Omega\)-cm\({}^{2}\) and a modified GDC-based cathode with Pd co-catalyst exhibits R\({}_{\rm{pol}}\) = 0.24 \(\Omega\)-cm\({}^{2}\)[25]. Finally, Figure 8 shows the Arrhenius plot related to the LSCM/GDCE polarization resistance, exhibiting a good linearity over the whole temperature range investigated (700-900 \({}^{\circ}\)C). From the linear fit, an activation energy of the polarization process equal to \(\sim\)160 kJ mol\({}^{-1}\) can be derived. Figure 7: Nyquist plot at OCV of the LSCM/GDCE at 900 \({}^{\circ}\)C.