## 3 Results and Discussion
### Oxygen Mobility in the NCNCO Materials
The superior performance of the NCNCO02 electrode in this series can explain its better electrical characteristics (Section 3.3 and [49]) compared to NCNCO00. Indeed, the application of the highly conducting LNF + 3 wt.% CuO current collector lowered the difference between the NCNCO00-NCNCO02 electrodes, as can be seen from the concentration dependencies of the total \(R_{p}\) at 700 \({}^{\circ}\)C, presented in Figure S21. For instance, \(R_{p}\) of the NCNCO02 electrode with the collector layer was 0.42, 0.078, 1.89, and 3.37 \(\Omega\) cm\({}^{2}\) at 850, 800, 750, and 700 \({}^{\circ}\)C compared to the NCNCO electrode amounting 0.47, 0.87, 2.35, and 4.26 \(\Omega\) cm\({}^{2}\) at 850, 800, 750, and 700 \({}^{\circ}\)C, respectively. Another probable reason for the superior NCNCO02 performance is its better adhesion to the electrolyte substrate compared to the pristine electrode due to enhancing the sintering properties of the electrodes with increased copper  
Figure 9: Nyquist plots obtained for the Nd\({}_{1.6}\)Ca\({}_{0.4}\)Ni\({}_{1-y}\)Cu\({}_{y}\)O\({}_{4+S}\)/SDC symmetrical cells with functional layers sintered at 1000 \({}^{\circ}\)C: at 700 \({}^{\circ}\)C (**a**) and at 600 \({}^{\circ}\)C (**b**), humidified air. Ohmic electrolyte resistance was subtracted from the spectra forthe sake of easier comparison of the electrode performances. content. For instance, despite of closeness of the \(S_{BET}\) values (2.62 (3) and 2.43 (7) m\({}^{2}\) g\({}^{-1}\)), analysis of the microstructure of the NCNCO01 and NCNCO02 functional layers sintered at 1000 \({}^{\circ}\)C demonstrated an increase in the average particle size from 1.5 (1) to 2.3 (1) \(\upmu\)m. SEM images and particle size data are presented in the supplementary materials in Figure S22. Analysis of the Distribution Functions of Relaxation Times (DFTRs) [86] was applied as a powerful method to identify the electrode processes on the spectra. The impedance \(Z(\omega)\) is related to the DFTRs \(\gamma(\tau)\), according to Equation (5). Calculations were performed on the spectra obtained at different temperatures for the Nd1\({}_{6}\)Ca0\({}_{4.4}\)Ni\({}_{1-y}\)CuyO\({}_{4+\delta}\)/SDC symmetrical cells, with functional layers sintered at 1000 \({}^{\circ}\)C (Figure 9) using Tikhonov regularisation and a Gaussian-type function in pyDRTtools [87]. A regularization parameter (RP) was chosen according to a Bayesian approach described elsewhere [88]. The obtained DFTRs for the NCNCO electrodes with different copper content are shown in Figure 10a,b (NCNCO00 and NCNCO02) and in the supplementary materials in Figure S23a-c (NCNCO01, NCNCO03, and NCNCO04). The curves demonstrate the presence of at least five contributions to the polarization resistance of the Nd1\({}_{6}\)Ca0\({}_{4.4}\)Ni\({}_{1-y}\)CuyO\({}_{4+\delta}\)/SDC cells. The narrows on the figures show the process evolution upon cooling. \[Z(\omega)=R_{hf}+\int_{0}^{+\infty}\frac{\gamma(\tau)}{1+j\omega\tau}d\tau \tag{5}\]  
where \(R_{hf}\) corresponds to the ohmic resistance (electrolyte), the integral is the polarization resistance, and \(\gamma(\tau)\) is the DRT function. One can observe two relatively small peaks in the high (P\({}_{1}\)) frequency range and three significantly larger overlapping peaks in the middle frequency (P\({}_{2}\)) and low-frequency range (P\({}_{3}\), P\({}_{4}\), and P\({}_{5}\)). The P\({}_{1}\) process with a capacitance of \(\sim\)10\({}^{-6}\) F cm\({}^{-2}\), at a frequency of \(\sim\)50 kHz, is most likely related to the interfacial charge transfer between the electrode and electrolyte, while middle-frequency process P\({}_{2}\) (C\(\sim\)10\({}^{-5}\) F cm\({}^{-2}\),\(f\)-2-3 kHz) may be related to the charge transfer in the MIEC electrode volume [48; 89; 90; 91].