## 3 Results and Discussion
### Oxygen Mobility in the NCNCO Materials
The P\({}_{3}\) (C\(\sim\)10\({}^{-4}\)-10\({}^{-2}\) F cm\({}^{-2}\),\(f\)-100 Hz) and P\({}_{4}\) (C\(\sim\)10\({}^{-3}\)-10\({}^{-1}\) F cm\({}^{-2}\),\(f\)-10 Hz) processes are usually described as being related to the oxygen solid-state diffusion and surface oxygen exchange in the electrode material, respectively [89; 91].The last low-frequency process, P\({}_{5}\), with C\(\sim\)1-10 F cm\({}^{-2}\) and \(f\)-0.1 Hz, is usually related to the oxygen gas-phase diffusion in the electrode pores and also to the limitations of oxygen exchange at the electrode/gas-phase interface [48; 92]. Comparing the DFTRs for the series for the electrodes sintered at 1000 \({}^{\circ}\)C, one can see that this process gives the lowest contribution to the electrode with the op  
Figure 10: DFRTs obtained from the EIS data (at 600-800 \({}^{\circ}\)C) for the NCNCO00/SDC (**a**) and NCNCO02/SDC (**b**) symmetrical cells with the functional layers sintered at 1000 \({}^{\circ}\)C.  
timized microstructure (y = 0.2). The growing contribution of the diffusion processes (P\({}_{3}\)-P\({}_{5}\)) to the overall polarization resistance correlates well with the oxygen mobility data (Section 3.4). The introduction of the collector layer significantly reduces the total polarization resistance (Figure 11a).The collector layer has a positive effect on all electrochemical processes (Figure 11b), reducing the resistance of interfacial exchangeapproximately three times, which is possibly due to a more uniform current distribution over the electrode surface. Gas diffusion limitations due to the presence of the collector layer can contribute only at low temperatures (600 \({}^{\circ}\)C); at higher temperatures, the P\({}_{5}\) process contribution is negligible (Figure S24). Finally, the electrochemical testing of the electrode with the optimal copper content (y = 0.2) was performed in the cells with the proton-conducting electrolytes. The use of the LNF collector layer led to the delaminating of the electrode, caused by a significant difference in TEC values of the LNF electrode material and BaCeO\({}_{3}\) or BaCe(Zr)O\({}_{3}\)-based electrolytes (14 and 8-10 \(\times\) 10\({}^{-6}\) K\({}^{-1}\), respectively). Thus, we increased the sintering temperature up to 1100 \({}^{\circ}\)C and applied collector layers based on LSM possessing TEC values of 11.4 \(\times\) 10\({}^{-6}\) K\({}^{-1}\)) and obtained the electrodes with excellent adhesion properties and superior electrode performance (Figure 12). The values of the polarization resistance were in a range of 0.34-0.69 \(\Omega\) cm\({}^{2}\) at 850 \({}^{\circ}\)C and 2.73-4.79 \(\Omega\) cm\({}^{2}\) at 700 \({}^{\circ}\)C, with the \(E_{a}\) values in a range of 1.17-1.42 eV. The presence of partial electronic conductivity in the proton-conducting electrolytes in humidified air [21; 22] may facilitate the charge transport across the electrode/electrolyte interface, and this decreased both the polarization resistance and the activation energy of the polarization conductivity of the electrodes in contact with them. Additionally, chemical compatibility tests were performed, which demonstrated that there was no chemical interaction of the NCNCO02 electrode materials with all considered electrolytes up to 1100 \({}^{\circ}\)C, except for BCSCuO. To prevent interaction, for this electrolyte material, the sintering temperature of the electrode layer should be decreased below this temperature level. The results of the chemical interaction are presented in Table S3. Figure 11: EIS spectra (**a**) and DFTRs (**b**) (at 700 \({}^{\circ}\)C) for the symmetrical cells with the NCNCO00 and NCNCO02 functional layers sintered at 1000 \({}^{\circ}\)C and the LNF + 3 wt.% CuO collector sintered at 900 \({}^{\circ}\)C.  
The results on the electrode polarization resistance in contact with protonic conductors are close to those presented recently for substituted Nd\({}_{2}\)NiO\({}_{4+\delta}\) electrodes in protonic ceramic electrochemical cells(Table S4; [37, 41, 92, 93, 94, 95, 96, 97, 98, 99]).