## Results and Discussion
### Electrical Properties of the Electrolyte BCGCuO Film Formed on Various Cathode Substrates  
For the electrochemical studies of the half-cells of BCGCuO/LBNO\({}_{\text{nc}}\)/LNFO\({}_{\text{P}}\), BCGCuO/LNFO\({}_{\text{P}}\) and BCGCuO/LBNO\({}_{\text{8s}}\) (Table 2) were used. For that, Pt collectors were symmetrically deposited on both sides of the half-cells. Figure 9a shows examples of the impedance spectra of the Pt[BCGCCuO/LNFO\({}_{\text{P}}\)]Pt cell obtained at a temperature of 600 \({}^{\circ}\)C in wet and dry air atmospheres. In the first experiment, the air (flow rate of 2 L/h) was bubbled through the bubbled heated up to 25 \({}^{\circ}\)C; in the second experiment, the air went through the container with zeolites. The processing of the spectra was carried out by a circuit of series-connected resistance R\({}_{\text{el}}\) and three parallel-connected RQ chains. The high-frequency response in the spectrum with a characteristic frequency of 1.5-2 MHz in the wet and dry air, respectively, and with a characteristic capacitance value of \(\sim\)10\({}^{-8}\) F, as widely accepted, refers to the grain boundaries of the electrolyte [33; 34]. Figure 8: SEM images of the BCGCuO electrolyte in the BCGCuO/LBNO\({}_{\text{ss}}\_1\) half-cell (after 3 cycles of deposition/sintering): surface (**a**); EDX images-integrated (**b**) and for individual elements (**c**); the an EDX image of the cross-section of BCGCuO/LBNO\({}_{\text{ss}}\_2\) taken after the electrochemical study(**d**). The electrode response with a characteristic capacitance of \(\sim\)10\({}^{-4}\) F and a characteristic frequency of \(\sim\)1-8 kHz probably refers to oxygen diffusion in the electrode. With transition from the dry to the wet air atmosphere, the relaxation frequency decreases, which indicates process slowdown. The low frequency process with a capacity of \(\sim\)10\({}^{0}\) F and a frequency in the maximum of \(\sim\)1 Hz is typically related to gas diffusion limitations in the porous electrode structure and on the electrode surface. It also becomes more pronounced in the wet air. The presence of water vapor partially blocks the active electrode sites towards the oxygen reduction reaction [35], which leads to an increase in the total electrode polarization resistance. At the same time, the process of charge transfer through the electrode-electrolyte interface, enhanced owing to an increased electronic conductivity in the protonic electrolyte, is overlapped by the slower electrode processes and not observed on the spectra. The electrolyte resistance, \(\mathrm{R_{el}}\), was taken as an interception of the right end of the depressed semicircle, fitting the grain boundary response with the \(\mathrm{Z_{real}}\) axis (Figure 9a). It is seen that in the dry air, electrolyte resistance increases due to decreasing the partial protonic conductivity [6,34]. Figure 9b shows Arrhenius dependences of the reciprocal \(\mathrm{R_{el}}\) (electrical conductivity) of the BCGCuO films on various cathode substrates obtained in this study. For the sake of comparison, the conductivity of the BCGCuO film deposited on the dense model LBNO\({}_{\mathrm{ss}}\) cathode and the conductivity of the BCGCuO ceramic sample, measured by the four-probe method in wet air [16], are also presented. The film deposited on the LBNO\({}_{\mathrm{ss}}\) substrate showed the highest conductivity, close to that of the compact sample. The reduction in the total conductivity value for the films deposited on the LBNO\({}_{\mathrm{nc}}\)/LNFO\({}_{\mathrm{P}}\) and LNFO\({}_{\mathrm{P}}\) substrates is probably the result of Ba-deficiency. This generally has a significant effect on the electrical properties [20]. When La diffuses into the film and there is partial substitution in both the Ba and Ce positions, then the conductivity can also be reduced in comparison to the Gd-doped BaCeO\({}_{3}\)[8]. The latter factor seems to be more pronounced for the film deposited on the LNFO\({}_{\mathrm{P}}\) substrate, which has the lowest conductivity value.