## Results and Discussion
### Formation of the BCGCuO Electrolyte Films on the LNFO Substrates with the Deposited LBNOnc Sublayer  
According to the results of the test deposition, EPD (U = 80 V, deposition time 1 min) for the deposition on porous LBNOnc/LNFOP and LBNOnc/LNFOss substrates was selected based on estimates of the required film thickness (up to 10 \(\upmu\)m with a deposition weight of 6.3 mg/cm\({}^{2}\)). The current strength during deposition on the LBNOnc/LNFOP substrate was 5.84 mA, the deposition weight of the BCGCuO electrolyte layer reached 4.5 mg/cm\({}^{2}\) (film thickness of 7 \(\upmu\)m), while during the deposition on the LBNOnc/LNFOss substrate the current strength was 6.38 mA, and the deposition weight was significantly lower, reaching 1.3 mg/cm\({}^{2}\) (film thickness of 2 \(\upmu\)m). After deposition, the obtained samples BCGCuO/LBNOnc/LNFOP and BCGCuO/LBNOnc/LNFOss were sintered at a temperature of 1350 \({}^{\circ}\)C for 1 h.  
To increase the film thickness on the BCGCuO/LBNOnc/LNFOss substrate, the deposition/sintering cycle was repeated under the same conditions. The total weight of the obtained BCGCuO layer after repeated deposition was 4.5 mg/cm\({}^{2}\), which corresponded to a coating thickness of 7 \(\upmu\)m. It is similar to the thickness of the electrolyte film obtained on the LBNOnc/LNFOP substrate. The final sintering of the BCGCuO/LBNOnc/LNFOP and BCGCuO/LBNOnc/LNFOss half-cells was carried out at 1450 \({}^{\circ}\)C, 2 h. The rate of heating and cooling was 1 \({}^{\circ}\)C/min. Figure 4: SEM images of the initial BCGCuO powder (**a**) and the BCGCuO film deposited on the Ni-foil and annealed at 600 \({}^{\circ}\)C, 1 h (**b**); EDX mapping images—integrated (**c**) and for the individual elements (**d**). The shrinkage of the porous substrates \(\text{LNFO}_{\text{P}}\) and \(\text{LNFO}_{\text{ss}}\) under the electrolyte sintering conditions was 0.84% and 2.29%, respectively, while maintaining their porous structure (Figure 5). The results are in good agreement with those obtained on the preservation of the supported cathode porous structure when sintering the EPD deposited CeO\({}_{2}\)-based electrolyte films obtained from nano-sized powders [26; 27]. After sintering at a temperature of 1450 \({}^{\circ}\)C, no Ba was detected in the composition of the electrolyte films in both half-cells which may be due to its evaporation during sintering from a thin BCGCuO electrolyte layer (total thickness of less than 10 \(\upmu\)m). To reduce Ba loss, an attempt was made to increase electrolyte thickness. For this purpose, the EPD from the BCGCuO suspension with iodine was repeated for both half-cells. Thus, after the sintering at 1450 \({}^{\circ}\)C, the thickness of the electrolyte films was 12 and 10 \(\upmu\)m, respectively. Figure 6 shows the structure of the BCGCuO/LBNO\({}_{\text{nc}}\)/LNFO\({}_{\text{ss}}\) half-cell after the final sintering. The electrolyte film surface (Figure 6a) is characterized by the absence of a pronounced grain structure with the presence of bound chains and pores between them. It is seen on the cross-section image of the half-cell structure (Figure 6b) that the thickness of the BCGCuO layer is about 10 \(\upmu\)m, which agrees well with the evaluated thickness value. According to the EDX analysis, barium is absent in the film even after the cycling deposition when the thickness of the film was increased. The sintering character of the electrolyte film (lack of grain structure) was possibly influenced by the absence of barium due to its evaporation. As can be seen from Figure 6b,c, barium is distributed in the \(\text{LNFO}_{\text{ss}}\) substrate, possibly due to its partial diffusion from the LBNO sublayer. Additionally, La diffusion from the substrate to the electrolyte film was also registered.