## 4 Conclusions  
This paper presents the results of the study of the formation by electrophoretic deposition of the thin-film BCGCuO proton-conducting solid electrolyte on the porous LBNO\({}_{\text{ss}}\), LNFO\({}_{\text{ss}}\), and LNFO\({}_{\text{p}}\) cathode substrates, including the LNFO\({}_{\text{p}}\) and LNFO\({}_{\text{ss}}\) substrates with the LBNO\({}_{\text{nc}}\) sublayer. It focuses on the preventive measures to preserve barium content in the electrolyte at the nominal level during deposition and high-temperature sintering. Special attention is also given to the preservation of the porous structure of the cathode substrates during all deposition/sintering cycles. The EPD modes for deposition of LBNO\({}_{\text{nc}}\) and BCGCuO films were established in the test depositions on the Ni-foil. The influence of molecular iodine on the deposition kinetics was studied. It was shown that the addition of iodine allowed a significant increase in the deposition weight of the BCGCuO coatings. As a result of a series of experiments on the formation of the BCGCuO electrolyte layer on porous LNFO cathodes (with and without the thin LBNO sublayer (\(\sim\)10 \(\upmu\)m)), it was determined that electrolyte thickness plays a major role in ensuring its nominal composition. Thus, the preservation of barium in the electrolyte layer after sintering at a temperature of 1450 \({}^{\circ}\)C (2 h) was achieved only at a thickness of \(\sim\)20 \(\upmu\)m and more. When using the bulk LBNO\({}_{\text{ss}}\) cathode (\(\sim\)1 mm), barium was retained during sintering, even at the electrolyte film thickness of 10 \(\upmu\)m, which revealed the role of the LBNO\({}_{\text{ss}}\) substrate as a barium source. The film obtained on the LBNO\({}_{\text{ss}}\) substrate, according to the impedance spectroscopy study, possessed the highest electrical conductivity among the films deposited on the various cathode substrates. Nevertheless, an increase in BCGCuO film thickness on the bulk LBNO\({}_{\text{ss}}\) substrate (over about 17 \(\upmu\)m) led to delamination and cracking of the electrolyte due to internal stresses in the layer caused by the thermal expansion mismatch of the materials. Thus, the use of bulk LBNO substrates is not the optimal solution to the problem and, for the assured formation of the electrolyte films in the required thickness range, additional studies are necessary to determine the optimal thickness of the LBNO sublayer to prevent Ba loss, using it as a Ba source and, at the same time, preserving the quality of the electrolyte films. The following are available online at [[http://www.mdpi.com/2076-3417/10/18/6535/s1](http://www.mdpi.com/2076-3417/10/18/6535/s1)]([http://www.mdpi.com/2076-3417/10/18/6535/s1](http://www.mdpi.com/2076-3417/10/18/6535/s1)). Conceptualization, methodology, investigation, formal analysis, writing--original draft preparation, E.K. ; formal analysis, visualization, A.K. ; investigation, K.S. ; investigation, formal analysis, visualization, A.F. ; conceptualization, supervision, writing--review and editing, E.P. All authors have read and agreed to the published version of the manuscript. This research received no external funding  
This work was performed in the framework of the IEP UB RAS state assignment (EPD technology development) and the IHTE UB RAS budget task (SOFC technology development). The XRD and microstructure study was carried out using the equipment of the Shared Access Center \"Composition of compounds\" (Institute of High Temperature Electrochemistry, Ural Branch of the Russian Academy of Sciences, Yekaterinburg, Russia).