## 1 Introduction
Ba loss leads to redistribution of the acceptor dopant, occupying the B-position, on both A- and B-sublattices, which results in a decrease in a reduced concentration of oxygen vacancies responsible for co-ionic transport and causes violation of the electrical properties, segregation of secondary phases on the grain boundaries, degradation of the mechanical properties, and even electrolyte decomposition [20]. Ba evaporation becomes even more pronounced in the case of thin films. The problem of redistribution and barium depletion in BaCeO\({}_{3}\)-based films with a thickness of less than 10 microns was considered in a number of studies where various strategies were proposed to prevent cation disbalance in the sintered films, for example, sintering a film in a powder of the same composition or BaCeO\({}_{3}\)[21] or application of a protective BaCeO\({}_{3}\) layer on the top of the film before its sintering [22]. In [16], a study was conducted of the methods for forming a thin-film electrolyte BaCe\({}_{0.89}\)Gd\({}_{0.1}\)Cu\({}_{0.01}\)O\({}_{3\cdot\delta}\) (BCGCCuO) on dense model substrates La\({}_{2}\)NiO\({}_{4+\delta}\) (LNO) and La\({}_{1.7}\)Ba\({}_{0.3}\)NiO\({}_{4+\delta}\) (LBNO) by the EPDmethod. In particular, a BCGCuO film was deposited on a LNO substrate and a half-cell was sintered in the BCGCuO powder; a BCGCuO film was deposited on a LNO substrate and a BaCeO\({}_{3}\) protective film was deposited on the top of the BCGCuO film and co-sintered; the BCGCuO film was deposited on a LBNO substrate followed by sintering. The Ba loss observed in both BCGCuO films deposited on the LNO substrate was mainly due to the diffusion of barium into the substrate, thus the use of protective BaCeO\({}_{3}\) film was ineffective. At the same time, the Ba content was nominal in the BCGGuO film deposited and sintered on the LBNO substrate without additional protective measures. It was supposed that the LBNO substrate may play a role of a source of Ba, compensating its evaporation during the sintering. In this study, in order to further develop EPD technology for the formation of a thin-film proton-conducting BCGCuO electrolyte, its deposition was performed on porous cathode substrates: LaNi\({}_{0.6}\)Fe\({}_{0.4}\)O\({}_{3-8}\) (LNFO) substrates, fabricated from the powders obtained by solid state reaction and Pechini methods, on LBNO substrates fabricated from the solid state reaction powder, and bi-layered LNFO/LBNO cathode substrates, where the LBNO cathode sublayer was deposited by the EPD method form the suspension, prepared from the citrate-nitrate powder, on the top of porous LNFO substrates. The aim of the study was to maintain the nominal barium content in the BCGCuO electrolyte film during sintering to ensure the required conductivity characteristics along with preservation of the porous structure of the substrates. The use of cathode material LNFO with high electronic conductivity (~700 S/cm at 700 \({}^{\circ}\)C) as a cathode collector can increase cell performance [23; 24]. In addition, LNFO possesses a moderate value of the thermal expansion coefficient (TEC) of 12.5 \(\times\) 10\({}^{-6}\) K\({}^{-1}\) in the temperature range 50-900 \({}^{\circ}\)C. While the use of LBNO material as a functional cathode layer directly in contact with a proton-conducting electrolyte will not only reduce mutual chemical interaction of the materials, it will also increase electrochemical activity [25]. A basic investigation of the bilayer porous substrates for the deposition of oxygen ion-conducting electrolytes and conditions to preserve the supporting cathode structure during electrolyte film sintering was presented in [26; 27]. The results were adopted for use in this study, taking into account the features of the Ba-containing electrolyte. The technology developed makes it possible to determine further directions in the EPD application for producing cathode-supported SOFCs with proton-conducting electrolytes.