Solid oxide fuel cells (SOFCs) are electrochemical systems converting the energy released during fuel oxidation into electrical energy. SOFCs are considered as a promising clean energy technology due to the high efficiency of fuel-to-power conversion and environmental friendliness. The potential applications of SOFCs extend from stationary power generation units for industrial and household facilities to auxiliary power units in vehicles and portable power sources. One of the main elements of SOFCs is a solid oxide electrolyte possessing ionic conductivity at high temperatures (above 700 °C). The main challenge in the SOFC commercialization is related to their high operating temperature, which entails materials degradation, short life-time, long start-up and shut-down times, and high cost. One of the most effective ways to reduce the SOFC operating temperature is to minimize the electrolyte thickness. In this regard, fabrication of SOFCs with a thin film electrolyte has been attracting high research activity over the past few decades. Different fabrication techniques were reported to be applicable for manufacturing thin film SOFCs, and the fuel cell performance was found to be highly dependent on the appropriate selection of materials and processing technologies. The present review is focused on state-of-the-art fabrication technologies of the thin film SOFCs. A brief survey of configurations and geometries of the thin film SOFCs and methods of deposition of solid-oxide films is given. Special attention is focused on the electrical generation performance of the thin film SOFCs.

The effect of Sr-nonstoichiometry on phase composition, microstructure, defect chemistry and electrical conductivity of Sr_xZrO_3−δ and Sr_xZr_0.95Y_0.05O_3−δ ceramics (SZx and SZYx, respectively; x = 0.94–1.02) was investigated via X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and impedance spectroscopy followed by distribution of relaxation times analysis of impedance data. It was shown that at low Sr deficiency (x > 0.96 and 0.98 for SZx and SZYx, respectively) a solid solution of strontium vacancies in strontium zirconate crystal structure forms, whereas at higher Sr deficiency the secondary phase, zirconium oxide or yttrium zirconium oxide, is precipitated. Yttrium solubility limit in strontium zirconate was found to be close to 2 mol%. Y-doped strontium zirconates possess up to two orders of magnitude higher total conductivity than SZx samples. A-site nonstoichiometry was shown to have a significant effect on the electrical conductivity of SZx and SZYx. The highest total and bulk conductivity were observed at x = 0.98 for both systems. Increasing the conductivity with a rise in humidity indicates that proton conduction appears in the oxides in wet conditions. A defect model based on consideration of different types of point defects, such as strontium vacancies, substitutional defects and oxygen vacancies, and assumption of Y ions partitioning over Zr and Sr sites was elaborated. The proposed model consistently describes the obtained data on conductivity.

The work studies chemical stability and thermal compatibility of composite electrodes in contact with proton electrolyte based on calcium zirconate. Composite of electrolytes of CaZr_0.95Sc_0.05O_3–δ and CaZr_0.9Y_0.1O_3–δ with Fe, Ni, Cu, and Pd metals and also with the perovskite oxide of SrTi_0.8Fe_0.2O_3–δ are considered. Temperature dependences of resistance of porous electrodes made of these materials are studied.