Solid Oxide Fuel Cells with a Thin Film Electrolyte: A Review on Manufacturing Technologies and Electrochemical Characteristics

Received: 10 August 2022. Accepted: 10 September 2022.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

Effect of Sn doping on sinterability and electrical conductivity of strontium hafnate

Received: 16.02.23. Revised: 13.03.23. Accepted: 14.03.23. Available online: 17.03.23.SEM and XRD experiments were done using the facilities of the shared access centre "Composition of compounds” (Institute of High-Temperature Electrochemistry, Ural Branch of the Russian Academy of Sciences). The authors are grateful to Artem Tarutin for the help with the meas-urements of conductivity by the DC 4-probe method.Ceramic samples SrHfxSn1–xO3–δ (x = 0–0.16) were obtained by the solid-phase method.Sn doping enhances the sintering ability of ceramics.Sn doping results in an increase in conductivity by more than 2 orders of magnitude.The effect of isovalent substitution of hafnium by tin in strontium hafnate on sinterability and electrical conductivity was studied for the first time. The ceramic samples SrHfxSn1–xO3–δ (x = 0–0.16) were synthesized by solid-state reaction and sintered at 1600 °C for 5 h. The samples were examined using the methods of X-ray diffraction, scanning electron microscopy, impedance spectroscopy, and four-probe direct current technique. It was shown that all samples were phase pure and had the orthorhombic structure of SrHfO3 with the Pnma space group. Sn doping resulted in an increase in grain size, relative density and conductivity; the sample with x = 0.08 demonstrated the highest conductivity, which was ~830 times greater than that of undoped strontium hafnate at 600 °C. The conductivity of SrHf0.92Sn0.08O3–δ was 4.1∙10–6 S cm–1 at 800 °C in dry air. The possible reasons for the effect of Sn on the electrical properties of strontium hafnate were discussed

Advanced Measurement and Modeling Techniques for Improved SOFC Cathodes

The goal of this project was to develop an improved understanding of factors governing performance and degradation of mixed-conducting SOFC cathodes. Two new diagnostic tools were developed to help achieve this goal: (1) microelectrode half-cells for improved isolation of cathode impedance on thin electrolytes, and (2) nonlinear electrochemical impedance spectroscopy (NLEIS), a variant of traditional impedance that allows workers to probe nonlinear rates as a function of frequency. After reporting on the development and efficacy of these tools, this document reports on the use of these and other tools to better understand performance and degradation of cathodes based on the mixed conductor La{sub 1-x}Sr{sub x}CoO{sub 3-{delta}} (LSC) on gadolinia or samaria-doped ceria (GDC or SDC). We describe the use of NLEIS to measure O{sub 2} exchange on thin-film LSC electrodes, and show that O{sub 2} exchange is most likely governed by dissociative adsorption. We also describe parametric studies of porous LSC electrodes using impedance and NLEIS. Our results suggest that O{sub 2} exchange and ion transport co-limit performance under most relevant conditions, but it is O{sub 2} exchange that is most sensitive to processing, and subject to the greatest degradation and sample-to-sample variation. We recommend further work that focuses on electrodes of well-defined or characterized geometry, and probes the details of surface structure, composition, and impurities. Parallel work on primarily electronic conductors (LSM) would also be of benefit to developers, and to improved understanding of surface vs. bulk diffusion

Factors Governing Performance of Mixed-Conducting SOFC Cathodes

This presentation discusses factors governing the performance of mixed-conducting SOFC cathodes

Acceptor doping effects on microstructure, thermal and electrical properties of proton-conducting BaCe0.5Zr0.3Ln0.2O3-δ (Ln = Yb, Gd, Sm, Nd, la or Y) ceramics for solid oxide fuel cell applications

In the present work, six materials belonging to Ln-doped BaCeO3-BaZrO3 system (Ln = Yb, Y, Gd, Sm, Nd, La) are prepared and characterized. The impact of the type of the acceptor dopant on i) the microstructure (relative density, size and grain morphology), ii) the thermal properties (linear expansion, thermal expansion coefficient) and iii) the electrical properties (nature and value of conductivity), is identified. The method of the modified citrate-nitrate combustion synthesis is adopted in order to achieve single-phase ceramic samples with relative density higher than 94% at reduced sintering regime (1450 °C for 5 h). It is found that: (i) the mean grain size grows (from 1.4 to 3.8 μm), (ii) the thermal expansion coefficient increases (from 7.6·10-6 to 11.3·10-6 K-1 in the high-temperature range), (iii) the ionic conductivity decreases (from 10.2 to 0.3 mS cm-1 at 800°C) with increasing ionic radius of acceptor Ln-dopant. It is also found that BaCe0.5Zr0.3Y0.2O3-δ electrolyte can be considered as the most optimal one for IT-SOFC applications from the view point of electrical properties. However, in the temperature interval of 550-700°C, this sample possesses nonlinear thermal expansion. © 2016 Elsevier Ltd. All rights reserved

Proton-conducting BaCe0.5Zr0.3Ln0.2O3-δ (Ln = Yb, Gd, Sm, Nd, la or Y) ceramics for solid oxide fuel cell applications: Effects of acceptor-doping on microstructure, thermal and electrical properties

Six materials belonging to Ln-doped BaCeO3-BaZrO3 system (Ln = Yb, Y, Gd, Sm, Nd, La) are prepared and characterized in the present work. The impact of the type of the acceptor dopant on (i) the microstructure (relative density, size and type of grains), (ii) the thermal properties (linear expansion, thermal expansion coefficient) and (iii) the electrical properties (nature and value of conductivity) is identified. The modified citrate-nitrate combustion synthesis method is adopted in order to achieve single-phase ceramic samples with relative density higher than 94% at reduced sintering regime (1450°C for 5 h). It is found that: i) the mean grain size increases (from 1.4 to 3.8 μm), ii) the thermal expansion coefficient tends to growth (from 7.610-6 to 11.310-6 K-1 in the high temperature range), iii) the ionic conductivity decreases (from 10.2 to 0.3 mS cm-1 at 800°C) with increasing ionic radius of acceptor Ln-dopant. It is also found that BaCeZr0.3Y0.2O3-δ electrolyte can be considered as the most optimal one for IT-SOFC applications from the view point of electrical properties. However, in the temperature interval of 550-700°C, this sample possesses non-uniform thermal expansion