Solid oxide fuel cells with a thin film electrolyte: A review on manufacturing technologies and electrochemical characteristics

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. keywords: electrode-supported SOFC, metal-supported SOFC, thin film electrolyte, film deposition, freestanding electrolyte DOI: https://doi.org/10.15726/elmattech.2022.1.00

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

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

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

Special Issue on Promising Materials and Technologies for Solid Oxide Electrochemical Devices

Solid oxide electrochemical devices, such as fuel cells, electrolyzers, pumps, sensors, etc [...

Electrical Conductivity of Thin Film SrTi0.8Fe0.2O3−δ-Supported Sr0.98Zr0.95Y0.05O3−δ Electrolyte

Thin films of Sr0.98Zr0.95Y0.05O3−δ (SZY) electrolyte were grown on porous supporting SrTi0.8Fe0.2O3−δ electrodes by the chemical solution deposition method from a low-viscous solution of inorganic salts. The films were characterized by X-ray diffraction and scanning electron microscopy. The gas-tightness of the films was evaluated using the differential-pressure method. The across-plane electrical conductivity of 1 mm thick SZY film was measured by impedance spectroscopy and compared to that of a massive ceramic sample. The revealed difference in electrical properties of the film and massive SZY samples indicates that diffusional interaction between the film and the substrate influences the performance of the supported electrolyte

Solid-Oxide Amperometric Sensor for Hydrogen Detection in Air

An amperometric sensor based on CaZr0.95Sc0.05O3−δ (CZS) proton-conducting oxide for the measurement of hydrogen concentration in air was designed and tested. Dense CZS ceramics were fabricated through uniaxial pressing the powder synthesized by the solid-state method and sintering at 1650 °C for 2 h. The conductivity of CZS was shown to increase with increasing air humidity, which indicates the proton type of conductivity. The sensor was made from two CZS plates, one of which had a cavity was drilled to form an inner chamber, that were then pressed against each other and sealed around the perimeter to prevent gas leaking. The inner chamber of the sensor was connected with the outer atmosphere via an alumina ceramic capillary, which acted as a diffusion barrier. The sensor performance was studied in the temperature range of 600–700 °C in the mixtures of air with hydrogen. The sensor signal, or the limiting current, was found to linearly increase with the hydrogen concentration, which simplifies the sensor calibration. The sensor demonstrated a high sensitivity of ~60 μA per 1% H2 at 700 °C, a fast response, high reproducibility, good selectivity, and long-term stability

Solid-Electrolyte Amperometric Sensor for Simultaneous Measurement of CO and CO₂ in Nitrogen

A solid-state amperometric sensor based on yttria-stabilized zirconia (YSZ) for the simultaneous measurement of CO and CO2 concentrations in inert gases was fabricated. The designed sensor consists of two electrically isolated ceramic cells made of YSZ and equipped with Pt electrodes. Ceramic capillaries connecting an inner gas chamber of each cell with the outside atmosphere serve as diffusion barriers. One of the cells is intended for sensing CO, whereas the other is for sensing CO2 in the gaseous atmosphere. The electrochemical response of the sensor was studied in the temperature range of 600–750 °C in the presence of up to 10% of CO and CO2 in nitrogen. The limiting currents of the two cells were shown to rise linearly with the relevant carbon oxide concentration, and no perceptible cross-sensitivity effect toward the other carbon oxide was found. The sensor demonstrated high stability and reproducibility of results and good dynamic characteristics. The novelty of this research lies in the development of a simple, reliable and fast solid-oxide sensor for simultaneous sensing of CO and CO2 in inert gases, which can be used for the control of atmosphere in, for example, pharmaceutical, chemical, food storage industries