Performance and short-term stability of single-chamber solid oxide fuel cells based on La0.9Sr0.1Ga0.8Mg0.2O3−δ electrolyte (original) (raw)
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Ceramic Engineering and Science Proceedings, 2006
ABSTRACT The influence of the anode thickness (9–60 μm) on the behaviour of SC-SOFCs was investigated in different total flows of a methane-air mixture to the anode. In order to eliminate the effects of the cathode with varying flow, a double chamber setup with separated fuel and air streams to the anode and cathode was used. The open circuit voltage (OCV) decreased with increasing gas flow and at the same time the power density increased. Oscillations of the OCV at high gas flows were observed for cells with thin anodes. Cells with thick anodes showed the highest OCV and the highest maximum power density. These anodes have a higher catalytic activity for the partial oxidation of methane and create a lower oxygen partial pressure at the anode/electrolyte interface. They also provide more hydrogen than thin anodes and can give a higher power output.
On the single chamber solid oxide fuel cells
Journal of Power Sources, 2008
Single chamber solid oxide fuel cells (SC-SOFCs) offer the possibility to simplify solid oxide fuel cells because only one gas compartment is necessary. Both, anode and cathode are exposed to the same mixture of fuel and oxidant. In such a system the driving force for the ionic current in the electrolyte is not due to the difference of oxygen partial pressures in the two sealed gas compartments. It is the selectivity of the two different electrodes for either the partial oxidation of a hydrocarbon at the anode or the reduction of oxygen at the cathode that allows for the generation of an electric current. SC-SOFCs have been demonstrated to give reasonably high power output comparable to conventional solid oxide fuel cells. However, the working principle of SC-SOFCs is not yet fully understood. This project aims at obtaining more insight into this type of fuel cell operating in methaneair mixtures. The thermodynamic equilibrium of the used gas mixtures was calculated for the experimental operating conditions and the kinetics of the oxidation reactions were studied experimentally. The studied SC-SOFCs were based on the oxygen-ion conducting gadolinia doped ceria (Ce 0.9 Gd 0.1 O 1.95) an anode material consisting of a mixture of metallic Nickel and gadolinia doped ceria and a cathode consisting of porous perovskite Sm 0.5 Sr 0.5 CoO 3-δ. The prepared cells generated 271 mW/cm 2 at 500°C and 468 mW/cm 2 at 600°C in flowing mixtures of methane and air. It was found that the open circuit voltage and the maximum power density greatly depended on the gas flow rate, the gas composition and the operating temperature but also on the thickness of the anode layer. Furthermore, a pronounced overheating of the cell to temperatures higher than the furnace temperature was observed. The reason for this temperature rise was the parasitic oxidation reaction of methane that occurs at both electrodes, however with the highest rates at the anode. In the second part of this work, different cell designs were evaluated that are not possible with conventional solid oxide fuel cells. A process was developed, by which micro SC-SOFCs with side by side placement of the electrodes were successfully prepared. Nineteen parallel connected cells with feature sizes in the micrometer range generated an open circuit voltage of 0.65-0.75 V in flowing mixtures of methane and air. The performance of the cell array was limited by the high ohmic resistances of the long conduction paths in the thin electrodes. It could be shown for the first time that a µ-SC-SOFC is a feasible device. Fully porous fuel cells with a flow-through configuration have been proposed in the literature but they have not been proven to function. Their proof of concept is given in this Summary VIII work. An anode-supported fully porous SC-SOFC was prepared and gave a reasonable open circuit voltage. The power output was very sensitive to the temperature, the CH 4 /O-ratio and the total gas flow rate through the cell. At 733°C an open circuit voltage of 0.52 V and a maximum power density of 10 mW/cm 2 for 1000 ml/min were measured. Thus, for the first time the fully porous design of SC-SOFCs with flow-through configuration has been demonstrated. IX Zusammenfassung Einkammerfestelektrolytbrennstoffzellen (EK-FEBZ) sind Brennstoffzellen mit nur einem Gasraum in dem sich ein Gasgemisch aus Brennstoff und Sauerstoff befindet. Die Anode und Kathode einer solchen Zelle werden demselben Gemisch aus Brenngas und Luft ausgesetzt. In einer solchen Zelle entsteht die treibende Kraft für einen elektrischen Strom nicht aufgrund unterschiedlicher Sauerstoffpartialdrücke auf beiden Seiten eines Festelektrolyten, sondern aufgrund der Selektivität der Anode für die Oxidation eines Kohlenwasserstoffs und der Selektivität der Kathode für die Reduktion von Luftsauerstoff. Solche Zellen ermöglichen eine drastische Vereinfachung des Designs von Festelektrolytbrennstoffzellen da statt zwei nur noch eine einzige Gaskammer benötigt wird. In der Vergangenheit konnte gezeigt werden, dass EK-FEBZ angemessene elektrische Leistungen liefern können vergleichbar mit jenen von konventionellen Festelektrolytbrennstoffzellen. Das genaue Funktionsprinzip von EK-FEBZ ist aber noch weitgehend unerforscht. Zielsetzung der vorliegenden Arbeit war es, ein besseres Verständnis für diese Art von Brennstoffzellen zu erarbeiten, die in Methan-Luft Gemischen betrieben werden. Zuerst wurden die Gleichgewichtszusammensetzungen von Methan-Luft Gemischen für den Temperaturbereich von 500 bis 800°C berechnet. Des Weiteren wurde die Kinetik der massgebenden Oxidationsreaktionen, die an den Elektroden auftreten gemessen. Es wurden Zellen untersucht, die auf dem ionenleitenden Elektrolyten, Cer-Gadoliniumoxid (Ce 0.9 Gd 0.1 O 1.95) basieren. Als Anodenmaterial wurde ein Gemisch von Nickel und Ce 0.9 Gd 0.1 O 1.95 eingesetzt und als Kathodenmaterial Sm 0.5 Sr 0.5 CoO 3-δ , welches in der Perowskit-Struktur vorliegt. Die hergestellten Zellen zeigten eine elektrische Leistung von 271 mW/cm 2 bei 500°C und 480 mW/cm 2 bei 600°C in strömenden Methan-Luft Gemischen. Die Leerlaufspannung wie auch die maximale Leistung hingen stark vom gewählten Gasfluss, der Gaszusammensetzung, und der Zelltemperatur ab, aber auch von der Anodendicke. Des Weiteren wurde festegestellt, dass im ganzen untersuchten Temperaturbereich immer beide Elektroden die Umsetzung des Methan Luft katalysieren, jedoch mit sehr unterschiedlichen Umsetzungsraten. Eine deutliche Überhöhung der Zelltemperatur im Vergleich zur Ofentemperatur kann auf die parasitärer Methanoxidation hauptsächlich an der Anode zurückgeführt werden. Im zweiten Teil der vorliegenden Arbeit wurden verschiedene, neuartige Zellendesigns erprobt, die mit konventionellen Festelektrolytbrennstoffzellen nicht möglich wären. Es Zusammenfassung X wurde ein Prozeß entwickelt, mit dem Mikro EK-FEBZ hergestellt werden konnten, bei denen beide Elektroden auf derselben Seite des Elektrolyts liegen und durch einen schmalen Spalt voneinander getrennt sind. Neunzehn parallelgeschaltete Zellen mit Elektroden in der Größenordnung von Mikrometern, zeigten eine Leerlaufspannung von 0.65-0.75°V in strömenden Methan-Luft Gemischen. Die Leistung der Zellenanordnung war durch den hohen elektrischen Widerstand der langen Strompfade in den dünnen Elektroden begrenzt. Gleichwohl konnte zum ersten Mal gezeigt werden, dass µ-EK-FEBZ realisierbare Brennstoffzellen sind. Ein zweites Design, welches bereits vor einigen Jahren vorgeschlagen wurde, aber bisher noch nie experimentell demonstriert wurde, ist das vollporöse Design. Der Nachweis, dass vollporöse Zellen, bei welchen das Gasgemisch durch die Zelle hindurch geleitet wird funktionieren, wurde hier erbracht. Die Zellen wurden von einem relativ dicken Anodensubstrat gestützt, welches den Zellen die mechanische Stabilität verlieh. Hierauf wurden poröse Schichten des Elektrolytmaterials und der Kathode aufgebracht und durch diese Dreischichtanordnung das Gasgemisch geleitet. Es konnten vernünftige Leerlaufspannungen an den Zellen gemessen werden. Die Leistung hing stark von der Temperatur, dem Verhältnis von Brenngas (CH 4) zu Sauerstoff, und dem totalen Gasfluss durch die Zelle ab. Bei 733°C konnte eine Leerlaufspannung von 0.52 V und eine maximale Leistung von 10 mW/cm 2 gemessen werden bei 1000 ml/min Gasfluss. Dies ist das erste Mal, dass eine vollporöse EK-FEBZ mit Durchflußkonfiguration erfolgreich getestet werden konnte. 1.2 Solid Oxide Fuel Cells The first solid oxide fuel cell (SOFC) was developed in 1937 by Baur and Preis [1]. Since then a lot of progress has been made in terms of materials and processing of SOFCs. An advantage of SOFCs is the possibility of using natural gas as the fuel [2] and the high reaction rates given by the relatively high operating temperature. Thus, expensive catalysts are not 2 G F E ∆ = ⋅ (1.4) to the environment encountered in a fuel cell [12]. The main problem of this material is the high operating temperature necessary to enable the migration of oxygen vacancies through the electrolyte. The anode of a fuel cell usually is a highly porous Ni-ceramic composite-a so-called cermet [13]. Cermets used in SOFCs need to be ionically and electronically conducting, should have a high porosity for unhindered gas flow to, and away from the reaction sites and bonding seals materials like high-B 2 O 3 glasses [24], earth-alkali silicate glasses such as BaO•Al 2 O 3 •SiO 2 [25] or glass ceramics are commonly used. 1.2.5 Current Fields of Research One of the main problems of SOFCs is the high operating temperature leading to a high degradation rate of cell performance and the need for more expensive interconnect and sealing materials. The operating temperature of the cell is mainly determined by the electrolyte resistance. Two ways are possible to decrease the latter, either by using alternative electrolyte
Upgrading the performance of La2Mo2O9-based solid oxide fuel cell under single chamber conditions
International Journal of Hydrogen Energy, 2012
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Journal of the Ceramic Society of Japan
In this study, La 0.8 Sr 0.2 Ga 0.8 Mg 0.2 O 3¹¤ (LSGM)-supported micro tubular solid oxide fuel cells (T-SOFCs) with two different configurations, one containing an LSGMCe 0.6 La 0.4 O 2¹¤ (LDC) bi-layer electrolyte (Cell A) and one containing an LDCLSGM LDC tri-layer electrolyte (Cell B), were fabricated using extrusion and dip-coating. After optimizing the paste formulation for extrusion, the flexural strength of the dense and uniform LSGM micro-tubes sintered at 1500°C was determined to be approximately 144 MPa. Owing to the insertion of an LDC layer between LSGM electrolyte and La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3¹¤ (LSCF) LSGM cathode, the ohmic resistances of Cell B were slightly larger than those of Cell A at the operating temperatures investigated, mainly because of interfacial resistance, but Cell B exhibited slightly lower polarization resistance than Cell A. The maximum power densities (MPDs) of Cell A were 0.25, 0.35, 0.43, and 0.47 W cm ¹2 at 650, 700, 750, and 800°C, respectively, which are slightly larger than those of Cell B, i.e., 0.23, 0.33, 0.42, and 0.41 W cm ¹2 , respectively, owing to the facts that Cell A exhibited a slightly higher open-circuit voltage and a smaller R t value. Cell A containing the LSGM (288¯m)LDC (8¯m) bilayer electrolyte can be operated at approximately 650°C with an MPD value of approximately 0.25 W cm ¹2 ; however, a similarly structured single cell containing a Zr 0.8 Sc 0.2 O 2¹¤ (ScSZ) (210¯m) electrolyte need to be operated at 900°C, and one containing an Ce 0.8 Gd 0.2 O 2¹¤ (GDC; 285¯m)ScSZ (8¯m) bi-layer electrolyte has to be operated at 700°C. Thus, the advantage of using LSGM as an electrolyte for micro T-SOFC single cells is apparent.
Bitlis eren üniversitesi fen bilimleri dergisi/Bitlis Eren üniversitesi fen bilimleri dergisi, 2024
This study presents a cathode-supported planar solid oxide fuel cell (SOFC) fabrication made via a single step co-sintering method and investigation of its performance. The materials used are NiO-CGO, CGO and CGO-LSCF for anode, cathode, electrolyte, respectively. Our study shows that increasing the cell size has a detrimental effect on cell single step co-sinterability. Increasing cathode thickness and reducing electrolyte thickness led to curvature decrease at the edges, however these adjustments were not enough to achieve a curvature-free cathode-supported cell. Thus, three porous alumina cover plates (total mass of 49.35 g) placed on the top of the cell during sintering were utilized to suppress curvature formation, and as a result, a nearly curvature-free cathode-supported cell was obtained. Performance of the cells were investigated. The results showed that increasing cathode thickness and decreasing electrolyte thickness had negative effects on cell performance despite enhanced single step co-sinterability of the cell. The maximum power density and OCV of the final planar cell (thickness 60-40-800 µm, anodeelectrolyte-cathode) were found to be 1.71 mW cm-2 and 0.2 V, respectively, in a fuel rich condition (R:1.6). Additionally, the maximum OCV and power density among the all cells were measured from the cell (thickness 60-40-400 µm, anodeelectrolyte-cathode) as 0.56 V and 24.79 mW cm-2 , respectively, in a fuel rich condition (R:2.4).
Energies, 2018
We investigated the effect of electrolyte thickness and operating temperature on the heat and mass transfer characteristics of solid oxide fuel cells. We conducted extensive numerical simulations to analyze single cell performance of a planar solid oxide fuel cell (SOFC) with electrolyte thicknesses from 80 to 100 µm and operating temperatures between 700 • C and 800 • C. The commercial computational fluid dynamics (CFD) code was utilized to simulate the transport behavior and electrochemical reactions. As expected, the maximum power density increased with decreasing electrolyte thickness, and the difference became significant when the current density increased among different electrolyte thicknesses at a fixed temperature. Thinner electrolytes are beneficial for volumetric power density due to lower ohmic loss. Moreover, the SOFC performance enhanced with increasing operating temperature, which substantially changed the reaction rate along the channel direction. This study can be used to help design SOFC stacks to achieve enhanced heat and mass transfer during operation.
From macro- to micro-single chamber solid oxide fuel cells
Journal of Power Sources, 2007
Single chamber solid oxide fuel cells (SC-SOFCs) with interdigitating electrodes were prepared and operated in CH 4 /air mixtures. Both electrodes (Ni-Ce 0.8 Gd 0.2 O 1.9 cermet and Sm 0.5 Sr 0.5 CoO 3−δ perovskite) were placed on the same side of a Ce 0.8 Gd 0.1 O 1.95 electrolyte disc. The separating gap between the electrodes was varied from 1.2 to 0.27 mm and finally down to 10 m. Screen-printing was used for the preparation of the cells with a gap in the millimetre range, whereas micromolding in capillaries (MIMIC) was used for the preparation of the micro-SC-SOFCs.
Anode Supported Single Chamber Solid Oxide Fuel Cell in CH-Air Mixture
Journal of the …, 2004
In this study, yttrium-stabilized zirconia ͑YSZ͒ thin films 1-2 m thick electrolyte have been prepared using NiO-YSZ anode as substrates. Fuel cell test was conducted with the single chamber configuration in methane-air gas mixture using (La,Sr)(Co,Fe)O 3 ͑LSCF͒ as the cathode. Test results showed that the open-circuit voltage to be Ͼ0.8 V, with power density as high as 0.12 W cm Ϫ2 . It was also shown that gas flow rate has a large influence on the performance of the fuel cell, which indicates the importance of the geometrical design for anode support fuel cell system.
Performance of a porous electrolyte in single-chamber SOFCs
Journal of the …, 2005
A cell which consists of a porous 18 m thick Y-doped ZrO 2 ͑YSZ͒ electrolyte (23 Ϯ 3 vol % open porosity͒ on a NiO-YSZ anode substrate and a cathode using (La, Sr͒͑Co, Fe͒O 3 has been investigated in the single-chamber configuration. The cell performance and catalytic activity of the anode was measured in a flowing air-methane gas mixture with various flow rates. The results showed that the open-circuit voltage and the power density increased as the gas flow rate increased. The cell generated an open-circuit voltage of about 0.78 V, which was only about 0.1 V lower than that observed with dense electrolyte specimens. A maximum power density of 660 mW cm Ϫ2 ͑0.44 V͒ was obtained at set temperature ϭ 606°C ͑cell temperature ϭ 744°C) in the flow rate of 900 cm 3 min Ϫ1 , where the current efficiency was about 5% determined from fuel consumption.
Temperature and performance variations along single chamber solid oxide fuel cells
Journal of Power Sources, 2009
The catalytic activity of single chamber solid oxide fuel cells (SC-SOFCs) with respect to hydrocarbon fuels induces a major overheating of the fuel cell, temperature variations along its length, and changes in the original fuel/air composition mainly over the anode component. This paper assesses the temperature gradients and the variations in performance along electrolyte-supported Ni-YSZ/YSZ/LSM cells fed with methane gas. The investigations are performed in a useful range of CH 4 /O 2 ratios between 1.0 and 2.0, in which the furnace temperature and flow rate of methane-air mixtures are held constant at 700 • C and 450 sccm, respectively. Electrochemical impedance spectroscopy (EIS) is used to sense the temperature at the location where smaller size cathodes are positioned on the opposite side of a full-size anode. Due to temperature increases, cells always perform better when the small cathodes are located at the inlet as well as at a CH 4 /O 2 ratio of 1.0. With an increase in ratio, the results show the presence of artefacts due to the use of an active LSM material for the combustion of methane, and open-type gas distribution plates for the single chamber reactor.