Anode-supported Tubular Solid Oxide Fuel Cell Research Articles

A new method for manufacturing anode supported solid oxide fuel cells with AFL

In this study, two new methods are proposed for manufacturing anode-supported tubular SOFCs (solid oxide fuel cells) with AFL (anode functional layer). The anode supports are manufactured via thermoplastic extrusion. PEG is used as a secondary binder in the anode tubes and it is selectively removed by water debinding and sweat debinding methods and an AFL layer is obtained with different microstructure and porosity. The Sweat debinding method is suggested as a new method for forming an alternative layer with a different microstructure than the main body of the anode support. Full cells are produced from the altered anode supports. The peak power densities of the cells are measured as 0.38 W/cm2 for Sweat Debound cells, while it is 0.29 W/cm2 for the Water Debound cells.

Thermally self-sustaining operation of tubular solid oxide fuel cells integrated with a hybrid partial oxidation reformer using propane

Abstract Tubular solid oxide fuel cells (SOFCs) can be applied in a diverse range of applications, such as critical military missions, auxiliary power units, and portable power generators. In particular, portable power-generation devices may have to meet the requirements of rapid start-up, thermally self-sustaining operation, high thermal shock resistance, and high power density relative to the weight. This work presents the design and performance of a tubular SOFC stack integrated with a hybrid catalytic partial oxidation (CPOX) reformer, an afterburner (A/B), and a heat exchanger (HEX), which enables the stack operation without any external heat source with propane as a fuel. The SOFC stack that was made with four anode-supported tubular SOFCs was assembled with fuel and air chambers. The hybrid COPX reformer that was fed with a pre-mixture of propane and air acted as a start-up burner at the initial period operation to heat the stack up and then a reformer to provide a syngas to the stack when it reached an elevated temperature (700–800 °C). The A/B also provided heat energy to the stack by oxidizing the unreacted fuel and air of the stack anode and cathode exhaust, respectively. The stack first underwent a pre-treatment which reduced the anode support in a programmable furnace. The preliminary electrochemical performance of the stack was assessed while feeding a mixture gas of H2 and N2 as the fuel. Next, the pre-treated stack was integrated with the hybrid reformer, A/B, and HEX and insulated to investigate the thermally self-sustaining rapid operation capabilities by using propane as the fuel. In the integrated SOFC system, the stack reached 780 °C within an hour upon operation and generated 12 W of output power, thus demonstrating the feasibility of the system for portable power generations.

Effects of cell geometries on performance of tubular solid oxide fuel cell

A two-dimensional model comprising fuel channel, anode, cathode and electrolyte for an anode-supported tubular solid oxide fuel cell (AST-SOFC), has been developed, considering mass and charge transport. By using the model approach, different geometries of the AST-SOFC are proposed and simulated, further analyzing and discussing species transport phenomena and current distribution inside the cell. The results illustrate that effects of current collectors are more remarkable to cell performances for AST-SOFC having a larger current collector than that holding smaller one. The cell with thinner anode is in need of the bigger anode current collecting area to have a high performance. While the cell has the bigger diameter, the current demands the wider path to flow from anode to cathode, thus demanding the thicker anode support for obtaining the higher performance. These calculations can be used to design and optimize the AST-SOFC.

Highly Durable Cathode Materials with High Performance for Protonic Ceramic Fuel Cells

Solid oxide fuel cells (SOFCs) have attracted clean alternative power sources because of their have high energy conversion efficiency, multi-fuel flexibility and no use of precious metal catalysts. However, high operating temperatures (800 – 1000 oC) deteriorate the long term durability and fabrication cost of SOFCs [1]. Recently protonic ceramic fuel cells (PCFCs) based on proton-conducting electrolytes may be one of solutions to decrease operating temperatures due to high proton conductivity at intermediate temperature (IT; 400 – 600 oC) [2]. Doped barium zirconate (BZO) and barium cerate (BCO) based electrolytes have been studied extensively for use in PCFCs [3]. Even though BCO exhibits high proton conductivity, it is not suitable owing to its poor CO2 tolerance. On the other hand, BZO shows high chemical stability with good mechanical strength under CO2atmospheres. However, the proton conductivity of BZO-based materials is lower than that of BCO at the IT. Hence, the compound materials (BZCO) of BZO and BCO have attracted as a candidate electrolyte for PCFCs, BZCO exhibits high proton conductivity as well as maintains good chemical stability. In particular, co-doped BZCO materials with Y and Yb (BaZr0.1Ce0.7Y0.1Yb0.1O3– δ; BZCYYb) have been reported to exhibit high proton conductivity and the excellent catalytic activity for reforming of hydrocarbons with the conversion of H2S to SO2[3] For PCFCs, the reactions at the cathode can be expressed as Eq. (1) and water generates at three phase boundaries (TPBs) of cathode side [4]: (1) 4OH. o + O2 + 4e- --> 2H2O + 4Ox o This phenomenon makes their cathode reactions more complex and results in high cathode polarization resistances. Until now, however, mixed ionic and electronic conductors for oxygen conducting SOFCs have used as the cathode materials for PCFCs, such as Ba0.6Sr0.4Co0.2Fe0.8O3– δ (BSCF), La0.6Sr0.4Co0.2Fe0.8O3– δ(LSCF). Therefore, in this work suitable cathode materials are proposed for highly durable PCFCs with the improved performance. The cathode materials for PCFCs are required to the properties of high electric and ionic conductivity, high catalytic activity, good thermal compatibility with the electrolyte, and chemical stability in a humid oxidizing atmosphere [5-7]. For achieving these goals, several double perovskite-structure cathode materials are investigated under various operating conditions, such as flow rate of gas, amount of humidification and operating temperature in terms of the performance and long-term durability through the use of electrochemical and physicochemical analysis. Materials for fuel-cell technologies, Brain C. H. Steele, Angelika Heinzel, Nature , 414, 345 (2001).Lowering the temperature of solid oxide fuel cells, Kang Taek Lee, Eric D. Wachsman, Science , 334, 935 (2011).Enhanced sulfur and coking tolerance of a mixed ion conductor for SOFCs: BaZr0.1Ce0.7Y0.2–xYbxO3-δ, Lei Yang, Shizhong Wang, Kevin Blinn, Mingfei Liu, Ze Liu, Zhe Cheng, Meilin Liu, Science , 326, 9127 (2009).Reaction model for cathodes cooperated with oxygen-ion conductors for solid oxide fuel cells using proton-conducting electrolytes, Ling Zhao, Beibei He, Jiaqiang Gu, Feng Liu, Xiangfeng Chu, Changrong Xi, Int. J. Hydrogen energy,37, 548 (2012).Anode-supported tubular SOFCs based on BaZr0.1Ce0.7Y0.1Yb0.1O3−δ electrolyte fabricated by dip coating, Changcheng Chen, Mingfei Liu, Yaohui Bai, Lei Yang, Erqing Xie, Meilin Liu, Electrochemistry Communications, 13, 615 (2011).BaZr0.9Yb0.1O3 -δ-modified bi-electrode supported solid oxide fuel cells with enhanced coking and sulfur tolerance, Kevin S. Blinn, Meilin Liu, J. Power Sources, 243, 24 (2013).Comparative study of electrochemical properties of different composite cathode materials associated to stable proton conducting BaZr0.7Pr0.1Y0.2O3-δ electrolyte, Electrochimica Acta, 146, 1 (2014). * Corresponding author: jyoung@sejong.ac.kr (J.-Y. Park).

A carbon-air battery for high power generation.

We report a carbon-air battery for power generation based on a solid-oxide fuel cell (SOFC) integrated with a ceramic CO2-permeable membrane. An anode-supported tubular SOFC functioned as a carbon fuel container as well as an electrochemical device for power generation, while a high-temperature CO2-permeable membrane composed of a CO3(2-) mixture and an O(2-) conducting phase (Sm(0.2)Ce(0.8)O(1.9)) was integrated for in situ separation of CO2 (electrochemical product) from the anode chamber, delivering high fuel-utilization efficiency. After modifying the carbon fuel with a reverse Boudouard reaction catalyst to promote the in situ gasification of carbon to CO, an attractive peak power density of 279.3 mW cm(-2) was achieved for the battery at 850 °C, and a small stack composed of two batteries can be operated continuously for 200 min. This work provides a novel type of electrochemical energy device that has a wide range of application potentials.

Fabrication of composite cathode by a new process for anode-supported tubular solid oxide fuel cells

Anode-supported tubular solid oxide fuel cells (SOFCs) fabricated by traditional method suffered from the charge exchange constraint on the interface of electrolyte and cathode. In this work, we introduced a new sintering process to obtain the dense and porous electrolyte bi-layer structure on anode-supported tubular SOFCs. The cathode was built by infiltrating nano-catalyst La0.6Sr0.4Fe0.9Sc0.1O3-δ (LSFSc) into the porous electrolyte, which showed better electrochemical activity than traditional LSM cathode. The functional fuel cells showed the maximum power density of 292.3mW·cm−2 at 800°C with H2 as fuel and air as oxidant. This unique performance was due to the porous electrolyte provided more specific surface area for cathode and the nanostructured cathode catalyst showed high electro-catalysis for oxygen reduction reaction. Moreover, a long term test was carried out, demonstrating the excellent stability which was extremely important for application in the future.

Enhancing the performance of doped ceria interlayer for tubular solid oxide fuel cells

Doped ceria interlayer fabricated by conventional wet ceramic process such as dip-coating often suffers from high resistance due to either low density or solid-state reaction with yttria-stabilized zirconia (YSZ) electrolyte in solid oxide fuel cells (SOFCs). This work presents a new route to reduce the resistance by increasing the density while minimizing the solid-state reaction through impregnating samaria-doped ceria (SDC) nano-particles to porous SDC interlayer of anode-supported tubular SOFCs. Results show that impregnated fine structure can substantially reduce the ohmic resistance, from 0.140 to 0.087 Ω cm2 at 750 °C, and consequently significantly improve the fuel cell performance, peak power density from 1.01 to 1.50 W cm−2 at 750 °C. The significant improvements demonstrate that impregnation is an effective method to improve the interlayer performance.

Experimental characterization of an anode-supported tubular SOFC generator fueled with hydrogen, including a principal component analysis and a multi-linear regression

Solid oxide fuel cell (SOFC) power generators can now be commercialized as heat and power micro-cogenerator. Few well-documented field tests have been conducted to date on these units’ tubular cell architecture, however, and little has been done to derive general rules for a thorough understanding of these units’ operation. The present work focuses on characterizing the hydrogen-powered Acumentrics Gen521 (rated 2.5 kW) under various stable conditions. A test rig was installed at the Dipartimento di Energetica of the Università Politecnica delle Marche (Ancona, Italy) to ascertain the main characteristic curves of the Acumentrics Gen521. A multivariate data analysis was performed on the experimental data collected to establish the operating parameters most influential for the stack voltage (SV) and the DC stack output power generated in different working conditions. Some multi-linear response surfaces are suggested for predicting the SV and the DC power in different operating conditions.

Anode-supported tubular SOFCs based on BaZr 0.1Ce 0.7Y 0.1Yb 0.1O 3 − δ electrolyte fabricated by dip coating

Anode-supported tubular solid oxide fuel cells (SOFCs) based on a proton and oxide ion mixed conductor, BaZr 0.1Ce 0.7Y 0.1Yb 0.1O 3 − δ (BZCYYb), have been fabricated using a dip coating and co-firing process. This new fabrication technique effectively reduced the Ohmic resistances of tubular cells to ~ 0.1 and ~ 0.3 Ω cm 2 at 750 and 600 °C, respectively. Typical tubular cells with Ni-BZCYYb anode, BZCYYb electrolyte, and La 0.6Sr 0.4Co 0.2Fe 0.8O 3 − δ (LSCF)-BZCYYb composite cathode demonstrated much-improved performance, achieving peak power densities of 1.13, 0.81, 0.63, and 0.53 W cm − 2 at 750, 700, 650, and 600 °C, respectively, when humidified (3 v% water vapor) hydrogen was used as fuel and ambient air as oxidant.

Transport, sensitivity, and dimensional optimization studies of a tubular Solid Oxide Fuel Cell

In this paper, the impact of the design and operating parameters of a tubular Solid Oxide Fuel Cell (SOFC) is studied using a well-validated steady-state model. The profiles of species concentrations and pressure in the flow channels when the cell terminal voltage is changed are studied. In addition, both the axial and radial profiles of the species concentrations inside the electrodes are presented. The model is also used to study the effects of the parameters that can significantly influence the design criteria of an anode-supported tubular SOFC. The effects of the flowrate of H 2 , inlet pressure, and the cell temperature on the power output from the cell are studied. Cell characteristic parameters such as the porosity of the electrodes, effective diffusivity of the species, and the rate of the electrochemical reactions are varied and their impact on the cell performance is observed. The influence of the cell design parameters such as the thickness of the electrodes and the electrolyte on the steady-state polarization curve are also studied. Finally, a dimensional study is presented. In the dimensional study, the radius of the anode flow channel, the length of the cell, and the annulus size are varied keeping the solid volume and the total cell volume constant. This study shows that it is possible to design guidelines for the optimum performance of the cell.

Modeling of gas transport through a tubular solid oxide fuel cell and the porous anode layer

A design model is a necessary tool to understand the gas transport phenomena that occurs in a tubular solid oxide fuel cell (SOFC). This paper describes a computational model, which studies the gas flow through an anode-supported tubular SOFC and the subsequent diffusion of gas through its porous anode. The model is a numerical solution for the gas flow through a plug flow reactor with a diffusion layer, which includes the activation, ohmic, and concentration polarizations. Gas diffusion is modeled using the dusty-gas equations which include Knudsen diffusion. Mercury intrusion porosimetry (MIP) is used to experimentally determine micro-structural parameters such as porosity, tortuosity and effective diffusion coefficients, which are used in the diffusion equations for the porous anode layer. It was found that diffusion in the anode plays a key role in the performance of a tubular SOFC. The concentration gradient of hydrogen and water results in a lower concentration of hydrogen and a higher concentration of water at the reactive triple phase boundary (TPB) than in the fuel stream which both lead to a lower cell voltage. The gas diffusion determines the limiting current density of the cell where a higher concentration drop of hydrogen results in a lower limiting current density. The model validates well with experimental data and is used to improve micro-tubular solid oxide fuel cell designs.

Isothermal models for anode-supported tubular solid oxide fuel cells

Modeling of solid oxide fuel cells (SOFCs) has gained considerable significance in recent years. A detailed phenomenological model for SOFC can be used to understand performance limitations, optimization, in situ diagnostics and control. In this paper, we study the transport and various electrochemical phenomena in an anode-supported tubular SOFC using a steady-state model. In particular, we discuss the importance of modeling different phenomena vis-a-vis their impact on the prediction capability of the model. It is observed that even a reasonably simple model can be sufficiently predictive in a particular operating range. As the operating range of the cell is increased, the predictive capability of a model validated in a narrow range cannot be guarantied. It has also been observed that neglecting momentum conservation in the model for a tubular SOFC can affect the predictive capability of the model at higher overpotentials. An extensively validated model is used to study the percentage conversion of oxygen and oxygen concentration profile within a cell at different operating conditions. All of the simulation studies are supported by experimental data that spans a wide range of operation in terms of the DC polarization, reactant flow rates and operating temperatures.

Fabrication and properties of anode-supported tubular solid oxide fuel cells

Abstract Tubular solid oxide fuel cell (SOFC) systems have many desirable characteristics over their planar counter-parts. Anode-supported tubes provide an excellent platform for individual cells. They allow for a thin electrolyte layer to be applied to the outside of the tube, which helps to minimize polarization losses. This paper describes the fabrication of nickel–zirconia (Ni–YSZ)-based anode tubes via extrusion of a plastic mass through a die of the required dimensions. The anode tubes were then dried and fired. Tests were performed on the tubes to determine the effects of firing temperature on porosity to allow for a pinhole-free electrolyte coating to be applied. Thin layer coating techniques, including vacuum-assisted dip coating and painting, were compared. Ni–YSZ anode-supported tubular SOFCs with a gas-tight thin YSZ electrolyte layer were then realized. Microstructure of the anode support, electrolyte and cathode thin films was also examined.

Fabrication and Characterization of Anode-Supported Tubular SOFCs with Zirconia-Based Electrolyte for Reduced Temperature Operation

An anode-supported tubular solid oxide fuel cell (SOFC) with a thin electrolyte film for reduced temperature operation was fabricated by a wet cofire process. Instead of the traditional extrusion method, the anode substrate was formed by a tape-cast method. This allows design the substrate with some advantageous configurations that can improve the performance of SOFCs. and -stabilized zirconia electrolyte films were fabricated on the substrate by a modified slurry dip-coating method and then cofired. In order to use cathode, a thin interlayer was also fabricated by the slurry dip-coating method. The fabricated tubular cell generated electricity successfully between 600 and 850°C. Power density of ca. 170 and was achieved at 600 and 700°C, respectively, however, the ohmic resistance was larger than expected. Because interlayer was used, ohmic resistance could be high due to the formation of a layer of solid solution at the zirconia/ceria interface. The gaseous diffusion resistance governed the performance between 700 and 850°C. Better performances of the anode-supported tubular SOFCs can be achieved by further optimizations for the zirconia/ceria interface, control of both porosity and thickness of the anode substrate, as well as improvement of the cathode. © 2004 The Electrochemical Society. All rights reserved.