Conventional SOFC Research Articles

Novel Procedures for the Microstructural Design of SOFC Materials

Here we report two novel procedures that may lead to enhanced efficiencies of a SOFC via a precise control of the electrode microstructure and through the fabrication of a new type of electrolyte-supported SOFC. The first route is a simple and cost-effective method that allows the material-engineering for creation of a 2D/3D matrix of cross-linked channels through the whole SOFC electrode materials. The size of the channels can be precisely tailored from few microns up to hundreds of microns and remains stable up to 1500ºC. Due to the versatility of the method proposed it can be applied to practically any type of material commonly used in SOFC technology or in other fields. The second route is a novel design, alternative to the conventional electrolyte-supported SOFC with a honeycomb-electrolyte fabricated from hexagonal cells, providing high mechanical strength to the whole structure and supporting the thin layer used as electrolyte of a SOFC. The main feature of this design is the reduction of ~70% of the support material, rendering volumetric power densities of 1.22 W/cm3 and a high OCV of 1.13 V under pure CH4 at 900 ºC using standard SOFC materials

The Use of Conventional SOFC Electrodes in High Temperature Water Electrolysis Mode: An Electrochemical Study of Ni-Cermet and LSM

Ni-Cermet and LSM were synthesized and tested respectively as solid oxide electrolyser cathode and anode using three-electrode techniques between 973K and 1173K. YSZ was used as the electrolyte and Pt as the counter electrode. Polarization curves and impedance spectra have been analyzed for different gas compositions. The present results highlight a mechanism changing on Ni-cermet electrode upon gas composition. Oxygen ion oxidation on LSM electrode should be described using a Tafel's law depending on oxygen concentration. Moreover resistance polarization electrode exhibits a same magnitude order for LSM electrode as for Ni-YSZ cermet electrode.

The Use of Conventional SOFC Electrodes in High Temperature Water Electrolysis Mode: An Electrochemical Study of Ni-Cermet and LSM

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Fabrication and Characterization of Light-Weighted Micro Tubular SOFCs

Micro tubular SOFCs have shown characteristic features as high thermal stability during rapid heat cycling and high volumetric power output, which is expected to overcome several problems shown in conventional (planar) SOFCs. Here we report light-weighted tubular solid-oxide fuel cells under 1 mm diameter operable under 600oC. The cell consists of ordinary materials but has new anode microstructure with high porosity of 46 % (before reduction) and reduced anode thickness of less than 200 B12-0794RB12-0794R mm. Thus, the weight of the single cell was 0.015 g per 1 cm length, 0.06 g per 1cm2 surface (electrode) area) The results showed that the performance of the cell was 628, 1017 and 1293 mW/cm2 at 500, 550 and 600oC with wet H2 fuel, respectively.

Selective control of voltage polarity in a single‐chamber solid‐oxide fuel cell using the same catalytic electrodes with different sizes

AbstractThe selective control of the voltage polarity in a single‐chamber solid‐oxide fuel cell (SC‐SOFC) constituting the anode and cathode arranged at the same electrolyte surface of yttria‐stabilized zirconia (YSZ) or samaria‐doped ceria (SDC) and which can operate in a flowing mixture of hydrogen and oxygen is discussed on the basis of the dissociation and adsorption reactions due to the catalytic materials and electrode configurations. The open circuit voltage (OCV) of SC‐SOFC showed the highest value when the H2:O2 ratio was around 2:1, which might be equal to the mol ratio of oxygen and hydrogen based on the reaction of water formation by the electrochemical reaction in the cell. The voltage polarity of the cell using the Pt and LSM (La0.7Sr0.3MnO3) catalysts was the same as in the conventional SOFC such that in the Pt catalysis the anode became negative whereas in the LSM catalysis the cathode was independent of the electrode configurations. In SC‐SOFC using the same Pt catalyst, the larger Pt electrode functioned as the cathode desorbing the oxide ion conducting in YSZ or SDC. As a result, it was confirmed that the voltage polarity of SC‐SOFC could be selectively controlled by making use of the same catalytic electrodes with different sizes, and that the I–V characteristic of the cell improved by using SDC with Pt electrodes with a surface area ratio of 2:1. © 2008 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Efficiency and fuel utilization of methane-powered single-chamber solid oxide fuel cells

The single-chamber solid oxide fuel cell (SC-SOFC) is a simplification of the conventional dual-chamber SOFC and has great potential for meeting portable power generation needs. While the high energy density of hydrocarbon fuels makes SC-SOFC a promising candidate as a power source for scenarios where portability is most preferred, the low efficiency and fuel utilization reported by many experimental groups have presented a major barrier keeping it from real application. Based on an experimentally validated numerical model, this work systematically investigates the fuel cell efficiency and fuel utilization of a methane-powered SC-SOFC as a function of operating parameters including flow rate, fuel-to-oxygen ratio, fuel cell layout and balance gas. We predict that the maximum achievable efficiency of a single-cell SC-SOFC is above 10% and the efficiency at typical operating conditions is above 5%, significantly higher than the reported 1% in literature. Optimization approaches are proposed at different levels in terms of both improving the power output and reducing the unspent fuel.

Single-Chamber SOFC Operating with Hydrocarbon-Air and Hydrogen-Oxygen Gas Mixtures

A single-chamber solid oxide fuel cell (SC- SOFC), which is operated in a mixture of fuel and oxidant gas, provides several advantages over the conventional SOFC such as simplified cell structure (no sealing required). SC-SOFC allows using a variety of fuels without carbon deposition by selecting appropriate electrode materials and cell operating conditions. Operating conditions of single chamber SOFC was studied using hydrocarbon- air gas mixtures for a cell composed of NiO-YSZ/YSZ/LSCF-Ag. The cell performance and catalytic activity of the anode was measured at various gas flow rates. The results showed that the open-circuit voltage and the power density increased as the gas flow rate increased. A similar cell was tested in a double chamber configuration using hydrogen-air mixtures by controlling the hydrogen/air ratio at cathode and anode. Simulation of single chamber conditions in double chamber configurations allows distinguishing and better understanding of the electrode reactions in the presence of mixed gases. The effect of hydrogen-air mixtures as a fuel on the performance of anode and cathode materials in single-chamber and double- chamber SOFC configurations is presented.

Fabrication of Micro-Tubular SOFC Stack Using Ceramic Manifold

Micro tubular SOFCs have been expected to overcome shown many desirable characteristics over conventional (planar) SOFCs such as high thermal stability during rapid heat cycling and high packing density of the cells, which enables to realize micro SOFC systems applicable to portable devices and auxiliary power units for automobile. Our research project Advance Ceramic Reactors aims to develop innovative processing method to fabricate such new micro tubular SOFCs and their stacks. In this study, new micro tubular SOFC stacks was fabricated and the performance of the stack was investigated.

Anode Polarization in Liquid Tin Anode Solid Oxide Fuel Cell

The Liquid Tin Anode Solid Oxide Fuel Cell (LTA-SOFC) is a modified version of SOFC that allows the direct conversion of carbonaceous fuels. The LTA-SOFC uses conventional SOFC electrolytes and cathodes but its anode is liquid tin allowing direct oxidization of fuel without reforming or other fuel processing. A porous ceramic separator was introduced in CellTech Power's Gen 2 and Gen 3 LTA-SOFC designs. The separator holds the liquid tin anode in place while allowing free exchange of fuel molecules and products. This paper describes anode polarization of LTA-SOFC and a capillary model for porous tin anode separator

Liquid Tin Anode Solid Oxide Fuel Cell for Direct Carbonaceous Fuel Conversion

The Liquid Tin Anode Solid Oxide Fuel Cell (LTA-SOFC) is a modified version of SOFC that allows the direct oxidation of carbonaceous fuels. The LTA-SOFC uses many conventional SOFC components but differs from conventional SOFC because its anode is liquid tin allowing directly oxidization of fuel without fuel reforming or other fuel processing. In addition, the anode stores energy, allowing the cell to deliver power in case fuel flow has been interrupted. As a result, the LTA-SOFC requires less components resulting in simpler and more efficient system. This paper describes the basic LTA-SOFC cell architecture and cell/stack test results using carbonaceous fuels such as JP-8, natural gas, coal, bio-mass and plastic feedstock.

Thin-Film Electrolytes for Reduced Temperature Solid Oxide Fuel Cells

AbstractSolid oxide fuel cells produce electricity at very high efficiency and have very low to negligible emissions, making them an attractive option for power generation for electric utilities. However, conventional SOFC's are operated at 1000 °C or more in order to attain reasonable power density. The high operating temperature of SOFC's leads to complex materials problems which have been difficult to solve in a cost-effective manner. Accordingly, there is much interest in reducing the operating temperature of SOFC's while still maintaining the power densities achieved at high temperatures. There are several approaches to reduced temperature operation including alternative solid electrolytes having higher ionic conductivity than yttria stablilized zirconia, thin solid electrolyte membranes, and improved electrode materials. Given the proven reliability of zirconia-based electrolytes (YSZ) in long-term SOFC tests, the use of stabilized zirconia electrolytes in reduced temperature fuel cells is a logical choice. In order to avoid compromising power density at intermediate temperatures, the thickness of the YSZ electrolyte must be reduced from that in conventional cells (100 to 200 μm) to approximately 4 to 10 μm. There are a number of approaches for depositing thin ceramic films onto porous supports including chemical vapor deposition/electrochemical vapor deposition, sol-gel deposition, sputter deposition, etc. In this paper we describe an inexpensive approach involving the use of colloidal dispersions of polycrystalline electrolyte for depositing 4 to 10 μm electrolyte films onto porous electrode supports in a single deposition step. This technique leads to highly dense, conductive, electrolyte films which exhibit near theoretical open circuit voltages in H2/air fuel cells. These electrolyte films exhibit bulk ionic conductivity, and may see application in reduced temperature SOFC's, gas separation membranes, and fast response sensors.

Comparative Evaluation of the Performance Potentials of Ten Prominent SOFC Configurations

Performance potentials of prominent SOFC configurations are studied under EPRI Contract No. RP1676-15. For lack of experimental data an analytical approach is chosen. For identical materials and operating conditions the power losses of the different geometries are determined. A differential equation is solved to identify the cross-plane and in-plane resistance of the SOFC elements. The in-plane resistance, dominant in conventional concepts, is virtually eliminated in planar designs. Consequently, the power potentials of planar SOFC configurations are up to twice of what can be expected for conventional SOFC geometries.