Type Solid Oxide Fuel Cell Research Articles

Performance Improvement of (La,Sr)MnO3 and (La,Sr)(Co,Fe)O3-Type Anode-Supported SOFCs

Targets in the development of anode-supported or planar solid oxide fuel cells (SOFCs) are low operation temperatures, high durability, high reliability, high power density, and low production costs. During the past ten years steps have already been taken at Forschungszentrum Jülich to lower the operating temperatures while maintaining the power output. This was achieved by optimizing processing and microstructural parameters of the electrodes. This paper presents the latest results concerning performance improvement through variations of the processing route and the microstructure of La0.65Sr0.3MnO3 (LSM) and La0.58Sr0.4Co0.2Fe0.8O3−δ (LSCF)-type SOFCs. In the case of the LSM-type single cells, the following aspects relating to the electrochemical performance were investigated in more detail: (1) production of the anode substrate by tape casting versus warm pressing; (2) deposition of the anode functional layer (AFL) and electrolyte by screen printing versus vacuum slip casting; (3) use of noncalcined and non-ground YSZ for applying the cathode functional layer (CFL); and (4) sintering temperature of the CFL and cathode current collector layer (CCCL). In the case of LSCF-type cells, a systematic approach was initiated for optimizing the Ce0.8Gd0.2O2−δ (CGO) diffusion barrier layer: (1) deposition techniques of the CGO layer and (2) sintering temperature of the screen-printed CGO layer. Results have shown that certain modifications of the processing route led to a slightly lower electrochemical performance, whereas others did not affect the performance at all. Regarding LSCF-type SOFCs, a slight improvement of the performance was achieved by optimizing the sintering temperature of the CGO layer.

Numerical study of a flat-tube high power density solid oxide fuel cell: Part II: Cell performance and stack optimization

The flat-tube high power density (HPD) solid oxide fuel cell (SOFC) is a geometry based on a tubular type SOFC, and is being developed by Siemens Westinghouse and other international companies in Japan and Korea. It has increased power density, but still maintains the beneficial feature of secure sealing for a tubular SOFC. In this paper, the electric performance of a flat-tube HPD SOFC is studied. This paper also investigates the effects of the stack chamber number, stack shape, and other stack geometry features on the performance of the flat-tube HPD SOFC. The results show that the performance of a flat-tube HPD SOFC is better than a tubular SOFC with the same active cell surface, and that increasing the number of chambers number can improve the overall performance of a flat-tube HPD SOFC. The height of a flat-tube HPD SOFC and the thickness of the ribs do not have much effect on the performance of the cell as is expected. This study will help to design and optimize the flat-tube HPD SOFC.

The Development of Several 100 kW-Class Tubular Type Solid Oxide Fuel Cell System (SOFIT)

Electric Power Development Co., Ltd. (JPOWER) started SOFC development in collaboration with Mitsubishi Heavy Industries, Ltd. in 1991. When development of a pressurized SOFC 10 kW module was completed, radical improvement of the modular structure was performed, aiming for further improvement in reliability and lower cost. It has been checked that there is no technical problem in the new structure of SOFC module. We plan to examine several prototype 100 kW-class atmospheric SOFC co-generation systems (SOFIT) from 2006 to verify the SOFC system using the new structure module, and the reliability of more than 10,000 hours operation at JPOWER's Chigasaki laboratory.

Numerical study of a flat-tube high power density solid oxide fuel cell: Part I. Heat/mass transfer and fluid flow

The flat-tube high power density (HPD) solid oxide fuel cell (SOFC) is a new design developed by Siemens Westinghouse, based on their formerly developed tubular type SOFC. It has increased power density, but still maintains the beneficial feature of secure sealing of a tubular SOFC. In this paper, a three-dimensional numerical model to simulate the steady state heat/mass transfer and fluid flow of a flat-tube HPD-SOFC is developed. In the numerical computation, governing equations for continuity, momentum, mass, and energy conservation are solved simultaneously. The highly coupled temperature, concentration and flow fields of the air stream and the fuel stream inside and outside the different chambers of a flat-tube HPD-SOFC are investigated. The variation of the temperature, concentration and flow fields with the current output is studied. The heat/mass transfer and fluid flow modeling and results will be used to simulate the overall performance of a flat-tube HPD-SOFC, and to help optimize the design and operation of a SOFC stack in practical applications.

Simulation of membrane microreactor for fuel cell with methane feed

Microreactors are composed of channels with a dimension of 1–1000 μm in width and depth. Three types of membrane microreactors for production of electric power by fuel cells with methane feed, i.e. (1) Pd membrane microreactor (Pd-MMR) followed by polymer electrolyte fuel cell (PEFC), (2) oxide-ion conducting solid oxide fuel cell (SOFC) and (3) proton conducting solid oxide fuel cell (H +-SOFC) were simulated and compared. The Pd-MMR followed by PEFC was the most effective system for electric power generation compared with the other two types of SOFC although the system was rather complex. However, the performances were dependent on the permeation properties of membranes (Pd, YSZ, perovskite) as well as kinetics of catalysts.

Modeling of Mass and Heat Transport in Planar Substrate Type SOFCs

A mathematical model is presented that incorporates the mass transport by diffusion in the porous structure of thick substrate type solid oxide fuel cells (SOFCs). On the basis of the mean transport pore model a multidimensional study allows for an optimization of the structural parameters of the substrates with respect to cell performance. Next to the mass transport in the porous substrates the electrochemical kinetics, methane/steam reforming and shift reaction, and energy equations are integrated in the model and boundary as well as operation conditions can be varied. Two-dimensional simulations for both anode as well as cathode substrate type SOFC operating on partially prereformed methane are presented and discussed. © 2003 The Electrochemical Society. All rights reserved.

Interfacial layers in tape cast anode-supported doped lanthanum gallate SOFC elements

Lanthanum gallate doped with strontium and magnesium (LSGM) is a promising electrolyte system for intermediate temperature solid oxide fuel cells (SOFCs). The reported formation of interfacial layers in monolithic type SOFCs based on lanthanum gallate is of concern because of its impact on the performance of the fuel cell. Planar anode-supported SOFC elements (without the cathode) were prepared by the tape casting technique in order to determine the nature of the anode/electrolyte interface after sintering. Two anode systems were studied, one a NiO–CeO 2 cermet, and the other, a modified lanthanum gallate anode containing manganese. Sintering studies were conducted at 1250, 1300, 1350, 1400 and 1450 °C to determine the effect of temperature on the interfacial characteristics. Scanning electron microscopy (SEM) revealed a significant diffusion of Ni from the NiO–CeO 2 anode resulting in the formation of an interfacial layer regardless of sintering temperature. Significant La diffusion from the electrolyte into the anode was also observed. In the case of the modified lanthanum gallate anode containing manganese, there was no interfacial layer formation, but a significant diffusion of Mn into the electrolyte was observed.

2256 10kW 級 SOFC システムの開発

The Solid Oxide Fuel Cell (SOFC) is composed of ceramics of the solid, and has the feature of high power generation efficiency and flexibility of fuel. TOTO LTD. has been conducting research and development of Tubular Type SOFC since 1989. We succeeded in the power generation of 3kW stack in 2000. Now we are developing the thermally self-sustaining module since 2001. Our development target is 10kW class SOFC cogeneration system for a apartment and a small-scale business use.

F202 MULTI-STAGE MODEL FOR INDIRECT INTERNAL REFORMING TYPE SOLID OXIDE FUEL CELLS

A multi-stage model of SOFC (Solid Oxide Fuel Cell) has been developed for the system analysis of SOFC/MGT (Micro Gas Turbine). With the present multi-stage model, a fuel cell is divided into several stages (or control volumes) so that it can take into account the spatial variation of the quantities to be treated to some extent. Therefore, it provides information about the internal phenomena of SOFC closer to the reality. Then, a thermodynamic model of a hybrid system has been constructed based on the developed multi-stage model of SOFC. Radiation between solid parts of fuel cell is also taken into consideration. The constructed model was then applied to analyze the performance of an indirect internal reforming type SOFC (IIR-SOFC), commercialized by Siemens-Westinghouse. The predicted results of design point analysis of a 220kW SOFC/MGT hybrid system are in good agreement with the predicted data by Siemens-Westinghouse. Effects of the number of the stages on the performance of hybrid system are also discussed.

448 10kW 級 SOFC システムの開発

The Solid Oxide Fuel Cell (SOFC) is composed of ceramics of the solid, and has the feature of high power generation efficiency and flexibility of fuel. TOTO LTD. has been conducting research and development of Tubular Type SOFC since 1989. We succeeded in the power generation of 3kW class in 2000. Now we are developing the thermally self-sustaining module since 2001. Our development target is 10kW class SOFC cogeneration system for a housing complex and a small-scale business use.

P14-14 加圧内部改質型 SOFC10kW 級モジュールの開発

Electric Power Development Co., Ltd. (EPDC) and Mitsubishi Heavy Industries, Ltd. (MHI) have succeeded in the continuous internal reforming 755 hours operation of a pressurized 10kW class module in August 2001. Compressed natural gas was used as fuel. In 1989,we started the development of the module of tubular type Solid Oxide Fuel Cells (SOFC). In 1998,we developed a pressurized 10kW class module, which was operated for 7,000 hours (continuously)^<(1)>. This module does not need heating supports to maintain the operating temperature, and its maximum power output was 21kW and the efficiency was 35% (HHV as H_2) at 75% fuel utilization without fuel recycle system. On the other hand, MHI has developed a new fabrication technology to reduce the cell cost. Instead of plasma spray coating method, co-sintering method was adopted in the new fabrication technology. In 2001,we developed the pressurized internal reforming type 10kW class module, and its operating power output was 11kW and the system efficiency was 41.5% (HHV). Steam for internal reforming was supplied by recycled fuel exhaust.

Application of mist pyrolysis method to preparation of Ni/ZrO 2 anode catalyst for SOFC type reactor

The ultrasonic mist pyrolysis method (mist method), a novel technique for the production of fine powders, is applied to the preparation of cermet anodes for solid oxide fuel cell (SOFC) reactors. This method is very useful for the fixation of micron-scale metal-oxide cermet powders on the YSZ substrate. The powders are spherical, well dispersed and homogeneous. The oxidation of methane was studied in a SOFC reactor with Ni/ZrO 2 anodes. The Ni/ZrO 2 cermet prepared by the mist method was selective for the oxidative coupling of methane (OCM), while the Ni/ZrO 2 cermet prepared by the ordinary paste method was active for CO and CO 2 formation. Although the supported amount of the mist anode was 100 times less than the supported amount of the paste one, both anodes showed similar total yields. The variations in activity and selectivity may be due to the different morphologies resulting from the two preparation methods.

Use of effective conductivities and unit cell-based supraelements in the numerical simulation of solid oxide fuel cell stacks

The numerical simulation of current and temperature distribution in monolithic solid oxide fuel cell (SOFC) stacks requires fast computers because of the large number of mesh points required in casting a complex solid geometry into a finite difference form and the necessity to solve coupled, nonlinear differential equations. By analogy with the modelling of radiative heat transfer in packed bed reactors, a significant degree of simplification is achieved by defining effective electric and thermal conductivities for the repeating unit cell elements, identified as the basic building blocks of the SOFC stack. The effective conductivities are approximated by closed form formulae derived from the principles of electrostatics and heat conduction. The effect of radiation across the gas channels is incorporated into the expressions for the effective thermal conductivity. Using this approach, the unit cell geometry, local mass transfer processes and reaction kinetics are expressed in terms of a supraelement model in a finite difference grid for the numerical calculation of temperature and potential distributions in a stack by an iterative process. The simplifications thus provided render simulations of three-dimensional SOFC stacks tractable for desktop processors. By using the foregoing approach to numerical simulation, a parametric study of a cross-flow type SOFC is presented, and some of the results are compared with the available experimental data

固体酸化物型燃料電池性能に及ぼす海上大気塩分の影響

Fuel cells have worldwide impact as a new means of highly efficient and clean power generation, and they also have the possibility of application to the transports. We have researched on some problems of the solid oxide fuel cell (SOFC) applied to the power generation source for the ship in the future. The aim of this study is to make clear the influence of airborne-salt on the cell performance.The experiment was carried out with a small scale planner type SOFC in which the working air was accompanied with salted mist. As a result, a cell performance was not inferior to that in the case without salt, and rather showed some increasing tendency than that. It was also found that the inlet airborne-salt penetrated into the air-electrode but not into the electrolyte. In order to find out the cause for improvement in the cell performance, the behavior of the salt into the air-electrode was investigated and discussed.

Preparation and Examination of Planar Type Solid Oxide Fuel Cells

Preparation and Examination of Planar Type Solid Oxide Fuel Cells

Electrocatalysis in Solid Oxide Fuel Cell Electrode Domains

A significant improvement in power output is achieved by percolation of catalyst elements into the YSZ electrolyte surface during fabrication of a solid oxide fuel cell (SOFC). The resulting surface is referred to hereafter as a domain. The catalysts allow the electrochemical reactions to take place in the domain. Together with current collecting electrodes on the domains, a novel SOFC structure is fabricated. On the cathode domain Mn and Ce and on the anode domain Ni, Ru, and Pd are able to catalyze the reactions. The current and power densities of such cells are significantly higher than those obtained in the conventional sandwich type SOFC. The dispersion of electrocatalysts in the domain helps to achieve lower electrode overpotentials, because of its nanometric size. A redox mechanism is invoked for the catalysts in the domain. By using a less efficient oxygen reduction electrocatalyst such as Pt over the domains, it is shown that the electrode reaction occurs more easily in the domain and the contribution from the electronically conducting layer is predominantly charge collection. A friable layer of lanthanum strontium manganite can function as a good contact cathode over the domain. Pure Ni paint when applied over anodic domains is an excellent contact electrode.

1 kW Class Generation Test of MOLB Type SOFC

Mono-block Layer Built (MOLB) type Solid Oxide Fuel Cell (SOFC) has many advantages such as high density of electric power generation, small space requirement, suitableness for mass production, etc. Chubu Electric Power Company,Inc. (CEPCO) and Mitsubishi Heavy Industries, Ltd. (MHI) have jointly developed and evaluated the MOLB type SOFC on since 1990. In 1992, the maximum output of 1.32 kW was recorded on an 150 x 150mm 40-cell 3-stack and, in 1993, the advanced 150 x 150mm 10-cell 4-stack successfully demonstrated 1.27 kW. In Feb. 1994, a continuous operating test of 8,765 hours was performed on a 75 x 75mm 2-cell stack, and 5 kW class module will be the next milestone.