Solid Oxide Fuel Cells
The following general description of solid oxide fuel cells was taken from the Fuel Cell Handbook, Seventh Edition published by the U. S. Department of Energy. More information can be obtained by clicking here.
Solid Oxide Fuel Cells
The electrolyte in a solid oxide fuel cell (SOFC) is a solid, nonporous metal oxide, usually Y2O3-stabilized ZrO2.The cell operates at 600-1000 °C, where ionic conduction by oxygen ions takes place. Typically, the anode is Co-ZrO2 or Ni-ZrO2 cermet, and the cathode is Sr-doped LaMnO3.
Early on, the limited conductivity of solid electrolytes required cell operation at around 1000 °C; but more recently thin-electrolyte cells with improved cathodes have allowed a reduction in operating temperature to 650 - 850 °C. Some developers are attempting to push SOFC operating temperatures even lower. Over the past decade, this has allowed the development of compact and high-performance SOFC which utilized relatively low-cost construction materials.
Concerted stack development efforts, especially through the U.S. DOE's SECA program, have considerably advanced the knowledge and development of thin-electrolyte planar SOFC. As a consequence of the performance improvements, SOFCs are now considered for a wide range of applications, including stationary power generation, mobile power, auxiliary power for vehicles, and specialty applications.
Advantages: The SOFC is the fuel cell with the longest continuous development period, starting in the late 1950s, several years before the alkaline fuel cell (AFC). Because the electrolyte is solid, the cell can be cast into various shapes, such as tubular, planar, or monolithic. The solid ceramic construction of the unit cell alleviates any corrosion problems in the cell. The solid electrolyte also allows precise engineering of the three-phase boundary and avoids electrolyte movement or flooding in the electrodes. The kinetics of the cell are relatively fast; and CO is a directly useable fuel as it is in the molten carbonate fuel cell (MCFC). There is no requirement for CO2 at the cathode as with the MCFC. The materials used in SOFC are modest in cost. Thin-electrolyte planar SOFC unit cells have been demonstrated to be capable of power densities close to those achieved with polymer electrolyte fuel cells (PEFC). As with the MCFC, the high operating temperature allows use of most of the waste heat for cogeneration or in bottoming cycles. Efficiencies ranging from around 40 percent (simple cycle small systems) to over 50 percent (hybrid systems) have been demonstrated, and the potential for 60 percent+ efficiency exists as it does for MCFC.
Disadvantages: The high temperature of the SOFC has its drawbacks. There are thermal expansion mismatches among materials, and sealing between cells is difficult in the flat plate configurations. The high operating temperature places severe constraints on materials selection and results in difficult fabrication processes. Corrosion of metal stack components (such as the interconnects in some designs) is a challenge. These factors limit stack-level power density, thermal cycling and stack life.
The following general description of solid oxide fuel cells was taken from the Fuel Cell Handbook, Seventh Edition published by the U. S. Department of Energy. More information can be obtained by clicking here.
Solid Oxide Fuel Cells
The electrolyte in a solid oxide fuel cell (SOFC) is a solid, nonporous metal oxide, usually Y2O3-stabilized ZrO2.The cell operates at 600-1000 °C, where ionic conduction by oxygen ions takes place. Typically, the anode is Co-ZrO2 or Ni-ZrO2 cermet, and the cathode is Sr-doped LaMnO3.
Early on, the limited conductivity of solid electrolytes required cell operation at around 1000 °C; but more recently thin-electrolyte cells with improved cathodes have allowed a reduction in operating temperature to 650 - 850 °C. Some developers are attempting to push SOFC operating temperatures even lower. Over the past decade, this has allowed the development of compact and high-performance SOFC which utilized relatively low-cost construction materials.
Concerted stack development efforts, especially through the U.S. DOE's SECA program, have considerably advanced the knowledge and development of thin-electrolyte planar SOFC. As a consequence of the performance improvements, SOFCs are now considered for a wide range of applications, including stationary power generation, mobile power, auxiliary power for vehicles, and specialty applications.
Advantages: The SOFC is the fuel cell with the longest continuous development period, starting in the late 1950s, several years before the alkaline fuel cell (AFC). Because the electrolyte is solid, the cell can be cast into various shapes, such as tubular, planar, or monolithic. The solid ceramic construction of the unit cell alleviates any corrosion problems in the cell. The solid electrolyte also allows precise engineering of the three-phase boundary and avoids electrolyte movement or flooding in the electrodes. The kinetics of the cell are relatively fast; and CO is a directly useable fuel as it is in the molten carbonate fuel cell (MCFC). There is no requirement for CO2 at the cathode as with the MCFC. The materials used in SOFC are modest in cost. Thin-electrolyte planar SOFC unit cells have been demonstrated to be capable of power densities close to those achieved with polymer electrolyte fuel cells (PEFC). As with the MCFC, the high operating temperature allows use of most of the waste heat for cogeneration or in bottoming cycles. Efficiencies ranging from around 40 percent (simple cycle small systems) to over 50 percent (hybrid systems) have been demonstrated, and the potential for 60 percent+ efficiency exists as it does for MCFC.
Disadvantages: The high temperature of the SOFC has its drawbacks. There are thermal expansion mismatches among materials, and sealing between cells is difficult in the flat plate configurations. The high operating temperature places severe constraints on materials selection and results in difficult fabrication processes. Corrosion of metal stack components (such as the interconnects in some designs) is a challenge. These factors limit stack-level power density, thermal cycling and stack life.
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