Thermal Plasma Spraying Applied on Solid Oxide Fuel Cells
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D. Soysal, J. Arnold, P. Szabo, R. Henne, and S.A. Ansar (Submitted September 29, 2012; in revised form March 28, 2013) Solid oxide fuel cells (SOFCs), attractive for diverse applications in a broad range from small portable and auxiliary power units, up to central power systems, are conventionally produced by sintering methods. However, plasma spraying promises some advantages particularly for cells with metal support. In the present paper, research activities conducted in recent years at DLR as well as latest developments on plasma sprayed functional layers for SOFC as cathodes, electrolytes, and anodes are reported. Power densities of more than 800 mW/cm2 were achieved for plasma sprayed single cells of 12.56 cm2 size, and 300 mW/cm2, respectively, with a 250 W stack made of 10 cells. These values were attained at 0.7 V and 800 °C, with H2:N2 = 1:1 as fuel gas and air as oxidizing gas. Furthermore, continuous operation of more than 5000 h was attained with a plasma sprayed metal-supported SOFC stack which could also withstand more than 30 redox and thermal cycles.
Keywords
degradation, long-term stability, metal-supported SOFC, plasma sprayed functional layers, suspension plasma spraying
1. Fuel Cells—Devices Not Limited to Only One Single Application Present times are characterized by a general change in the energy supply. The scarcity of fossil resources requires a considerably higher efficiency in their use. At the same time a rapid increase of using renewable energy sources like solar radiation and wind can be observed. Therefore, hydrogen will become of increasing significance in the future as a carrier of energy for a society oriented to regenerative energy supply. It is storable and transportable, can be manufactured in a simple way by means of electrolysis and can be used to produce thermal and electrical power in a highly efficient and environmentally friendly form by fuel cells. As fuel cells transform combustion gas consisting mainly of hydrogen not only into thermal and electrical energy, but also in water and welldefined harmless exhaust emission, they can be used multi-functionally. This is shown in Fig. 1 using the example of applications in aviation. In addition to an auxiliary power unit (APU) for on-board electricity and replacing the ram air turbine (RAT) for the emergency power supply, the fuel cell may serve to reduce considerably the extra load of water before the start since service water needed in lavatory, e.g., is produced by the fuel cell during the flight. Moreover, the exhaust gases of the fuel
D. Soysal, J. Arnold, P. Szabo, R. Henne, and S.A. Ansar, German Aerospace Center (DLR), Stuttgart, Germany. Contact e-mail: [email protected].
Journal of Thermal Spray Technology
cell can be filled into the tanks of the airplane (being located in the wings) and, therefore, the development of explosive gas mixtures can be suppressed as the tank is getting depleted (‘‘inertisation’’). There are a number of different types of fuel cells operating from ambient temperature up to about 1
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