A novel concept for a metallic substrate supported thin-film SOFC to be operated at a reduced operating temperature of 700 800 °C has been developed by applying an ad vanced vacuum plasma spray process. This fabrication process enables the deposition of thin and dense electrolyte layers of about 30 50 pm in thickness as well as of controlled porosity electrodes in only one consecutive process step. The state of development of plasma sprayed thin-film cells is presented. The electrochemical characterization of the cells revealed a high electrochemical cell performance using H2 and air as the operating gases of 300 400 mW/cm2 at a reduced operating temperature of 750 800 °C. INTRODUCTION A common objective in current SOFC development work throughout the world is lowering the operating temperature of solid oxide fuel cells to below 800 °C. At these reduced temperatures lower stresses during thermal recycling and improved long-term stability of SOFC stacks is to be expected. Furthermore, intermediate SOFC operating temperatures in the range 600 800 °C result in reduced production costs of SOFC sys tems due to the possible use of lower cost materials particularly for containment. A fun damental precondition for SOFC operation at an intermediate temperature is given by minimized ohmic losses in the electrolyte which principally can be realized in two ways: either through the use of alternative electrolyte materials to the conventionally used yt tria-stabilized zirconia (YSZ) having enhanced ionic conductivity such as e. g. doped ceria (1) and doped lanthanum gallates (2,3) or novel thin-film concepts when using zir conia as the electrolyte material. Several processing techniques such as screen-printing (4), slip casting (5), tape cal endering (6), colloidal deposition (7), sol-gel deposition (8), PVD techniques (9) and reactive magnetron sputtering (10) have been applied to deposit thin-film electrolytes onto various substrates. The vacuum plasma spray technique (VPS) which has been fur ther developed and adapted to the specific requirements of SOFC fabrication at the DLR Stuttgart (11) has the potential to not only fabricate thin electrolytes but also the entire membrane-electrode assembly (MEA) in one consecutive spray process. Based on this technology thin-film cells of a metallic substrate supported planar SOFC concept have been developed (12). The utilization of plasma torches with specially developed Lavallike nozzles enables the consecutive deposition of thin and dense electrolyte layers as Electrochemical Society Proceedings Volume 99-19 893 Proceedings of The Electrochemical Society, PV 1999-19, 893-903 (1999) DOI: 10.1149/199919.0893PV © The Electrochemical Society ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 207.241.231.83 Downloaded on 2019-04-27 to IP well as of controlled porous electrodes. In the present paper the DLR spray concept for planar SOFC, the structural characterization and the electrochemical performance of plasma sprayed thin-film cells are presented. THE DLR SPRAY CONCEPT The principle of the DLR spray concept for a metallic substrate supported thin-film SOFC is demonstrated by the scheme shown in Fig. 1. In this planar SOFC design the electrolyte layer needs no longer to be the mechanically supporting component thus ena bling a significantly reduced electrolyte thickness compared to conventional selfsupporting SOFC cells. The spray process requires a substrate to be coated for which in this case an open porous metallic structure such as a porous plate or a felt of about 1 mm thickness is used. Onto this substrate which serves as a fuel gas distributor to the anode, the electrolyte and the cathode layer, each of about 30 50 pm in thickness, are con secutively deposited by the VPS process in only one process step. In order to provide a low ohmic contact to the bipolar plate a porous and ductile contact layer is also needed. For the bipolar plate facing the cathode side of the ME A a protective coating has been developed at the DLR (13). The substrate supported MEA is fitted into a recess within the bipolar plate and sealed by a glass sealant layer as it is shown in Fig. lb. Contact layer Cathode Electrolyte Anode Porous substrate Fuel gas supply Protective layer