Preparation and Characterization of LiCoO 2 and LiMg 0.05 Co 0.95 O 2 Thin Films on Porous Ni/NiO Cathodes for MCFC by C

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W. LADA*, A. DEPTULA*, B. SARTOWSKA*, T. OLCZAK*, A.G. CIMIELEWSKI*, M. CAREWSKA**, S. SCACCIA**, E. SIMONETTI**, L. GIORGI**, A. MORENO** *Institute of Nuclear Chemistry and Technology, 03-195 Warsaw, Poland, [email protected] ** ENEA, TEA-CCAT, Casaccia Casaccia, AD 00100 Roma, Italy, [email protected] ABSTRACT The major disadvantage of Ni/NiO cathodes for a Molten Carbonate Fuel Cells (MCFC) application is dissolution of NiO in K/Li electrolyte that significantly decreases the cell lifetime. Thin films of LiCoO 2 or LiMgo.o5Co0.950 2 were prepared on a cathode body in order to protect them against dissolution. For preparation of starting sols the Complex Sol-Gel Process (CSGP) has been applied. These sols have been prepared by adding of LiOH to aq. acetates solution of Co 2+(Mg2 รท) with ascorbic acid and then by alkalizing them with aqueous ammonia to pH=8. The cathode plates of various dimensions (to several hundreds cm 2) have been dipped in these sols and withdrawn at rate a 1.7 cm/s. Commercially sintered Ni plates were always initially oxidized by heating at various temperatures. Their microstructure and mechanical properties as a function of temperature were observed. Heat treatment should be carried out under the dead load of the ceramic plates in order to avoid their waving. The best non-folded plates were obtained by treating them for lh at 550'C. The covered substrates were calcined for lh at 650'C, using low heating ratel1C/min. The presence of LiCoO 2 in a deposited coating has been proved by EDS patterns. The resultant film thicknesses were measured by scanning electron microscopy (SEM) on the fractured cross-sections; they ranged from 0.5 to 2Ftm and depended on sol concentration and viscosity. A 350 hundred hours test in molten carbonates, proved that the cathode bodies covered with LiCoO2 are completely prevented from dissolution of Ni in a molten K/Li electrolyte. Dissolution of LiCoO2 coating was not observed as well. After treatment in a molten electrolyte SEM observations did not show any changes in microstructures and morphology of the covered cathodes.

INTRODUCTION Fuel cells are commonly recognized as the most promising power generation systems [1,2]. However, according to the opinion of "The Economist" (November 1998) the energy from fuel cells is actually several times more expensive than the energy from conventional power generation systems. The main perspective for a substantial cost reduction is the elaboration of cheaper components of fuel cells and the improvement of their quality. One of the most important type of a fuel cell, highly efficient and environmentally clean, are the Molten Carbonate Fuel Cells (MCFC) composed generally from Ni anode and NiO cathode and operated at 600-700 0C in the presence of a corrosive liquid Li/K carbonate [1,3]. The major disadvantage of this type of a cathode is dissolution of NiO in K/Li electrolyte, which decreases significantly the cell lifetime [1,4,5]. LiCoO 2 cathodes show less solubility [1,6] however, they are far more expen

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