20000

Fig.4 Cliange of cell resistance and cross-over over 20000 houis of operation

PROPERTIES OF LiCoO-COATED NiO MCFC CATHODE

S.T. Kuk, *H.J. Kwon, **H.S. Chun, K. Kim Department of Chemistry, Korea University, Seoul, 132-701, Korea * Samsung Electronics Co. Ltd., Suwon, 442-742, Korea ** Department of Chemical engineering, Korea University, Seoul, 132-701, Korea

Abstract

PVA-asssisted sol-gel method is useful in producing metal oxides with large surface area at low temperature. We fabricated LiCoOi-coated NiO(LC-NiO): cathode by PVA-asssisted sol-gel method and measured its properties. The electrical conductivity of LC-NiO cathode was measured to be more than 5 times as high as that of NiO and unit cell test showed improved performance. From the SEM images and Raman spectra, we confirmed that the structure of LC-NiO was different from that of NiO. For 250 hours of steady operation of unit cells, the mean voltage of the cells were 0.78V for NiO and 0.85V for LiCoOi-coated NiO at a current density of 150mA/cm2.

Introduction

The solubility of NiO cathode in molten carbonate fuel cell(MCFC) electrolyte has been identified as one of the major technical obstacles facing fuel cell commercialization. Lithium cobalt oxide, LiCoO; was selected as one of the new materials for MCFC cathode because the solubility of LiCoOi is small and the rate of dissolution into the melt is slower than that for NiO, although the electrical conductivity is lower than that of NiO. So we coated NiO which has higher electrical conductivity with stable LiCo02 in carbonate and got LiCoO^-coated NiO(LC-NiO) cathode by PVA-asssisted sol-gel method.

The use of PVA greatly suppressed the formation of precipitates from which the heterogeneity stems. Thereby, homogeneity in the composition of the precursor could be attained, eliminating the diffusion barrier. It is speculated that the hydroxy ligands on the PVA interact with, or are complexed to the metal ions, wrapping them and forming cocoons like local structure around the ions. This local isolation would prevent agglomeration of metal components, cutting off the proceeding toward the formation of precipitates. Presumably, this isolation would be conserved until the organic moieties are burned off by being heated. In this study, we measured properties of LC-NiO cathode fabricated by PVA-asssisted sol-gel method and investgated whether LC-NiO cathode had the possiblity as the MCFC cathode.

Experimental

At first, lithium acetate(CH3COO • Li • 2H;0) and cobalt acetate(Co(CH3COO)2 • 4H;0) were dissolved in water stoichiometrically. Another solution was prepared by dissolving PVA in water. The two solutions were mixed and heated to 60~80°C. Pure nickel electrodes were prepared by tape casting method and the electrodes were coated by viscous (Li,Co)-PVA solution. The electrode coating used dipping method at atmospheric pressure or at vacuum. After heat treatment at 800°C for 2 hours, the properties of LC-NiO electrodes were investgated by TGA, DSC, SEM, Raman spectroscopy, conductivity measurement, and unit cell test.

Results and Discussion

Figure 1 and figure 2 are TGA and DSC curves, respectively, of various electrodes and the (Li,Co)-PVA solution. The (Li,Co)-PVA solution shows a large weight loss and an endotherimc reaction curve at 50°C~150°C due to water evaporation The LC-NiO and NiO electrodes show a weight loss and exotherimc reaction curves at 300°C—500°C because of the oxidation of organic materials in the electrodes.. At 600°C~800°C, exotherimc reactions of LC-NiO and NiO electrodes are assumed due to the formation of oxides.

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