<p>Among the obstacles for the commercialization of the MoltenCarbonate Fuel Cell (MCFC), the dissolution of thestate-of-the-art lithiated NiO cathode is considered as aprimary lifetime limiting constraint. Development ofalternative cathode materials is considered as a main strategyfor solving the cathode dissolution problem. LiFeO<sub>2</sub>and LiCoO<sub>2</sub>had earlier been reported as the most promisingalternative materials; however, they could not satisfactorilysubstitute the lithiated NiO. On the other hand, ternarycompositions of LiFeO<sub>2</sub>, LiCoO<sub>2</sub>and NiO are expected to combine some desirableproperties of each component. The aim of this work was todevelop alternative cathode materials for MCFC in the LiFeO<sub>2</sub>-LiCoO<sub>2</sub>-NiO ternary system. It was carried out byinvestigating electronic conductivity of the materials, firstin the form of bulk pellets and then in ex-situ sinteredporous-gas-diffusion cathodes, and evaluating theirelectrochemical performance by short-time laboratory-scale celloperations.</p><p>Materials in the LiFeO<sub>2</sub>-NiO binary system and five ternary sub-systems,each with a constant molar ratio of LiFeO<sub>2</sub>:NiO while varying LiCoO<sub>2</sub>content, were studied. Powders withcharacteristics appropriate for MCFC cathode fabrication couldbe obtained by the Pechini method. The particle size of LiFeO<sub>2</sub>-LiCoO<sub>2</sub>-NiO powders considerably depends on thecalcination temperature and the material composition. Theelectrical conductivity study reveals the ability of preparingLiFeO<sub>2</sub>-LiCoO<sub>2</sub>-NiO materials with adequate electricalconductivity for MCFC cathode application.</p><p>A bimodal pore structure, appropriate for the MCFC cathode,could be achieved in sintered cathodes prepared usingporeformers and sub-micron size powder. Further, this studyindicates the nature of the compromise to be made between theelectrical conductivity, phase purity, pore structure andporosity in optimization of cathodes for MCFC application. Cellperformance comparable to that expected for the cathode in acommercial MCFC could be achieved with cathodes prepared from20 mole% LiFeO<sub>2</sub>- 20 mole% LiCoO<sub>2</sub>- 60 mole% NiO ternary composition. It shows aniR-corrected polarization of 62 mV and a iR-drop of 46 mV at acurrent density of 160 mAcm<sup>-2</sup>at 650 °C. Altogether, this study revealsthe possibility of preparing LiFeO<sub>2</sub>-LiCoO<sub>2</sub>-NiO cathode materials suitable for MCFCapplication.</p><p>Keywords: molten carbonate fuel cell (MCFC), MCFC cathode,LiFeO<sub>2</sub>-LiCoO<sub>2</sub>-NiO ternary compositions, electrical conductivity,porous gas diffusion electrodes, polarization, electrochemicalperformance, post-cell characterization.</p>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:kth-3811 |
| Date | January 2004 |
| Creators | Wijayasinghe, Athula |
| Publisher | KTH, Materials Science and Engineering, Stockholm : Materialvetenskap |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, text |
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