Neutron Diffraction Study of Nio/Licoo2 Electrodesfor Innovativefuelcell Development
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1262-W02-06
NEUTRON DIFFRACTION STUDY OF NIO/LICOO2 ELECTRODES FOR INNOVATIVE FUEL CELL DEVELOPMENT
R. Coppola (1), P. F. Henry (2) (4), A. Moreno (3), J. Rodriguez-Carvajal (2) , E. Simonetti (3) 1 2 3
ENEA-Casaccia, UTFISSM, Via Anguillarese 301, 00123 Roma, Italy ILL, 6, rue Jules Horowitz, 38042 Grenoble, France ENEA-Casaccia, UTRINN, Via Anguillarese 301, 00123 Roma, Italy 4
Helmholtz Zentrum Berlin, Hahn-Meitner-Platz 1, 14109, Berlin, Germany
Abstract Ni-NiO 30 wt% electrodes coated with LiMg0.05Co0.95O2 cobaltite deposited on the substrate by complex sol-gel process were investigated using powder neutron diffraction. As the catalytic layer is only 1-2 microns thick, the diffracting volume of the cobaltite phase was increased by stacking 20 small rectangular pieces cut from the original electrode, assuming that the catalytic layer on the electrodes was homogenous. A pure bulk cobaltite sample was used as a reference for identifying the diffraction peaks of the catalytic layer in the complete electrode. Both an as-received sample and a tested electrode (100 h at 650 °C in a cell) were measured. Despite the small diffracting volume of the catalytic layer, due to the high flux available at D20, it was possible to detect the hexagonal phase and estimate its volume fraction in the as-received sample. In the tested electrode, the cobaltite material is no longer present, while traces of magnesium oxide and cobalt oxide are detected, suggesting significant modifications take place during use.
1. Introduction Due mainly to its fast oxygen reduction reaction rate LixNi1-xO is considered as one of the best suited materials for the development of innovative Molten Carbonate Fuel Cells. However, due to its high rate of dissolution in molten carbonate, the cathodic nickel is dispersed and transported inside the electrolyte producing a concentration gradient under the electric field of the cell and a considerable decrease of the estimated life time. In order to avoid or to limit this effect, the electrode can be coated by a thin layer of material characterized by a lower solubility in molten carbonates such as ferrites, manganites and cobaltites (1-2) and more specifically lithium cobaltite (LiCoO2), which is commercially employed in lithium-ion batteries and in electrochromic films (3, 4). A process for the production of Mg doped LiCoO2 powders and the preparation of porous cathodes of 100 cm2 in size has been developed (3-9). The porous nickel cathode has been coated by a thin layer of Mg-doped LiCoO2; the complex sol-gel process technique was selected because of its effectiveness in covering the porous substrate deeply in the micro- and macro-holes. The morphology, crystallographic structure, conductivity, solubility of such electrodes have been investigated; in-cell tests have been carried out obtaining encouraging results from the electrochemical point of view in comparison with nickel oxide (9). Within this scientific frame, neutron diffraction has been utilized to characterize the crystallographic structure of
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