Mixed Ni-Li-M oxides as catalysts for the Oxygen evolution reaction

Mixed Li-Ni oxides are used as cathodes in molten carbonate fuel cells 1 (MCFC), where lithium-doping ensures an acceptable conductivity through a holehopping mechanism. However, these cathodes dissolve slowly in molten carbonates at 650°C, a problem which is alleviated by addition of other metals (M), and which has stimulated much research on stability and structure of these mixed oxides 2. The properties of Li-Ni oxides as catalysts in the oxygen evolution reaction (OER) have also been studied 3. However, the details of this reaction and the mechanism of “ageing” of these Ni electrodes in alkaline solution remain unknown. The purpose of this experimental study is to investigate how guest metals within the NiO fcc structure modify conduction, stability and catalytic properties of these promising compounds. Solid state reaction of finely dispersed powders of precursor has been used to produce mixed oxides of the quarternary system with Ni, Li, Co, Fe, for which crystal structures and solubility regions have been determined. Analyses at different field strength of the 7Li and 6Li NMR signals show that, at room temperature, most compounds of interest are near their antiferromagnetic N�??el point, where relaxation of lithium nuclei (both T1 and echo-decay T2) is driven by coupling with electrons modulated by the hopping process; in other words, the NMR data yield an information which complements that of DC-conductivity. Furthermore, details of the 7Li lineshape and the relaxation process reveals inhomogeneities in the Li-distribution which are not apparent from X-ray diffraction, but may assist interpretation of the electrochemical behavior.