ELECTROCATALYTIC PROPERTIES OF SPINEL-TYPE MNXFE3-X O-4 SYNTHESIZED BELOW 100-DEGREES-C FOR OXYGEN EVOLUTION IN KOH SOLUTIONS

Some spinel ferrites (MnxFe3-xO4; x = 0, 0.5, 1.0, 1.5) have been synt hesized at 70 degrees C by the method of precipitation, for electroche mical characterization as oxygen anodes. The electrodes were prepared as films on a nickel substrate by painting with an oxide-slurry, follo wed by sintering at 400 degrees C. The electrocatalytic activity for O -2 evolution was found to be a maximum with the MnFe2O4 electrode. Bas ed on the observed current density at 0.625 V, the activity of MnFe2O4 was 20 times higher than that of Fe3O4. The reaction followed approxi mately second-order kinetics in [OH-] at the pure and manganese-substi tuted ferrite film electrodes. The Tafel slope values were ca. RT/F on Fe3O4 and Mn0.5Fe2.5O4 and ca. 2RT/3F on MnFe2O4 and Mn1.5Fe1.5O4. Ba sed on the electrode kinetic results, a reaction mechanism for oxygen evolution is suggested.