ELECTROCATALYSIS OF TRANSITION-METAL OXIDES FOR REDUCTION AND OXIDATION OF NITRITE IONS

Electrodes of Mn, Fe, Co, Ni and Cu oxides supported on graphite substrates were prepared by pyrolysis of the metal nitrates. Ex situ X-ray photoelectron spectroscopy (XPS) revealed that Mn, Fe and Ni oxides at different chemical states were present at the electrode surfaces. The electrodes catalyzed the reduction and oxidation of NO2- in a weakly acidic medium (pH 2). All of the electrodes were deactivated by increasing the amount of metal oxide deposited, probably because of an increase in electric resistance of the deposited electrodes. The Fe oxide electrode with a small amount of deposited oxide exhibited the highest activity for the reduction and oxidation of NO2-.