Electrocatalytic properties of lanthanum manganites obtained by a novel malic acid-aided route

Abstract

Electrochemical properties of lanthanum manganite and its substituted derivatives for oxygen evolution in KOH solutions were studied by cyclic voltammetry, AC impedance and Tafel polarization techniques. The oxides were obtained by a sol-gel route, using malic acid as precursor. The catalytic activity of LaMnO3 electrode, prepared by this new method, was found to be approximately 15 times higher than the one obtained by ceramic method. The introduction of 0.2-0.4 mole Sr in the perovskite lattice further improved the activity of the catalyst. However, other Sr-substitutions (0.1 and 0.6 mole) appeared to be less beneficial. 0.2 mole Pb-substitution showed to be highly detrimental from the electrocatalysis point of view. The oxygen evolution reaction followed a first-order kinetics with respect to OH- concentration. The Tafel slope value was 108 ± 5 mV decade-1. © 1998 International Association for Hydrogen Energy.