The purpose of this work is to improve the electrocatalytic activity of Li-Ni mixed oxides by the addition of rare earth oxides (cerium or lanthanum). The influence of cerium and lanthanum on the electrocatalytic activity of these compounds was investigated by means of electrochemical impedance spectroscopy (EIS). The stability of these compounds was studied in a mixture of 62% lithium carbonate and 38% potassium carbonate at high temperature under an atmosphere rich in carbon dioxide to accelerate their dissolution. The morphology and the crystalline structure of the samples were not affected by the incorporation of cerium or lanthanum. The samples impregnated with CeO2 or La2O3 showed lower resistance to charger-transfer processes than the sample without earth rare oxides. Both cerium and lanthanum improved the charger-transfer processes for oxygen reduction in an atmosphere rich in carbon dioxide. The reason may be due to cerium oxide acting as oxygen donor, and lanthanum oxide capturing CO2, and the partial pressure of carbon dioxide on the surface of electrode. (c) 2005 Elsevier B.V. All rights reserved.