The cathodic process of the Pt(Ga2O3)/YSZ electrode in O-2, N-2 gas mixtures with and without NO is studied by electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV) in a wide range of gas composition at temperature range 450-800degreesC in order to investigate its electrocatalytic activity for the electrochemical reduction of oxygen and NO, respectively. The results of the impedance spectra and j(c)-eta(c) polarisation curves suggest different cathodic mechanisms at two temperature regions. For temperatures < 650 degreesC, the cathodic O-2 reduction occurs in two consecutive one-electron transfer steps. At theta > 650degreesC, O-2 reduction follows a two-electron transfer step. The electrocatalytic activity of the Pt/YSZ electrode is enhanced due to presence of NO in the gas mixture leading to a decrease of the apparent activation energy and an increase of the exchange current density. The admixture of Ga2O3 to Pt/YSZ shows an inhibitor effect on the cathodic O-2 reduction at low temperature. Aside from this, it has decreased the electrocatalytic efficiency of the Pt/YSZ electrode for cathodic NO reduction. (C) 2003 Published by Elsevier B.V.