The cathode performance of LSCM/GDC composite for high temperature CO2 electrolysis has been studied by electrochemical impedance spectroscopy (EIS) measurements in a three-electrode electrolysis cell using Pt paste as current collector. Themain feature of LSCM/GDC cathode is that it showed a Gerischer like impedance dispersion at 900 degrees C in all CO2-CO mixtures investigated here. With increasing CO concentration and operating potential, the Rs changes little whilst, the Rp declines markedly for LSCM/GDC composite cathode. The surface adsorption/desorption equilibration and/or surface diffusion processes play a dominant role in the electrochemical reduction of CO2 by SOEC. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.021203esl] All rights reserved.