An ageing investigation of LSCF/CGO/YSZ half-cell, at 700 degrees C in air at OCP, was performed for different CGO buffer layer thicknesses (0, 0.11, 0.45, 1.1 and 2 mu m), using impedance spectroscopy (IS). The ageing behavior of the half-cell has been found to be strongly dependent on the CGO thickness. With addition of the CGO buffer layer the initial apparent electrolyte resistance was significantly reduced, while the LSCF cathodes showed limited performance degradation over a period of 530 h. X-ray microanalyses have shown that the recorded degradation of the LSCF cathode without buffer layer is due to the diffusion and the segregation of Sr at the LSCF/YSZ interface. (C) 2013 Elsevier B.V. All rights reserved.