For an electron-blocking cell ZrO2(+8 m/o Y2O3)/Co1-deltaO/ZrO2(+8 m/o Y2O3), a full impedance spectrum has been constructed for a wide frequency range comprising diffusion, electrode and bulk by combining impedance data directly measured using a commercial impedance analyzer and the Fourier-Laplace transform of the dc relaxation into the frequency domain which carries the (ionic) information in the low frequency range including the dc limit. The ionic conductivity of Co1-deltaO was then extracted from the finite length Warburg impedance at the low end of the full impedance spectrum, which was in a good agreement with the literature. Disturbing artifacts associated with gas/solid reactions and the limitation of the method are discussed.