This dataset contains approximate experimental electrochemical impedance spectroscopy (EIS) values obtained from a solid oxide cell operating in electrolysis mode (SOEC). The data correspond to the coordinates Z' (real part) and –Z'' (imaginary part) used to construct Nyquist plots under different gas compositions (H₂/N₂/Ar). The dataset includes four data series (x1,y1; x2,y2; x3,y3; x4,y4) representing different experimental conditions. The data were used for electrochemical fitting and modeling of the cell operating as a fuel cell.