This paper treats an experimental and modeling study to predict the electrochemical performance of a Ni/YSZ supported planar SOFC with the air electrode made by LSFC-GDC. A complete electrochemical model is developed and calibrated on experiments to validate the numerical data. A detailed description is presented to show how the electrochemical parameters are fitted, the validity of proposed model and the fitting parameters is shown by comparing experimental data with numerical results. The parameters are discussed in comparison with the literature, and the effect of fuel dilution with N2 on the anodic activation is highlighted. Moreover, the effects of key operating parameters such as, hydrogen molar fraction, fuel flow rate and temperature, on the cell performance are investigated. Because the dependence of overpotentials on molar fraction, increasing the hydrogen molar fraction enhances the power density for both H2/H2O and H2/N2 mixtures. Similarly, the fuel flow rate presents the same trend as that of hydrogen molar fraction. The ohmic, activation and concentration overpotentials are affected by the operating temperature. Therefore, higher power density can be obtained at a higher temperature.