To improve the catalytic activity of La(Sr)FeO3 based perovskites (LSF) for CO2 reduction in solid oxide electrolysis cell (SOEC), CO2 adsorption and reduction reaction mechanism were investigated on 12 surface models describing the effects of surface oxygen vacancies and Ni/Mn doping (25% and 50% surface cation doping ratios). In particular, a phase diagram was established to find the most stable LSF structure under SOEC operating conditions. These were carried out using Density Functional Theory (DFT) + U calculations. A microkinetic model was then developed to simulate polarization curves and compared with the experimental data of pure LSF. Ni-Mn double doping with 2 surface oxygen vacancies of LSF was identified as the most effective electrocatalysts. This is attributed to fine tuning O affinity by Ni, Mn and Fe in B-site (catalytic active site), as indicated by the Bader charge analysis. Experimental studies for this material have yet to be reported in the literature. (C) 2020 Elsevier Inc. All rights reserved.