La_0.4Sr_0.6Co_0.7Fe_0.2Nb_0.1O_3-δ-Gd_0.2Ce_0.8O_2-δ (LSCFN-GDC) with high catalytic performance was synthesized by one-step co-synthesis method for developing a symmetrical reversible solid oxide cell (SOC) electrode. Electrolyte-supported symmetrical SOCs were fabricated by tape-casting and screen-printing methods with La_0.8Sr_0.2Ga_0.83Mg_0.17O_3-δ (LSGM) as the electrolyte and LSCFN-GDC as both anode and cathode. The configuration of SOC is LSCFN-GDC||LSGM||LSCFN-GDC. Solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes were used to test the performance of SOCs. The results show that the maximum power densities are 1.036, 0.996, 0.479, and 0.952 W/cm² under the atmosphere of fuel gas of H₂ (3% H₂O), H₂ (0.01% H₂S), CH₄, and C₃H₈ at 850 °C, respectively. The current density at the electrolytic voltage of 1.3 V is 0.943 A/cm² during the electrolysis of H₂ (50% H₂O). LSCFN-GDC has good coking-resistance, sulfur-tolerance, and redox stability, and its stable performance can be sustained for 700 h under the atmosphere of H₂ (0.01% H₂S), CH₄, H₂ (3% H₂O), and H₂ (50% H₂O). The results indicate that the one-step method is a facile and optimized fabrication procedure of electrode and LSCFN-GDC||LSGM||LSCFN-GDC SOCs have great potential in further application.