Fe-Doped Ba_0.9K_0.1Fe_xCo_1–xO_3−δ Perovskite Cathode Material for Low-Temperature Solid Oxide Fuel Cells

This study systematically investigated the effects of a single B-site dopant (Fe, x = 0–1.0) on the structure and oxygen reduction reaction of the Ba_0.9K_0.1CoO_3−δ (BKC) material used as a cathode for low-temperature solid oxide fuel cells (LT-SOFCs). The structural, electronic, and electrocatalytic properties of the cathode materials prepared by a sol–gel method were comparatively characterized. The results indicated that cubic perovskite structure BKF_xC (Fe, x = 0.5, 0.6) materials had been formed by calcination at 900 °C for 5 h. Moreover, in order to examine the electrochemical properties of BKF_xC, the BKF_xC cathode was constructed on the Sm_0.075Nd_0.075Ce_0.85O_2−δ (SNDC) electrolyte (BKFC/SNDC/BKFC: denoted as symmetric cells); the lowest polarization resistance (R_P) was obtained for the BKF_0.5C symmetric cell (1.6 Ω·cm² at 550 °C), which demonstrated much higher electrocatalytic activity than that of a similar cell with the BKF_0.6C cathode (2.87 Ω·cm² at 550 °C). A single cell with the BKF_0.5C cathode achieved a top power density of 752 mW·cm^–2 at 550 °C, which is 0.35 times higher than that of the single cell with the BKF_0.6C cathode (power density: 556 mW·cm^–2). The corresponding total interface R_P of the fuel cell was 0.303 Ω·cm², lower than that of the doping amount of 0.6 (550 °C, 0.402 Ω·cm²). Meanwhile, O₂ temperature-programmed desorption (O₂-TPD) and thermogravimetric (TG) analysis were used to characterize the valence of Fe and Co changing from +4 to +3 as well as the stable structure of the material from room temperature to 600/1000 °C. As a result, a highly efficient method for the innovative BKFC cathode was developed in this work.