BaCe_xFe_1-xO_3-δ-Based Cobalt-Free Perovskite Cathodes For Proton-Conducting Solid Oxide Fuel Cells

As a clean and efficient power generation device,solid oxide fuel cell（SOFC）is of great importance to alleviate the energy crisis and environmental pollution problems.However,the high operating temperature is one of the key factors hindering its practical commercial application.Due to the lower activation energy of proton transfer,proton-conducting SOFC（H-SOFC）is more suitable for low temperature operation than oxygen ion conducting SOFC（O-SOFC）,but the larger cathodic polarization resistance limits the current development of H-SOFC.Therefore,developing cathode materials for H-SOFC is urgent.In order to develop practical and high-performance cobalt-free cathodes,this work mainly focuses on the optimization of BaCe_xFe_1-xO_3-δ-based materials to improve their oxygen reduction reaction activity.BaCe_0.2Fe_0.6Gd_0.15X_0.05O_3-δ（X=Mo,Cu,In,Gd）cathode materials are synthesized.Their porperties including cystal structure,electrical conductivity,electrical conductivity relaxation behavior and catalytic activity are studied.The BaFe O_3-δphase of BaCe_0.2Fe_0.6Gd_0.2O_3-δis maintained with the doping of Mo and In,while the doping of Cu brings an orthorhombic perovskite phase and makes the BaFe O_3-δphase closest to its cubic structure.Mo and Cu doping significantly increase the electrical conductivity and the oxygen activity of BaCe_0.2Fe_0.6Gd_0.2O_3-δ.A single cell with BaCe_0.2Fe_0.6Gd_0.15Cu_0.05O_3-δ-BaZr_0.1Ce_0.7Y_0.2O_3-δcathode and a 50μm-thick BaZr_0.1Ce_0.7Y_0.2O_3-δelectrolyte layer shows the highest maximum power density(P_max)of 396 m W cm^-2 at 700 ^°C,indicating that Cu doped BaCe_0.2Fe_0.6Gd_0.2O_3-δis a potential cobalt-free cathode for H-SOFC.BaCe_0.2Fe_0.8-xPr_xO_3-δ（x=0,0.1,0.2,0.3）are studied as cobalt-free cathode materials for H-SOFC.They are composed of cubic BaFe O_3-δand orthorhombic BaCe O_3-δphases,and Pr is doped in both phases.The partial substitution of Pr for Fe decreases the content of the BaFe O_3-δphase,leading to a lower electrical conductivity.BaCe_0.2Fe_0.6Pr_0.2O_3-δ(BCFP_0.2)has the most adsorbed oxygen and Fe³⁺on the surface,resulting in the fastest oxygen surface exchange kinetics and the highest activity.The partial pressure of H₂O shows a negligible effect on the polarization resistance（R_p）of the cathode.In contrast,the R_p increases remarkably with the decrease of oxygen partial pressure,indicating that the rate of the cathode process is controlled by the surface exchange of oxygen.At 700 ^°C,BCFP_0.2shows the lowest R_p of 0.057Ωcm²,and a single cell with that cathode exhibits the highest P_max of 562 m W cm^-2.The results demonstrate that BCFP_0.2 is a promising cobalt-free cathode material for H-SOFC.