Preparation And Property Of BaFe_1-xBi_xO_3-δ It-sofc Cathode Materials

Solid Oxide Fuel Cells (SOFCs), which convert the chemical energy to electricenergy directly, is one research focus. To improve the cell performance, developinga new cathode with high performance, together with optimizing the electrolyte isimportant. Higher oxygen vacancy concentration, lower oxygen migration enthalpyand lager free volume are beneficial to improve the cathode performance. BaFeO3-δwas selected as the initial material, and Bi2O3was chosed as the dopant because ofthe above mentioned reasons. BaFe1-xBixO3-δcathode was synthesized, together withits properties were evaluated to optimize its performance.After the Bi-doping, the cubic perovskite phase of BaFe1-xBixO3-δweresuccessfully formed. XRD patterns demonstated that the crystal cell parameter, cellvolume and the cell free volume increased with the doping amount, which isbeneficial to the oxygen ion migration. Due to the higher valence of Bi, both the Fevalence and the oxygen vacancy decreased, however the xygen vacancy content isstill higher than common Fe-based cathodes.With the increase of Bi doping amount, the sintering property of the BFBcathode improved greatly. When the temperature is below800℃, the weight lossand the thermal expansion reduced with the doping amount. However when thetemperature become higher, both increased showed the reversing trend.The electrical conductivity accorded with the small polaron hoppingmechanism, and BFB10has its maximum conductivity of28.10S·cm-1at750℃.The best preparation process of the cathode were determined by theelectrochemical impedance spectroscopies, and list as: using ethyl cellulose asbinder and pore former and printing three layers. The suitable sintering temperature,decreased with the doping amount due to the better sintering property. Based on theoptimized parameters, the polarization resistance and the electrode reactionactivation increased gradually with the increased Bi2O3doping amount. Theactivation energy for reaction of BFB10is1.00eV, with is much lower than that of1.231eV for Ba0.5Sr0.5FeO3-δand1.92eV for La0.5Sr0.5FeO3-δ.The polarizationresistance of BFB10is0.133·cm2at750℃, with the calculated i0is308.2mA·cm-2, which is about1.6times for194mA·cm-2of LSM-YSZ cathode at810℃.The diacharging performance of NiO/YSZ|YSZ|GDC|BFB10cell was646.28mW·cm-2at750℃using H2as fuel and air as oxidant.