Synthesis And Assesment Of Ba_1-xBi_0.05Co_0.95-yNb_yO_3-δ As Cathodes For Inter-mediated Temperature Solid Oxide Fuel Cells

As highly efficient and environmentally friendly devices, solid oxide fuel cells are becoming the new reaearch trend. Recently, considerable efforts are focused on lowering the working temperature to an intermediate range of 600-800 °C. It is critical to exploit novel cathode materials with superior catalytic activity for intermediate temperature solid oxide fuel cells(IT-SOFCs). For perovskite cathodes, the Nb doping in B-site can not only stabilize the phase structure but also enhance the electrochemical performances, whereas the cation deficiency in A-site is beneficial for the generaion of oxygen vacancy and hence better performances. Therefore, Ba1-xBi0.05Co0.95-yNbyO3-δ(B1-xBCNy) are synthesized by solid state reaction methode and evaluated as potential cathode materials for IT-SOFCs.XRD measurement demonstrates that it is 1100 °C that Ba Bi0.05Co1-yNbyO3-δ cathodes are successfully synthesized. Highly charged Nb5+ successfully stabilizes the cubic perovskite structure to room temperature with Nb doping content y ≥ 0.1. With the increase of Nb doping content, the lattice parameter increa ses first and then decrease for BBCNy, whereas it gradually decreases with the increase of A-site deficiency content. Therefore, BBCN0.15 has the largest cell volume. Compared with YSZ electrolyte, B1-xBCNy cathodes exhibit excellent chemical compatibility with GDC at 950 °C for 5 h in air. With the increase of Nb replacing concentration and/or A-site deficiency content, the thermal expansion coefficients(TECs) for the samples steadily decrease.With Nb doping, the electrical conductivity for BBCNy gradually decreases, whereas the electrical conductivity for B1-xBCN steadily increases with A-site deficiency. Electrochemical impedance spectra(EIS) demonstrate that B0.95BCN0.15 exhibits the lowest polarization resistance, i.e. 0.056 Ω·cm2 at 700 °C. However, BBCN0.2 owns the lowest activation energy, i.e. 87.7 k J·mol-1.The single cell with the configuration of Ni-YSZ|YSZ|GDC|B0.95BCN0.15 has the highest maximum power density, i.e. 1.41 W·cm-2 at 750 °C. Good long-term stability of the single cell with BBCN0.15 as the cathode is also demonstrated under a constant current density 280 m A·cm-2. The roles of different oxygen reduction reaction processes are confirmed, at least in part, by the EIS of the single cell Ni-YSZ|YSZ|GDC|BBCN0.15 at different dc voltages. These results demonstrate that B0.95BCN0.15 is a very promising cathode material for IT-SOFCs.