| Solid oxide fuel cells?SOFC?have become a hot research topic in recent years due to their high efficiency,sustainability,and non-polluting products.The key to the development of SOFC is to reduce the operating temperature?600800°C?which can decrease the manufacturing cost and improve the long-term stability.A major challenge in reducing operating temperature is the rapid increasment of cathodic polarization resistance.Therefore,the development of new cathode is important to SOFC.Co element has good oxygen catalytic activity.The ionic radius of Ba in BaCoO3 is large,resulting in the low resistance of oxygen ion transportation through Ba-Co-Ba triangle.Therefore,BaCoO3 is used as the matrix.Nb and Ta are co-doped to increase the density of states of the Co-bit adjacent to the Fermi level,thereby increasing the electron exchange rate of oxygen adsorbed at the Co site.BaCo0.95-xNb0.05Tax O3-?powder was synthesized by solid state reaction method.The optimal calcination?1100°C for 10 h?is determined by XRD analysis.The doping of Nb and Ta stabilize the cubic perovskite structure.At 1050°C,the shrinkage rates of BaCo0.95-x.95-x Nb0.05Tax O3-??x=0-0.2?were 5.73%,5.38%,3.1%,1.87%,and 1.32%,respectively.With the increase of Ta doping content,the linear shrinkage and the maimum shrinkage rate of the sample decreased.According to Arrhenius method and main sintering curve method,the densification activation energy of BaCo0.8Nb0.05Ta0.15O3-?is calculated to be 425 kJ mol-1 and 450 kJ mol-1respectively.Moreover,the growth index is determined to be 3,which indicates that the grain growth process is controlled by lattice diffusion.BaCo0.80Nb0.05Ta0.15O3-?has good chemical compatibility with GDC electrolyte.The average thermal expansion coefficients of BaCo0.95-x.95-x Nb0.05Tax O3-??x=0-0.2?are 19.8×10-6,18.2×10-6,17.3×10-6,16.7×10-6,and 16.1×10-6 K-1 in the temperature range of 50900°C,that Ta doping reduce the coefficient of thermal expansion.According to XPS analysis,the valence of Co element are+3 and+4,and both Nb and Ta are+5.The conductivity of BaCo0.95-x.95-x Nb0.05Tax O3-?sample is a p-type semiconductor,which increases with temperature,and that decreases with the increase of doping content.At 800°C,it?x=0-0.2?was 33.1,26.4,19.2,13.9,and8.7 S cm-1,respectively.BaCo0.80Nb0.05Ta0.15O3-?are specific resistance is 0.098?cm2 at 700°C.The maximum power density is 494,681,903 mW cm-2 for the single cell with BaCo0.80Nb0.05Ta0.15O3-?cathode at 700,750,and 800°C.The mentioned results show that the co-doping of Nb and Ta improve the performance of BaCoO3 base cathode. |
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