Synthesis And Characterizations Of Multilayered GDC/YSZ Eletrolyte Of Oxygen Ionic Conductor

Solid oxide fuel cell(SOFC) is the third generation of fuel cell systems with the highest conversion efficiency(50-70%).Reducing the working temperature from 1000℃to intermediate temperature of 500-800℃(IT) can decrease high temperature solid reaction between SOFC components,lower the cost and lengthen the usage period,therefore IT SOFCs have been the research focus in fuel cell field.Ohmic resistance of oxygen ionic conductor electrolyte,a main component of SOFC,is one of the main factors determining the SOFC efficiency,so various work has been done in decreasing it for IT SOFC.Multilayered GDC/YSZ oxygen ionic conductors with different modulation structures are synthesized on(0001) single crystal sapphire by using reactive magnetron sputtering method.The phase,structures,surface morphologies and electrical properties of the multilayers are characterized by X-ray Diffraction(XRD), X-ray Reflection(XRR),Atomic Force Microscopy(AFM) and AC impedance measurement.The XRD and XRR results show that GDC/YSZ multilayers with good superlattice structures are synthesized.As compared with GDC and YSZ single films, GDC/YSZ multilayers have the surface morphology of dense growth islands in smaller sizes and much smoother surface(Rms＜0.3nm),indicated by AFM measurement.Electrical properties of GDC/YSZ multilayers changed with modulation periods, modulation ratio,interface structure as well as the measurement atomosphere.The results show that,first,with bigger modulation periods,the conductivities first increase accordingly and then decrease from the periods of bigger than 6nm,which can be explained by the nanosize effect in two phase heterostructures.Second, conductivities increase with GDC/YSZ modulation ratio,i.e,the more GDC in the multilayers,the bigger the conductivities.Third,based on the fact that interface defects can provide faster diffusion path for charge carriers with resulting bigger mobilities,the GDC/YSZ multilayers with mixed interfaces appear larger conductivities than those with superlattice structures.Finally,we measured the conductivities in the atmospheres of N2,Ar,air and O₂ and found that GDC/YSZ multilayers generally show larger conductivities and smaller activation energy in the atmosphere with smaller oxygen partial pressure and especially much larger conductivities are obtained in N₂ due to the increased oxygen vacancy concentration by substitution of oxygen with nitrogen.