The Effect of ca+2 Addition on the Properties of ce0.8gd0.2o2-δ(GDC) Electrolyte for IT-SOFCs

Ceria has fluorite type crystal structure. The structure can be viewed as an FCC array of Ce ions with the oxygen ions residing in the tetrahedral holes. The 1:2 statiometric is maintained. Pure ceria it shows high electronic conductivity than ionic conductivity. However, the ionic conductivity of ceria based electrolytes can be improved by introducing aliovalent cations to doped ceria.When aliovalant cations (Ca2+,Sr2+,Ba2+,Ln3+,Sm3+,Gd3+,Nd+3) are doped in ceria it shows higher ionic conductivity due to generation of oxygen vacancies in the sub lattice. This paper reports the effect of Ca2+ addition on the structural and electrical properties of Ce0.8Gd0.2O2-δ(GDC) electrolyte for low temperature solid oxide fuel cell application. The Ca2+ (0, 0.5, 1 and 2 mol %) doped GDC solid electrolytes have been prepared by solid state method. The sintered densities of the samples are greater than 95%.. Raman spectra show the presence of GDC single phase. AC impedance analysis is used to measure the ionic conductivity of the electrolyte. Among all the compositions, the highest conductivity is observed in the GDC sample with 0.5 mol% Ca2+ addition. Nyquist plots resulted in multiple redoxation process such as grain and grain boundary conductions to final conductivity. The XRD study reveals cubic structure with increase in lattice parameter with Ca2+content in pure GDC electrolyte. It is observed that grain size increases by increasing Ca2+ concentration up-to 1 mol% from 1.72 to 10.20 µm. The GDC electrolyte containing 0.5mol% Ca2+ had an estimated blocking factor that is lower, suggesting that the inclusion of Ca2+ enhanced grain boundary conduction. The Arrhenius plot was used to compute the activation energies, which are in the region of 1eV.