Divalent cations modified grain boundary scavenging in samarium doped ceria electrolyte for solid oxide fuel cells

Abstract

Grain boundary conductivity of samarium doped ceria electrolyte (SDC) depends on the space charge potential and oxygen vacancy concentration existing at the grain boundary region. Here, we report the effect of co-doping 1 mol% divalent alkaline earth metals in samarium doped ceria (Ce0.78Sm0.2A0.01O1.89, [ASDC], A = Mg, Ca, Sr, Ba) on the grain boundary conductivity. The increase (Ca2+, Sr2+, Ba2+) or decrease (Mg2+) in lattice parameter in comparison to SDC (0.5445 nm) depends on the ionic radii of the co-dopant. The oxygen vacancy concentration of ASDC system, quantified from the Raman spectra, increased from 2.98 × 1021 cm−3 (SDC) to 3.18 × 1021 cm−3. The samples sintered at 1400 °C for 5 h, resulted in a dense electrolyte with a relative density of 98–99%. Calcium co-doped SDC (CSDC) showed the highest conductivity of 2.04 × 10−3 S/cm at 700 °C with activation energy of 0.90 eV. The oxygen vacancy profile at the space charge layer was found to be higher for CSDC while the potential reduced from 0.24 V (SDC) to 0.18 V. The observed lower space charge potential in co-doped SDC, contributed to the enhancement in oxygen vacancy concentration at the space charge layer and increased the grain boundary conductivity. Thus the present study highlights the correlation of space charge potential, oxygen vacancy concentration to grain boundary conductivity and provide a profound insights on the grain boundary understandings for improving the performance of the electrolyte for solid oxide fuel cell application.