Layered double perovskite oxide of the type LnBaCo2O5+δ had been proposed as a potential candidate for intermediate temperature solid oxide fuel cell cathode. LnBaCo2O5+δ perovskite oxide showed enhanced properties of oxygen transport, oxygen anion surface exchange, and oxygen anion diffusivity compared to simple perovskites. Despite many advantages of double perovskites, slow oxygen reduction reaction limits the application of these materials for intermediate temperature range solid oxide fuel cells. Chemical substitution and strain engineering provide a way of tailoring the properties of the perovskite materials. Present study focuses on the effect of Sr cation doping at A′ site and biaxial strain on the electrocatalytic properties of the NdBaCo2O5+δ layered double perovskite material. Density functional theory and molecular dynamics based simulations are performed to calculate surface energies of different surface terminations and oxygen anion diffusivity of NdBaCo2O5+δ. Ba/Co termination is observed as a stable termination among different surface terminations along (001) direction. This shows the possibility of Ba cation segregation on the surface. The effect of Sr doping at A′ site leads to less Sr dopant cation segregation than Ba cations on the surface as obtained from segregation energy calculations. Oxygen anion diffusion coefficient of NdBaCo2O5.5 is obtained 2.09 × 10-7 cm2sec-1 at 973 K. 25%, 50%, 75%, and 100% Sr doping is performed at A′ site of NdBaCo2O5+δ, the oxygen anion diffusivity is observed to be increasing with increasing Sr concentration at A′ site. Effect of strain on surface energetics and oxygen anion diffusivity is studied for ±4%, ±3%, ±2%, and ±1% tensile and compressively strained NdBaCo2O5+δ system. Among different surface terminations along (001) direction, Ba/Co surface termination's decreasing surface energies indicate more Ba cation segregation on tensile strain. Oxygen anion diffusivity is observed to increase with increasing tensile strain in NdBaCo2O5+δ system.

Understanding surface cation segregation and strain effects in NdBa1-xSrxCo2O5+δ double perovskite for energy storage applications

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