Crystal structure, electrical and electrochemical properties of Cu co-doped Pr1.3Sr0.7NiO4+δ mixed ionic-electronic conductors (MIECs)

Abstract

Room temperature crystal structure, electrical properties and electrochemical properties in the temperature range 25–700 °C of Cu co-doped Pr1.3Sr0.7NiO4+δ prepared by acetate combustion is investigated from intermediate temperature solid oxide fuel cell cathode viewpoint. The Pr1.3Sr0.7Ni1−xCuxO4+δ (PSNCO) solid solutions have a tetragonal I4/mmm K2NiF4-type structure which consists of a (Pr1.3Sr0.7) (Ni1.xCux)O3 perovskite unit and a (Pr1.3Sr0.7)O rock salt unit in the whole compositional range 0 ≤ x ≤ 0.4. A reduction in bond-length of Ni/Cu-O resulting from PSNCO lattice contraction eases hop of small polaron from Ni3+ to Ni2+/Cu2+ in (Ni1−xCux)-O layer with low activation energy, which increases electron conductivity. The maximum electronic conductivity (σ = Ω cm−1) with minimum activation energy (Ea = eV) is observed at x = 0.3. Lattice expansion along c-direction owing to Cu2+ doping facilitates hop of O2− from its occupied interstitial site (O3) to nearby equivalent site assisted by anisotropic thermal motion of apical oxygen O2 resulting in increase in ionic conductivity. The minimum polarization resistance value (Rp = 0.13 (2) Ω cm2) and activation energy (Ea = 1.321 (5) eV) at x = 0.3 is attributed to high electronic and ionic conductivities compared to other compositions. Complex impedance spectroscopy studies suggest that the ORR is co-limited by O2− diffusion and O2 surface exchange.