Computational study of the mixed B-site perovskite SmBxCo1−xO3−d (B = Mn, Fe, Ni, Cu) for next generation solid oxide fuel cell cathodes

Abstract

SmCoO₃ is a promising perovskite material for the next generation of intermediate temperature solid oxide fuel cells (SOFC), but its potential application is directly linked to, and dependent on, the presence of dopant ions. Doping on the Co-site is suggested to improve the catalytic and electronic properties of this cathode material. Fe, Mn, Ni, and Cu have been proposed as possible dopants and experimental studies have investigated and confirmed the potential of these materials. Here we present a systematic DFT+U study focused on the changes in electronic, magnetic, and physical properties with B-site doping of SmCoO₃ to allow cathode optimization. It is shown that doping generally leads to distortion in the system, thereby inducing different electron occupations of the Co d-orbitals, altering the electronic and magnetic structure. From these calculations, the 0 K electronic conductivity (σ_e) was obtained, with SmMn_xCo_1−xO₃ having the highest σ_e, and SmFe_xCo_1−xO₃ the lowest σ_e, in agreement with experiment. We have also investigated the impact of dopant species and concentration on the oxygen vacancy formation energy (E_f), which is related to the ionic conductivity (σ_O). We found that the E_f values are lowered only when SmCoO₃ is doped with Cu or Ni. Finally, thermal expansion coefficients were calculated, with Mn-doping showing the largest decrease at low x and at x = 0.75. Combining these results, it is clear that Mn-doping in the range x = 0.125–0.25 would imbue SmCoO₃ with the most favorable properties for IT-SOFC cathode applications.