High proton conductivity in Nb5+-doped BaScO2.5

Abstract

Ceramic proton conductors are promising materials for clean energy. In contrast to the conventional acceptor doping, donor doping into the oxides with intrinsic oxygen vacancies is a novel strategy to achieve the reduced proton trapping. Here, we report high proton conductivity (e.g., 0.01 S cm⁻¹ at 320 °C) and high chemical stability of pentavalent donor doped BaScO_2.5, BaSc_0.75Nb_0.25O_2.75. The high proton conductivity is attributable to high proton concentration and high proton diffusion coefficient. The high proton concentration is ascribed to a large amount of oxygen vacancies in BaSc_0.75Nb_0.25O_2.75 and full hydration in hydrated BaSc_0.75Nb_0.25O_2.75. The high proton diffusion coefficient is attributable to its low activation energy, suggesting reduced proton trapping due to the repulsion between the donor Nb⁵⁺ dopant and protons. The repulsion is clearly shown by the ab initio molecular dynamics simulations.