High proton conduction by full hydration in highly oxygen deficient perovskite

Abstract

Ceramic proton conductors are important in various applications such as fuel cells. In contrast to the conventional acceptor doping into the perovskite-type oxide without oxygen vacancies, donor doping into highly oxygen deficient perovskite is a novel strategy to achieve reduced proton trapping. Here, we report high proton conduction (e.g., 10 mS cm⁻¹ at 235 °C) and chemical stability of highly oxygen deficient perovskite, W⁶⁺-donor-doped BaScO_2.5 (BaSc_0.8W_0.2O_2.8). The high conductivity is attributed to both high proton concentration and proton diffusion coefficient D. The high D at low and intermediate temperatures is attributed to its low activation energy, suggesting reduced proton trapping. The high proton concentration is ascribed to both high oxygen deficiency in BaSc_0.8W_0.2O_2.8 and full hydration in hydrated BaSc_0.8W_0.2O_2.8 (BaSc_0.8W_0.2O_3.0H_0.4). A reason for the higher proton conductivity of BaSc_0.8W_0.2O_2.8 compared with BaSc_0.8Mo_0.2O_2.8 is higher fractional water uptake of BaSc_0.8W_0.2O_2.8, which is attributable to the larger lattice volume of BaSc_0.8W_0.2O_2.8 due to the larger sized W cation than the Mo cation. Present findings would open new avenues for clean energy societies.