Superprotonic Conduction in Donor Co-Doped Perovskites

Donor doping of oxygen-deficient BaScO_2.5 is an unexplored strategy for achieving high proton conductivity at intermediate temperatures of 200-400 °C. In this work, a new series of BaSc_{1- x - y}Mo_xW_yO_{3- δ} compounds was prepared via Mo/W donor co-doping where x is the Mo content, y is the W content, and δ is the amount of oxygen vacancies. The present work reports the enhancement of proton conductivity by the Mo/W donor co-doping of BaScO_2.5. BaSc_0.8Mo_0.1W_0.1O_2.8 exhibits exceptional proton conductivity-0.10 S cm^{- 1} at 315 °C and 0.01 S cm^{- 1} at 193 °C-alongside outstanding chemical stability in CO₂, O₂, and H₂ atmospheres. The high proton conductivity originates from the synergistic effects of abundant oxygen vacancies (δ = 0.2) and full hydration, yielding a high proton concentration, coupled with high proton diffusivity. The high diffusivity is attributable to the reduced proton trapping compared with acceptor and isovalent doping and overdoping due to higher proton concentration. In contrast to the acceptor co-doping, the donor co-doping does not increase the activation energy, resulting in lower activation energy and higher proton conductivity. These findings establish donor co-doping into the oxygen-deficient perovskites as a powerful design principle for next-generation proton conductors with high proton conductivity at intermediate temperatures.