Enhanced Low-Temperature Proton Conductivity in Hydrogen-Intercalated Brownmillerite Oxide

Solid oxide ionic conductors are employed in a wide range of energy-conversion applications, such as electrolytes in fuel cells. Typically, conventional ionic conductors based on metal oxides require elevated temperatures above approximately 500 ? to activate ionic transport, but the ability to operate at lower temperature could avoid mechanical instability and operating complexities. Here we report a solid oxide proton conductor, HSrCoO2.5, which shows unusually high proton conductivity between 40 ? and 140 ?. The proton conductivity was between 0.028 S cm(-1) to 0.33 S cm(-1) in this temperature range, with an ionic activation energy of approximately 0.27 eV. Combining experimental results and first-principles calculations, we attribute these intriguing properties to the high proton concentration and the well-ordered oxygen vacancy channels granted by the hydrogen-intercalated brownmillerite crystalline structure. Our results open the possibility of using solid oxide materials as the proton-conducting electrolytes in low-temperature devices.