Hydride-ion-conducting K2NiF4-type Ba–Li oxyhydride solid electrolyte

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Abstract
Hydrogen transport in solids, applied in electrochemical devices such as fuel cells and electrolysis cells, is key to sustainable energy societies. Although using proton (H+) conductors is an attractive choice, practical conductivity at intermediate temperatures (200–400 °C), which would be ideal for most energy and chemical conversion applications, remains a challenge. Alternatively, hydride ions (H–), that is, monovalent anions with high polarizability, can be considered a promising charge carrier that facilitates fast ionic conduction in solids. Here, we report a K2NiF4-type Ba–Li oxyhydride with an appreciable amount of hydrogen vacancies that presents long-range order at room temperature. Increasing the temperature results in the disappearance of the vacancy ordering, triggering a high and essentially temperature-independent H– conductivity of more than 0.01 S cm–1 above 315 °C. Such a remarkable H– conducting nature at intermediate temperatures is anticipated to be important for energy and chemical conversion devices.
Funding Information
  • MEXT | Japan Society for the Promotion of Science (19H04710, 18H05518, 17H06145, 17H05492, 18H05516, 20H02828, 15H05497, 17H06145)
  • New Energy and Industrial Technology Development Organization (16823906, 16823906)
  • MEXT | JST | Precursory Research for Embryonic Science and Technology (JPMJPR1295)

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