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


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.

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Fig. 1: Crystal structures of as-synthesized K2NiF4-type oxyhydrides at room temperature.
Fig. 2: Structural phase transition of Ba1.75LiH2.7O0.9 prepared by ambient-pressure synthesis.
Fig. 3: Hydride conductivity of Ba1.75LiH2.7O0.9.
Fig. 4: Molecular-level H dynamics.
Fig. 5: Comparison of H conductivities of Ba1.75LiH2.7O0.9 and other materials.

Data availability

The data presented in the current study are available from the corresponding author on reasonable request. Source data are provided with this paper.


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This work was supported by the Precursory Research for Embryonic Science and Technology programme of the Japan Science and Technology Agency, no. JPMJPR1295 (G.K.); Grants-in-Aid nos 15H05497 (G.K.), 17H05492 (G.K.), 17H06145 (R.K.), 18H05516 (G.K.), 18H05518 (T.O.), 19H04710 (F.T.) and 20H02828 (G.K.) from the Japan Society for the Promotion of Science; and the Advanced Research Program for Energy and Environment Technologies from the New Energy and Industrial Technology Development Organization, no. 16823906 (R.K.). Synchrotron and neutron radiation experiments were approved by the Japan Synchrotron Radiation Research Institute (2016A1673, 2016B1767 and 2018B1099), the Neutron Scattering Program Advisory Committee of the Institute of Materials Structure Science, the High Energy Accelerator Research Organization (2014S06, 2014S10 and 2019S10) and the Institut Laue-Langevin ( Electrochemical impedance spectroscopy measurements were supported by N. Higuchi (Toyo Corporation). The authors thank T. Yamamoto and T. Broux for their helpful suggestions regarding structural refinement. D.B. acknowledges the NanoSciences Programme of the Atomic Energy Commission (CEA, France) and the EU/CEA Enhanced Eurotalents Fellowship for financial support.

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Authors and Affiliations



G.K. conceived, supervised and designed the whole study. A.W., Y.I. and M.N. synthesized the material. F.T., A.W., K.O. and Y.I. carried out the electrochemical measurements. F.T., A.W., A.A., M.Y., T.S., K.I., T.O., T.K. and G.K. collected and refined the powder SXRD and ND data. D.B., S.L., B.F. and G.K. conducted the neutron quasi-elastic measurements and analysis. All authors discussed the results; F.T. and G.K. wrote the manuscript with discussions mainly with S.L., D.B., B.F. and R.K.

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Correspondence to Genki Kobayashi.

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Nature Materials thanks John Irvine and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Information

Supplementary Figs. 1–14, Discussions 1–4 and Tables 1–4.

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Takeiri, F., Watanabe, A., Okamoto, K. et al. Hydride-ion-conducting K2NiF4-type Ba–Li oxyhydride solid electrolyte. Nat. Mater. 21, 325–330 (2022).

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