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High H ionic conductivity in barium hydride


With hydrogen being seen as a key renewable energy vector, the search for materials exhibiting fast hydrogen transport becomes ever more important. Not only do hydrogen storage materials require high mobility of hydrogen in the solid state, but the efficiency of electrochemical devices is also largely determined by fast ionic transport. Although the heavy alkaline-earth hydrides are of limited interest for their hydrogen storage potential, owing to low gravimetric densities, their ionic nature may prove useful in new electrochemical applications, especially as an ionically conducting electrolyte material. Here we show that barium hydride shows fast pure ionic transport of hydride ions (H) in the high-temperature, high-symmetry phase. Although some conductivity studies have been reported on related materials previously, the nature of the charge carriers has not been determined. BaH2 gives rise to hydride ion conductivity of 0.2 S cm−1 at 630 °C. This is an order of magnitude larger than that of state-of-the-art proton-conducting perovskites or oxide ion conductors at this temperature. These results suggest that the alkaline-earth hydrides form an important new family of materials, with potential use in a number of applications, such as separation membranes, electrochemical reactors and so on.

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Figure 1: Crystallographic information for BaD2.
Figure 2: High-temperature phase of BaD2.
Figure 3: Impedance spectrum of BaH2 at 320 °C, showing grain boundary and electrode response, with respective summit frequencies.
Figure 4: Plot of bulk conductivity for BaH2, extracted from fitted impedance data up to 420 °C.
Figure 5: Results for the concentration cell experiment carried out on BaH2 and experimental set-up.
Figure 6: Comparison of bulk conductivities for BaH2 and various ionic conductors.


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We thank EPSRC for support through a Platform Grant, the Royal Society for a Wolfson Merit award and Institut Laue-Langevin for provision of neutron beam time.

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M.C.V. contributed significantly to all aspects, C.C. to synthesis and characterization, E.S. to neutron diffraction and J.T.S.I. to concept and manuscript.

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Correspondence to John T. S. Irvine.

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The authors declare no competing financial interests.

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Verbraeken, M., Cheung, C., Suard, E. et al. High H ionic conductivity in barium hydride. Nature Mater 14, 95–100 (2015).

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