High-capacity, reversible hydrogen storage using H<sup>-</sup>-conducting solid electrolytes.

Hirose, Takashi; Matsui, Naoki; Itoh, Takashi; Hinuma, Yoyo; Ikeda, Kazutaka; Gotoh, Kazuma; Jiang, Guangzhong; Suzuki, Kota et al. · Science · 2025

basic_science · Level V

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Abstract

Hydrogen absorption and desorption in solids are pivotal reactions involved in batteries and hydrogen storage devices. However, conventional thermodynamic and electrochemical hydrogen storage using high-capacity materials suffers from high hydrogen-desorption temperatures and instability of electrolytes. In this work, we explored electrochemical hydride ion (H<sup>-</sup>)-driven hydrogen storage and developed a solid electrolyte, anti-α-AgI-type Ba<sub>0.5</sub>Ca<sub>0.35</sub>Na<sub>0.15</sub>H<sub>1.85</sub>, which exhibits excellent H<sup>-</sup> conductivity and electrochemical stability. This electrolyte is compatible with several metal-hydrogen electrodes, such as titanim hydride and magnesium hydride (MgH<sub>2</sub>), allowing for high-capacity, reversible hydrogen storage at low temperatures. Specifically, Mg-H<sub>2</sub> cells operating as hydrogen storage devices (Mg + H<sub>2</sub> [Formula: see text] MgH<sub>2</sub>) achieved a reversible capacity of 2030 milliampere hours per gram at 90°C, offering safe and efficient hydrogen-electricity conversion and hydrogen storage devices.