High-capacity, reversible hydrogen storage using H ^– -conducting solid electrolytes

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^-)-driven hydrogen storage and developed a solid electrolyte, anti-α-AgI-type Ba_0.5Ca_0.35Na_0.15H_1.85, which exhibits excellent H^- conductivity and electrochemical stability. This electrolyte is compatible with several metal-hydrogen electrodes, such as titanim hydride and magnesium hydride (MgH₂), allowing for high-capacity, reversible hydrogen storage at low temperatures. Specifically, Mg-H₂ cells operating as hydrogen storage devices (Mg + H₂ [Formula: see text] MgH₂) achieved a reversible capacity of 2030 milliampere hours per gram at 90°C, offering safe and efficient hydrogen-electricity conversion and hydrogen storage devices.