A very large volume of hydrogen can be accommodated by making

A very large volume of hydrogen can be accommodated by making non-stoichiometric hydrides, also known as interstitial hydrides. Certain transition metals, such as palladium, titanium, and vanadium, possess the unique ability to absorb hydrogen into the interstitial sites of their metal lattices [2]. This absorption process allows these metals to store hydrogen at high volumetric energy densities, often exceeding the density of liquid hydrogen. These hydrides are termed non-stoichiometric because the ratio of hydrogen atoms to metal atoms is not a fixed whole number, varying with temperature and pressure [1][2]. This solid-state storage method is considered safer and more efficient than high-pressure gas or cryogenic liquid storage [1]. While alkali metal hydrides like lithium hydride exist, they are typically stoichiometric ionic compounds and do not offer the same reversible interstitial absorption capacity as transition metal non-stoichiometric hydrides.

Sources

1. [2] https://pmc.ncbi.nlm.nih.gov/articles/PMC9030770/
2. [1] https://www.sciencedirect.com/science/article/pii/S2352152X23018534