Metallic solid-state hydrogen storage crystals achieved through chemical precompression under ambient conditions

TL;DR

This paper reports a novel solid-state hydrogen storage crystal formed by chemical precompression, achieving high hydrogen density and metallic properties under ambient conditions, which could advance hydrogen storage technology.

Contribution

It introduces a new hydrogen storage crystal, H9@C20, stabilized by chemical precompression, enabling high-density hydrogen storage at ambient conditions.

Findings

H9@C20 remains stable under ambient conditions.

Hydrogen density exceeds that of solid hydrogen.

Filling voids increases hydrogen content without losing stability.

Abstract

Improving hydrogen storage density is essential for reducing the extreme conditions required in applications such as nuclear fusion. However, the recognition of metallic hydrogen as the "Holy Grail" of high-pressure science highlights the difficulty of high-density hydrogen aggregation. Here, we report a solid-state crystal H9@C20 formed by embedding hydrogen atoms into C20 fullerene cages and utilizing chemical precompression, which remains stable under ambient pressure and temperature conditions and exhibits metallic properties. This precompression effect is reflected in the formation of C-H bonds within the cage and C-C bonds between cages, resulting in the transformation of all C atoms from sp2 to sp3 hybridization with inward and outward distortions, while promoting delocalized multicenter bonding within the H9 aggregate. In particular, the hydrogen density inside the C20 cage exceeds that of solid hydrogen, achieving a uniform discrete distribution with H9 as monomers. Further study reveals that filling hydrogen molecules into voids between H9@C20 primitive cells can increase hydrogen content while maintaining structural stability, forming a solid-gas mixed hydrogen storage crystal. Our findings provide a basis for developing high-density hydrogen storage materials under ambient conditions.