A theoretical study of the hydrogen-storage potential of (H_2)_4CH_4 in metal organic framework materials and carbon nanotubes

TL;DR

This study explores the potential of using metal organic frameworks and carbon nanotubes to stabilize the hydrogen-rich compound H4M for efficient hydrogen storage, employing ab initio computational methods.

Contribution

It provides a theoretical analysis of H4M stability within MOFs and carbon nanotubes, highlighting the feasibility of room-temperature stabilization with nanotubes.

Findings

Carbon nanotubes can generate sufficient pressure to stabilize H4M at room temperature.

MOFs can create significant pressure but require cooling to stabilize H4M.

H4M has high hydrogen content, making it promising for storage applications.

Abstract

The hydrogen-methane compound (H_2)_4CH_4---or for short H4M---is one of the most promising hydrogen-storage materials. This van der Waals compound is extremely rich in molecular hydrogen: 33.3 mass%, not including the hydrogen bound in CH_4; including it, we reach even 50.2 mass%. Unfortunately, H4M is not stable under ambient pressure and temperature, requiring either low temperature or high pressure. In this paper, we investigate the properties and structure of the molecular and crystalline forms of H4M, using ab initio methods based on van der Waals DFT (vdW-DF). We further investigate the possibility of creating the pressures required to stabilize H4M through external agents such as metal organic framework (MOF) materials and carbon nanotubes, with very encouraging results. In particular, we find that certain MOFs can create considerable pressure for H4M in their cavities, but not enough to stabilize it at room temperature, and moderate cooling is still necessary. On the other hand, we find that all investigated carbon nanotubes can create the high pressures required for H4M to be stable at room temperature, with direct implications for new and exciting hydrogen-storage applications.