Promoting the Insertion of Molecular Hydrogen in Tetrahydrofuran Hydrate With the Help of Acidic Additives

Abstract

Among hydrogen storage materials, hydrogen hydrates have received a particular attention over the last decades. The pure hydrogen hydrate is generated only at extremely high-pressure (few thousands of bars) and the formation conditions are known to be softened by co-including guest molecules such as tetrahydrofuran (THF). Since this discovery, there have been considerable efforts to optimize the storage capacities in hydrates through the variability of the formation condition, of the cage occupancy, of the chemical composition or of the hydrate structure (ranging from clathrate to semi-clathrate). In addition to this issue, the hydrogen insertion mechanism plays also a crucial role not only at a fundamental level, but also in view of potential applications. This paper aims at studying the molecular hydrogen diffusion in the THF hydrate by in-situ confocal Raman microspectroscopy and imaging, and at investigating the impact of strong acid onto this diffusive process. This study represents the first report to shed light on hydrogen diffusion in acidic THF-H 2 hydrate. Integrating the present result with those from previous experimental investigations, it is shown that the hydrogen insertion in the THF hydrate is optimum for a pressure of ca . 55 bar at 270 K. Moreover, the co-inclusion of perchloric acid (with concentration as low as 1 acidic molecules per 136 water molecules) lead to promote the molecular hydrogen insertion within the hydrate structure. The hydrogen diffusion coefficient—measured at 270 K and 200 bar—is improved by a factor of 2 thanks to the acidic additive.

Hydrogen Inter-Cage Hopping and Cage Occupancies inside Hydrogen Hydrate: Molecular-Dynamics Analysis

“…Such an observation is confirmed by recent experimental results obtained on the H 2 long-range diffusion in gas hydrate-containing H-bond defects. In such ionic hydrates, the H 2 O relaxation occurs on a shorter timescale than hydrates without H-bond defects [46,47], facilitating cage deformation [48]; thus, the H 2 diffusion is measured to be faster than in the same hydrate without H-bond defects [49]. H2 diffusion is measured to be faster than in the same hydrate without H-bond defects [49].…”

“…In such ionic hydrates, the H 2 O relaxation occurs on a shorter timescale than hydrates without H-bond defects [46,47], facilitating cage deformation [48]; thus, the H 2 diffusion is measured to be faster than in the same hydrate without H-bond defects [49]. H2 diffusion is measured to be faster than in the same hydrate without H-bond defects [49]. The most probable origin of a lower activation energy for the higher-occupancy systems is the deformation of the cage due to the increased cage occupancy.…”

“Liquid-like” Water in Clathrates Induced by Host–Guest Hydrogen Bonding

“…Clathrates containing polar guests offer an effective gas-storing material since they form at low pressures. In particular, polar guests such as tetrahydrofuran (THF) and dioxolane form clathrates already at atmospheric pressures. − Recently, a better hydrogen storage was attained by the inclusion of perchloric acid as an additive to THF clathrate . In principle, polar molecules might induce additional defects in the host lattice that facilitate the uptake and diffusion of fuel gas molecules in the clathrate.…”

A Review of Reactor Designs for Hydrogen Storage in Clathrate Hydrates

“…In addition to the issues related to formation of the hydrate, the hydrogen-insertion mechanism plays also a crucial role not only at a fundamental level, but also in view of potential applications. In a study reported by Nguyen et al, the enhancement of the H 2 insertion within the THF hydrate achieved with the co-inclusion of acidic additive [11]. In gas hydrate structure, the acidic additive acts as a "flexibilizer" of the water cage through the addition of chemical water H-bond defects -promoting H 2 inter-cage diffusion [12].…”