(25e) Discovery of a New Mixed Methane-Hydrogen Hydrate Phase with Very High Hydrogen Storage Capacity

Hydrogen is considered to be a promising alternative to fossil fuels. Unfortunately, due to the difficulty in finding a practical storage medium, its use as a fuel, for instance for application in the automotive sector, is currently limited. In order to be considered practical, a hydrogen storage material should satisfy a number of requirements, including a high storage capacity (high hydrogen content by mass and volume), ambient storage temperature and pressure, a fast uptake of hydrogen, and reversible hydrogen release. So far, a material that meets these requirements is does not exist. In this work, we discovered a new hydrate phase that fulfills most of the above-mentioned requirements as a high capacity hydrogen storage material. The newly discovered mixed hydrate phase consists of water + methane + hydrogen. It is formed by addition of water to the Van der Waals compound tetrahydrogenmethane (CH4(H2)4), which contains as much as 33.4 wt% molecular hydrogen and is only stable at high pressures (5.4 GPa). Here, it is show that the required pressure can be decreased by more than 95% when water is added. Although the addition of a promoter molecule decreases the overall storage capacity, it still contains as much as 10-20 wt% hydrogen, making it a very interesting hydrogen storage material. The structure of the mixed hydrate phase was determined next using a combined experimental-theoretical approach. Results will be presented at the conference.