Trapping Hydrogen Clusters in Clathrate of Water Molecules for Potential Application to Hydrogen Separation and Storage

Abstract

Clathrate hydrate, commonly called gas hydrate is a nonstoichiometric solid hydrate of ‘host’ H2O molecules and ‘guest’ of low-molecularweight (i.e., CH4, N2, CO2, and H2, etc.).1 Due to its gas storage/separation potentials, various applications of gas hydrate have been investigated up to date including CO2 sequestration via natural gas hydrate deposit,2 CO2 separation from flue gases,3-4 wastewater purification,5 and H2 storage.6-8 We describe a new concept in energy science that accomplishes energy-efficient harvesting of hydrogen molecules in natural gas blends at low pressure (PH2= 3 MPa) using water molecules. With rising concerns about global CO2 emission, much efforts have been focused on using the hydrogen-natural gas blends (HNGB) which burn much cleaner than traditional hydrocarbon fuels (e.g. gasoline or diesel). More importantly, the ‘Power-to-Gas (P2G)’ strategy capable of converting the surplus electricity produced from sustainable energy sources into molecular hydrogen can use the existing natural gas pipelines and enable the widespread of hydrogen gas in residence and industrial sectors. HNGB can be a game changer combining the advantages of fossil fuels and sustainable energy systems. One key question is how we can store H2 in a safe way. In this study, we utilize HNGB hydrates (consisting of CH4, C2H6, and H2) created under moderate formation conditions with no organic promoter molecules involved. Some gas phase hydrocarbon promoters have been tried before; however, H2 cannot be multiply loaded in a single cage of pre-synthesized hydrocarbon hydrate via guest-exchange method. A key discovery of our study is the inclusion of clustered molecular hydrogens (up to 3 molecules per single site) when hydrate cages are finely tuned via direct transformation from ice particles into nanoporous framework, overcoming the storage capacity challenge for this class of materials. We achieve this by identifying the underlying cause of the promoting effect of clean gaseous molecules of CH4 and C2H6 and addressing it through harvesting hydrogen clusters in the clathrate hydrate lattice.