EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Gas hydrates represent a non-conventional material for capturing and storing small gas molecules such as CH4, CO2, and H2. The molecular confinement is based on weak Van der Waals interactions between gas molecules and clathrate cage. While water is an environmentally friendly host, CH4 is considered a transition fuel on the way to ecologically benign H2 fuels. The CO2 sequestration in gas hydrates is additional attractive perspective to face the greenhouse gases challenge.

We used improved van der Waals density functional (vdW-DF2) to account for dispersion forces associated with adsorption of H2, CH4 and CO2 in clathrates, focusing on structure I (sI). First, we analyzed the structural properties of the common hydrate phases of sI, sII and sH, in both empty and filled conditions, and results agreed well with previous experimental and computational studies. Our calculations showed : (1) the order of sI gas hydrate stability is CO2 > CH4 > H2; (2) H2 stability can be improved in H2-CO2 and H2-CH4 mixed systems with heterogeneous occupancy of different gases in the same cage; (3) multiple cage occupancies in cases of CO2 and H2; and (4) sI clathrate can store 5.56 wt%, 12.3 wt% and 42.9 wt% of H2, CH4 and CO2, respectively. We have also studied the rotational movement of gas molecules and the energy landscape of different gases and estimated the diffusion activation energy to be 0.22, 1.07 and 0.43 eV for H2, CH4 and CO2, respectively.

This set of computational results highlights the promising properties of sI clathrate for fuel storage and transportation. Another important application pointed out by our data is carbon capture and sequestration in clathrates. The data also revealed the possibility of using CO2 or CH4 sI clathrates as a ‘template’ or storage medium for hydrogen storage.