Thermal decomposition behaviors of an ultralow-density porous ice stored with H2

Abstract

Context

Porous ice with ultralow density has recently demonstrated remarkable hydrogen storage capacity. However, the thermal decomposition behavior of ultralow-density porous ice stored with H₂ had not been investigated. In this work, the decomposition behavior of an ultralow-density porous ice, known as EMT, filled with varying amounts of H₂ was studied using molecular dynamics (MD) simulations. It was found that hydrogen molecules can rapidly diffuse within the porous ice framework even at low temperatures. As the temperature increases, the diffusion of water molecules intensifies until the clathrate framework of H₂O breaks down. The decomposition temperature rises from 230 to 250 K at 1 bar as the number of H₂ molecules increases from 192 to 1632 in a supercell of EMT containing 2304 H₂O molecules. Notably, the decomposition temperature further increases to 270 K at 1 bar when each 4⁶6⁸ water cavity of EMT is occupied by a C₂H₆ molecule. This reveals the decomposition mechanism of EMT porous ice stored with H₂ and demonstrates that the stability of EMT porous ice can be significantly enhanced by encapsulating C₂H₆ within 4⁶6⁸ water cavities. These findings provide valuable insights into hydrogen storage in porous ice.

Method

Thermal decomposition behaviors of the ultralow-density porous ice EMT stored with H₂ were investigated by gradually increasing the temperature in steps of 10 K from 200 K at ambient pressure based on MD simulations. The consistent valence force field was employed to describe the intermolecular and intramolecular interactions of the system with NPT ensemble.