Hydrogen storage in nanoporous media: Molecular dynamics simulations of the confinement effects

Abstract

Hydrogen has attracted considerable interest as a clean substitute for fossil fuels. Especially, substantial efforts have been dedicated into the development of nanoporous materials for mobile H2 storage. However, the potential of this approach is significantly limited by the generally low H2 loading capacity. Moreover, the fundamental understanding of the H2 behavior in confined spaces is still lacking. In this study, the enhancement of the fluid-wall interaction with decreasing pore sizes was first investigated using a simple numerical model. Subsequently, molecular dynamics simulations were conducted to discern the influencing factors on confined H2 density. The results confirmed the importance of pore size and fluid-wall interaction in determining the H2 storage capacity. Specifically, the confined density of H2 increased with shrinking pore sizes only when the nanoporous material met the energy requirement. The reverse trend of the optimal pore size below and above the threshold H2-wall interaction energy was attributed, respectively, to the absence and presence of the adsorbed H2 layers. It was also found that the benefit of confinement decays with increasing pressure due to the disproportional density change in the adsorption layers. The findings in this study shed light on the defining factors influencing the H2 storage in nanoporous media and provide guidance on the selection and synthesis of the H2 hosting materials.