First Principles Investigation of Hydrogen Physical Adsorption on Graphynes' layers

TL;DR

This study uses first principles calculations to explore hydrogen adsorption on graphynes, proposing a novel layered material with nanopores that could enhance hydrogen storage capabilities.

Contribution

It introduces a new graphtriyne-based layered carbon material with potential for improved hydrogen storage through physical adsorption.

Findings

Graphynes show larger binding energies for H2 than graphene.

A stable pore-centered minimum for H2 on graphtriyne is identified.

The proposed material allows H2 intercalation and diffusion with high storage potential.

Abstract

Graphynes are 2D porous structures deriving from graphene featuring triangular and regularly distributed subnanometer pores, which may be exploited to host small gaseous species. First principles adsorption energies of molecular hydrogen (H2) on graphene, graphdiyne and graphtriyne molecular prototypes are obtained at the MP2C level of theory. First, a single layer is investigated and it is found that graphynes are more suited than graphene for H2 physical adsorption since they provide larger binding energies at equilibrium distances much closer to the 2D plane. In particular, for graphtriyne a flat minimum located right in the geometric center of the pore is identified. A novel graphite composed of graphtriyne stacked sheets is then proposed and an estimation of its 3D arrangement is obtained at the DFT level of theory. In contrast to pristine graphite this new carbon material allow both H2 intercalation and out-of-plane diffusion by exploiting the larger volume provided by its nanopores. Related H2 binding energies for intercalation and in-pore adsorption are around 0.1 eV and they could lead to high storage capacities. The proposed carbon-based layered material could represent a safer and potentially cheaper alternative for hydrogen on-board storage than conventional solutions based on cryogenic liquefaction and/or high compression.