A low-surface energy carbon allotrope: the case for bcc-C6

TL;DR

This paper predicts that the bcc-C6 carbon allotrope has exceptionally low surface energy and unique electronic properties, which could explain its formation and potential for hydrogen storage, expanding understanding of carbon allotropes.

Contribution

First-principles prediction of bcc-C6 as a low-surface-energy carbon allotrope with distinct electronic and hydrogen storage properties.

Findings

bcc-C6 has low surface energy and minimal size dependence.

Different thin layers of bcc-C6 exhibit diverse electronic behaviors.

Li-doped bcc-C6 layers show increased hydrogen binding capacity.

Abstract

Graphite may be viewed as a low-surface-energy carbon allotrope with little layer-layer interaction. Other low-surface-energy allotropes but with much stronger layer-layer interaction may also exist. Here, we report a first-principles prediction for one of the known carbon allotropes, bcc-C6 (a body centered carbon allotrope with six atoms per primitive unit) that should have exceptionally low-surface energy and little size dependence down to only a couple layer thickness. This unique property may explain the existence of the relatively-high-energy bcc-C6 during growth. The electronic properties of the bcc-C6thin layers can also be intriguing: the (111), (110), and (001) thin layers havedirect band gap, indirect band gap, and metallic character, respectively. The refrained chemical reactivity of the thin layers does not disappear after cleaving, as lithium-doped (Li-doped) 3-layers (111) has a noticeably increased binding energies of H2 molecules with a maximum storage capacity of 10.8 wt%.