Mechanical properties of hydrogen functionalized graphene allotropes

TL;DR

This study uses molecular dynamics simulations to analyze how hydrogen functionalization affects the mechanical properties of various graphene allotropes, revealing significant deterioration beyond certain coverage thresholds.

Contribution

It provides new insights into the coverage-dependent mechanical deterioration of hydrogenated graphene allotropes, including failure processes and structural effects.

Findings

Mechanical properties deteriorate drastically with increased H-coverage

Young's modulus can decrease up to 70% in fully hydrogenated allotropes

Tensile strength drops by about 90% even with small H-coverage

Abstract

Molecular dynamics (MD) simulations have been performed to investigate the mechanical properties of hydrogen functionalized graphene allotropes (GAs) for H-coverage spanning the entire range (0-100%). Four allotropes (graphyne, cyclic graphene, octagonal graphene, and biphenylene) with larger unit lattice size than graphene are considered. The effect of the degree of functionalization and molecular structure on the Young's modulus and strength are investigated, and the failure processes of some new GAs are reported for the first time. We show that the mechanical properties of the hydrogenated GAs deteriorate drastically with increasing H-coverage within the sensitive threshold, beyond which the mechanical properties remain insensitive to the increase in H-coverage. This drastic deterioration arises both from the conversion of sp2 to sp3 bonding and easy rotation of unsupported sp3 bonds. Allotropes with different lattice structures correspond to different sensitive thresholds. The Young's moduli deterioration of fully hydrogenated allotropes can be up to 70% smaller than that of the corresponding pristine structure. Moreover the tensile strength shows an even larger drop of about 90% and higher sensitivity to H-coverage even if it is small. Our results suggest that the unique coverage-dependent deterioration of the mechanical properties must be taken into account when analyzing the performance characteristics of nanodevices fabricated from functionalized GAs.