Computational studies for reduced graphene oxide in hydrogen-rich environment

📝 Abstract

We employ molecular dynamic simulations to study the reduction process of graphene-oxide (GO) in a chemically active environment enriched with hydrogen. We examine the concentration and pressure of hydrogen gas as a function of temperature in which abstraction of oxygen is possible with minimum damage to C-sp $^2$ bonds hence preserving the integrity of the graphene sheet. Through these studies we find chemical pathways that demonstrate beneficiary mechanisms for the quality of graphene including formation of water as well as suppression of carbonyl pair holes in favor of hydroxyl and epoxy formation facilitated by hydrogen gas in the environment.

💡 Analysis

We employ molecular dynamic simulations to study the reduction process of graphene-oxide (GO) in a chemically active environment enriched with hydrogen. We examine the concentration and pressure of hydrogen gas as a function of temperature in which abstraction of oxygen is possible with minimum damage to C-sp $^2$ bonds hence preserving the integrity of the graphene sheet. Through these studies we find chemical pathways that demonstrate beneficiary mechanisms for the quality of graphene including formation of water as well as suppression of carbonyl pair holes in favor of hydroxyl and epoxy formation facilitated by hydrogen gas in the environment.

📄 Content

Computational studies for reduced graphene oxide in hydrogen-rich environment Ramin M. Abolfath1,2, Kyeongjae Cho2 1School of Natural Sciences and Mathematics, University of Texas at Dallas, Richardson, TX 75080 2Department of Materials Science, University of Texas at Dallas, Richardson, TX 75080 (Dated: November 1, 2013) We employ molecular dynamic simulations to study the reduction process of graphene-oxide (GO) in a chemically active environment enriched with hydrogen. We examine the concentration and pressure of hydrogen gas as a function of temperature in which abstraction of oxygen is possible with minimum damage to C-sp2 bonds hence preserving the integrity of the graphene sheet. Through these studies we find chemical pathways that demonstrate beneficiary mechanisms for the quality of graphene including formation of water as well as suppression of carbonyl pair holes in favor of hydroxyl and epoxy formation facilitated by hydrogen gas in the environment. I. INTRODUCTION Following the progress in the fabrication and me- chanical exfoliation of the graphene1–4, extraordinary low-dimensional electrical and mechanical properties of graphene have been revealed5. Currently, mass-scale fabrication of graphene-based devices free from defects and imperfections requires chemical processing with high quality product and is one of the challenging technologi- cal problems for graphene device technology. For exam- ple, the micro-mechanical cleavage of graphite6, epitaxial growth on silicon carbide7, chemical vapor deposition of hydrocarbons on transition metal surfaces8 have shown difficulties in obtaining processable graphene sheets in large quantities thus impeding full exploitation of its ex- citing properties. Chemical oxidation of graphite and subsequent exfoliation in solution allow a large scale pro- duction of isolated graphene oxide (GO). However, the reduction of GO is known to create many structural de- fects degrading the material properties of reduced GO. Hence identifying reliable methods that allow removal of oxygen from GO with minimum damage to C-sp2 bonds in graphene-structures is the focus of current research activities. Recently studies have shown that the chemical reduc- tion of graphite oxide can be a low-cost and scalable method9–11. It has been found that layered materials constituting graphene layers functionalized with epoxy and hydroxyl groups are easily exfoliated in water. The resulting graphene oxide (GO) monolayers can be de- posited in controllable density onto a large variety of sub- strates, thus enabling the preparation of thin conductive films on solid and flexible substrates12–14. It is accepted that GO can be described as a ran- dom distribution of oxidized areas with the oxygenated functional groups, combined with nonoxidized regions wherein most of the carbon atoms preserve sp2 hybridiza- tion15. GO is electrically insulating material, however, its conductivity can improve up to 4 orders of magni- tude by chemical reduction16–18, nevertheless the typical conductivities of reduced GO (RGO) is still lower than pristine graphene by a factor of 10-10019,20 due to pres- ence of residual functional groups remaining after reduc- tion. In contrast to mechanically exfoliated graphene, the chemically derived graphene (i.e., RGO) is found to con- tain a considerable amount of topological defects. Sim- ilar to other low-dimensional carbon nanostructures like carbon nanotubes21, graphene ribbons22–24, fullerenes25 and more recently graphene quantum dots26, topological defects and etch-holes (that are unavoidable products of the reduction process) are expected to strongly affect the device electronic and mechanical performance, and thus to account for the differences between RGO and pristine graphene. Recent advances in computational modeling of mate- rials such as molecular dynamic (MD) simulations and ab-initio calculation have enabled researchers to provide detailed studies in the microscopic level and allows a care- ful analysis of the chemical reactions and diffusion mech- anisms28–41,43,45. Such studies are helpful in identifying the experimental conditions that allows the minimization of mechanical and chemical damages to graphene and the optimization of their performance28,29. In this work we employ MD simulations based on ab- initio CPMD42 and ReaxFF43,45 which are the mathe- matical formulation that governs the appropriate dynam- ics of the molecular system to analyze the carbon-oxygen chemical reaction and reduction process. We show that the GO structural relaxation assisted with the oxygen surface diffusion that allows the migration of epoxy func- tional groups and protects the C-sp2 bonds, preserve the integrity of the graphene lattice structure and governs the dynamical pathway in low temperatures. In con- trast, in high temperatures, consistent with recent find- ing of Ref.28,29, we show that the formation of carbonyl is dynamically favorable and can be accounted for domi- nant mechan

This content is AI-processed based on ArXiv data.