Method of producing graphane and graphane-like materials

Abstract

The invention relates to nanotechnology and to producing graphane and graphane-like materials and associated structures, which can be used to create hydrogen fuel cell energy, particularly for transportation systems as well as for creating nanoelectronic systems, based on the use of graphene with controllable electronic properties. The method includes grapheme, or several layers of graphene, placed in water or electrolytic solution, an anode, a cathode, and an adjustable voltage source, where the graphene's potential is lower than the anode's potential. The technical result is an increase in the rate of hydrogenation reactions, which simplifies and lowers the cost of technologies necessary for producing graphane fuel cells and creating conditions to enable their mass production.

Description

FIELD OF THE INVENTION

The invention relates to methods of producing hydrogenated single-layered and N-layered graphene and hydrogen-containing graphene nanostructures (graphane-like materials), which are considered to have prospective applications in the areas of electronics and hydrogen power and/or energy, particularly as hydrogen fuel cells for electric vehicles.

BACKGROUND OF THE INVENTION

There exists a known method for producing fully hydrogenated graphene (graphane) using ion-plasma treatment on graphene (Novoselov K. S., Geim A. K., Morozov S. V., Jiang D., Zhang Y., Dubonos S. V., Grigorieva I. V., Firsov A. A, Electric field effect in atomically thin carbon films. Science 306, 666 (2004)). The essence of the method is to place a graphene sample into a vacuum chamber that contains a mixture of inert gas and hydrogen, anode and cathode at pressures of the order of 10⁻²-10⁻³ Pa, located between the anode and cathode, where an electric field causes a discharge and exposes the graphene to an electric current which results in dissociation of molecular hydrogen and activation of the graphene surface, which creates conditions for formation of hydrogen atom bonds, bombarding the graphene surface (Elias, D. C., Nair, R. R., Mohiuddin, T. M. G., Morozov, S. V., Blake, P., Halsall, M. P., Ferrari, A. C., Boukhvalov D. W., Katsnelson M. I., Geim A. K., Novoselov K. S. Control of Graphene's Properties by Reversible Hydrogenation: Evidence for Graphane. Science 2009, 323, 610-613).

A disadvantage of this method is that, due to the condition for the stable existence of plasma in a vacuum chamber, the stream of hydrogen ions necessary for graphene hydrogenation has to be very small in order for the rate of hydrogenation to be small, thus requiring a significant amount of time (the typical duration is several hours) for creating hydrogenated regions of even smaller dimensions (tens of microns). Furthermore, a significant amount of hydrogen ions from the plasma, having sufficiently high energies (tens of electron volts) easily pass through the graphene layer and, with a large probability, form H—C bonds (hydrocarbon bonds) on the reverse side of the graphene sheet, which forms graphene that is hydrogenated from two sides. Moreover, the level of hydrogenation (the ratio of H—C on the graphene surface) using such a method cannot be controlled. At the same time, the ability to control the formation of hydrogenated graphene is very important.

Material with fully saturated bonds on both graphene surfaces (H/C=1) has been named graphane (FIG. 1) in scientific literature and, in contrast to graphene, is dielectric. In this case, where not all links on the graphene surface are saturated with hydrogen (H/C<1), the material is referred to as a graphane-like material. The graphane-like material's properties entirely depend on the concentration of hydrogen. For example, if the hydrogen bonds in the graphane are strong enough, the energy produced from such material can be around 650 kJ/mol (J. O. Sofo, A. S. Chaudhari, G. D. Barber, Graphane: a two-dimensional hydrocarbon, Phys. Rev. B 75 (153401) (2007) 4). Such strong bonds demand too high a temperature for separating hydrogen and aren't suitable for use in transport systems such as electric vehicles. With graphane-like materials, at certain levels of hydrogenation, the energy level for hydrogen bonding can be obtained at significantly lower levels than graphane—200-300 kJ/mol—which allows for use of such materials as high-capacity hydrogen fuel cells.

Additional known methods involve using expensive equipment (e.g. vacuum chamber, system for generating and sustaining plasma, high voltage sources). Such costs make such a method unsuitable for mass production of graphane and graphane-like materials, which are essential for hydrogen power, particularly for fuel production for electric vehicles.

SUMMARY OF THE INVENTION

The essence of the invention is in the fact that graphene material is placed in a liquid medium, particularly water, containing hydrogen, located between an anode and cathode in the electrolytic bath where, under the influence of an electric field, the splitting of water molecules and activation of the graphene surface occurs. As a result, the hydrogen atoms and ions enter into a chemical bond with the graphene, forming graphane or a graphane-like structure, depending on the ratio of H/C (hydrogen-to-carbon) that is achieved during the process.

The technical result of the invention is an increase in the rate of graphene hydrogenation and simultaneous simplification of the graphane or graphane-like material production method by using electrolytic baths.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 displays the atomic structure of bilateral hydrogenated graphene with a hydrogen atom bonding energy of 650 kJ/mol.

FIG. 2 is a schematic for implementing the method disclosed in this invention, comprising an electrolytic cell 1, an anode 2, a cathode 3, a graphene or multilayered graphene target 4, and an adjustable voltage source (1-100 V) 5.

FIG. 3 displays a computer model of a deformed graphene sheet after unilateral hydrogenation, with a hydrogen atom bonding energy of 180-200 kJ/mol.

FIG. 4 displays a Raman spectra of graphene structures hydrogenated using the electrolytic method disclosed in the invention. FIG. 4(a) shows results for a hydrogenation time of one (1) minute, while FIG. 4(b) shows results for a hydrogenation time of four (4) minutes.

DETAILED DESCRIPTION OF THE INVENTION

The aim of the invention is to develop a novel process for producing single-layered and N-layered hydrogenated graphene and hydrogen-containing graphene nanostructures (graphane-like materials).

Technical result—increasing the rate of graphene hydrogenation while technically simplifying the method itself.

The achievable technical result—increasing the rate of graphene hydrogenation and simplification of the method by using electrolytic baths.

The proposed effective method for obtaining single-layer and N-layered hydrogenated graphene nanostructures (graphane-like materials) consists of submerging the graphene in a liquid medium, containing hydrogen, in particular water, positioned between an anode and cathode in the electrolytic bath, where the process occurs under the influence of an electric field.

Implementation of the method for hydrogenation of graphene is schematically shown in FIG. 2.

In order to implement the method disclosed in the invention, the graphene target 4 is placed in an electrolytic cell 1, containing an aqueous electrolytic solution or pure water, between anode 2 and cathode 3, such that it has the cathode's potential. Using an adjustable voltage source 5 between anode 2 and cathode 3 a potential difference is created, and hydrogenation of the target occurs. Meanwhile, regulating the output voltage source can produce hydrogenated graphene on only one side (see FIG. 3), or it may create the possibility of partial ion penetration on the reverse side of the graphene as well as its partial hydrogenation. With such a method of hydrogenation, the energy for hydrogen bonding sharply declines to 180-200 kJ/mol, which is acceptable for achieving the temperature effect on hydrogenated graphene in order to separate hydrogen for the vehicle engine. Since the density of the electric current during electrolysis is greater than the density of the current in the plasma discharge by about 10⁴ times, the time required for achieving the desired degree of hydrogenation is correspondingly lower. This method also allows rapidly producing hydrogenation of graphene targets of larger sizes.

FIG. 4 shows the Raman spectra obtained from hydrogenated samples. The spectra are identical to known spectra from samples hydrogenated with ion-plasma technology (Elias, D. C., Nair, R. R., Mohiuddin, T. M. G., Morozov, S. V., Blake, P., Halsall, M. P., Ferrari, A. C., Boukhvalov D. W., Katsnelson M. I., Geim A. K., Novoselov K. S. Control of Graphene's Properties by Reversible Hydrogenation: Evidence for Graphane. Science 2009, 323, 610-613), which confirms the formation of graphane-like structures as a result of using our method.

Claims

1. A method of producing graphane and graphane-like material, comprising: a hydrogen medium, anode, cathode, and target, consisting of N-layered graphene, positioned in the space between the anode and cathode, electrically connected to the cathode, implementing the use of water or electrolytic solution as a hydrogen-containing medium, where the graphene target is located in such water or hydrogen-containing medium and has a potential lower than the anode potential.