Production of graphene and graphane

Abstract

The present invention provides a method for the production in an electrochemical cell of one or more of graphene, graphite nanoplatelet structures having a thickness of less than 100 nm, and graphane, wherein the cell comprises: (a) a negative electrode which is graphitic; (b) a positive electrode which may be graphitic or another material; and (c) an electrolyte selected from (i) an ionic liquid; (ii) a deep eutectic solvent; and (iii) a solid ionic conductor, optionally further comprising (iv) one or more ionic species, wherein the amount of (i), (ii) or (iii) and (iv) is greater than 50 wt % based on the total weight of the electrolyte; and wherein the electrolyte includes a mixture of different cations; and wherein the method comprises the step of passing a current through the cell to intercalate ions into the graphitic negative electrode so as to exfoliate the graphitic negative electrode.

Claims

1. A method for production in an electrochemical cell of one or more of graphene, graphite nanoplatelet structures having a thickness of less than 100 nm, and graphane, wherein the electrochemical cell comprises: (a) a negative electrode which is graphitic; (b) a positive electrode which may be graphitic or another material; and (c) an electrolyte that is selected from: (i) an electrolyte comprising a deep eutectic solvent which comprises at least two constituent components, said deep eutectic solvent having a deep eutectic solvent melting point that is at least 10 C. lower than a component melting point of one of said constituent components, wherein the deep eutectic solvent is present in an amount that is greater than 90 wt % based on total weight of the electrolyte; and (ii) an electrolyte comprising a deep eutectic solvent which comprises at least two constituent components, said deep eutectic solvent having a deep eutectic solvent melting point that is at least 10 C. lower than a component melting point of one of said constituent components, the electrolyte further comprising one or more additional ionic species, wherein the deep eutectic solvent and the additional ionic species are present in an amount that is greater than 90 wt % based on total weight of the electrolyte; and wherein the electrolyte includes a mixture of different cations; and wherein the method comprises the step of passing a current through the electrochemical cell to intercalate ions into the graphitic negative electrode so as to exfoliate the graphitic negative electrode.

2. The method of claim 1, wherein the electrolyte is free of organic solvent and water.

3. The method of claim 1, wherein the electrolyte includes a metal cation and an organic cation.

4. The method of claim 1, wherein the amount of the deep eutectic solvent that is present in the electrolyte of (c)(i), or the amount of the deep eutectic solvent and the additional ionic species that is present in the electrolyte of (c)(ii), is greater than 99 wt % based on the total weight of electrolyte.

5. The method of claim 1, wherein the deep eutectic solvent comprises choline chloride and urea in a mole ratio of about 1:2.

6. The method of claim 1, wherein the electrolyte further comprises one or more salts selected from metal cation-containing salts and organic cation-containing salts.

7. The method of claim 1, wherein the graphitic negative electrode comprises highly ordered pyrolytic graphite.

8. The method of claim 1, wherein the method is a method for the production in an electrochemical cell of graphene and/or graphite nanoplatelet structures having a thickness of less than 100 nm.

9. The method of claim 1, wherein the method is a method for the production in an electrochemical cell of graphane.

10. The method of claim 1, wherein temperature of the electrochemical cell does not exceed 60 C.

11. The method of claim 1, wherein the method includes the step of functionalizing the graphene or graphite nanoplatelet structures such that material produced from the method contains one or more functionalized regions such that the material contains more than 5 at % total non-carbon elements based on total number of atoms in the material.

12. The method of claim 1, wherein a material comprising a surface is produced from the method and wherein the material contains on at least some of its surface a metal-containing material, wherein the metal is selected from Fe and Sn.

13. The method of claim 1, further comprising the step of isolating the one or more of graphene, graphite nanoplatelet structures, and graphane.

14. The method of claim 1, wherein temperature of the electrochemical cell does not exceed 40 C.

15. The method of claim 1, wherein the method includes the step of functionalizing the graphene or graphite nanoplatelet structures such that material produced from the method contains one or more functionalized regions such that the material contains more than 10 at % total non-carbon elements based on total number of atoms in the material.

16. The method of claim 1, wherein the method includes the step of functionalizing the graphene or graphite nanoplatelet structures such that material produced from the method contains one or more functionalized regions such that the material contains more than 30 at % total non-carbon elements based on total number of atoms in the material.

17. The method of claim 1, wherein a material comprising a surface is produced from the method and wherein the material contains on at least some of its surface metal-containing nanoparticles, wherein the metal is selected from Fe and Sn.

18. The method of claim 1, wherein a material comprising a surface is produced from the method and wherein the material contains on at least some of its surface metal-containing nanoparticles having a mean average diameter of less than 25 nm, wherein the metal is selected from Fe and Sn.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a typical Raman spectrum of the powder produced in Example 1;

(2) FIG. 2 shows a typical Raman spectrum of the powder produced in Example 2;

(3) FIG. 3 shows a typical FTIR spectrum of the powder produced in Example 2;

(4) FIG. 4 shows a band gap analysis of the powder produced in Example 2;

(5) FIG. 5 shows an XRD Pattern of the powder produced in Example 3 (lower trace) compared with the original graphite (upper trace);

(6) FIG. 6 shows a typical Raman spectrum for the powder produced in Example 3;

(7) FIG. 7 shows an SEM image of powder produced in Example 3;

(8) FIG. 8 shows a typical Raman spectrum for the powder collected on the cathode in Example 4;

(9) FIG. 9 shows a typical Raman spectrum for the powder collected on the cathode in Example 5;

(10) FIG. 10 shows a TEM image of iron nanoparticles on the graphene surface from the powder collected in Example 7;

(11) FIG. 11 shows a TEM image of Sn nanoparticles on the graphene surface from the powder collected in Example 8;

(12) FIG. 12A shows a TEM image of Sn-containing species from the powder collected in Example 9; and

(13) FIG. 12B shows an enlarged TEM image of Sn-containing species from powder collected in Example 9.

(14) The present invention is described in more detail by way of example only with reference to the following Examples.

EXAMPLES

(15) General Electrochemical Procedure

(16) All the electrochemical experiments were conducted in 50 ml air tight glass beakers. The beaker was sealed using rubber plug or custom-made plastic lid. The electrodes are fixed on the lid so that the electrode distance is fixed at 5 mm at the start of the run. To control the surface area of the electrodes, the electrodes were attached to stainless steel rods that are allowed to move vertically using a M4 screw threaded onto the lid.

(17) Analysis of Graphene by Raman Spectroscopy

(18) All the Raman spectroscopy was conducted using a 633 nm excitation laser.

(19) It is well established in the literature that Raman spectroscopy can be used to determine the number of layers that a carbon flake possesses through the shape, intensity and position of the D (1350 cm.sup.1), G (1580 cm.sup.1) and 2D (2700 cm.sup.1) peaks (the 2D peak may be alternatively referred to as the G peak).

(20) The exact positions of the Raman peaks depend on the excitation wavelength used and the level of doping in the sample [Ferrari 2006]. In general, the Raman spectrum for single layer graphene comprises a 2D peak which can be fitted with a single component and is similar or higher in intensity than the G peak. The 2D peak for monolayer graphene occurs at approximately 2637 cm.sup.1 when measured using a 633 nm excitation laser. As the number of layers increase, the 2D peak decreases in relative intensity to the G peak.

(21) The 2D peak would be expected to be centred at approximately 2637, 2663, 2665, 2675 and 2688 cm-1 for 1-layer, 2-layer, 3-layer, many-layer and graphite respectively using a 633 nm laser to measure graphene flakes deposited on an oxide-covered silicon wafer.

(22) The intensity of the D peak relative to the G peak also provides an indication of the number of structural defects such as graphene edges and sub-domain boundaries in the material produced. A D peak to G peak ratio (ID/IG) of around 0.2 may be expected for pristine graphene and the lower the ratio the better the quality material produced [Malard 2009].

Example 1

(23) A cell was assembled having graphite rods as working electrode, Li as counter electrode, and Ag/AgCl as reference electrode. The liquid electrolyte was an eutectic mixture of 1:2 Choline chloride: Urea with 2 M LiCl in the electrolyte. A potential of 10 V was applied to the working electrode versus Ag/AgCl for 8 hours. The Raman spectrum (FIG. 1) of the exfoliated carbonaceous material collected from the electrolyte shows few layer graphene features, i.e. large G band at 1585 cm.sup.1 and large symmetrical 2D band at 2650 cm.sup.1.

(24) There was no evidence of breakdown/decomposition of the liquid electrolyte.

Example 2

(25) Eutectic mixture of 1:2 Choline chloride: Urea were prepared in a glovebox under inert atmosphere. About 2 mole/liter of LiCl was added to the eutectic liquid to form the electrolyte. A cell was assembled having a graphite rod wrapped in a membrane as working electrode, Li as a counter electrode, and Ag/AgCl as reference electrode. A potential of 2.5 V was applied versus Ag/AgCl for 8 hours. The cell was continuously flushed with Ar gas.

(26) The first step of the exfoliation/hydrogenation process is believed to be the reduction of Et.sub.3N either electrochemically on the negative graphite electrode, or chemically by the adsorbed or deposited lithium:
(Et.sub.3NOH)++e.sup.=Et.sub.3N.sup.+.OH
Li+n(Et.sub.3N)=Li.sup.++e.sup.(Et.sub.3N)n
n(Et.sub.3N)+e.sup.=e.sup.(Et.sub.3N)n

(27) The ability of Li and Et.sub.3N to intercalate between the graphene layers in the graphite structure makes these reactions not limited only to the surface of the graphite electrode, but to some micron in the depth direction, depending on the density of the rod.

(28) The second step is believed to be the formation of a carbanion complex with the evolving of trimethylamine:
e.sup.(Et.sub.3N)n+C=C.sup.+nEt.sub.3N

(29) The carbanion complex then decomposes by the reaction with the hydroxyl radical resulting in the formation of a covalent hydrogenated carbon derivative:
C.sup.+.OH=CH+O.sup.

(30) This reaction competes with the formation of hydrogen, and/or lithium hydride:
C.sup.+OH=C+OH.sup.
Li.sup.++OH.sup.=LiOH

(31) The last reaction seems to be more dominant at high potential. The macroscopic appearance of hydrogenated graphene was very similar to that of the pristine samples, only the increased stability of the aqueous suspension, i.e., the significantly lower rate of sedimentation, indicated the modification of the surface.

(32) The same experimental procedure was used as Example 1, but using an applied potential of 2.5 V. The Raman spectrum (FIG. 2) shows a Large D band at 1330 cm.sup.1, a significant decrease in the 2D band, and merging of the D+D band at 2900 cm.sup.1, which indicates hydrogenation. FTIR analysis (FIG. 3) shows distinctive peaks at 2884 cm.sup.1 and 2912 cm.sup.1 corresponding to the aliphatic CH stretch vibrations. These peaks were not observed in this region for graphite nor for the graphene prepared in Example 1. The band gap of the hydrogenated sample was determined (FIG. 4) to be 4 eV by using UV-Vis spectroscopy and Tauc's equation.

(33) These results, including the determination of the 4 eV band gap demonstrates that graphane had been formed. This is particularly significant because it means that hydrogenation of the graphite surface occurred in-situ. In other words there is no need for a second step of hydrogenation. This demonstrates not only a new efficient route for the preparation of graphane but also that the use of the specific type of electrolyte described herein together with a graphitic negative electrode provides wide flexibility for functionalization of the graphite-derived material. This versatility is a valuable step forward in the scale-up of the production of graphene and graphene-type materials.

(34) There was no evidence of breakdown/decomposition of the liquid electrolyte.

Example 3

(35) A eutectic mixture of ferrous chloride and triethylamine hydrochloride (Et.sub.3NHCl) was prepared under inert atmosphere at room temperature. Two graphite rods were used as electrodes. A potential difference of 15 V was applied for 1 hour with the current being limited to 0.5 A. The electrode polarity was switched every 3 minutes. By the end of the electrolysis, the brown colour of the electrolyte was changed into black. After the end of the run, the electrolyte was leached in a multistep process using acidified water, distilled water, ethanol, and acetone. The resulted powder was filtered out using 100 nm pore diameter filter paper.

(36) The produced powder was characterised using XRD and Raman spectroscopy. The XRD pattern of the obtained powder is illustrated in FIG. 5 together with that of the initial graphite powder used as the electrode (upper trace is graphite starting material; lower trace is the collected powder). The strong 002 peak that characterises the - stacked layers in the graphite was weakened (e.g. less intense) after electrolysis indicating some disruption in the - stacked layers. The 2D band in the Raman spectrum (FIG. 6) is at 2667 cm.sup.1 and the full width at half-maximum (FWHM) of the 2D band is 64.4 cm.sup.1 which is very close to the characteristic values of four layer graphene. An SEM image of the powder is shown in FIG. 7.

(37) There was no evidence of breakdown/decomposition of the liquid electrolyte.

Example 4

(38) The experimental procedure in Example 1 was followed except that the polarity of the potential difference was reversed every 30 seconds over a 15 minute period. Thus, for half of the process (including the first and last phases) the graphitic electrode was the negative electrode and the electrode on which graphene was produced.

(39) The Raman spectrum is shown in FIG. 8. Clearly the position of the 2D peaks was shifted to 2657 cm.sup.1. Although this value is close to the typical position of 2D band in bilayer graphene, the width of this peak is much higher (72.5 cm.sup.1).

(40) There was no evidence of breakdown/decomposition of the liquid electrolyte.

Example 5

(41) The experimental procedure in Example 4 was followed except that but the electrolyte used was a mixture of aluminium chloride-triethylamine hydrochloride. The Raman spectrum shows (FIG. 9) graphenic structure with intense 2D band centred at 2654 cm.sup.1.

(42) There was no evidence of breakdown/decomposition of the liquid electrolyte.

Example 6

(43) A cell composed of a graphite working electrode, Pt counter electrode and Ag/AgCl reference electrode was used. The electrolyte was an eutectic mixture of SnCl.sub.2Et.sub.3NHCl. The potential was switched between 5 to 5 V versus the reference every 2 minutes for 2 hours. The Raman analysis shows intense symmetric 2D band at 2652 cm.sup.1.

(44) There was no evidence of breakdown/decomposition of the liquid electrolyte.

Example 7

(45) Natural graphite powder was pressed into a pellet, wrapped by a silver wire into a nickel rod current collector. The pellet was then wrapped in a porous membrane, and the whole assemblage served as working electrode. The counter and the reference electrodes were Pt and Ag/AgCl respectively. The electrolyte was eutectic mixture of ferrous chloride and triethylamine hydrochloride as in Examples 3 and 5. The applied potential was switched between 2.8 and 2.8 V with the interval of 1 minute for the first hour. The potential at the working electrode was then held at 2.8 V for the next 30 minutes. The cathode assemblage was removed from the cell, washed with distilled water and dilute acetic acid to remove any residual salt. To minimize the electrochemical corrosion during washing, the pellets were cathodically protected by applying 1.2 V versus Ag/AgCl electrode. The samples were then rinsed in ethanol and dried in a vacuum oven. The TEM image (FIG. 10) showed nanoparticles of iron on the graphene surface. The magnetic properties of the resultant hybrid were easily detected by a magnet.

(46) Thus, the method of the present invention provides a convenient, safe and efficient way of producing, in a single step, hybrid materials comprising graphene and metal-containing nanoparticles. As is clear from the TEM image, dispersion of the nanoparticles is good.

(47) There was no evidence of breakdown/decomposition of the liquid electrolyte.

Example 8

(48) The experimental procedure in Example 7 was followed except that a eutectic mixture of SnCl.sub.2-Et.sub.3NHCl was used as electrolyte. The TEM image (FIG. 11) revealed the deposition of Sn species nanoparticles on the surface of the graphene.

(49) Again, this demonstrates the versatility of the method of the present invention. The provision of well dispersed nanoparticles, particularly metal-containing nanoparticles and especially Sn-containing nanoparticles in the context of a clean and scalable process represents a valuable contribution to the art.

(50) There was no evidence of breakdown/decomposition of the liquid electrolyte.

Example 9

(51) The experimental procedure in Example 6 was followed except that a potential deference of 4 V was applied between graphite cathode and Pt anode for 2 hours. The SEM images (FIGS. 12A and 12B) showed graphene sheets heavily decorated by Sn-containing species.

(52) There was no evidence of breakdown/decomposition of the liquid electrolyte.

Example 10

(53) A two-terminal cell was used. The cathode was made of graphite rod wrapped in a membrane and the anode was Pt wire. The electrolyte used was 1 M LiCl in a mixture of methyl urea and choline chloride (2:1 by weight). The applied voltage was 15 V for 4 hours. The powder was subjected to several steps of washing and drying before conducting Raman analysis. The Raman collected spectrums indicate a symmetric 2D band at 2655 cm.sup.1 confirming the graphenic nature of the produced powder.

Example 11

(54) The procedure of Example 10 was followed except that the electrolyte was 1M LiCl in acetamine-choline chloride eutectic mixture. The Raman spectrum of the produced powder showed typical features of graphene materials with G, and 2D bands at 1885 and 2660 cm.sup.1 respectively.

Example 12

(55) The electrochemical experiments were conducted in a molten salt reactor consisting of a vertical tubular alumina vessel with 70 mm inside diameter and 500 mm height placed inside a vertical tube furnace. About 200 mm of the top part of the vessel was kept outside the furnace and the vessel was sealed by silicone stopper that worked as the lid. The electrolyte used was a mixture of aluminum sodium chloride (NaAlCl.sub.4) and triethylamine hydrochloride (9:1 by wight) at 180 C. The electrochemical experiment was conducted using a two-terminal programmable power supply, the anode was a Pt wire, and the cathode was a graphite rod. Both electrodes were attached to 3 mm diameter stainless steel rods that work as a current collectors and was attached to the reactor lid. The electrolyte was heated at 1 C./min up to the target temperature and kept at that temperature for 30 minutes before introducing the cell electrodes. A potential difference of 3 V was applied for 4 hours. The cell was then was allowed to cool in the furnace under a continuous flow of argon gas. The cell was then removed from the furnace, and washed with water and dilute hydrochloric acid solution to dissolve the solidified salts. The liquor was then filtered to separate the produced powder. The powder was then dried over night at 60 C. and subjected to analysis. The G band (1,580 cm.sup.1) and 2D band are clearly visible in all cases. It was possible to detect flakes with intense symmetric 2D band at 2650 cm.sup.1.

Example 13

(56) The procedure of Example 12 was followed except that the electrolyte was a eutectic mixture of LiClKCl at 600 C. The applied voltage was switched between 0.5 V and 3V every 20 second for 4 hours. The powdered collected from the electrolyte was found to be few layers graphene from analysis of the Raman spectrum.

(57) Other Experiments

(58) Data from preliminary experiments indicates that the general electrochemical approach described herein can also be used to exfoliate other 2D materials, especially those having graphite-like structures. An example of a suitable 2D material is MoS.sub.2. Indeed, the present inventors have acquired TEM and AFM data which support a conclusion that exfoliation of MoS.sub.2 occurs in the electrochemical cell.

REFERENCES

(59) The following documents are all incorporated herein by reference. [Novoselov 2004] Electric field effect in atomically thin carbon films, K. S. Novoselov et al., Science, 2004, 5296, pp 666-669. [Ruoff 2009] Chemical methods for the production of graphenes, S. Park and R. S. Ruoff, Nature Nanotechnology, 2009, DOI:10.1038/nnano.2009.58 [Bae 2010] Roll-to-roll production of 30-inch graphene films for transparent electrodes, S. Bae et al. Nature Nanotechnology, 2010, DOI: 10.1038/NNANO.2010.132 [Ang 2009] High-Throughput Synthesis of Graphene by Intercalation-Exfoliation of Graphite Oxide and Study of Ionic Screening in Graphene Transistor, P. K. Ang et al., ACS Nano, 2009, 3(11), pp. 3587-3594 [Wang 2010] Direct exfoliation of natural graphite into micrometre size few layers graphene sheets using ionic liquids, X. Wang et al., Chem. Commun., 2010, 46, pp. 4487-4489 [Liu 2008] N. Liu et al, One-Step Ionic-Liquid-Assisted Electrochemical Synthesis of Ionic-Liquid-Functionalized Graphene Sheets Directly from Graphite. Adv. Funct. Mater. 2008, 18, pp. 1518-1525 [Lu 2009] One-Pot Synthesis of Fluorescent Carbon Nanoribbons, Nanoparticles, and Graphene by the Exfoliation of Graphite in Ionic Liquids, ACS Nano, 2009, 3(8) pp. 2367-2375 [Simonet 1977] J. Simonet and N. Lund, Electrochemical Behavious of Graphite Cathodes in the Presence of Tetralkylammonium Cations, J. Electroanal. Chem., 1977, 75, pp. 719-730 [Hsu, 1995] W. K. Hsu, J. P. Hare, M. Terrones, H. W. Kroto and D. R. M. Walton, Condensed phase nanotubes, Nature, 377, 687 (1995) [Kinloch, 2003] I. A. Kinloch et al, E lectrolytic, TEM and Raman studies on the production of carbon nanotubes in molten NaCl, Carbon, 2003, 41, pp. 1127-1141 [Coleman 2008 & 2009] Y. Hernandez, et al, Nat. Nanotechnol., 2008, 3, 563; M. Lotya, et al, J. Am. Chem. Soc., 2009, 131, 3611. [Valles 2008] Valles, C. et al. Solutions of negatively charged graphene sheets and ribbons. J. Am. Chem. Soc. 130, 15802-15804 (2008). [Ferrari 2006] Ferrari, A. C. et al. Raman Spectrum of Graphene and Graphene Layers. Phys Rev Lett, 97 (2006), 187401 [Hao 2010] Hao, Y et al., Probing Layer Number and Stacking Order of Few-Layer Graphene by Raman Spectroscopy, Small, 2010, 6(2), 195-200 [Wang 2011] Wang, J., et al., High-yield synthesis of few-layer graphene flakes through electrochemical expansion of graphite in propylene carbonate electrolyte, JACS, 2011, 133, 8888-8891 [Gao 2008] Gao, L., et al., Electrodeposition of Aluminum from AlCl3/Et3NHCl Ionic Liquids, Acta Physico-Chimica Sinica, Volume 24, Issue 6, June 2008, Pages 939-944 [Simate 2010] The production of carbon nanotubes from carbon dioxide: challenges and opportunities, Simate, G. S. et al. Journal of Gas Chemistry, 2010, 19(5), 453; [DeWulf 1989] Electrochemical and Surface Studies of Carbon Dioxide Reduction to Methane and Ethylene at Copper Electrodes in Aqueous Solution, J. Electrochem. Soc. 1989, 136(6), 1686. [Suzuki 2012] Journal of Physics: Conference Series, 2012, 379(1):012038. [Malard 2009] Malard L. M. et al., Raman spectroscopy in graphene, Phys. Rep. 473, 51-87 (2009). [Zhong 2012] Y. L. Zhong, T. M. Swager, J. Am. Chem. Soc. 2012, 134, 17896-17899 [Huang 2012] Huang et al, J. Mater. Chem., 2012, 22, 10452-10456 [Zhang 2012] Zhang et al, Chem. Soc. Rev., 2012, 41, 7108-7146. [Geim 2009] Geim A K. Graphene: Status and Prospects. Science 2009; 324:1530. [Matis 2011] Matis B R, Burgess J S, Bulat F A, Friedman A L, Houston B H, Baldwin J W. Surface Doping and Band Gap Tunability in Hydrogenated Graphene. ACS Nano 2011; 6:17. [Jaiswal 2011] Jaiswal M, Yi Xuan Lim C H, Bao Q, Toh C T, Loh K P, zyilmaz B. Controlled Hydrogenation of Graphene Sheets and Nanoribbons. ACS Nano 2011; 5:888. [Gao 2011] Gao H, Wang L, Zhao J, Ding F, Lu J. Band Gap Tuning of Hydrogenated Graphene: H Coverage and Configuration Dependence. The Journal of Physical Chemistry C 2011; 115:3236. [Sofo 2007] Sofo J O, Chaudhari A S, Barber G D, Graphane: A two-dimensional hydrocarbon. Phys. Rev. B 2007; 75. [Elias 2009] 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. [Ryu 2008] Ryu S, Han M Y, Maultzsch J, Heinz T F, Kim P, Steigerwald M L, Brus L E. Reversible Basal Plane Hydrogenation of Graphene. Nano Letters 2008; 8:4597. [Guisinger 2009] Guisinger N P, Rutter G M, Crain J N, First P N, Stroscio J A. Exposure of Epitaxial Graphene on SiC(0001) to Atomic Hydrogen. Nano Letters 2009; 9:1462. [Wang 2010] Wang Y, Xu X, Lu J, Lin M, Bao Q, Ozyilmaz B, Loh K P. Toward High Throughput Interconvertible Graphane-to-Graphene Growth and Patterning. ACS Nano 2010; 4:6146. [Poh 2012] Poh H L, Sanek F, Sofer Z, Pumera M. High-pressure hydrogenation of graphene: towards graphane. Nanoscale 2012; 4:7006. [Yang 2012] Yang Z, Sun Y, Alemany L B, Narayanan T N, Billups W E. Birch Reduction of Graphite. Edge and Interior Functionalization by Hydrogen. Journal of the American Chemical Society 2012; 134:18689. [Schfer] Schfer R A, Englert J M, Wehrfritz P, Bauer W, Hauke F, Seyller T, Hirsch A. On the Way to GraphanePronounced Fluorescence of Polyhydrogenated Graphene. Angewandte Chemie International Edition 2013; 52:754.