Graphane Research

ABSTRACT: Graphene’s chemical versatility is unique among two-dimensional materials. One of the simplest and most well-studied chemical modifications of graphene is hydrogenation. The electronic, optical, and mechanical properties of hydrogenated graphene can differ significantly from those of unmodified graphene, and the tunability of these properties has played a major factor in the broad interest in hydrogenated graphene throughout the scientific community. Here, the author presents a practical review of the state of the art in hydrogenated graphene research. The target audience is the researcher who is interested in working with hydrogenated graphene but lacks practical experience with the material. The author focuses on considerations of the working scientist, highlighting subtleties in preparation and characterization that are generally only gained by experience in the laboratory. In addition, the author enumerates a number of the most important categories of results concerning the properties of hydrogenated graphene. In particular, the author examines what these results mean for potential near- and long-term applications of hydrogenated graphene.

ABSTRACT: Graphene-based materials have attracted considerable attentions due to their unique properties. However, the negligible and uncontrollable band gap of graphene greatly limits its further applications. Hydrogenation is a facile and well-studied chemical modification technique to widen the band gap of graphene with a high tunability. Herein, we reveal the structure, properties, and forming mechanism of hydrogenated graphene, summarize recent advances in its synthesis and engineering in terms of plasma hydrogenation, thermal cracking, Birch reduction, and electrochemical reduction, and discuss its potential applications in hydrogen storage, electronics, biomedicines, etc. In the last part, we further outline the challenges and future research directions for highly efficient graphene hydrogenation.

ABSTRACT: Atomically thin crystals have recently been the focus of attention, in particular, after the synthesis of graphene, a monolayer hexagonal crystal structure of carbon. In this novel material class, the chemically derived graphenes have attracted tremendous interest. It was shown that, although bulk graphite is a chemically inert material, the surface of single layer graphene is rather reactive against individual atoms. So far, synthesis of several graphene derivatives have been reported such as hydrogenated graphene ‘graphane’ (CH), fluorographene (CF), and chlorographene (CCl). Moreover, the stability of bromine and iodine covered graphene were predicted using computational tools. Among these derivatives, easy synthesis, insulating electronic behavior and reversibly tunable crystal structure of graphane make this material special for future ultra‐thin device applications. This overview surveys structural, electronic, magnetic, vibrational, and mechanical properties of graphane. We also present a detailed overview of research efforts devoted to the computational modeling of graphane and its derivatives. Furthermore recent progress in synthesis techniques and possible applications of graphane are reviewed as well.

ABSTRACT: Nanosized and crystalline sp3-bonded carbon materials were prepared over large surface areas up to ∼33 × 51 µm2 from the exposure of few-layer graphene (FLG) to H radicals produced by the hot-filament process at low temperature (below 325 °C) and pressure (50 Torr). Hybrid materials were also obtained from the partial conversion of FLG. sp3-C related peaks from diamond and/or lonsdaleite and/or hybrids of both were detected in UV and visible Raman spectra. Csingle bondH bonding was directly detected by Fourier Transform Infrared (FTIR) microscopy over an area of ∼150 µm2 and one single component attributed to sp3-Csingle bondH mode was detected in the Csingle bondH stretching band showing that carbon is bonded to one single hydrogen and strongly suggesting that the sp3-C materials obtained are ultrathin films with basal planes hydrogenated. The experimental results are compared to computational predictions and comprehensively discussed. Those materials constitute new synthetic carbon nanoforms after fullerenes, nanodiamonds, carbon nanotubes and graphene. This opens the door to new research in multiple areas for the development of new potential applications and may have wide scientific impact, including for the understanding of extraterrestrial diamond-related structures and polytype formation mechanism(s).

ABSTRACT: The effective storage of H2 gas represents one of the major challenges in the wide spread adoption of hydrogen powered fuel cells for light vehicle transportation. Here, we investigate the merits of chemically hydrogenated graphene (graphane) as a means to store high-density hydrogen fuel for on demand delivery. In order to evaluate hydrogen storage at the macroscale, 75 g of hydrogenated graphene was synthesized using a scaled up Birch reduction, representing the largest reported synthesis of this material to date. Covalent hydrogenation of the material was characterized via Raman spectroscopy, X-ray diffraction (XRD), and thermogravimetric analysis (TGA). We go on to demonstrate the controlled release of H2 gas from the bulk material using a sealed pressure reactor heated to 600 °C, identifying a bulk hydrogen storage capacity of 3.2 wt%. Additionally, we demonstrate for the first time, the successful operation of a hydrogen fuel cell using chemically hydrogenated graphene as a power source. This work demonstrates the utility of chemically hydrogenated graphene as a high-density hydrogen storage medium, and will be useful in the design of prototype hydrogen storage systems moving forward.

ABSTRACT: The major challenge in the application of hydrogen powered fuel cells for military applications, is the safe and effective high-density storage of the hydrogen. To this end, NRL has demonstrated for the first time the large-scale synthesis and characterization of chemically hydrogenated graphite in order to quantify its bulk hydrogen storage capacity and understand its thermal decomposition under relevant operating conditions. Post-synthetic purification strategies were developed to reduce residual alkali-based by-products persisting from the synthesis of the chemically hydrogenated graphite. Multi-gram quantities of hydrogenated graphite samples were quantitatively analyzed using a high pressure hydrogen generator. Under an evacuated atmosphere at 550 °C, hydrogenated graphite was found to generate a gas mixture composed of 92% H₂, which was purified using a commercial carbon filter. The H₂ gas generated corresponded to an H₂ storage capacity of 4.26 wt. %.

ABSTRACT: Chemically hydrogenated graphene possesses a theoretical hydrogen storage capacity of 7.7 wt%, and will release H₂ gas upon thermal decomposition, making it an intriguing material for hydrogen storage applications. Recent works have demonstrated that this material can be synthesized at multi-gram scale quantities, and it has already been safely demonstrated as a hydrogen source to power a PEM fuel cell. While these results are promising, further characterization and evaluation of this material as it pertains to hydrogen storage must be carried out. In this work, we characterize various properties of chemically hydrogenated graphene, which will be key in the application of this material as a hydrogen storage medium moving forward. These include: theoretical calculation of the material’s total volumetric energy density, the dependence of both temperature and surrounding atmosphere on the release of hydrogen gas, thermal expansion of the material upon heating, and the activation energy associated with hydrogen release.

ABSTRACT: Graphane, fully hydrogenated graphene with the composition (C1H1)n, has been theoretically predicted but never experimentally realized. Graphane stands out of the variety of heteroatom modified graphene for its well defined structure. Here we show that by employing Birch reduction on graphite nanofibers, one can reach hydrogenation levels close to 100%. We name this material graphane or graphane-like since its composition is relatively close to ideal theoretical stoichiometry C1H1. We systematically study the effect of the size and structure of the starting material and conditions of the synthesis. The morphology and properties of the synthesized graphane-like material are strongly dependent on the structure of the starting material. The extremely highly hydrogenated nanographanes should find applications ranging from nanoelectronics to electrochemistry such as in supercapacitors or electrocatalysts.

ABSTRACT: Many efforts have been devoted to understanding the origin and effects of magnetic moments induced in graphene with carbon atom vacancy, and light adatoms like hydrogen or fluorine. In the meantime, the large negative magnetoresistance (MR) widely observed in these systems is not well understood, nor has it been associated with the presence of magnetic moments. In this paper, we study the systematic evolution of the large negative MR of in-situ hydrogenated graphene in ultrahigh-vacuum (UHV) environment. We find for most combinations of electron density (ne) and hydrogen density (nH), MR at different temperature can be scaled to α=μBB/kB(T−T*), where T* is the Curie-Weiss temperature. The sign of T∗ indicates the existence of tunable ferromagneticlike (T*>0) and antiferromagneticlike (T*<0) coupling in hydrogenated graphene. However, the lack of hysteresis of MR or anomalous Hall effect below |T*| points to the fact that long-range magnetic order did not emerge, which we attribute to the competition of different magnetic orders and disordered arrangement of magnetic moments on graphene. We also find that localized impurity states introduced by H adatoms could modify the capacitance of hydrogenated graphene. This work provides a way to extract information from large negative MR behavior and can be a key to understanding interactions of magnetic moments in graphene.

ABSTRACT: Hydrogenated graphene is an important graphene derivative with semiconductor properties. A novel and convenient approach via defluorination and hydrogenation of fluorographite, not previously used Birch-type reduction, is developed to prepare highly hydrogenated graphene in ethylenediamine at room temperature via wet-chemical reduction of commercially available fluorographite containing electropositive C atoms in polar CF bonds, using NaK alloy as reductant and isopropanol as quenching agent. The hydrogen content of our sample is 7.28 wt%, higher than any value ever reported, and its chemical composition can be identified as (C1.04H)n, which is quite close to theoretical graphane of (C1.00H)n. Moreover, band gap of hydrogenated graphene was found to be highly related with its H content. All these results provide potential resources towards new semiconductor materials and devices.

ABSTRACT: The hydrogenation and deuteration of graphite with potassium intercalation compounds as starting materials were investigated in depth. Characterization of the reaction products (hydrogenated and deuterated graphene) was carried out by thermogravimetric analysis coupled with mass spectrometry (TG-MS) and statistical Raman spectroscopy (SRS) and microscopy (SRM). The results reveal that the choice of the hydrogen/deuterium source, the nature of the graphite (used as starting material), the potassium concentration in the intercalation compound, and the choice of the solvent have a great impact on the reaction outcome. Furthermore, it was possible to prove that both mono- and few-layer hydrogenated/deuterated graphene can be produced.

ABSTRACT: The so-called graphane is a fully hydrogenated form of graphene. Because it is fully hydrogenated, graphane is expected to have a wide bandgap and is theoretically an electrical insulator. The transition from graphene to graphane is that of an electrical conductor, to a semiconductor, and ultimately to an electrical insulator. This unique characteristic of graphane has recently gained both academic and industrial interest. Towards the end of developing novel applications of this important class of nanoscale material, computational modeling work has been carried out by a number of theoreticians to predict the structures and electronic properties of graphane. At the same time, experimental evidence has emerged to support the proposed structure of graphane. This review article covers the important aspects of graphane including its theoretically predicted structures, properties, fabrication methods, as well as its potential applications.

ABSTRACT: Graphane, the fully hydrogenated analogue of graphene, and its partially hydrogenated counterparts are attracting increasing attention. We review here its structure and predicted material properties, as well as the current methods of preparation. Graphane and hydrogenated graphenes are far more complex materials than graphene, expected to have a tuneable band gap via the extent of hydrogenation, as well as exhibit ferromagnetism. The methods for hydrogenated graphene characterization are discussed. We show that hydrogenation methods based on low or high pressure gas hydrogenation lead to less hydrogen saturation than wet chemistry methods based on variations of Birch reduction. The special cases of patterning of hydrogenated graphene strips in a graphene lattice are discussed.