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: 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: 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.