1393wileyonlinelibrary.com the practical applications of SIBs have been hamstrung by the lack of suitable anode materials to host Na + , which has a larger radius than that of Li + . Graphite with a highly ordered structure is considered to be not suitable to accommodate Na + because Na hardly forms staged intercalation compounds with graphite. [ 2 ] Twodimensional layered metal sulfi des (LMSs) with analogous structures to graphite, such as MoS 2 , [ 3 ] WS 2 , [ 4 ] SnS, [ 5 ] and SnS 2 , [ 6 ] have been reported as potential electrode materials for SIBs. The open framework of these types of materials allows Na + to insert reversibly with acceptable mobilities. However, the further application of 2D LMSs is impeded by their inherent limitations. First, these semiconductor metal sulfi des have inherently low electronic conductivity, which affects their electrochemical performances for Na + storage. Second, owing to the high surface energy and interlayer van der Waals attractions, [ 7 ] these thermally unstable 2D nanomaterials have a tendency to restack to minimize the surface energy. Furthermore, the signifi cant volume change and mechanical stress as a concomitant of sodium-ion insertion and extraction can induce the failure of the electrode and the loss of contact between active materials and the current collector, resulting in poor cycling stability.Graphene has established itself as a promising candidate to circumvent these challenges. For example, WS 2 /graphene, [ 4 ] SnS/graphene, [ 5b ] and SnS 2 /graphene [ 6 ] nanocomposites have already been successfully applied as anode materials for SIBs, showing a synergistic effect for sodium-ion storage, including improved capacity, rate capability, and cycling stability. In these reports, it is generally recognized that the enhanced electrochemical performances are attributed to the good electronic conductivity and mechanical resilience of graphene as 2D conformal building blocks for these layered sulfi des. However, a fundamental understanding of the exact interaction mechanism between LMSs and graphene for improving Na + storage performance is still not clear. The heterointerface between LMSs and graphene has been proven to contribute to novel properties and new functionalities that cannot be achieved by individual constituting materials. [ 8 ] Therefore, investigations Graphene has been widely used as conformal nanobuilding blocks to improve the electrochemical performance of layered metal sulfi des (MoS 2 , WS 2 , SnS, and SnS 2 ) as anode materials for sodium-ion batteries. However, it still lacks in-depth understanding of the synergistic effect between these layered sulfi des and graphene, which contributes to the enhanced electroactivity for sodium-ion batteries. Here, MoS 2 /reduced graphene oxide (RGO) nanocomposites with intimate two-dimensional heterointerfaces are prepared by a facile one-pot hydrothermal method. The heterointerfacial area can be effectively tuned by changing the ratio of MoS 2 to RGO. When used as anode materials for sodiu...
Abstract:A principle of enhancement CO adsorption was developed theoretically by using density functional theory through doping Al into graphene. The results show that the Al doped graphene has strong chemisorption of CO molecule by forming Al−CO bond, where CO onto intrinsic graphene remains weak physisorption. Furthermore, the enhancement of CO sensitivity in the Al doped graphene is determined by a large electrical conductivity change after adsorption, where CO absorption leads to increase of electrical conductivity upon via introducing large amount of shallow acceptor states. Therefore, this newly developed Al doped graphene would be an excellent candidate for sensing CO gas.
Although the reversible wettability transition between hydrophobic and hydrophilic graphene under ultraviolet (UV) irradiation has been observed, the mechanism for this phenomenon remains unclear. In this work, experimental and theoretical investigations demonstrate that the H2O molecules are split into hydrogen and hydroxyl radicals, which are then captured by the graphene surface through chemical binding in an ambient environment under UV irradiation. The dissociative adsorption of H2O molecules induces the wettability transition in graphene from hydrophobic to hydrophilic. Our discovery may hold promise for the potential application of graphene in water splitting.
A high-capacity hydrogen storage medium-Al-adsorbed graphene-is proposed based on densityfunctional theory calculations. We find that a graphene layer with Al adsorbed on both sides can store hydrogen up to 13.79 wt % with average adsorption energy −0.193 eV/ H 2 . Its hydrogen storage capacity is in excess of 6 wt %, surpassing U. S. Department of Energy ͑DOE's͒ target. Based on the binding-energy criterion and molecular-dynamics calculations, we find that hydrogen storage can be recycled at near ambient conditions. This high-capacity hydrogen storage is due to the adsorbed Al atoms that act as bridges to link the electron clouds of the H 2 molecules and the graphene layer. As a consequence, a two-layer arrangement of H 2 molecules is formed on each side of the Al-adsorbed graphene layer. The H 2 concentration in the hydrogen storage medium can be measured by the change in the conductivity of the graphene layer.
Graphane, hydrogenated graphene, was very recently synthesized and predicted to have great potential applications. In this work, we propose a new promising approach for hydrogenation of graphene based on density functional theory (DFT) calculations through the application of a perpendicular electric field after substitutionally doping by nitrogen atoms. These DFT calculations show that the doping by nitrogen atoms into the graphene layer and applying an electrical field normal to the graphene surface induce dissociative adsorption of hydrogen. The dissociative adsorption energy barrier of an H 2 molecule on a pristine graphene layer changes from 2.7 to 2.5 eV on N-doped graphene, and to 0.88 eV on N-doped graphene under an electric field of 0.005 au. When increasing the electric field above 0.01 au, the reaction barrier disappears. Therefore, N doping and applying an electric field have catalytic effects on the hydrogenation of graphene, which can be used for hydrogen storage purposes and nanoelectronic applications.
Innovation in transition-metal nitride (TMN) preparation is highly desired for realization of various functionalities. Herein, series of graphene-encapsulated TMNs (FeMnCo-N@C) with well-controlled morphology have been synthesized through topotactic transformation of metal-organic frameworks in an N atmosphere. The as-synthesized FeMnCo-N@C nanodices were systematically characterized and functionalized as Fenton-like catalysts for catalytic bisphenol A (BPA) oxidation by activation of peroxymonosulfate (PMS). The catalytic performance of FeMnCo-N@C was found to be largely enhanced with increasing Mn content. Theoretical calculations illustrated that the dramatically reduced adsorption energy and facilitated electron transfer for PMS activation catalyzed by MnN are the main factors for the excellent activity. Both sulfate and hydroxyl radicals were identified during the PMS activation, and the BPA degradation pathway mainly through hydroxylation, oxidation, and decarboxylation was investigated. Based on the systematic characterization of the catalyst before and after the reaction, the overall PMS activation mechanism over FeMnCo-N@C was proposed. This study details the insights into versatile TMNs for sustainable remediation by activation of PMS.
The oxidation of CO molecules on Al-embedded graphene has been investigated by using the first principles calculations. Both Eley-Rideal (ER) and Langmuir-Hinshelwood (LH) oxidation mechanisms are considered. In the ER mechanism, an O 2 molecule is first adsorbed and activated on Al-embedded graphene before a CO molecule approaches, the energy barrier for the primary step (CO + O 2 / OOCO) is 0.79 eV. In the LH mechanism, O 2 and CO molecules are firstly co-adsorbed on Al-embedded graphene, the energy barrier for the rate limiting step (CO + O 2 / OOCO) is only 0.32 eV, much lower than that of ER mechanism, which indicates that LH mechanism is more favourable for CO oxidation on Al-embedded graphene. Hirshfeld charge analysis shows that the embedded Al atom would modify the charge distributions of co-adsorbed O 2 and CO molecules. The charge transfer from O 2 to CO molecule through the embedded Al atom plays an important role for the CO oxidation along the LH mechanism.Our result shows that the low cost Al-embedded graphene is an efficient catalyst for CO oxidation at room temperature.
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