No abstract

This study reports the preparation of a set of hybrid materials consisting of Molybdenum disulfide (MoS2) nanopatches on reduced graphene oxide (rGO) nanosheets by applying the microwave specific heating of...

A study of the detonation synthesis method to make graphene and the properties of the resulting graphene is presented. The gaseous precursors are mixtures of oxygen and acetylene with oxygen/carbon molar ratios of O/C = 0.25 to 0.75. Chamber pressure and temperature data indicate pressures ≤ 300 psi and temperatures of 2550 ± 100K after initiation of the reaction mixture. The graphene material collected from the chamber after the detonation was characterized by Raman, XRD (X‐ray diffraction), BET, SEM (scanning electron microscopy), TEM (transmission electron microscopy), and so on. The material properties divide into two groups: low O/C (≤ 0.45) and high O/C (≥ 0.5). Low O/C graphene appears as a low density, aerosol gel with ∼8 weakly associated, disordered turbostratic layers with a lateral extent of 20 to 30 nm. High O/C graphene appears as a denser powder with ∼30 weakly associated turbostratic layers, with a lateral extent of 100 to 200 nm. We conclude, as we have previously, that the high detonation temperature during the reaction is the primary reason that graphene is formed rather than soot. Differentiation into two types of graphene products is hypothesized to be a result of aggregation kinetics to form a static gel that pre‐empts layering (stacking) when O/C is low.

Rechargeable aqueous zinc ion batteries (AZIB) are an emerging topic in the battery research due to the high volumetric capacity of the zinc anode (5855 mAh/cm3), low cost, environmental friendliness and safety. But the development of the zinc ion batteries has been hindered by the slow insertion/extraction kinetics of the multivalent Zn2+ ions in the host structure mainly due to the larger ionic radii of the hydrated zinc ion (~4.60 Å) and stronger electrostatic interaction of the divalent metal cation with the host structure that monovalent Li+ ions. These factors make the existing Li-ion battery (LIB) cathode materials unfit for the intercalation/deintercalation of Zn2+ ion. Transition metal dichalcogenides like Molybdenum disulfide (MoS2) have caught the attention as a host for both monovalent and divalent ion storage due to their two-dimensional layered structure and high theoretical specific capacity for Li-ion storage (670 mAh g-1). The MoS2 structure consists of a two-dimensional (2D) layered structure with a layer of molybdenum atoms covalently bonded between two layers of sulfur atoms. The triatomic layers of MoS2 are linked by weak van der Waals forces similar to graphene, which can effectively accommodate the volume expansion to facilitate reversible intercalation/deintercalation of metal ions. Despite the advantages, MoS2 suffers from low electrical conductivity and pulverization of the structure after few intercalation/deintercalation cycles which causes rapid capacity fading. These problems can be mitigated by modifying the structure through (1) increasing the interlayer spacing (2) introducing active defects in the MoS2 structure to enhance Zn2+ ion adsorption, and (3) forming a hybrid structure with carbonaceous materials to improve the electrical conductivity, mechanical strength, and structural stability of MoS2 layers. Among which, defect engineering has been recently explored as an effective approach to enhancing the specific capacity of MoS2 towards the storage of monovalent and divalent ions including Li+, Na+, Zn2+ ions.In this work, the preparation of a set of hybrid materials consisting of Molybdenum disulfide (MoS2) nanopatches on reduced graphene oxide (rGO) nanosheets with controllable defect density and its impact on the storage of Li+ and Zn2+ ions will be presented and discussed. The MoS2/rGO hybrid materials are synthesized by applying the novel microwave specific heating of graphene oxide and molecular molybdenum precursors followed by a thermal annealing in 3% H2 and 97% Ar. The microwave process converts graphene oxide to ordered rGO nanosheets that are sandwiched between uniform thin layers of amorphous Molybdenum trisulfide (MoS3). The subsequent thermal annealing converts the intermediate layers into MoS2 nanopatches with 2D layered structures whose defect density is tunable by controlling the annealing temperature at 250°C (MoS2/rGO-250), 325°C (MoS2/rGO-325) and 600°C (MoS2/rGO-600), respectively. The defect-free MoS2/rGO-600 material performs well as an anode for Li+ io...

Rechargeable aqueous zinc ion batteries are an emerging topic in the battery research due to its high volumetric capacity (5855 mAh/cm3), low cost, environmental friendliness and safety. But the development of the zinc ion batteries have been seriously hindered by the slow insertion/extraction kinetics of the multivalent Zn2+ ions in the host structure. Two-dimensional (2D) transition metal oxides are intensely studied for various energy storage applications such as batteries and supercapacitors but controlled synthesis and tunable nanoscale properties are still a challenge. Herein we present and discuss the self-assembly of a hybrid material of microwave-exfoliated Vanadium pentoxide (V2O5) nanoribbons (NRs) on graphene oxide (GO) nanosheets as a potential host for zinc ion storage. Vanadium pentoxide have several advantages such as high discharge capacity (294 mAhg-1) and large abundance but suffers from low electrical conductivity and poor stability. Using a thermal treatment, the GO template is converted to reduced graphene oxide (rGO) which improves the electrical conductivity of the hybrid. Multiple divalent cations such as Zn2+ and Mn2+ have been used in the self-assembly process to bind the negatively charged V2O5 NRs and GO nanosheets to improve the stability of the hybrid and accommodate the intercalation/deintercalation of the Zn2+ ions. Incorporation of 0.0357 M Mn2+ along with 0.10 M Zn2+ in the assembly process has been found to form a stoichiometric composition of Mn0.15Zn0.08V2O5 by XPS, which provides the high specific capacity of 295 mAh g-1 at 0.5 A g-1 and a high stability with the capacity retention of ~81.3% after 500 cycles at 4 A g-1.