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A natural hydrogen donor, i.e., a subfraction of the coker gas oil, was used in thermal upgrading of the Venezuela extra-heavy oil. The role of hydrogen donor was quantitatively studied by a combin...

Graphene is considered to be a promising candidate as electrode material for supercapacitor due to its unique structure and excellent electrochemical properties. Nevertheless, the extremely low bulk packing density of graphene hinders its application. Here, a novel strategy for preparing high density graphene flakes (HDGF) for high-performance supercapacitors is reported. HDGF is simply prepared by shredding thermally reduced graphene oxide film into small pieces. High packing density, as well as fast electron and ion transportation have been achieved simultaneously by breaking the continuity of graphene film, while keeping its dense structure. The as-prepared HDGF exhibits high gravimetric capacitance (237 F g−1) and volumetric capacitance (261 F cm−3) simultaneously, as well as excellent cycling stability with 98% of its initial capacitance after 10,000 cycles. Moreover, the symmetrical supercapacitor using HDGF as the electrode materials can obtain volumetric capacitances of up to 16 Wh L−1 at a power density of 88 W L−1 in the aqueous system. This strategy provides a new way to design high volumetric capacitance supercapacitors for energy storage applications in the future.

Porous silicon–carbon (Si–C) composites have been considered to be one of the most effective architectures to improve the cycle life of Si based anode because of its native ability to accommodate the large volume change during discharge/charge process. It is found that lots of reported porous Si–C electrodes employed large amount of binder materials to enhance the structural stability which significantly decreased gravimetric capacity of the whole electrode with limited active materials. In this work, without loss of active materials, various conducting agents were used to build electrical bridges between porous Si–C composites, which significantly improved the structural stability and hence the cycle life. Due to the increase of connection possibilities, cycle life of zero-dimensional MCMB bridged electrode reaches 80 cycles with a capacity retention of 80%, and it can be further promoted to 200 cycles for the VGCF bridged electrode and 220 cycles for the rGO bridged electrode. This work paves an effective route to construct stable Si electrode with porous structures as building blocks without the decrease of active materials.

1-Thiohydroxypyrene(1) and its two intermediates, 1-pyrenyl-O-thiocarbamate(2) and 1-pyrenyl-S-thiocarbamate(3), were synthesized using 1-hydroxypyrene as the starting material. The key synthetic step is Newman-Kwart rearrangement. The results indicate that the Newman-Kwart rearrangement is more effective in suitable solvent than conventional method based on pure organic compound. The structures of compounds 1–3 were characterized by FTIR, NMR, GC-MS and elementary analysis. The crystal structures of two new compounds(2 and 3) were determined by single crystal X-ray diffraction analysis. The whole synthetic process is simple, mild and with high yield.

The Fe-doping LiMnPO4 (LiMn1−xFexPO4, x ≤ 0.5) nanomaterials are solvothermally synthesized in a mixed solvent of water and polyethylene glycol (PEG). The particle morphology can be controlled simply by adjusting the pH values of precursor suspensions. Electrochemical test shows that LiMn0.9Fe0.1PO4 nanoplates with a thickness of 20–30 nm could deliver the largest discharge capacity, which is attributed to the fast Li+ diffusion in the diffusion path of [010] crystallographic axis along the short radial direction of the nanoplates. It is demonstrated that Fe doping could significantly increase the initial reversible capacity, cycle performance and rate capability. The first discharge capacities of Fe-doped LiMnPO4 are all above 150 mAh g−1 at the discharge rate of 0.05 C. Especially, LiMn0.5Fe0.5PO4 delivers 100% capacity retention with the reversible capacity of 147 mAh g−1 at the discharge rate of 1 C, and losses only about 23.4% capacity with the discharge rate varying from 0.1 C to 5 C. The variation of energy density predicts that LiMn0.5Fe0.5PO4 shows the potential application for high-power devices.

A simple method to prepare nitrogen-doped graphene (NG) by a pressure-promoted process at relatively low temperatures is demonstrated. The NG with an atomic N content higher than 10% can be obtained by heating graphene oxide and NH4HCO3 in a sealed autoclave at a temperature as low as 150 °C. The product exhibits a specific capacitance of 170 F g−1 at 0.5 A g−1 in 5 M KOH, and a high retention rate of 96.4% of its initial capacitance after 10,000 charge/discharge cycles at a current density of 10 A g−1. Such an easy, cost-effective and low-temperature doping process will be promising for preparing devices based on NG.

Ag–graphene/epoxy nanocomposites were prepared by an in situ method using Ag–graphene nanocomposites as additives. The electrical properties of the Ag–graphene/epoxy nanocomposites were investigated by current–voltage ( I – V ) tests. The result showed that the nanocomposites with filler contents between 0.8 and 3.0 wt.% exhibited a varistor effect. This reversible electrical nonlinearity resulted from the defects in the GO-derived graphene structure and the presence of the Ag nanoparticles.