Limin Ma

MOF-derived NixCo1−x(OH)2 composite microspheres for high-performance supercapacitors

NixCo1−x(OH)2 composite microspheres with uniform sizes are successfully synthesized with the assistance of alkali solution by employing a bimetallic Co–Ni–metal organic framework (Co–Ni–MOF) as both the precursor and the self-sacrificing template. The as-obtained NixCo1−x(OH)2 composite demonstrates excellent electrochemical performance, including a high specific capacitance of 1235.9 F g−1 at a current density of 0.5 A g−1, good electrochemical stability, with ∼73% retention of its initial capacitance after 10 000 cycles, and a high rate capability; this composite exhibits great application prospects as a novel electrode material for supercapacitors.

Covalent Functionalization of Fluorinated Graphene and Subsequent Application as Water-based Lubricant Additive

Although the fluorinated graphene (FG) possesses numerous excellent properties, it can not be really applied in aqueous environments due to its high hydrophobicity. Therefore, how to achieve hydrophilic FG is a challenge. Here, a method of solvent-free urea melt synthesis is developed to prepare the hydrophilic urea-modified FG (UFG). Some characterizations via transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier transfer infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and thermo gravimetric analysis (TGA) demonstrate that the urea molecules can covalently functionalize the FG and the hydrophilic UFG can be prepared. According to the tribological tests run on an optimal-SRV-I reciprocation friction tester, it can be found that the antiwear ability of water can be largely improved by adding the appropriate UFG. When the concentration of UFG aqueous dispersion is 1 mg/mL, the sample of UFG-1 has the best antiwear ability with a 64.4% decrease of wear rate compared with that of the pure water (UFG-0), demonstrating the prepared UFG can be used as a novel and effective water-based lubricant additive.

High efficiency shear exfoliation for producing high-quality, few-layered MoS2 nanosheets in a green ethanol/water system

This work presented a feasible strategy to generate molybdenum disulfide (MoS2) nanosheets by a direct liquid shear exfoliation technique in a green mixed solvent system of ethanol/water. The volume ratio of ethanol/water and the initial concentration of the bulk MoS2 powders were found to have significant impacts on the final exfoliation yield. The best ratio and initial concentration for optimal shear exfoliation were finally selected as 45 vol% and 10 mg mL−1, respectively. According to the proper shear strength and matching viscosity, systematic analysis on the exfoliation mechanism indicated that shear and collision effects would play the major role when the shearing occurred at a high speed of 10 000 rpm. The higher cumulative yield and better quality (up to 30% after 10 times of shear cycling, comparatively large sizes d ∼ 4 μm) were confirmed by detailed experimental characterizations. Moreover, the photothermal performance was also investigated and the prepared MoS2 nanosheets exhibited great efficiency in transforming near-infrared light into heat. It is expected to be a promising strategy for large-scale production of MoS2 nanosheets with excellent properties in a low-cost and green solvent system.

Fluorine Doping Strengthens the Lithium-Storage Properties of the Mn-Based Metal–Organic Framework

The electrochemical properties of the metal-organic framework (MOF)-based composite as electrode material can be significantly improved by means of partial destruction of the full coordination of linkers to metal ions and replacing with other small ions, which make metal centers become more accostable and consequently more effective for the lithiation/delithiation process. In this paper, F- was chosen to replace some of the benzenedicarboxylate (BDC) linkers because of its better interaction with the Li+ than the oxide ion. Whats more, the formed M-F bond promotes the Li+ to transfer at the active material interface and protects the surface from HF attacking. The as-synthesized F-doped Mn-MOF electrode maintains a reversible capacity of 927 mA h g-1 with capacity retention of 78.5% after 100 cycles at 100 mA g-1 and also exhibits a high discharge capacity of 716 mA h g-1 at 300 mA g-1 and 620 mA h g-1 at 500 mA g-1 after 500 cycles. Even at 1000 mA g-1, the electrode still maintains a high reversible capacity of 494 mA h g-1 after 500 cycles as well as a Coulombic efficiency of nearly 100%, which is drastically increased compared with pure Mn-MOF material as expected.

Graphene-wrapped CNT@MoS2 hierarchical structure: synthesis, characterization and electrochemical application in supercapacitors

Layered transition metal dichalcogenides (TMDs) have attracted widespread attention for developing electrochemical energy storage due to their unique graphite-like structure and high theoretical capacity. However, the semiconductor character of TMDs affects their electrical conductivity, causing low specific capacitance, rapid capacity fading and poor cyclic stability. Herein, a hierarchical graphene-wrapped CNT@MoS2 (CMG) electrode material has been fabricated aiming at enhancing the conductivity and structural stability during continuous charge–discharge processes, thus improving its electrochemical properties. As a novel electrode material, the prepared CMG electrode delivers a high specific capacitance of 498 F g−1 and excellent long-term cycle-life stability (only 5.7% loss of its initial capacitance after 10 000 cycles at a high current density of 5 A g−1), as well as improved rate performance, indicating that such a composite material is an ideal electrode material for supercapacitors. Its outstanding electrochemical performance can be ascribed to an expanded interlayer spacing of MoS2 and its unique hierarchical architecture. More importantly, this method can be readily extended to the construction of other TMD-based electrodes which were hampered in electrochemical applications owing to their poor electrical conductivity.

Graphene oxide-templated growth of MOFs with enhanced lithium-storage properties

Herein, Mn-MOF/RGOn composites have been successfully synthesized using terephthalic acid non-covalent functionalized graphene oxide (GO) sheets acting as efficient nucleation sites and structure-directing templates to direct the growth of MOFs. The electrochemical performance of the Mn-MOF/RGOn composite electrode was much better than that of the pristine Mn-MOF when used as a candidate anode material for lithium-ion batteries due to the synergetic advantages of RGO and Mn-MOF, improved electrical conductivity, and mechanical flexibility of Mn-MOF. Especially, the Mn-MOF/RGO10 composite electrode maintains a reversible discharge capacity of 715 mA h g−1 with a capacity retention of 98% after 100 cycles at 100 mA g−1 and also exhibits a high discharge capacity of 485 mA h g−1 at 300 mA g−1, 432 mA h g−1 at 500 mA g−1 while still maintaining 348 mA h g−1 at 1000 mA g−1 after 500 cycles, which is greatly higher as compared to that of the pure Mn-MOF material as expected.