Jianlin Huang

Morphology and crystal phase evolution induced performance enhancement of MnO2 grown on reduced graphene oxide for lithium ion batteries

MnO2 nanorods grown on reduced graphene oxide (MnO2-NR/rGO) have been synthesized through a hydrothermal treatment of the reaction product between KMnO4 and 2-(N-morpholino)ethanesulfonic acid in the presence of graphene oxide. When tested as an anode in a lithium-ion battery (LIB), the obtained MnO2-NR/rGO exhibits a significant enhancement in electrochemical performance, especially after being discharged/charged for 300 cycles. Characterization of the microscopic features suggests that the morphology and crystal structure of the MnO2 nanorods evolve gradually during cycling, transforming the product of the MnO2-NR/rGO into a unique electrode architecture consisting of well-separated rGO coated with well-crystallized λ-MnO2 after 300 cycles. The significantly enhanced electrochemical performance of the MnO2-NR/rGO electrode after 300 cycles is attributed mainly to the resulting electrode architecture, which enhances the interaction between MnO2 and rGO, reduces the charge transfer resistance across the MnO2/rGO interface, and makes the rGO readily accessible to lithium ion storage. The demonstrated specific capacity and rate capability are among the best ever reported for transition metal oxide based electrodes for LIBs.

General synthesis of MFe2O4/carbon (M = Zn, Mn, Co, Ni) spindles from mixed metal organic frameworks as high performance anodes for lithium ion batteries

A general method has been developed for the synthesis of the spindle-like MFe2O4/C (M = Zn, Co, Ni, Mn). The synthetic procedure involves the preparation of mixed metal organic frameworks (i.e. Fe2M-MOFs) and their subsequent calcination. The obtained MFe2O4/C spindles show an intriguing structure, which consists of carbon coated secondary MFe2O4 nanoparticles with an interconnected carbon network. This makes them highly promising as the active materials for various applications with enhanced performance. For example, when used as the anode for lithium ion batteries (LIBs), the MFe2O4/C spindles exhibit higher reversible capacities and higher cycling stability in comparison to the MFe2O4 materials reported previously. Most interestingly, these MFe2O4/C spindles exhibit good morphology preservation during cycling. This shows that the volumetric expansion of MFe2O4 upon lithiation leads to the leaching of some active materials to the surface of the MFe2O4/C spindles along the percolation channels. This alleviates the volumetric expansion energy and prevents the structural destruction of MFe2O4/C spindles. The leached active materials do not detach from the MFe2O4/C spindles and participate in the lithiation/delithiation reactions throughout the whole cycling process, giving the MFe2O4/C spindles with high specific capacity and good durability. The approach reported here is highly versatile and might be applicable to the synthesis of other MFe2O4/C spindles for various applications.

Naked Au nanoparticles monodispersed onto multifunctional cellulose nanocrystal–graphene hybrid sheets: towards efficient and sustainable heterogeneous catalysts

A simple, clean, and efficient synthesis method has been developed for deposition of ∼3 nm monodisperse “naked” gold nanoparticles (Au NPs) onto cellulose nanocrystal–graphene (CNC–G) hybrid sheets without the use of additional reducing and capping agents. The as-prepared catalysts (Au@CNC–G) were examined using FT-IR spectroscopy, thermogravimetric analysis (TGA), atomic force microscopy, electron microscopy, wide-angle X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). After some optimization, the Au@CNC–G catalyst exhibited robust catalytic activity, impressive stability, and good flexibility for the “one-pot” reaction of an alkyne, an amine, and an aldehyde (A3-coupling) in water. The catalytic activity of the Au@CNC–G catalyst could be attributed to the synergistic effect derived from the coexistence of CNC and graphene. The Au3+ ions could be in situ reduced to create fine Au NPs and simultaneously anchored on the surface of CNC–G hybrid sheets through coordination, leading to the uniform dispersion of the Au NPs. Moreover, the Au@CNC–G catalyst could be conveniently recycled and reused many times, thus lowering the cost and minimizing the environmental pollution caused by organic solvents and heavy metal ions.