Xiangzhong Ren

Molecular dynamics study on ion diffusion in LiFePO4 olivine materials.

Molecular dynamics (MD) simulations have been employed to investigate the ionic diffusion and the structure of LiFePO 4 cathode material. The results correspond well with the published experimental observations. The simulation results indicated that the diffusion of lithium ions was thermally activated and more significant than those of other ions. Compared with other cathode materials, the shifts of ions were less significant in LiFePO 4. This suggested that LiFePO 4 was more thermally stable. The snapshots of the positions of lithium atoms over a range of the steps provided a microscopic picture and the picture showed the lithium ions migrated through one-dimension channels.

Preparation of well-defined core-shell particles by Cu2+-mediated graft copolymerization of methyl methacrylate from bovine serum albumin.

Small well-defined core-shell poly(methyl methacrylate)-bovine serum albumin (PMMA-BSA) particles have been prepared in a direct one-step graft copolymerization of MMA from BSA at 75 degrees C in water with a trace amount of Cu2+ (5 microM). Initially, BSA generates free radicals and acts as a multifunctional macroinitiator, which leads to the formation of an amphiphilic PMMA-BSA grafting copolymer. Such formed copolymer chains act as a polymeric stabilizer to promote further emulsion polymerization of MMA inside, resulting in surfactant-free stable core-shell particles, confirmed by a transmission electron microscopic (TEM) analysis. The PMMA-BSA copolymers as well as PMMA homopolymer inside the particles were isolated by Soxhlet extraction and characterized by Fourier transform infrared spectroscopy (FT-IR) and thermogravimetry (TG). The highest grafting efficiency was approximately 80%. Effects of the reaction temperature, the MMA/BSA ratio, and the concentrations of Cu2+ and BSA on such core-shell particle formation have been systematically studied. Due to their inert PMMA core and biocompatible BSA shell, these small polymer particles are potentially useful in biomedical applications.

Effects of Fe2O3 content on microstructure and mechanical properties of CaO–Al2O3–SiO2 system

Abstract The effects of Fe 2 O 3 content on the microstructure and mechanical properties of the CaO–Al 2 O 3 –SiO 2 system were investigated by differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), electron spin resonance (ESR), and Mossbauer spectroscopy. The results show that the addition of Fe 2 O 3 does not affect the main crystalline phase in the prepared glasses, but it reduces the crystallisation peak temperature, increases the crystallisation activation energy, and reduces the crystal granularity. The ESR results indicate that Fe 2 O 3 can promote crystallization, as it leads to the phase separation of the CaO–Al 2 O 3 –SiO 2 system due to axial distortion. Moreover, Fe 2 O 3 alters the network structure of the CaO–Al 2 O 3 –SiO 2 system, allowing Fe 3+ to enter octahedral sites that exhibit higher symmetry than tetrahedral sites. All of these factors are favourable to increasing the bending strength. The Mossbauer results reveal that there are two types of coordination for both Fe 3+ and Fe 2+ and the bending strength of the CaO–Al 2 O 3 –SiO 2 system increases with the amount of six-coordinate Fe 3+ . The increasing interaction between Fe 3+ and Fe 2+ can also enhance the bending strength of the CaO–Al 2 O 3 –SiO 2 system. The microhardness of the CaO–Al 2 O 3 – SiO 2 system was determined to be HV 896.9 and the bending strength to be 217 MPa under the heat treatment conditions of nucleation temperature of 700 °C and nucleation time of 2 h, crystallization temperature of 910 °C and crystallization time of 3 h.

Carbon-coated LiFePO4 synthesized by a simple solvothermal method

A LiFePO4/C composite was directly synthesized via a simple solvothermal method. Ferric nitrate nonahydrate, Fe(NO3)3·9H2O, was selected as a low cost iron source in the ethanol process and glucose as the carbon source. Through SEM images, it was found that the concentration of the glucose solution has an important influence on the morphology of particles. The samples were characterized by Raman spectroscopy and TEM measurements, showing the formation of graphitic carbon, which is desirable for its contribution to the electronic conductivity. XPS analysis verified that Fe3+ was almost completely reduced to Fe2+. CV (cyclic voltammetry), EIS (electrochemical impendence spectroscopy), and galvanostatic charge/discharge tests were conducted to further study the electrochemical properties of the LiFePO4/C composite. The results reveal that the LiFePO4/C composite with a rodlike shape has the highest specific capacity of 147 mA h g−1 at 0.1C, and the capacity retention remains 100% after 50 cycles.

Atomistic simulation of defected magnesium hydroxide as flame retardants

The mechanical properties and the point defect energy of magnesium hydroxide (Mg(OH)2) were studied using the molecular dynamics. Moreover, the microelectronic structure of Mg(OH)2 with point defects in the bulk and on its surface were investigated using the first principles. The simulation results indicate that Mg(OH)2 was easily modified by other cations because of its strong, favorable interstitial and substitution defects via point defect energy calculation. Mg(OH)2 can provide high-efficiency flame retardancy because of the strong OH (OH Schottky defect) or H bond (H Frenkel defect and Schottky defect). The potential model of Mg(OH)2 was established, and molecular dynamics simulation was used to investigate the relations between the crystal structure and the mechanical properties. Mg(OH)2 with special morphology such as nano-sheets was a prior consideration to maintain the composite mechanical properties. The detailed electronic structures of Mg(OH)2 with defects were determined. This work may provide theoretical guidance for choosing dopant element and reveal the element doping mechanism of Mg(OH)2.

Electrospun NiCo 2 S 4 with extraordinary electrocatalytic activity as counter electrodes for dye-sensitized solar cells

The performance of dye-sensitized solar cells (DSSCs) is critically dependent on the catalytic activity of their counter electrode (CE) materials. There are great research interests to develop alternative CE materials to replace the conventional Pt electrode. Herein, nickel cobalt sulfide (NiCo2S4, NCS) particles were prepared through sulfurization of NiCo2O4 (NCO) electrospun nanofibers. The bimetallic sulfide was used as CE for DSSC and exhibited an excellent photoenergy conversion efficiency (PCE) of 7.12%, which is higher than the dye-sensitized solar cells using NCO (5.24%) and Pt CEs (7.05%). Systematic electrochemical characterization suggests that this extraordinary performance of NCS might be related to the improved electrocatalytic ability and electrical conductivity. In view of the low-cost synthesis and outstanding electrochemical performance, the NCS counter electrode would hold great promise for applications in dye-sensitized solar cells.

Preparation of PPy film and its Application to Glucose Biosensor

Polypyrrole film was obtained by Chronopotentiometry method of electrochemical polymerization, with paratoluenesulfonic acid as supporting electrolyte and triple-electrode as working system. The polypyrrole film was characterized by infrared spectra (IR) and Scan electron microscope (SEM); And how its electrical conductivity affected by polymerization temperature and pyrrole concentration was studied. A glucose oxidase electrode with polypyrrole film as immobilizing carrier was prepared by a multiple-step electrochemical polymerization. The effects of reaction conditions such as temperature, solution pH, glucose concentration on the electrode bioelectrochemical response were discussed. Experimental results showed that the linear response range of glucose oxidase electrode was 1.0 times 104 ~2.0 times 10-2 mol/L and the detection limit was 1.0 times 10-7mol/L. Its response time was 9 seconds.

Spinel photocatalysts for environmental remediation, hydrogen generation, CO2 reduction and photoelectrochemical water splitting

Over the past few decades, owing to their unique functional properties such as physical, chemical, optical and electronic properties, spinel materials have attracted significant scientific attention in heterogeneous photocatalyst research. Here, we review the main fundamental understanding of the correlations between the performance of spinel structures and their particle shape, size, chemical composition, and photo-Fenton reactions for photocatalytic applications; these include photocatalytic dye degradation for environmental remediation, photocatalytic hydrogen generation, CO2 reduction and photoelectrochemical water splitting. In addition, the key factors and essential strategies to improve their performance and functionality are discussed in detail. Future research pathways and perspectives on the progress of these high performance and cost effective renewable energy materials are provided, along with the improvements in material properties that are necessary to replace current commercial energy materials. It is envisioned that further investigations should focus on surface modification, integrating conductive matrixes and regulating the spinel composition, which will make spinels promising photocatalysts.

PdNi alloy decorated 3D hierarchically N, S co-doped macro–mesoporous carbon composites as efficient free-standing and binder-free catalysts for Li–O2 batteries

A novel free-standing and binder-free air electrode with excellent electrochemical performance was designed for highly reversible Li–O2 batteries. The 3D hierarchically N, S co-doped macro–mesoporous carbon (NSMmC) was deposited on carbon paper (CP) via a template method, and then uniformly decorated with PdNi nanoparticles. The macropores of the porous carbon can provide enough space to accommodate discharge products, while the interconnected pores and channels efficiently facilitate oxygen and electrolyte diffusion. The introduction of PdNi nanoparticles greatly reduce the charge transfer resistance, resulting in the improvement of electron mobility of the whole cathode. Compared with Pd–NSMmC/CP and NSMmC/CP cathodes, the PdNi–NSMmC/CP cathode shows considerable enhancement of Li–O2 battery performance. The ultrafine and evenly distributed PdNi nanoparticles can not only provide enough catalytic sites, but can also tailor the discharge products into a cage-like morphology, which provides enough channels for electron and lithium ion transport. Moreover, the smaller size of the cage-like Li2O2 makes it decompose more easily, resulting in lower charge overpotential. This study provides a promising strategy to design 3D structured air cathodes for Li–O2 batteries with high electrocatalytic performance.

LiFePO4/RGO composites synthesized by a solid phase combined with carbothermal reduction method

ABSTRACT LiFePO4/reduced graphene oxide composites (LiFePO4/RGO) were synthesized via a simple solid phase combined with carbothermal reduction method. The samples were characterized by X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). Furthermore, cyclic voltammetry (CV), electrochemicaal impendence spectroscopy (EIS) and galvanostatic charge/discharge tests were conducted to further study the electrochemical properties of LiFePO4/RGO composites. The initial discharge specific capacity of LiFePO4/RGO was 151.5 mAh g−1 at 0.1C, and after 50 cycles, it still remains 149.2 mAh g−1. The results reveal that LiFePO4/RGO composites improved the discharge specific capacity and rate charge-discharge performance.