Xuan Du

Preparation of activated carbon hollow fibers from ramie at low temperature for electric double-layer capacitor applications

Activated carbon hollow fibers (ACHFs) with high surface area were prepared from inexpensive, renewable ramie fibers (RFs) by a single-step activation method under lower temperature than that of other reports. The effects of activation conditions on the pore structure and turbostratic structure of ACHFs were investigated systematically. The results show that ACHFs surface area decreased but micropore volume and conductivity increased as the increase of activation temperature and activation time. The electrochemical measurements of supercapacitors fabricated from these ACHFs electrodes reveal that the electrochemical properties improved with the enhancing of activation degree. However, too high activation temperature can make the ion diffusion resistance increase. It suggests that pore structure and conductivity are as important as surface area to decide the electrochemical performances of ACHFs electrode materials. A maximum capacity of 287 F g(-1) at 50 mA g(-1) was obtained for the ACHFs electrode prepared under suitable conditions.

Pd catalyst supported on a chitosan-functionalized large-area 3D reduced graphene oxide for formic acid electrooxidation reaction

A large-area three-dimensional (3D) reduced graphene oxide (TRGO) material was obtained by facile heat treatment of a two-dimensional (2D) reduced graphene oxide (RGO) material. X-ray diffraction (XRD), scanning electron microscopy (SEM) and nitrogen adsorption results reveal that the new material is composed of small and fluffy graphene nanosheets, with many graphene arrays as well as 3D interconnected macropores and mesopores in some local positions, and possesses an ultrahigh specific surface area (>1000 m2 g−1) and large pore volume. The material was used to support a Pd catalyst for formic acid electrooxidation, demonstrating a much better electrocatalytic activity in terms of the onset potential and peak current density (seven times larger) than that of conventional carbon black, the most popular catalyst support. To tailor the electronic properties, the TRGO material was further functionalized with chitosan (CS). Compared to the Pd loaded on TRGO, Pd nanoparticles supported on the CS-functionalized TRGO show a better catalytic activity and good stability. This work provides a promising catalyst support material for direct formic acid fuel cells.

Effect of the electropulsing on mechanical properties and microstructure of an ECAPed AZ31 Mg alloy

The mechanical properties and corresponding microstructure development of the AZ31 Mg alloy after treatment with equal channel angular pressing (ECAP) and subsequent electropulsing (ECP) was investigated. Comparing the ECAP+ECP-treated AZ31 alloy with the ECAP-treated alloy, the elongation to failure was improved significantly, while the yield stress and the ultimate tensile strength were not decreased, the grain sizes were slightly increased and more homogeneous, and the texture was barely changed. The main mechanism for the evolution of the structures and properties might be ascribed to the increased nucleation rate on recrystallization and the decreased dislocation density during the ECP treatment. It was reason-able to expect that the ECAP+ECP treatment would provide a promising approach for enhancing the mechanical properties of the Mg alloys.

Thermally treated 3-D nanostructured graphene-supported Pd catalyst for significantly improved electrocatalytic performance towards ethanol electrooxidation

Catalyst supports are known to play a critical role in high catalytic performance. A novel nanostructured graphene was obtained by facile thermal treatment of the three-dimensional (3-D) graphene material. X-ray diffraction (XRD), scanning electron microscopy (SEM) and nitrogen adsorption results reveal that the new material is composed of smaller and looser graphene nanosheets, and possesses an ultrahigh specific surface area, large pore volume and rich 3-D interconnected macropores and mesopores. The material was further used to support a Pd catalyst towards ethanol electrooxidation in alkaline media, demonstrating much better electrocatalytic activity in respect of the Pd utility ratio, onset potential and peak current density than that of pristine 3-D graphene material and carbon black, the most popular catalyst support, and thus rendering a promising catalyst support material for fuel cells.

Cauliflower-like Co 3 O 4 /three-dimensional graphene composite for high performance supercapacitor applications

Cauliflower-like Co3O4/three-dimensional (3D) graphene nanocomposite material was synthesized by a facile two-step synthesis route (heat reduction of graphite oxide (GO) and hydrothermal synthesis of Co3O4). The phase composition, morphology, and structure of the as-obtained products were characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD). Electrochemical properties as supercapacitor electrode materials were systematically investigated by cyclic voltammetry (CV) and constant current charge-discharge tests. It was found that the Co3O4/3D graphene composite showed a maximum specific capacitance of 863 Fg-1, which was obtained by means of CVs at a scan rate of 1 mVs-1 in 6 M KOH aqueous solution. Moreover, the composite exhibited improved cycling stability after 1,000 cycles. The good supercapacitor performance is ascribed to the combination of 3D graphene and cauliflower-like Co3O4, which leads to a strong synergistic effect to remarkably boost the utilization ratio of Co3O4 and graphene for high capacitance.

Research on the formation mechanism of composites from lignocelluloses and CaCO3

The purpose of this work is to explore the formation mechanism of lignocellulose composites in ionic liquids, which is very important for the potential applications of lignocellulose composites. In this study, the lignocellulose/CaCO3 composites have been synthesized using different concentrations of CaCO3 by a rapid and green microwave-ionic liquid method. In view of the experimental results and literature, the formation mechanism of the composites from lignocelluloses and CaCO3 was proposed. It is suggested that lignocelluloses accumulated Ca(2+) ions due to the complexation of the Ca(2+) ions and the highly anionic polysaccharide groups of lignocelluloses, and CaCO3 was obtained by the strong electrostatic interactions between carbonate anions and calcium cations. When the content of CaCO3 reached a certain level, the activity of CaCO3 in the composites was mainly as aggregation. Using lignocelluloses instead of cellulose as a template to synthesize the organic-inorganic composites was a facile method, which does not need to separate the lignocelluloses and can utilize all the main components of lignocelluloses.

Recycled LiCoO2 in spent lithium-ion battery as an oxygen evolution electrocatalyst

Lithium cobalt oxide (LCO) is a common cathode material in lithium ion batteries (LIBs). On the other hand, the recycling of electrode materials in LIBs has attracted serious attention due to environmental, resourcing and energy issues. In order to reduce the cost of the recycling and make full use of the transition metal in the cathode materials in LIBs, herein, we developed a simple method to convert the recycled LCO from spent LIBs into an efficient electrocatalyst for oxygen evolution reaction (OER). The long-time cycling of LCO in a LIB would lead to several structural changes in terms of chemical composition, particle size and metal valence etc. The altered structural properties of the recycled LCO with a relatively smaller particle size and activated surface may contribute to enhanced electrocatalytic activity for OER. The electrocatalytic activity improves with the increase of the cycle number of LIBs. As an electrocatalysts for OER, the recycled LCO from spent LIBs after cycling for 500 cycles can deliver a current density of 9.68 mA cm−2 at 1.65 V, which is about 3.8 times that of pristine LCO (2.50 mA cm−2).

Influence of sedimentation on crystallization of charged colloidal particles

The method of density matching between the solid and liquid phases is often adopted to effectively eliminate the effect of sedimentation of suspensions on dynamic behavior of a colloidal system. Experiments on crystallization of charged colloidal microspheres with diameter of 98 nm dispersed in density-matched and -unmatched media (mixtures of H2O and D2O in proper proportion) are compared to examine the influence of sedimentation. Reflection spectra of colloidal suspensions were used to monitor the crystallization process. Results showed that the crystal size of the density-unmatched (namely, in the presence of sedimentation) sample grew faster than that of the density-matched (in the absence of sedimentation) case at the initial stage of the crystallization, and then the latter overtook and outstripped the former. To explain these observations, we assume that in the settling of crystals sedimentation facilitates result in more particles getting into the crystal structures. However, as the crystals increase to varying sizes, the settling velocities become large and hydrodynamic friction strips off some particles from the delicate crystal structures. Overall, the sedimentation appears to accelerate the crystal size growth initially and then retard the growth. In addition, the crystal structures formed under microgravity were more closely packed than that in normal gravity.

Novel palladium-gadolinium (Pd-Gd/C) bimetallic catalysts for electrooxidation of methanol in alkaline media

Pd/C and Pd-Gd/C catalysts were synthesized and their catalytic performance for methanol electrooxidation in alkaline solution was compared. The structure, morphology and nature of surface species of these catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CA), and CO stripping results show that the 20%Pd-10%Gd/C catalyst has better electrocatalytic activity and durability, as well as higher resistance to CO poisoning than that of the 20%Pd/C catalyst. Furthermore, the insight for the promoting effect of Gd on the specific activity is discussed in this work.