Jiangping Tu

Bismuth telluride nanotubes and the effects on the thermoelectric properties of nanotube-containing nanocomposites

Nanotubes of quasilayered bismuth telluride compound were prepared by hydrothermal synthesis. Nanotubes have diameters smaller than 100nm and spiral tube-walls. The low-dimensional morphology and hollow structure enable bismuth telluride nanotubes to be a potential thermoelectric material with a high figure of merit due to the efficient phonon blocking effect. The experimental results show that the addition of nanotubes leads to a remarkable decrease in the thermal conductivity with the electrical conductivity much less affected and thus to an increase in the figure of merit of the Bi2Te3-based material.

Green and Facile Fabrication of Hollow Porous MnO/C Microspheres from Microalgaes for Lithium-Ion Batteries

Hollow porous micro/nanostructures with high surface area and shell permeability have attracted tremendous attention. Particularly, the synthesis and structural tailoring of diverse hollow porous materials is regarded as a crucial step toward the realization of high-performance electrode materials, which has several advantages including a large contact area with electrolyte, a superior structural stability, and a short transport path for Li(+) ions. Meanwhile, owing to the inexpensive, abundant, environmentally benign, and renewable biological resources provided by nature, great efforts have been devoted to understand and practice the biotemplating technology, which has been considered as an effective strategy to achieve morphology-controllable materials with structural specialty, complexity, and related unique properties. Herein, we are inspired by the natural microalgae with its special features (easy availability, biological activity, and carbon sources) to develop a green and facile biotemplating method to fabricate monodisperse MnO/C microspheres for lithium-ion batteries. Due to the unique hollow porous structure in which MnO nanoparticles were tightly embedded into a porous carbon matrix and form a penetrative shell, MnO/C microspheres exhibited high reversible specific capacity of 700 mAh g(-1) at 0.1 A g(-1), excellent cycling stability with 94% capacity retention, and enhanced rate performance of 230 mAh g(-1) at 3 A g(-1). This green, sustainable, and economical strategy will extend the scope of biotemplating synthesis for exploring other functional materials in various structure-dependent applications such as catalysis, gas sensing, and energy storage.

Hierarchical NiCo2O4@NiCo2O4 Core/Shell Nanoflake Arrays as High-Performance Supercapacitor Materials

Hierarchical NiCo2O4@NiCo2O4 core/shell nanoflake arrays on nickel foam for high-performance supercapacitors are fabricated by a two-step solution-based method which involves in hydrothermal process and chemical bath deposition. Compared with the bare NiCo2O4 nanoflake arrays, the core/shell electrode displays better pseudocapacitive behaviors in 2 M KOH, which exhibits high areal specific capacitances of 1.55 F cm(-2) at 2 mA cm(-2) and 1.16 F cm(-2) at 40 mA cm(-2) before activation as well as excellent cycling stability. The specific capacitance can achieve a maximum of 2.20 F cm(-2) at a current density of 5 mA cm(-2), which can still retain 2.17 F cm(-2) (98.6% retention) after 4000 cycles. The enhanced pseudocapacitive performances are mainly attributed to its unique core/shell structure, which provides fast ion and electron transfer, a large number of active sites, and good strain accommodation.

An investigation of the sliding wear behavior of Cu-matrix composite reinforced by carbon nanotubes

Abstract The friction and wear behavior of Cu-matrix composite reinforced by carbon nanotubes (Nanotube/Cu composite) were investigated. By scanning electron microscopy (SEM) and X-ray diffraction (XRD), the worn surfaces and the worn chips were analyzed. The volume fraction of nanotubes is a main factor for the decrease of the wear rate of The Nanotube/Cu composite, which is associated with carbon nanotubes forming a protective oxide film on the sliding surface of the specimen. The optimum nanotubes content is 12–15%. Both the coefficients of friction and weight loss of the Nanotube/Cu composite are lower than those for Cu-matrix composite reinforced by carbon fiber (CF/Cu) owing to the much high intensity of nanotube.

Freestanding Co3O4 nanowire array for high performance supercapacitors

We report a single-crystalline Co3O4 nanowire array grown on a nickel foam prepared by a hydrothermal synthesis method for supercapacitor application. The Co3O4 nanowires show sharp tips and have an average diameter of 70 nm, and a length up to 25 μm. Impressively, the as-prepared single-crystalline Co3O4 nanowire array exhibits noticeable pseudocapacitive performance with a high capacitance of 754 F g−1 at 2 A g−1 and 610 F g−1 at 40 A g−1 as well as excellent cycling stability. The enhanced supercapacitor performance is due to the unique one-dimensional (1D) architecture, which provides fast diffusion paths for ions and facilitates the electron and ion transfer on the Co3O4/electrolyte interfaces. Moreover, the 1D nanowire array can accommodate the volume expansion and restrain the pulverization and deterioration of Co3O4 during the repeated cycling process, resulting in enhanced cycling stability.

Transition Metal Carbides and Nitrides in Energy Storage and Conversion

High‐performance electrode materials are the key to advances in the areas of energy conversion and storage (e.g., fuel cells and batteries). In this Review, recent progress in the synthesis and electrochemical application of transition metal carbides (TMCs) and nitrides (TMNs) for energy storage and conversion is summarized. Their electrochemical properties in Li‐ion and Na‐ion batteries as well as in supercapacitors, and electrocatalytic reactions (oxygen evolution and reduction reactions, and hydrogen evolution reaction) are discussed in association with their crystal structure/morphology/composition. Advantages and benefits of nanostructuring (e.g., 2D MXenes) are highlighted. Prospects of future research trends in rational design of high‐performance TMCs and TMNs electrodes are provided at the end.

Hierarchically porous NiO film grown by chemical bath deposition via a colloidal crystal template as an electrochemical pseudocapacitor material

Hierarchically porous NiO film has been successfully prepared by chemical bath deposition through monolayer polystyrene sphere template. The film possesses an architecture with a substructure of NiO monolayer hollow-sphere array and a superstructure of porous net-like NiO nanoflakes. The pseudocapacitive behavior of the NiO film is investigated by cyclic voltammograms (CV) and galvanostatic charge-discharge tests in 1 M KOH. The hierarchically porous NiO film exhibits weaker polarization, better cycling performance and higher specific capacitance in comparison with the dense NiO film. The specific capacitance of the porous NiO film is 309 F g−1 at 1 A g−1 and 221 F g−1 at 40 A g−1, respectively, much higher than that of the dense NiO film (121 F g−1 at 1 A g−1 and 99 F g−1 at 40 A g−1). The hierarchically porous architecture is responsible for the enhancement of electrochemical properties.

Solution synthesis of metal oxides for electrochemical energy storage applications

This article provides an overview of solution-based methods for the controllable synthesis of metal oxides and their applications for electrochemical energy storage. Typical solution synthesis strategies are summarized and the detailed chemical reactions are elaborated for several common nanostructured transition metal oxides and their composites. The merits and demerits of these synthesis methods and some important considerations are discussed in association with their electrochemical performance. We also propose the basic guideline for designing advanced nanostructure electrode materials, and the future research trend in the development of high power and energy density electrochemical energy storage devices.

Tribological Behavior of Carbon-Nanotube-Filled PTFE Composites

Carbon nanotube/polytetrafluoroethylene (CNT/PTFE) composites with different volume fractions were prepared and their friction and wear properties were investigated using a ring-on-block under dry conditions. It was found that CNTs signifi-cantly increased the wear resistance of PTFE composites and decreased their coefficient of friction. PTFE composites with 15–20 vol.% CNTs exhibited very high wear resistance. The significant improvements in the tribological properties of CNT/PTFE composites are attributed to the super-strong mechanical properties and the very high aspect ratio of CNTs. The CNTs greatly reinforce the structure of the PTFE-based composites and thereby greatly reduce the adhesive and plough wear of CNT/PTFE composites. The CNTs are released from the composite during sliding and transferred to the interface of the friction couples. They thus serve as spacers, preventing direct contact between the mating surfaces and thereby reducing both wear rate and friction coefficient.

Hydrothermally synthesized WO3 nanowire arrays with highly improved electrochromic performance

A hexagonal WO3 nanowire array film is obtained using a template-free hydrothermal method by adding ammonium sulfate as a capping agent. The WO3 nanowires grown vertically on a FTO-coated glass substrate are woven together at the surface of the film, forming well-aligned arrays at the bottom part and a porous surface morphology. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) reveal that each nanowire is a hexagonal single crystal and their long axes are oriented toward the [0001] direction. Due to the highly porous surface, good contact with the conductive substrate and large tunnels of the hexagonal-structured WO3, a fast switching speed of 7.6 and 4.2 s for coloration and bleaching, respectively, and a high coloration efficiency of 102.8 cm2C−1 are achieved for the WO3 nanowire array film.