Wei-Tang Yao

Flexible all-solid-state high-power supercapacitor fabricated with nitrogen-doped carbon nanofiber electrode material derived from bacterial cellulose

To meet the pressing demands for portable and flexible equipment in contemporary society, it is strongly required to develop next-generation inexpensive, flexible, lightweight, and sustainable supercapacitor systems with large power densities, long cycle life, and good operational safety. Here, we fabricate a flexible all-solid-state supercapacitor device with nitrogen-doped pyrolyzed bacterial cellulose (p-BC–N) as the electrode material via a low-cost, eco-friendly, low-temperature, and scalable fabrication hydrothermal synthesis. The pliable device can reversibly deliver a maximum power density of 390.53 kW kg−1 and exhibits a good cycling durability with ∼95.9% specific capacitance retained after 5000 cycles. Therefore, this nitrogen-doped carbon nanofiber electrode material holds significant promise as a flexible, efficient electrode material.

Synthesis of unique ultrathin lamellar mesostructured CoSe2-amine (protonated) nanobelts in a binary solution.

Unique ultrathin CoSe(2)-DETA (protonated) mesostructured nanobelts with multiple stacked layers which are highly parallel to the axial direction have been first prepared in a binary solution composed of organic amine and water under mild solvothermal conditions. This synthesis strategy may open new avenues toward the syntheses of other new mesostructured nanomaterials, which may bring new nontrivial functionalities.

A Methanol‐Tolerant Pt/CoSe2 Nanobelt Cathode Catalyst for Direct Methanol Fuel Cells

Direct methanol fuel cells (DMFCs) have received considerable and persistent attention, because methanol is an abundant, inexpensive liquid fuel that is easier to store and transport than hydrogen. Despite the great advances made in this field, two main issues affecting efficiency and power density must still be considered, that is, sluggish kinetics of the fuel-cell anode reaction and so-called methanol crossover. The small methanol molecule can easily cross over from the anode to the cathode side through the polymer membranes of DMFCs, and then reacts directly with the cathode catalyst and O2 to decrease the cathode potential and thus reduce fuel efficiency. One approach to addressing this problem is the development of methanol-tolerant cathode catalysts for the oxygen reduction reaction (ORR). Recent research on methanol-tolerant catalysts has shown that transition metal macrocycles, Ru-based chalcogenides, and some platinumbased alloys all show methanol tolerance while retaining catalytic activity for the ORR. Nevertheless, disadvantages still exist. For instance, Pt-free electrocatalysts often show much lower activity and inferior long-term stability under fuel-cell conditions; Pt-based alloy cathode electrocatalysts are available only with low metal loading and thus are not quite suitable for DMFCs. Therefore, development of novel methanol-tolerant electrocatalysts with considerable stability and high ORR activity is important. Currently, cobalt chalcogenides are attracting enormous interest as new ORR electrocatalysts. Cobalt sulfides such as Co3S4 and Co9S8 are rather active for four-electron ORR in acidic electrolytes. In addition, cobalt selenides and tellurides show electrocatalytic ORR activity in nanocrystal form. In particular, the CoSe2/C nanoparticles fabricated by Alonso-Vante et al. exhibit good methanol tolerance. However, the ORR activity of these materials is still low, and they are far from DMFC application. Recently, we described a synthetic strategy that allows large-scale fabrication of ultrathin lamellar mesostructured CoSe2/diethylenetriamine (DETA) nanobelts in a binary solution. The lamellar nanobelts have several advantages over previous cobalt chalcogenides: homogeneously distributed, copious surface amino groups that allow loading of highly dispersed metal nanoparticles, and exceptional stability under strongly acidic conditions. With these merits, we expect that methanoltolerant electrocatalysts with high performance can be designed on the basis of this material. Here we report that a new methanol-tolerant Pt/CoSe2 nanobelt electrocatalyst for DMFC applications can be synthesized by in situ loading of Pt nanoparticles on CoSe2/ DETA nanobelts through a polyol reduction approach. The Pt/CoSe2 electrocatalysts display relatively high ORR catalytic activity in acidic medium. More importantly, the nanohybrid structures are highly resistant to methanol, even at concentrations of up to 5m. Mesostructured CoSe2/DETA nanobelts were first synthesized in high yield by a simple solvothermal strategy reported previously. Then, Pt NPs were synthesized in situ on the surface of CoSe2/DETA nanobelts through a facile polyol reduction approach. The multilayered CoSe2/DETA nanobelts are highly acid resistant, although selenides are generally vulnerable to attack by acids. The H2SO4 treatment process is followed the recent report by Kanatzidis et al. on treatment of mesostructured c-C20PyPtSnSe materials with strong acids. The H2SO4-treated sample retains the singlecrystalline nature and growth direction of the original CoSe2/ DETA nanobelts (see Supporting Information Figure S1). High-resolution (HR) TEM studies along the lateral thickness direction of H2SO4-treated CoSe2/DETA nanobelts showed that interlayer distance decreased from 1.08 to 0.67 nm (see Supporting Information Figure S1d). In fact, acid treatment is a simple ion-exchange process. Only protonated DETA molecules between two neighboring CoSe2 slabs are replaced by protons, and then the flexible inorganic skeleton contracts accordingly. The results suggest that the nanobelts have exceptional stability under strongly acidic conditions and retain their shape, composition, structural integrity, and single-crystalline nature. Moreover, they have a high BET surface area of 77 m g 1 (see Supporting Information Figure S2). Loading of Pt NPs on the surface of CoSe2/DETA nanobelts was confirmed by XRD patterns (see Supporting Information Figure S3c, left). The TEM images in Figure 1a and b show that Pt NPs are homogeneously decorated on the backbone of CoSe2/DETA nanobelts. The average size of the Pt NPs is about 8.3 nm (inset in Figure 1a), which corresponds [*] Dr. M.-R. Gao, Q. Gao, J. Jiang, C.-H. Cui, W.-T. Yao, Prof. Dr. S. H. Yu Division of Nanomaterials & Chemistry Hefei National Laboratory for Physical Sciences at Microscale Department of Chemistry, University of Science and Technology of China Hefei 230026 (P. R. China) Fax: (+ 86)551-360-3040 E-mail: shyu@ustc.edu.cn Homepage: http://staff.ustc.edu.cn/~ yulab/

Templating synthesis of uniform Bi2Te3 nanowires with high aspect ratio in triethylene glycol (TEG) and their thermoelectric performance

Highly uniform Bi2Te3 nanowires with a length of tens of micrometres and a diameter of 15–17 nm can be synthesized through a simple and fast solution process by using ultrathin Te nanowires as sacrificial templates. Different from previous template-directed hydrothermal synthesis, here we used heating mantle as the reactor for preparing Bi2Te3 nanowires, which not only makes the reaction perform more efficiently and be finished within one hour, but also can achieve more uniform nanowires. As-synthesized Bi2Te3 nanowires have a hexagonal-phase single crystalline structure. It was found that using triethylene glycol (TEG) as solvent and precise controlling reaction temperature and time were crucial to obtain high-quality single crystal Bi2Te3 nanowires. The formation process of Bi2Te3 nanowires was believed to include both Kirkendall effect and Ostwald ripening, according to the experimental observations. Compared with other Bi2Te3 nanostructures and bulk Bi2Te3 materials, the thermal conductivity of Bi2Te3 nanowire pellet decreased evidently, verifying that one-dimensional thermoelectric nanomaterials indeed exhibit lower thermal conductivity.

In situ controllable synthesis of magnetite nanocrystals/CoSe2 hybrid nanobelts and their enhanced catalytic performance

Fe3O4 nanoparticles (NPs) with sizes of ca 5.3, 6.6, and 9.8 nm can be successfully loaded on the surface of CoSe2-DETA hybrid nanobelts via a facile thermal reduction process in polyol solution. The resulting multifunctional nanocomposites are superparamagnetic at room temperature. Most interestingly, the electrocatalytic activity for the O2 reduction reaction (ORR) of the constructed Fe3O4-decorated CoSe2 nanobelts yield a decent enhancement compared with original CoSe2-DETA catalysts, i.e., the onset potential and current density show 1.01 mA cm−2 and 0.05 V increase at 0.3 V, 1600 rpm, respectively. Additionally, the number of electrons transferred (n) increases from 2.1 to 3.6 after integrating with Fe3O4 nanoparticles. The work described here has provided a promising route to the design and development of new Pt-free catalysts with high-performance by introducing other cheap NPs.

Sacrificial Templating Synthesis of Hematite Nanochains from [Fe18S25](TETAH)14 Nanoribbons: Their Magnetic, Electrochemical, and Photocatalytic Properties†

Unique hematite nanochains self-assembled from α-Fe(2)O(3) nanoparticles can be synthesized by thermal decomposition of [Fe(18)S(25)](TETAH)(14) as an appropriate nanoribbon precursor (TETAH = protonated triethylenetetramine). Magnetic studies have revealed greatly enhanced coercivity of the 1D hematite nanochains compared with that of dispersed α-Fe(2)O(3) nanoparticles at low temperature, which may be attributed to their increased shape anisotropy and magnetocrystalline anisotropy. The photocatalytic properties of the hematite nanochains have been studied, as well as their electrochemical properties as cathode materials of lithium-ion batteries. The results have shown that both properties are dependent on the BET specific surface areas of the 1D hematite nanochains.

Controllable Synthesis of Zinc-Substituted α-and β-Nickel Hydroxide Nanostructures and Their Collective Intrinsic Properties

A new controllable homogeneous precipitation approach has been developed to synthesize zinc-substituted nickel hydroxide nanostructures with different Zn contents from a zinc nanostructured reactant. As typical layered double hydroxides (LDHs), zinc-substituted nickel hydroxide nanostructures can be formulated as NiZnx(Cl)y(OH)2(1+x)-y.z H2O (x=0.34-0.89, y=0-0.24, z=0-1.36). The structure and morphology of zinc-substituted nickel hydroxide nanostructures can be systematically controlled by adjustment of the zinc content. The effects of temperature and the amounts of ammonia and zinc nanostructured precursor on the reaction were systematically investigated. In our new method, although zinc-substituted alpha-and beta-nickel hydroxides have the typical 3D flowerlike architecture and stacks-of-pancakes nanostructures, respectively, their growth processes are different from those previously reported. A coordinative homogeneous precipitation mechanism is proposed to explain the formation process of zinc-substituted nickel hydroxide nanostructures. The zinc-substituted nickel hydroxide nanostructures exhibit some interesting intrinsic properties, and changing the zinc content can effectively tune their optical, magnetic, and electrical properties.

Selective Synthesis of Fe7Se8 Polyhedra with Exposed High‐Index Facets and Fe7Se8 Nanorods by a Solvothermal Process in a Binary Solution and Their Collective Intrinsic Properties

Fe(7)Se(8) polyhedra with high-index facets and Fe(7)Se(8) nanorods can be selectively synthesized by a solvothermal reaction in a mixed solvent of diethylenetriamine (DETA) and deionized water (DIW). It is found that the morphologies of Fe(7)Se(8) nanocrystals can be effectively controlled by adjusting the volume ratio of DETA and DIW. The unusual polyhedral crystals are bounded by two {001} and twelve {012} facets. The intrinsic properties of Fe(7)Se(8) nanocrystals have been investigated. Magnetic measurements indicate that the obtained polyhedra and nanorods show a weak ferromagnetic ordering at room temperature. In particular, a new photoluminescence emission at 403 nm from the Fe(7)Se(8) nanocrystals has been observed. The described solvothermal reaction in a mixed solvent may be extended to the synthesis of other transition-metal chalcogenide crystals with controlled shape, facets, and structure, which may bring new functionalities.

Coupling Microbial Growth with Nanoparticles: A Universal Strategy To Produce Functional Fungal Hyphae Macrospheres

Macroscale assembly of nanoscale building blocks is an intriguing way to translate the unique characteristics of individual nanoparticles into macroscopic materials. However, the lack of the efficient universal assembly strategy seriously hinders the possibility of macroscale architectures in practical applications. Herein, we develop a general, environment-friendly, and scalable microbial growth method for the construction of macroscopic composite assemblies with excellent mechanical strength by in situ integrating various types of nanoparticles into fungal hyphae (FH) macrospheres. Notably, the size of the FH-based composite spheres and the loading amount of the nanoparticles with different dimensions can be well tuned by controlling the cultivation time and the dosage of nanoparticles, respectively. Interestingly, bifunctional FH-based core-shell macrospheres can also be achieved by programmed assembling two different kinds of nanoparticles in the cultivation process. The produced multifunctional FH-based composite spheres exhibit wide potential applications in magnetic actuation, photothermal therapy, and contaminant adsorption, etc.

Self-catalytic synthesis of hierarchical vanadium nitride/carbon superconducting nanocomposites

An easy way to produce VN nanocomposites at relatively low temperature (800 °C) using simple precursors is presented. A self-catalytic growth approach has been developed for spontaneous preparation of superconducting VN/C nanocomposites composed of VN nanoparticles and well-defined carbon nanofibers. The carbon nanofibers were found to grow by a self-catalytic process through tiny VN nanocrystals. In this case, a homogeneous gel-like starting product has been formed that is converted by calcination into the corresponding metal nitride, without any preliminary treatments or further purification. The samples were characterized by XRD, TEM, SEM, and BET. The as-obtained nanocomposite shows an onset superconducting temperature at ∼9 K, which is similar to that reported for bulk VN. The procedure has been shown to be rather general and it was possible to open a new avenue toward the scale-up syntheses of other new transition metal nitride nanocomposites.