Jiaqin Yang

Solvothermal synthesis of hierarchical flower-like β-NiS with excellent electrochemical performance for supercapacitors

A hierarchical flower-like β-NiS architecture has been successfully synthesized via a solvothermal method with diethanolamine as the coordination agent and solvent. When evaluated as an electrode material for supercapacitors, impressive electrochemical performances are achieved, with high specific discharge capacitances of 857.76 F g−1 at 2 A g−1 and 512.96 F g−1 at 5 A g−1.

Facile synthesis and superior supercapacitor performances of three-dimensional cobalt sulfide hierarchitectures

Formation of three-dimensional cobalt sulfide hierarchitectures through a mechanism similar to Ostwald ripening has been investigated. Electrochemical measurements reveal that the CoS1.097nanostructure exhibits superior supercapacitor performances with high specific capacitances (555 F g−1 at 5 mA cm−2 and 464 F g−1 at 100 mA cm−2) and excellent cycle life in 2 M KOH solution.

General One-Pot Template-Free Hydrothermal Method to Metal Oxide Hollow Spheres and Their Photocatalytic Activities and Lithium Storage Properties

A general and facile one-pot template-free hydrothermal strategy has been developed to synthesize various metal oxide (TiO2, SnO2 and α-Fe2O3) hollow spheres with unified morphologies. The formation of hollow structure involves a trifluoroacetic acid (TFA)-assisted Ostwald ripening process. Photocatalytic activities of the as-prepared TiO2 product are evaluated by the photodegradation of Rhodamine B (RhB), which the TiO2 hollow spheres obtained from 450 °C thermal treatment exhibit higher photocatalytic activity than Degussa P25. In addition, electrochemical measurements demonstrate that all of the as-prepared metal oxides hollow spheres have the potential applications in lithium-ion battery. We have a great expectation that this synthesis strategy can afford a new universal route for functional metal oxide hollow materials preparation without using template.

Facile carbonaceous microsphere templated synthesis of Co3O4 hollow spheres and their electrochemical performance in supercapacitors

Co3O4 hollow spheres assembled from nanoparticles have been successfully synthesized by a one-pot hydrothermal carbonization and calcination method. In this method, carbon spheres obtained through hydrothermal carbonization at a low temperature of 140 °C are used as sacrificial templates. The carbonization process was monitored by Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy. Both the carbon sphere soft templates and the NH3 released from hexamethylenetetramine play key roles in the formation of these novel hollow structures. The formation of the Co3O4 hollow spheres using hydrothermal carbon spheres as templates can be attributed to the synergetic effect of metal ion adsorption and heterogeneous nucleation of Co(OH)2, which is different from the traditional adsorption theory. The as-obtained Co3O4 hollow microspheres exhibit excellent cycling performance and good rate capacity when used as electrode materials in supercapacitors, which can be attributed to the small particle size of Co3O4 and the sufficient space available to interact with the electrolytes. This facile strategy may be extended to synthesize other metal oxide hollow spheres, which may find application in sensors and catalysts due to their unique structural features.Graphical abstract

NiO nanomaterials: controlled fabrication, formation mechanism and the application in lithium-ion battery

A variety of mesoporous nickel oxide (NiO) nanostructures have been prepared by annealing the corresponding β-Ni(OH)2 precursor nanostructures synthesized through manipulating the reaction parameters (e.g., alkaline sources, reactant concentration). Moreover, the formation mechanisms of different nanostructures were tentatively discussed, based on their morphological evolution processes. Furthermore, experimental results indicate that the electrochemical performances of as-synthesized NiO nanomaterials are correlated to their morphologies and reaction scheme, and their cyclic stability should be improved for potential application in lithium-ion batteries.

Controllable hydrothermal synthesis of manganese dioxide nanostructures: shape evolution, growth mechanism and electrochemical properties

In this work, four well-defined morphologies, including nanorod, nanowire, nanoflower and nanowall, of MnO2 nanostructures with different crystal phases (α-, β-, and δ-MnO2) have been synthesized employing a simple hydrothermal process. The samples are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), and Brunauer–Emmett–Teller (BET) spectrometry. Our experimental results demonstrate that the concentration of KMnO4 plays a key role in forming different shapes and phases of MnO2 nanostructures. Specifically, the K+ concentration can affect the crystal phase of MnO2 seeds in the nucleation processes and the decomposition rate of MnO4− can influence the number of MnO2 nuclei at the initial nucleating stage and also can affect the subsequent crystal growth process. Moreover, the effects of reaction temperature on the morphology of the δ-MnO2 nanowall are systematically studied. The electrochemical performances of the as-prepared MnO2 as the positive material of rechargeable Li-ion batteries have also been researched. It is found that the δ-MnO2 nanowall possesses largely enhanced electrochemical activity compared to α-MnO2 nanowires and β-MnO2 nanorods. The vast difference in electrochemical activity is discussed in terms of the morphology, crystal phase and specific surface area of MnO2 nanostructures. It is highly expected that these findings are useful in understanding the formation of MnO2 nanocrystals with different morphologies, which are also applicable to other metal oxides nanocrystals.

Facile preparation and electrochemical properties of hierarchical chrysanthemum-like WO3·0.33H2O

A symmetrical 3D chrysanthemum-like WO3·0.33H2O hierarchitecture has been prepared via a facile hydrothermal approach. A growth mechanism has been proposed for the hierarchitecture. With preferable electrochemical properties, WO3·0.33H2O displays potential application in lithium ion batteries.

Superior gas-sensing and lithium-storage performance SnO2 nanocrystals synthesized by hydrothermal method

SnO2 nanocrystals with diameters of 2.5–4.1 nm were successfully synthesized by a facile hydrothermal method. The as-synthesized SnO2 nanocrystals were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), transmission electronic microscopy (TEM) and high-resolution transmission electronic microscopy (HR-TEM) and nitrogen adsorption. Moreover, it was found that acetic acid played a crucial role in determining the dispersion and crystal size of the SnO2 samples. In addition, the as-synthesized SnO2 nanocrystals not only displayed excellent gas-sensing properties such as very fast response and recovery speed, excellent repeatability and good selectivity, but also high discharging capacity and good cycling performance in lithium ion batteries.

Morphology-controllable ZnO rings: Ionic liquid-assisted hydrothermal synthesis, growth mechanism and photoluminescence properties

Morphology-controllable ZnO rings with high crystallinity were synthesized by a simple hydrothermal approach, using ionic liquid (through surface energy conditioning) as a stabilizing agent or template. The growth mechanism of these ring-like ZnO crystals was explored based on first-principles calculations and a series of controlled experiments where the concentration of the ionic liquid 1-propyl-3-methylimidazolium bromide ([C3mim]Br) was tuned. With the increase of the concentration of [C3mim]Br, the aspect ratio of ZnO product increases, and the morphology changes from ring to tube. FTIR and theoretical calculations indicate that [C3mim]Br prefers to adsorb on the ZnO (100) facets, which lowers the surface energy so as to protect the lateral facets from growing too fast to vanish and result in the formation of disk-like structures. Furthermore, the relatively high density of the defects and dislocations on the exposed (000) facet at the center of ZnO disks results in a higher etching rate of (000) facet by H+, driven by the reduction of strain energy associated with dislocations. Therefore, the selective etching of ZnO disks leads to formation of ring-like structure for final products. With the increase of the concentration of [C3mim]Br, the selective adsorption of [C3mim]Br will also promote the growth along the [0001] direction to form a tube-like structure. In addition, the photoluminescence spectra reveal that the as-prepared ZnO rings exhibit blue emission related to their oxygen vacancy as well as various other barely avoidable impurities and defects.

Surfactant-free synthesis of Zn2SnO4 octahedron decorated with nanoplates and its application in rechargeable lithium ion batteries

We demonstrate the fabrication of a Zn2SnO4 octahedron decorated with nanoplates via a facile surfactant-free hydrothermal method. A high initial discharge capacity of 1629.9 mA h g−1 is obtained and the capacity is maintained at 642.2 mA h g−1 after 20 cycles at the current density of 50 mA g−1. The excellent electrochemical performance suggests that the electrode is a promising candidate for the next generation lithium ion batteries (LIBs).