Xianghua Zeng

One-pot construction of three dimensional CoMoO4/Co3O4 hybrid nanostructures and their application in supercapacitors

A facile one-pot hydrothermal method was developed to synthesize a CoMoO4/Co3O4 hybrid nanostructure where CoMoO4 nanosheets were supported by a hierarchical framework assembled by Co3O4 nanorods. The morphology and structure of this three dimensional nanocomposite were characterized in detail and a rational growth mechanism was proposed based on them. The unique structural features of our CoMoO4/Co3O4 hierarchical nanohybrid allow for high specific surface and multiple faradaic redox reactions for electrode materials of supercapacitors. Consequently, a high specific capacitance (1062.5 F g−1 at the current density of 1 A g−1) and an excellent cyclic performance (90.38% of the initial capacitance retained after 2000 cycles at a current density of 20 A g−1) were obtained. In addition, an asymmetric supercapacitor with high energy density of 31.64 W h kg−1 was achieved at a power density of 7270 W kg−1. This work thus provides an excellent candidate for high-performance supercapacitor fabrication.

Nanoplate-Built ZnO Hollow Microspheres Decorated with Gold Nanoparticles and Their Enhanced Photocatalytic and Gas-Sensing Properties.

Hierarchical porous ZnO microspheres decorated with gold nanoparticles (AuNPs) were successfully synthesized by a facile solvothermal route. The hierarchical ZnO superstructure was constructed of interconnected nanoplates with numerous voids. Photoluminescence, X-ray photoelectron spectroscopy, and electron paramagnetic resonance measurements demonstrated that the main defects were oxygen vacancies (V(O)(•)) with minor interstitial oxygen (O(i)(-)) in the hierarchical ZnO hollow microspheres. The as-prepared hierarchical ZnO hollow microspheres and the AuNPs used to decorate them were examined for their photocatalytic degradation ability and as gas sensors. The photodegradation results demonstrated that the degradation rate constant on rhodamine B for undecorated ZnO microspheres was 0.43 min(-1), which increased to 1.76 min(-1) for AuNP-decorated ZnO microspheres. The AuNP-functionalized ZnO microspheres displayed superior sensing properties, with a 3-fold enhancement in their gas response to 1 ppb of dibutyl phthalate.

High-efficiency photocatalytic activity of type II SnO/Sn3O4 heterostructures via interfacial charge transfer

Flower-like hollow microspheres were synthesized on a large scale using a one-step hydrothermal route. The as-prepared products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and UV-vis diffuse reflectance spectroscopy. The results showed that the shells of the hollow microspheres were composed of numerous type II SnO/Sn3O4 heterostructures. A 500 °C annealing treatment changed the type II SnO/Sn3O4 heterostructures into type I SnO2/Sn3O4 heterostructures; at 700 °C, the products were pure SnO2 semiconductors. A photocatalytic degradation test showed that the highest efficiency degradation of rhodamine B (RhB) was obtained using type II SnO/Sn3O4 heterostructure semiconductors with a degradation rate constant of 2.3 × 10−3 min−1. This highly efficient activity was induced by enhanced charge separation in type II SnO/Sn3O4 heterostructure semiconductors.

First-Row Transition Metal Based Catalysts for the Oxygen Evolution Reaction under Alkaline Conditions: Basic Principles and Recent Advances

Owing to its abundance, high gravimetric energy density, and environmental friendliness, hydrogen is a promising renewable energy to replace fossil fuels. One of the most prominent routes toward hydrogen acquisition is water splitting, which is currently bottlenecked by the sluggish kinetics of oxygen evolution reaction (OER). Numerous of electrocatalysts have been developed in the past decades to accelerate the OER process. Up to now, the first-row transition metal based compounds are in pole position under alkaline conditions, which have become subjects of extensive studies. Recently, significant advances in providing compelling catalytic performance as well as exploring their catalytic mechanisms have been achieved in this area. In this review, we summarized the fundamentals and recent progresses in first-row transition metal based OER catalysts, with special emphasis on the pathways of promoting catalytic performance by concrete strategies. New insight into material design, particularly the role of experimental approaches in the electrocatalytic performance and reaction mechanisms of OER are expected to be provided.

In situ electrochemical formation of core–shell nickel–iron disulfide and oxyhydroxide heterostructured catalysts for a stable oxygen evolution reaction and the associated mechanisms

For electrochemical production of H2 fuels from water splitting, the development of efficient and economic catalysts for the oxygen evolution reaction (OER) is still a challenging issue. This is because an OER process usually involves multiple electron-transfer and reaction steps; these result in large overpotentials and significant energy loss. Thus, a smart design of highly efficient, stable and cheap OER electrocatalysts is important for the improvement of energy conversion efficiency and reduction of water splitting procedure cost. In this work, we find that a thin crystalline oxyhydroxide layer has been in situ electrochemically formed on the surfaces of conductive nickel–iron disulfide nanostructures; such a heterostructure takes advantage of highly catalytically active oxyhydroxide surfaces and excellent conductivity of the interior disulfide phase. This results in a very low overpotential of 230 mV at a current density of 10 mA cm−2, which is among the best OER catalysts in alkaline electrolyte ever reported. The crystalline oxyhydroxide layer can effectively prevent the disulfide core from further oxidation, maintains the core–shell structure of the catalyst and is considered to be critical for stable and efficient OER performances.

Loss mechanism and microwave absorption properties of hierarchical NiCo2O4 nanomaterial

Understanding the loss mechanism of microwave absorption is of great significance for the design and fabrication of low-cost, high-efficient and light-weight microwave absorbing materials. In this study, the microwave absorption of a hierarchical NiCo2O4 nanomaterial synthesized via a hydrothermal method and a subsequent annealing process was investigated in detail. The effects of the annealing temperature on the phase evaluation and microwave absorption properties were also investigated to reveal the microwave loss mechanism of NiCo2O4 nanostructures. The results show that the Debye relaxation and superior electric conductivity of NiCo2O4 are beneficial to its excellent microwave absorption performance. This study will be useful for the fundamental understanding of microwave absorption in NiCo2O4 nanomaterial, and for the design of a novel microwave absorbent.

Green and Tunable Decoration of Graphene with Spherical Nanoparticles Based on Laser Ablation in Water: A Case of Ag Nanoparticle/Graphene Oxide Sheet Composites.

A simple and green strategy is presented to decorate graphene with nanoparticles, based on laser ablation of targets in graphene auqeous solution. Ag and graphene oxide (GO) are chosen as model materials. The surface of GO sheets is strongly anchored with spherical Ag nanoparticles. The density and size of the Ag nanoparticles can be easily tuned by laser ablation conditions. Further, the GO sheets can be decorated with other nanoparticles from simple metals or semiconductors to multicomponent hybrids. Additionally, the Ag nanoparticle/GO sheet colloids can be utilized as blocks to build three-dimensional structures, such as sandwich membranes by evaporation-induced self-assembly. These graphene-based composite materials could be very useful in catalysis, sensors, and nanodevices. Particularly, the Ag nanoparticle/GO sheet sandwich composite membranes exhibit excellent surface-enhanced Raman scattering performance and possess the huge potential in trace-detecting persistent organic pollutants in the environment.

Mesoporous multi-shelled ZnO microspheres for the scattering layer of dye sensitized solar cell with a high efficiency

Both light scattering and dye adsorbing are important for the power conversion efficiency PCE performance of dye sensitized solar cell (DSSC). Nanostructured scattering layers with a large specific surface area are regarded as an efficient way to improve the PCE by increasing dye adsorbing, but excess adsorbed dye will hinder light scattering and light penetration. Thus, how to balance the dye adsorbing and light penetration is a key problem to improve the PCE performance. Here, multiple-shelled ZnO microspheres with a mesoporous surface are fabricated by a hydrothermal method and are used as scattering layers on the TiO2 photoanode of the DSSC in the presence of N719 dye and iodine–based electrolyte, and the results reveal that the DSSCs based on triple shelled ZnO microsphere with a mesoporous surface exhibit an enhanced PCE of 7.66%, which is 13.0% higher than those without the scattering layers (6.78%), indicating that multiple-shelled microspheres with a mesoporous surface can ensure enough light sca...

Quantitative Fermi level tuning in amorphous organic semiconductor by molecular doping: Toward full understanding of the doping mechanism

The doping mechanism in organic-semiconductor films has been quantitatively studied via ultrahigh-sensitivity ultraviolet photoelectron spectroscopy of N,N-bis(1-naphthyl)-N,N-diphenyl-1,1-biphenyl-4,4-diamine (α-NPD) films doped with hexaazatriphenylene-hexacarbonitrile [HAT(CN)6]. We observed that HOMO of α-NPD shifts to the Fermi level (EF) in two different rates with the doping concentration of HAT(CN)6, but HOMO distributions of both pristine and doped amorphous α-NPD films are excellently approximated with a same Gaussian distribution without exponential tail states over ∼5 × 1018 cm−3 eV−1. From the theoretical simulation of the HAT(CN)6-concentration dependence of the HOMO in doped films, we show that the passivation of Gaussian-distributed hole traps, which peak at 1.1 eV above the HOMO onset, occurs at ultralow doping [HAT(CN)6 molecular ratio (MR) < 0.01], leading to a strong HOMO shift of ∼0.40 eV towards EF, and MR dependence of HOMO changes abruptly at MR ∼ 0.01 to a weaker dependence for MR...

Electrophoretic fabrication of silver nanostructure/zinc oxide nanorod heterogeneous arrays with excellent SERS performance

A simple and green strategy is presented to fabricate Ag-decorated ZnO nanorod arrays based on electrophoretic deposition in a Ag colloidal solution prepared by laser ablation in water. The edges or corners of each nanorods upper surface feature dendritic aggregates consisting of nanoparticles, and the other surfaces exhibit irregular particles of less than 200 nm in size. Overall, the created Ag nanostructure/ZnO nanorod is hierarchically micro/nanostructured and very rough at the nanoscale. The inter-particle spacings in the decoration layer are nanometers to tens of nanometers in scale. Further experiments have revealed that suitable electrophoretic potential and sufficient growth duration are crucial for obtaining complete coverage on every nanorod. The site-specific deposition of Ag nanoparticles on ZnO nanorods can be explained by the different distributions of the electric field and the colloidal concentration during electrophoresis. Such heterogeneous nanorod arrays are functionalized and exhibit excellent surface-enhanced Raman scattering performance. This study provides a new method for creating decorated nanorod arrays with novel nanostructures by using unstable colloidal nanoparticles as building blocks and deepens the understanding of the physical mechanisms of electrophoretic deposition.