Publications

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    ABSTRACT: NiO/graphene nanocomposites are fabricated via a solvothermal method. Scanning and transmission electron microscopy results indicate that the NiO nanoplates (length, ~100 nm) were homogeneously distributed on the graphene sheets. The electrochemical properties of the samples as active cathode catalysts for rechargeable Li-air batteries are evaluated by constant current charge-discharge cycling. The composites exhibit a reversible capacity of 1160 mAh g−1 after 50 cycles at a discharge current density of 50 mA g−1; this reverse capacity is much higher than that of pure NiO nanoplates (30 mAh g−1). Using graphene as a conductive matrix, a homogeneous distribution of NiO nanoplates is accomplished and graphene serves as a framework for loading as produced Li2O2 during the discharge process, resulting in the excellent electrochemical performance of the composites. The mesoporous structure of the NiO nanoplates is suitable for the transfer of O2 and deposition of Li2O2 produced by the electrochemical reaction. NiO/graphene nanocomposites are a candidate material for high-capacity, low-cost, and nontoxic cathode catalysts in rechargeable Li-air batteries.
    Materials Letters 02/2015; 141:43-46. · 2.27 Impact Factor
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    ABSTRACT: The development of a scalable, low-cost and versatile biosensor platform for the sensitive and rapid detection of human metabolites is of great interest for healthcare, pharmaceuticals and medical science. Based on hierarchically nanostructured conducting polymer hydrogels, we designed a flexible biosensor platform that can detect various human metabolites, such as uric acid, cholesterol and triglycerides. Owing to the unique features of conducting polymer hydrogels, such as high permeability to bio-substrates and rapid electron transfer, our biosensors demonstrate excellent sensing performance with a wide linear range (uric acid, 0.07~1 mM; cholesterol, 0.3~9 mM and triglycerides, 0.2~5 mM), high sensitivity, low sensing limit and rapid response time (~3 s). Given the facile and scalable processability of hydrogels, the proposed conductive hydrogels-based biosensor platform shows great promise as a low-cost sensor kit for healthcare monitoring, clinical diagnostics and biomedical devices.
    Nano letters. 01/2015;
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    ABSTRACT: Ferroelectric organic field-effect transistors (Fe-OFETs) have been attractive for a variety of non-volatile memory device applications. One of the critical issues of Fe-OFETs is the improvement of carrier mobility in semiconducting channels. In this article, we propose a novel interfacial buffering method that inserts an ultrathin poly(methyl methacrylate) (PMMA) between ferroelectric polymer and organic semiconductor layers. A high field-effect mobility (mFET) up to 4.6 cm2/Vs is obtained. Subsequently, the programming process in our Fe-OFETs is mainly dominated by the switching between two ferroelectric polarizations rather than by the mobility-determined charge accumulation at the channel. Thus, the ‘‘reading’’ and ‘‘programming’’ speeds are significantly improved. Investigations show that the polarization fluctuation at semiconductor/insulator interfaces, which affect the charge transport in conducting channels, can be suppressed effectively using our method.
    Scientific Reports 11/2014; 4:7227. · 5.08 Impact Factor
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    ABSTRACT: Molybdenum disulfide is considered as one of the most promising two-dimensional semiconductors for electronic and optoelectronic device applications. So far, the charge transport in monolayer molybdenum disulfide is dominated by extrinsic factors such as charged impurities, structural defects and traps, leading to much lower mobility than the intrinsic limit. Here, we develop a facile low-temperature thiol chemistry to repair the sulfur vacancies and improve the interface, resulting in significant reduction of the charged impurities and traps. High mobility greater than 80cm2 V-1 s-1 is achieved in backgated monolayer molybdenum disulfide field-effect transistors at room temperature. Furthermore, we develop a theoretical model to quantitatively extract the key microscopic quantities that control the transistor performances, including the density of charged impurities, short-range defects and traps. Our combined experimental and theoretical study provides a clear path towards intrinsic charge transport in two-dimensional dichalcogenides for future high-performance device applications.
    Nature Communications 08/2014; 5. · 10.74 Impact Factor
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    ABSTRACT: Superhydrophobic surfaces are of immense scientific and technological interests for a broad range of applications. However, a major challenge remains in developing scalable methodologies that enable superhydrophobic coatings on versatile substrates with a combination of strong mechanical stability, optical transparency, and even stretchability. Herein, we developed a scalable methodology to versatile hydrophobic surfaces that combine with strong mechanical stability, optical transparency, and stretchability by using a self-assembled hydrogel as the template to in situ generate silica microstructures and subsequent silanization. The superhydrophobic coatings can be enabled on virtually any substrates via large-area deposition techniques like dip coating. Transparent surfaces with optical transmittance as high as 98% were obtained. Moreover, the coatings exhibit superior mechanical flexibility and robustness that it can sustain contact angles ∼160° even after 5000 cycles of mechanically stretching at 100% strain. The multifunctional surfaces can be used as screen filters and sponges for the oil/water separation that can selectively absorb oils up to 40× their weight.
    Nano Letters 06/2014; · 12.94 Impact Factor
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    ABSTRACT: Single-walled carbon nanotubes/polymer composites typically have limited conductivity due to a low concentration of nanotubes and the insulating nature of the polymers used. Here we combined a method to align carbon nanotubes with in situ polymerization of conductive polymer to form composite films and fibers. The use of the conducting polymer raised the conductivity of the films by two orders of magnitude. On the other hand, CNT fiber formation was made possible with the in situ polymerization to provide more mechanical support to the CNTs from the formed conducting polymer. The carbon nanotube/conductive polymer composite films and fibers had conductivities of 3,300 and 170 S/cm, respectively. The relatively high conductivities were attributed to the polymerization process, which doped both the SWNTs and the polymer. In situ polymerization can be a promising solution-processable method to enhance conductivity of carbon nanotube films and fibers.
    ACS Applied Materials & Interfaces 06/2014; · 5.90 Impact Factor
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    ABSTRACT: Electrochemically active conducting polymers are an important class of materials for applications in energy storage devices such as batteries and supercapacitors, owing to their advantageous features of unique three-dimensional (3D) porous microstructure, high capacitive energy density, scalable synthesis and light weight. Here, we synthesized a nanostructured conductive polypyrrole (PPy) hydrogel via an interfacial polymerization method. The simple synthesis chemistry offers the conductive hydrogel tunable nanostructures and electrochemical performance, as well as scalable processability. Moreover, the unique 3D porous nanostructure constructed by interconnected polymer nanospheres endows PPy hydrogels with good mechanical properties and high performance acting as supercapacitor electrodes with a specific capacitance of 380 F g−1, excellent rate capability, and areal capacitance as high as 6.4 F cm−2 at a mass loading of 20 mg cm−2.
    J. Mater. Chem. A. 04/2014; 2(17).
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    ABSTRACT: Co3O4/graphene nanosheet (GNS) composites were synthesized via the in situ growth of mesoporous Co3O4 nanoparticles on graphene. The as-prepared Co3O4/GNS composites exhibited superior Li-ion battery performance and showed a large reversible capacity, excellent cycling, and good rate capability when used as an anode material in lithium ion batteries (LIBs). The uniform coating of Co3O4 around the graphene surface ensured tight electrical contact, resulting in a material with higher specific capacity and enhanced cycling performance compared with pure Co3O4 electrodes. The composites delivered a reversible capacity of 900 mA h g−1 at a discharge current density of 100 mA g−1 with good cycling ability. Moreover, the composites showed exceptional high-current charge–discharge performance, achieving 650 mA h g−1 at a current density of 1000 mA g−1.
    Materials Letters 03/2014; 119:12–15. · 2.27 Impact Factor
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    ABSTRACT: Pressure sensing is an important function of electronic skin devices. The development of pressure sensors that can mimic and surpass the subtle pressure sensing properties of natural skin requires the rational design of materials and devices. Here we present an ultra-sensitive resistive pressure sensor based on an elastic, microstructured conducting polymer thin film. The elastic microstructured film is prepared from a polypyrrole hydrogel using a multiphase reaction that produced a hollow-sphere microstructure that endows polypyrrole with structure-derived elasticity and a low effective elastic modulus. The contact area between the microstructured thin film and the electrodes increases with the application of pressure, enabling the device to detect low pressures with ultra-high sensitivity. Our pressure sensor based on an elastic microstructured thin film enables the detection of pressures of less than 1 Pa and exhibits a short response time, good reproducibility, excellent cycling stability and temperature-stable sensing.
    Nature Communications 01/2014; 5:3002. · 10.74 Impact Factor
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    ABSTRACT: CuO nanoparticles are directly formed on graphene nanosheets through the in situ chemical decomposition of Cu(NO3)2·3H2O and are anchored tightly on the graphene surface. The lithiation-induced strain is naturally accommodated, owing to the constraint effect of the graphene matrix. Electrochemical characterization shows that CuO nanoparticles anchored on graphene sample exhibits a high capacity of about 660 mAh/g at a discharge current density of 100 mA/g and a good cycling ability. During the charge–discharge process, graphene nanosheets not only served as a three-dimensional conductive network for CuO nanoparticles, but also improve the detachment and agglomeration of CuO nanoparticles. This CuO/graphene nanocomposite displays superior Li-battery performance with large reversible capacity, excellent cyclic performance, and good rate capability.
    Materials Letters 08/2013; 105:242–245. · 2.27 Impact Factor
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    ABSTRACT: Silicon has a high-specific capacity as an anode material for Li-ion batteries, and much research has been focused on overcoming the poor cycling stability issue associated with its large volume changes during charging and discharging processes, mostly through nanostructured material design. Here we report incorporation of a conducting polymer hydrogel into Si-based anodes: the hydrogel is polymerized in-situ, resulting in a well-connected three-dimensional network structure consisting of Si nanoparticles conformally coated by the conducting polymer. Such a hierarchical hydrogel framework combines multiple advantageous features, including a continuous electrically conductive polyaniline network, binding with the Si surface through either the crosslinker hydrogen bonding with phytic acid or electrostatic interaction with the positively charged polymer, and porous space for volume expansion of Si particles. With this anode, we demonstrate a cycle life of 5,000 cycles with over 90% capacity retention at current density of 6.0 A g(-1).
    Nature Communications 06/2013; 4:1943. · 10.74 Impact Factor
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    ABSTRACT: Glucose enzyme biosensors have been shown useful for a range of applications from medical diagnosis, bioprocess monitoring, to beverage industry and environmental monitoring. We present here a highly sensitive glucose enzyme sensor based on Pt nanoparticles (PtNPs)-polyaniline (PAni) hydrogel heterostructures. High-density PtNPs were homogeneously loaded onto the three-dimensional (3D) nanostructured matrix of the PAni hydrogel. The PtNP/PAni hydrogel heterostructure-based glucose sensor synergizes the advantages of both the conducting hydrogel and the nanoparticle catalyst. The porous structure of the PAni hydrogel favored the high density immobilization of the enzyme and the penetration of water-soluble molecules, which helped efficiently catalyze the oxidation of glucose. In addition, the PtNPs catalyzed the decomposition of hydrogen peroxide that was generated during the enzymatic reaction. The transferred charges from these electrochemical processes were efficiently collected by the highly conducting PtNP/PAni hydrogel heterostructures. The glucose enzyme sensor based on this heterostructure exhibited unprecedented sensitivity, as high as 96.1 μA●mM-1●cm-2, with a response time as fast as 3 s, a linear range of 0.01 to 8 mM, and a low detection limit of 0.7 μM.
    ACS Nano 03/2013; · 12.03 Impact Factor
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    ABSTRACT: The exciting development of advanced nanostructured materials has driven the rapid growth of research in the field of electrochemical energy storage (EES) systems which are critical to a variety of applications ranging from portable consumer electronics, hybrid electric vehicles, to large industrial scale power and energy management. Owing to their capability to deliver high power performance and extremely long cycle life, electrochemical capacitors (ECs), one of the key EES systems, have attracted increasing attention in the recent years since they can complement or even replace batteries in the energy storage field, especially when high power delivery or uptake is needed. This review article describes the most recent progress in the development of nanostructured electrode materials for EC technology, with a particular focus on hybrid nanostructured materials that combine carbon based materials with pseudocapacitive metal oxides or conducting polymers for achieving high-performance ECs. This review starts with an overview of EES technologies and the comparison between various EES systems, followed by a brief description of energy storage mechanisms for different types of EC materials. This review emphasizes the exciting development of both hybrid nanomaterials and novel support structures for effective electrochemical utilization and high mass loading of active electrode materials, both of which have brought the energy density of ECs closer to that of batteries while still maintaining their characteristic high power density. Last, future research directions and the remaining challenges toward the rational design and synthesis of hybrid nanostructured electrode materials for next-generation ECs are discussed.
    Nano Energy 03/2013; 2(2):213–234. · 10.21 Impact Factor
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    ABSTRACT: Mesoporous TiO2 interwoven with multilevel carbon networks was obtained by in situ self-assembly of TiO2 and P123 micelles within the nanospace of thermally exfoliated graphene. The nanocomposite exhibited excellent capacity retention and good rate capability as a material for lithium-ion battery anodes.
    RSC Advances 01/2013; 3(47):24882. · 3.71 Impact Factor
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    ABSTRACT: A strategy of using structurally matched alumina insulation to produce lateral electrodes on semiconductor nanowires is presented. Nanowires in the architecture are structurally matched with alumina insulation using selective anodic oxidation. Lateral electrodes are fabricated by directly evaporating metallic atoms onto the opposite sides of the nanowires. The integrated architecture with lateral electrodes propels carriers to transport them across nanowires and is crucially beneficial to the injection/extraction in optoelectronics. The matched architecture and the insulating properties of the alumina layer are investigated experimentally. ZnO nanowires are functionalized into an ultraviolet photodiode as an example. The present strategy successfully implements an advantageous architecture and is significant in developing diverse semiconductor nanowires in optoelectronic applications.
    Nanotechnology 12/2012; 24(2):025204. · 3.67 Impact Factor
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    ABSTRACT: A continuous mesoporous iron oxide nanofilm was directly formed on graphene nanosheets through the in situ thermal decomposition of Fe(NO3)3·9H2O and was anchored tightly on the graphene surface. The lithiation-induced strain was naturally accommodated, owing to the constraint effect of graphene and the mesoporous structure. Hence, the pulverization of the iron oxide nanofilm was effectively prevented.
    RSC Advances 12/2012; 3(3):699-703. · 3.71 Impact Factor
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    ABSTRACT: Conducting polymer hydrogels represent a unique class of materials that synergizes the advantageous features of hydrogels and organic conductors and have been used in many applications such as bioelectronics and energy storage devices. They are often synthesized by polymerizing conductive polymer monomer within a nonconducting hydrogel matrix, resulting in deterioration of their electrical properties. Here, we report a scalable and versatile synthesis of multifunctional polyaniline (PAni) hydrogel with excellent electronic conductivity and electrochemical properties. With high surface area and three-dimensional porous nanostructures, the PAni hydrogels demonstrated potential as high-performance supercapacitor electrodes with high specific capacitance (~480 F·g(-1)), unprecedented rate capability, and cycling stability (~83% capacitance retention after 10,000 cycles). The PAni hydrogels can also function as the active component of glucose oxidase sensors with fast response time (~0.3 s) and superior sensitivity (~16.7 μA · mM(-1)). The scalable synthesis and excellent electrode performance of the PAni hydrogel make it an attractive candidate for bioelectronics and future-generation energy storage electrodes.
    Proceedings of the National Academy of Sciences 05/2012; 109(24):9287-92. · 9.81 Impact Factor
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    ABSTRACT: Chemical reduction of graphene oxide represents an important route towards large-scale production of graphene sheets for many applications. Thus far, gas-phase reactions have been demonstrated to efficiently reduce graphene oxide, but a molecular understanding of the reaction processes is largely lacking. Here, using molecular dynamics simulations, we compare the reduction of graphene oxide in different environments. We find that NH3 affords more efficient reduction of hydroxyl and epoxide groups than H2 and vacuum annealing partly due to lower energy barriers. Various reduction paths of oxygen groups in NH3 and H2 are quantitatively identified. Furthermore, we show that with the combination of vacancies and oxygen groups, pyridinic- or pyrrolic-like nitrogen can readily be incorporated into graphene. All of these nitrogen configurations lead to n-doping of the graphene. Our results are consistent with many previous experiments and provide insights towards doping engineering of graphene.
    Nano Research 05/2012; 5(5). · 6.96 Impact Factor

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