L. J. Pan

Phytochemistry

PhD
35.83

Publications

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    ABSTRACT: Two-dimensional transition-metal dichalcogenides (WS2 and SnS2) have recently joined the family of energy storage materials (for lithium-ion batteries and supercapacitors) as a result of their favorable ion intercalation. So far, challenges in the synthesis of phase-pure WS2, restacking between WS2 nanosheets, low electronic conductivity, and the brittle nature of WS2, severely limit its use Li-ion battery application. Herein, we develop a facile low temperature solution sulfuration process to improve battery performance dramatically. The sulfuration process is demonstrated to be effective in converting WO3 impurities to WS2, and in repairing the sulfur vacancies, to improve cyclability and rate capability. Lithium-ion battery measurements demonstrate that the stable capacity of the WS2 anode could be enhanced by 48.4% via sulfuration reprocessing, i.e., from 381.7 to 566.8 mAh/g at a relatively high current density of 0.8 A/g after 50 cycles. We further show that the sulfuration process can be readily extended to other dichalcogenides, and may provide a class of versatile electrode materials for lithium-ion batteries with improved electrochemical characteristics. [Figure not available: see fulltext.] © 2015 Tsinghua University Press and Springer-Verlag Berlin Heidelberg
    No preview · Article · Jan 2016 · Nano Research
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    ABSTRACT: Carbon capture and sequestration from point sources is an important component in the CO2 emission mitigation portfolio. In particular, sorbents with both high capacity and selectivity are required for reducing the cost of carbon capture. Although physisorbents have the advantage of low energy consumption for regeneration, it remains a challenge to obtain both high capacity and sufficient CO2/N2 selectivity at the same time. Here, we report the controlled synthesis of a novel N-doped hierarchical carbon that exhibits record-high Henry's law CO2/N2 selectivity among physisorptive carbons while having a high CO2 adsorption capacity. Specifically, our synthesis involves the rational design of a modified pyrrole molecule that can co-assemble with the soft Pluronic template via hydrogen bonding and electrostatic interactions to give rise to mesopores followed by carbonization. The low-temperature carbonization and activation processes allow for the development of ultra-small pores (d <0.5 nm) and preservation of nitrogen moieties, essential for enhanced CO2 affinity. Furthermore, our described work provides a strategy to initiate developments of rationally-designed porous conjugated polymer structures and carbon-based materials for various potential applications.
    No preview · Article · Dec 2015 · Journal of the American Chemical Society
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    Full-text · Dataset · Dec 2015
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    Full-text · Article · Dec 2015 · Advanced Functional Materials
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    ABSTRACT: Hierarchical structures, with a high mass-loading of nanostructured lithium (Li) storage medium grafted upon large trunk framework, represent a novel approach towards high capacity and stable Li-ion batteries. We here report a new hierarchical structure of crystalline Si nanowires (c-Si NWs) grafted upon ultra-long tin dioxide (SnO2) NW trunks, where the latter frame up a large, conductive and stable architecture (i) to achieve a high mass-loading of c-Si NWs for Li-ion storage and (ii) to guarantee a good electric contact and fast charging process. The Si NWs branches are produced via a low-temperature vapor-liquid-solid (VLS) growth catalyzed by Sn droplets produced during a simple H2 plasma treatment upon the SnO2 trunks. Compared to other Si or SnO2 NW-based anodes structures, the c-Si/SnO2 NWs hierarchical structure demonstrates an outstanding performance with a high mass-load (~1.5 mg/cm2) and a high areal capacity (~1.8 mAh/cm2) after 100 cycles, without the use of any additional conductive polymer binder, highlighting the unique synergistic benefit of this hierarchical structure in boosting simultaneously the capacity and stability of Si-loaded Li-ion batteries.
    Full-text · Article · Nov 2015 · Nano Energy
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    ABSTRACT: Seeking long cycle lifetime and high rate performance are still challenging aspects to promote the application of silicon-loaded lithium ion batteries (LIBs), where optimal structural and compositional design are critical to maximize a synergistic effect in composite core-shell nanowire anode structures. We here propose and demonstrate a high quality conformal coating of amorphous Si (a-Si) thin film over a matrix of highly cross-linked CuO nanowires (NW). The conformal a-Si coating can serve as both a high capacity storage medium and a high quality binder that joins crossing CuO NWs into a continuous network. And the CuO NWs can be reduced into highly conductive Cu cores in a low temperature H2 annealing. In this way, we have demonstrated an excellent cycling stability that last more than 700 (or 1000) charge/discharge cycles at a current density of 3.6A/g (or 1A/g), with a high capacity retention rate of 80%. Remarkably, these Cu/a-Si core-shell anode structure can survive extremely high charging current density of 64A/g for 25 runs, and then recover 75% initial capacity when returning to 1A/g. We also present the first and straigthforward experimental proof that these robust highly-cross-linked core-shell network can preserve the structural integrity even after 1000 runs of cycling. All hese results indicate a new and convenient strategy towards a high performance Si-loaded battery application.
    Full-text · Article · Nov 2015 · Nanoscale
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    Yaqun Wang · Ye Shi · Lijia Pan · Yu Ding · Yu Zhao · Yun Li · Yi Shi · Guihua Yu
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    ABSTRACT: Conducting polymer hydrogels emerge as a novel class of polymeric materials that show great potential in many energy, environmental, and biomedical devices. We describe here for the first time a general supramolecular approach toward controlled in situ synthesis of one-dimensional nanostructured conductive hydrogels (polypyrrole (PPy) as a model system) using a rational dopant counterion, which is a disc-shaped liquid crystal molecular copper phthalocyanine-3,4',4″,4‴-tetrasulfonic acid tetrasodium salt (CuPcTs). The dopant molecule CuPcTs cross-linked the PPy chains to form a three-dimensional network that gelated into a hydrogel. The PPy hydrogel could be synthesized in bulk quantities with uniform morphology of self-assembled interconnected nanofibers. The tetra-functional dopant favors a supramolecular self-assembly mechanism to form one-dimensional PPy nanostructures. Furthermore, the enhanced interchain charge transport of CuPcTs doped PPy resulted in greatly enhanced conductivity and pseudocapacitance compared with pristine PPy.
    Full-text · Article · Oct 2015 · Nano Letters
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    ABSTRACT: The reduction of contact resistance in ferroelectric organic field-effect transistors (Fe-OFETs) by buffering the interfacial polarization fluctuation was reported. An ultrathin poly(methyl methacrylate) layer was inserted between the ferroelectric polymer and organic semiconductor layers. The contact resistance was significantly reduced to 55 kΩ cm. By contrast, Fe-OFETs without buffering exhibited a significantly larger contact resistance of 260 kΩ cm. Results showed that such an enhanced charge injection was attributed to the buffering effect at the semiconductor/ferroelectric interface, which narrowed the trap distribution of the organic semiconductor in the contact region. The presented work provided an efficient method of lowering the contact resistance in Fe-OFETs, which is beneficial for the further development of Fe-OFETs.
    Full-text · Article · Aug 2015 · Applied Physics Letters
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    ABSTRACT: Performance characteristics, such as dark current and response time, of ZnO nanowire (NW) photodetectors are usually degraded by H2O/O2 adsorption on the NW surfaces. In this work, ZnO NW photodetectors based on Au Schottky contact through passivating surface states were investigated. ZnO NW photodetectors were fabricated with a lateral electrode structure, in which Au served as Au/ZnO Schottky contact and semi-transparent top electrode. Specifically, passivation of the surface states of ZnO NWs by using highly intensive UV irradiation effectively improved the photoresponse. A physical model based on surface band theory was developed to understand the origin of the performance improvement of the photodetector. The present device architecture prevents ZnO NWs photodetector from H2O/O2 adsorption in air and efficiently extracts photogenerated carriers across a diametrical direction.
    Full-text · Article · Jul 2015 · Optics Communications
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    ABSTRACT: Surface-diffusion-induced spontaneous Ga incorporation process is demonstrated in ZnO nanowires grown on GaN substrate. Crucially, contrasting distributions of Ga atoms in axial and radial directions are experimentally observed. Ga atoms uniformly distribute along the ~10 μm long ZnO nanowire and show a rapidly gradient distribution in the radial direction, which is attributed substantially to the difference between surface and volume diffusion. The understanding on the incorporation process can potentially modulate doping and properties in semiconductor nanomaterials.
    No preview · Article · Jul 2015 · physica status solidi (RRL) - Rapid Research Letters
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    ABSTRACT: Highly graphitic materials with record breaking surface area, large pore volume and hierarchical pores are introduced. These hold promise for applications such as supercapacitors and lithium sulfur batteries.
    Preview · Article · May 2015
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    Lanlan Li · Ye Shi · Lijia Pan · Yi Shi · Guihua Yu
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    ABSTRACT: Conducting polymer hydrogels (CPHs) are conducting polymer-based materials that contain high water content and have physical properties, resembling the extracellular environment. Synergizing the advantages of both the organic conductors and hydrogels, CPHs emerged to be candidates for high performance biosensors by providing advantageous interfaces for electrochemical bio-electrodes. Examples include the following: (1) the interface between a biomaterial and an artificial inorganic electrode material; (2) the hybrid electronic interface between an ionic carrier and an electron charge carrier; and (3) the extension of the planar electrode surface to a three-dimensional (3D) porous surface. CPHs with rationally designed 3D nanostructures and molecular structures are advantageous for enhancing the biocompatibility of the electrode, improving enzyme immobilization, creating protective layers to control diffusion, and wiring the electron transference. This review presents a brief overview of the current state-of-the-art research in electrochemical biosensors based on CPHs and describes future directions.
    Full-text · Article · Mar 2015
  • Danfeng Qiu · Gang Bu · Bin Zhao · Zixia Lin · Lin Pu · Lijia Pan · Yi Shi
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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.
    No preview · Article · Feb 2015 · Materials Letters
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    ABSTRACT: A nonselective micropatterning method of self-assembled monolayers (SAMs) based on laser and phase-shifting mask (PSM) is demonstrated. Laser beam is spatially modulated by a PSM, and periodic SAM patterns are generated sequentially through thermal desorption. Patterned wettability is achieved with alternating hydrophilic/hydrophobic stripes on octadecyltrichlorosilane monolayers. The substrate is then used to assemble CdS semiconductor nanowires (NWs) from a solution, obtaining well-aligned NWs in one step. Our results show valuably the application potential of this technique in engineering SAMs for integration of functional devices.
    Full-text · Article · Jan 2015 · Applied Physics Letters
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    Lanlan Li · Yaqun Wang · Lijia Pan · Ye Shi · Wen Cheng · Yi Shi · Guihua Yu
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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.
    Full-text · Article · Jan 2015 · Nano Letters
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    ABSTRACT: To develop a novel cell-seeding technique on artificial vascular scaffolds. Methods: The rat endothelial progenitor cells differentiated from adipose-derived stem cells were seeded on the surface of scaffold fabricated by electrospinning polycaprolactone through alginate hydrogel conglutinate cells (AHCCs) and natural sedimentation seeding cells (NSSCs). The cell morphology was observed by immunofluorescence and scanning electron microscopy after cultivation for 1, 3, 7 days, respectively. Results: More adhesion and proliferation was noticed in AHCC scaffolds than NSSC scaffolds at the same time point. In the AHCC group, cells could adhere directly on the vascular scaffolds, avoiding the time delay in the NSSC group prior to cell adhesion. Conclusion: Alginate hydrogel conglutinate cells are effectively seeded on the vascular scaffolds, which could avoid the time delay before cell adhesion.
    No preview · Article · Jan 2015 · Journal of Biomaterials and Tissue Engineering
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    Full-text · Dataset · Nov 2014
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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.
    Full-text · Article · Nov 2014 · Scientific Reports
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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.
    Full-text · Article · Aug 2014 · Nature Communications
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    ABSTRACT: High-performance flexible energy-storage devices have great potential as power sources for wearable electronics. One major limitation to the realization of these applications is the lack of flexible electrodes with excellent mechanical and electrochemical properties. Currently employed batteries and supercapacitors are mainly based on electrodes that are not flexible enough for these purposes. Here, a three-dimensionally interconnected hybrid hydrogel system based on carbon nanotube (CNT)-conductive polymer network architecture is reported for high-performance flexible lithium ion battery electrodes. Unlike previously reported conducting polymers (e.g., polyaniline, polypyrrole, polythiophene), which are mechanically fragile and incompatible with aqueous solution processing, this interpenetrating network of the CNT-conducting polymer hydrogel exibits good mechanical properties, high conductivity, and facile ion transport, leading to facile electrode kinetics and high strain tolerance during electrode volume change. A high-rate capability for TiO2 and high cycling stability for SiNP electrodes are reported. Typically, the flexible TiO2 electrodes achieved a capacity of 76 mAh g–1 in 40 s of charge/discharge and a high areal capacity of 2.2 mAh cm–2 can be obtained for flexible SiNP-based electrodes at 0.1C rate. This simple yet efficient solution process is promising for the fabrication of a variety of high performance flexible electrodes.
    Full-text · Article · Aug 2014 · Advanced Energy Materials

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