Lei Zhai

University of Central Florida, Orlando, Florida, United States

Are you Lei Zhai?

Claim your profile

Publications (73)360.77 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Cable-shaped supercapacitors (SCs) have recently aroused significant attention due to their attractive properties such as small size, lightweight, and bendability. Current cable-shaped SCs have symmetric device configuration. However, if an asymmetric design is used in cable-shaped supercapacitors, they would become more attractive due to broader cell operation voltages, which results in higher energy densities. Here, a novel coil-type asymmetric supercapacitor electrical cable (CASEC) is reported with enhanced cell operation voltage and extraordinary mechanical-electrochemical stability. The CASECs show excellent charge-discharge profiles, extraordinary rate capability (95.4%), high energy density (0.85 mWh cm(-3) ), remarkable flexibility and bendability, and superior bending cycle stability (≈93.0% after 4000 cycles at different bending states). In addition, the CASECs not only exhibit the capability to store energy but also to transmit electricity simultaneously and independently. The integrated electrical conduction and storage capability of CASECS offer many potential applications in solar energy storage and electronic gadgets. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Small 08/2015; DOI:10.1002/smll.201501802 · 8.37 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Supercapacitors have drawn considerable attention in recent years due to their high specific power, long cycle life, and ability to bridge the power/energy gap between conventional capacitors and batteries/fuel cells. Nanostructured electrode materials have demonstrated superior electrochemical properties in producing high-performance supercapacitors. In this review article, we describe the recent progress and advances in designing nanostructured supercapacitor electrode materials based on various dimensions ranging from zero to three. We highlight the effect of nanostructures on the properties of supercapacitors including specific capacitance, rate capability and cycle stability, which may serve as a guideline for the next generation of supercapacitor electrode design.
    Energy & Environmental Science 03/2015; 8(3):702-730. DOI:10.1039/C4EE03229B · 20.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Lei Zhai is an associate professor at the NanoScience Technology Center (NSTC) and Department of Chemistry. He received his Ph.D. from Carnegie Mellon University in 2002 and worked as a postdoctoral research associated at Massachusetts Institute of Technology before he joined the University of Central Florida in 2005. He is a recipient of NSF CAREER Award and a Scialog Fellow of Research Corporation for Science Advancement. His research focuses on conjugated polymers and composites for energy conversion and storage, surface science and engineering, and polymer derived ceramics.
    Nano Today 02/2015; 9(6). DOI:10.1016/j.nantod.2014.10.004 · 15.00 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Asymmetric supercapacitors (ASCs) have played a leading role in realizing energy storage devices with high energy and power densities. While both anode and cathode materials are important for high performance ASCs, more research effort has been devoted to developing cathode materials because the energy source of an ASC is mostly attributed to the cathode. However, the development of anode materials is essential in order to achieve high power density as well as stable long-term cycle life of ASCs. In this study, functionalized graphene aerogel (GA) decorated with palladium (Pd) nanoparticles is used as an efficient ASC anode material. The high surface area (328 m2 g−1) and low electrical resistivity (50 times lower than one without Pd) of the GA composite grants a high specific capacitance (175.8 F g−1 at 5 mV s−1), excellent rate capability (48.3% retention after a 10 fold increase of scan rate), and remarkable reversibility. ASCs assembled from manganese dioxide (cathode) and GA composite (anode) show stable extended cell voltage, fast charge-discharge capability, excellent cycle stability (89.6% retention after 3,000 cycles), and high energy and power densities (average of 13.9 Wh kg−1 and 13.3 kW kg−1). These results demonstrate the great potential of the GA composite as an efficient anode material for high performance energy storage devices.
    Nano Energy 01/2015; 11:611-620. DOI:10.1016/j.nanoen.2014.11.030 · 10.33 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Photorefractive polymer composites have gained considerable attention due to their fascinating applications like 3D displays and 3D Telepresence. In this report, the performance of a novel PR polymer composite doped with graphene is studied. The addition of graphene laminates to a photorefractive composite results in up to threefold enhancement of space charge (SC) field build-up time. From our optical and electrical measurements, the faster build-up time is attributed to larger charge generation resulting from electronic interaction between graphene and the 7-DCST chromophores.
    07/2014; 2(36). DOI:10.1039/C4TC00782D
  • [Show abstract] [Hide abstract]
    ABSTRACT: The assembling behavior of four thiophene-containing conjugated polymers, regioregular poly(3-hexythiophene) (rr-P3HT), poly(3,3-didodecylquaterthiophene) (PQT-12), poly(2,5-bis(3- tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT-14), and poly(2,5-bis(3-tetradecylthiophen-2-yl)thiophen-2-yl)thiophen-2-ylthiazolo[5,4-d]thiazole) (PTzQT-14), on carbon nanotubes was investigated through microscopic studies of nanowire formation and theoretical simulation. It is found that polymer backbone rigidity and shape influence the attachment mode on carbon nanotubes. rr-P3HT and PQT-12 have a zigzag backbone structure that allows a thermodynamically stable coaxial attachment on CNTs, providing an ordered growth front for the nanowire formation. In contrast, fused rings in PTzQT-14 and PBTTT-14 create a stair-step like backbone structure that causes a kinetically controlled wrapping conformation on CNTs, generating a twisted growth front that hinders the nanowire formation. In addition, the rigidity of polymer backbone influences the wrapping mode. Polymers with more flexible backbones (i.e., PBTTT-14) would take a dense irregular wrapping mode on CNTs. The CNT diameter plays an important role in the nanowire formation when CPs attach to the CNT in the wrapping mode. Larger nanotubes with smaller surface curvature provides a less twisted polymer growth front, allowing the formation of CPNWs.
    Macromolecules 12/2013; 47(2). DOI:10.1021/ma401609q · 5.80 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: This chapter reviews stimuli-responsive conjugated polymer (CP) systems with respect to the fabrication of CPs such as electro-oxidation, chemical oxidation, and living polymerization, the responsive mechanism of CP systems and the applications including chemical sensing, bioimaging, and actuators. It is important to point out that other major applications of CPs including field-effect transistors, molecular electronics, supercapacitors, and organic photovoltaics have been actively explored. The chapter focuses on the recent advances in the electrochemical fabrication of CP films which may have application in the design of artificial muscles. It also focuses on the properties of stimuli-responsive CP nanostructures specific for biomedical applications such as drug delivery, bioimaging, sensing (gas sensors, biosensors), tissue engineering, and neural probes.
    Intelligent Stimuli-Responsive Materials, 08/2013: pages 423-470; , ISBN: 9781118452004
  • Lei Zhai
    [Show abstract] [Hide abstract]
    ABSTRACT: Stimuli-responsive polymer films undergo interesting structural and property changes upon external stimuli. Their applications have extended from smart coatings to controlled drug release, smart windows, self-repair and other fields. This tutorial review summarizes non-covalent bonding, reversible reactions and responsive molecules that have played important roles in creating stimuli-responsive systems, and presents the recent development of three types of responsive polymer systems: layer-by-layer polymer multilayer films, polymer brushes, and self-repairing polymer films, with a discussion of their response mechanism. Future research efforts include comprehensive understanding of the response mechanism, producing polymer systems with controlled response properties regarding single or multiple external signals, combining polymer film fabrication with nanotechnology, improving the stability of polymer films on substrates, and evaluating the toxicity of the degradation products.
    Chemical Society Reviews 06/2013; 42(17). DOI:10.1039/c3cs60023h · 33.38 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: By controlling the deposition rate of Zn atoms, we simultaneously synthesized ZnO particles on the upper surface of a horizontal silicon substrate, and ZnO rods array on its lower surface via a thermal evaporation process. The deposition rate of Zn atoms not only affects the morphologies of the final ZnO products, but also consequently leads to ZnO particles and ZnO rods array that have different photoluminescence properties and wetting behaviors. These two morphological ZnO products have just opposite relative intensities of UV emission to visible emission. ZnO rods array has a water contact angle of 160.3°, while ZnO particles film has a water contact angle of 150.4°, and their wetting behavior changed from the Cassie state to the Wenzel state during the process of droplet evaporation.
    Journal of Alloys and Compounds 05/2013; 560:156-160. DOI:10.1016/j.jallcom.2013.01.167 · 3.00 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The electrochemical oxidation of methanol and ethanol in acidic media was studied using electrodes composed of multi-walled carbon nanotubes (MWCNTs) decorated with Pt, Ru and ceria nanoparticles. Polystyrene sulfonate (PSS) was used to disperse the MWCNTs in water and provide nucleation sites for the growth of catalyst nanoparticles. Composite electrodes were characterized for structural and electrochemical properties and all electrodes modified with Ru displayed greater catalytic ability for alcohol oxidation than those without Ru. In addition, the inclusion of ceria seemed to increase the catalytic ability in every sample suggesting a synergistic effect between Pt, Ru and ceria for the oxidation of methanol and ethanol. The catalytic effect of Pt and Ru concentration was studied by holding Ru concentrations constant and increasing the concentration of Pt. The same concentration of ceria was used for all modified electrodes. The results of this study show that the electrode prepared from 3:1 Pt:Ru solutions with ceria showed the highest peak current density for methanol oxidation (at 0.6 V vs. Ag/AgCl/Cl– which was nearly 20 times greater than that for an unmodified Pt electrode. Similar results were seen for ethanol oxidation on the same electrode which resulted in peak current densities greater than 20 times those for the unmodified Pt electrode at 0.8 V versus Ag/AgCl/Cl–.
    Materials Express 03/2013; 3(1). DOI:10.1166/mex.2013.1103 · 2.26 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We report the synthesis of a soluble, amorphous, and adhesive electrolyte based on poly(ethylene glycol). A high molecular weight poly(PEGMA-co-MMA-co-IBVE) random copolymer with the lithium ion conductivity of 4.8 × 10− 5 S/cm at room temperature was synthesized through a facile statistical copolymerization of poly(ethylene glycol) methyl ether methacrylates (PEGMA), methyl methacrylate (MMA), and isobutyl vinyl ether (IBVE). The polymer composition, thermal properties, adhesion, and electrochemical properties are presented. Such a copolymer has the adhesion strength to permanently hold 800 times its own weight, and high solubility in water and organic solvents for easy material processing. Its unique and versatile properties belong to a class of multifunctional soft matter electrolytes.
    Solid State Ionics 02/2013; 232:37–43. DOI:10.1016/j.ssi.2012.11.007 · 2.56 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The association of cellular toxicity with the physiochemical properties of graphene-based materials is largely unexplored. A fundamental understanding of this relationship is essential to engineer graphene-based nanomaterials for biomedical applications. Here, an in vitro toxicological assessment of graphene oxide (GO) and reduced graphene oxide (RGO) and in correlation with their physiochemical properties is reported. GO is found to be more toxic than RGO of same size. GO and RGO induce significant increases in both intercellular reactive oxygen species (ROS) levels and messenger RNA (mRNA) levels of heme oxygenase 1 (HO1) and thioredoxin reductase (TrxR). Moreover, a significant amount of DNA damage is observed in GO treated cells, but not in RGO treated cells. Such observations support the hypothesis that oxidative stress mediates the cellular toxicity of GO. Interestingly, oxidative stress induced cytotoxicity reduces with a decreasing extent of oxygen functional group density on the RGO surface. It is concluded that although size of the GO sheet plays a role, the functional group density on the GO sheet is one of the key components in mediating cellular cytotoxicity. By controlling the GO reduction and maintaining the solubility, it is possible to minimize the toxicity of GO and unravel its wide range of biomedical applications.
    Particle and Particle Systems Characterization 02/2013; 30(2). DOI:10.1002/ppsc.201200066 · 3.08 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We report the first fully compressed Li4Ti5O12 electrode designed by an aqueous process. An adhesive, elastomeric, and lithium ion conductive PEG-based copolymer is used as a binder for the aqueous fabrication thick, flexible, and densely packed Li4Ti5O12 (LTO) electrodes. Self-adherent cathode films exceeding 200 μm in thickness and withholding high active mass loadings of 28 mg/cm2 deliver 4.2 mAh/cm2 at C/2 rate. Structurally defect-free electrodes are fabricated by casting aqueous cathode slurries onto nickel foam, dried, and hard-calendared at 10 tons/cm2. As a multifunctional material, the binder is synthesized by the copolymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA), methyl methacrylate (MMA), and isobutyl vinyl ether (IBVE) in optimal proportions. Furthermore, coordinating the binder with lithium salt is necessary for the electrode to function.
    Electrochimica Acta 01/2013; 88:536–542. DOI:10.1016/j.electacta.2012.10.139 · 4.50 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Structural order of conjugated polymers at different length scales direct the optoelectronic properties of the corresponding materials, thus it is of critical importance to understand and control conjugated polymer morphology for successful application of these materials in organic optoelectronics. Herein, with the aim of probing the dependence of single chain folding properties on the chemical structure and rigidness of the polymer backbones, single molecule fluorescence spectroscopy was applied to four thiophene-based conjugated polymers. These include regioregular poly (3-hexylthiophene) (RR-P3HT), poly(2,5-bis(3-tetradecylthiophen-2-yl)-thieno[3,2-b]thiophene) (PBTTT-14), poly(2,5-bis(3-tetradecylthiophen-2-yl)thiophene-2-yl)thiophen-2-ylthiazolo[5,4-d]thiazole) (PTzQT-12) and poly(3,3-didodecyl-quaterthiophene)] (PQT-12). Previous work has shown that RR-P3HT and PBTTT-14 polymer chains fold in their nanostructures, while PQT-12 and PTzQT-12 do not fold in their nanostructures. At the single molecule level, it was found that RR-P3HT single chains almost exclusively fold into loosely and strongly aggregated conformations, analogous to the folding properties in nanostructures. PQT-12 displays significant chain folding as well, but only into loosely aggregated conformations, showing an absence of strongly aggregated polymer chains. PBTTT-14 exhibits a significant fraction of rigid polymer chain. The findings made for single molecules of PQT-12 and PBTTT-14 are thus in contrast with the observations made in their corresponding nanostructures. PTzQT-12 appears to be the most rigid and planar conjugated polymer of these four polymers. However, while the presumably non-folding polymers PQT-12 and PTzQT-12 exhibit less folding than RR-P3HT, there is still a significant occurrence of chain folding for these polymers at the single molecule level. These results suggest that the folding properties of conjugated polymers can be influenced by the architecture of the polymer backbones, however, other factors such as intermolecular stacking interactions, solvent environment and side chain interactions in corresponding materials should also be taken into account to predict conjugated polymer material morphology.
    The Journal of Physical Chemistry B 12/2012; 117(16). DOI:10.1021/jp308497k · 3.30 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Electronic transport of regioregular poly(3-hexylthiophene)-block-poly styrene (rr-P3HT-b-PS) copolymer in field effect transistor (FET) geometry with different surface treatment and different temperature is investigated. The devices show p type behavior with a maximum saturation mobility of 6 × 10−3 cm2/V s and current on/off ratio of 2.6 × 104 in an OTS treated sample at room temperature, which is lower compared to the controlled P3HT sample of same molecular weight fabricated with the same surface treatment. The mobility measured at different temperatures (300–150 K) show thermally activated hopping type transport mechanism with gate bias dependent activation energy of 100–270 meV which is higher compared to the reported value of pristine P3HT FET. The higher activation energy in hopping behavior and lower mobility in this block copolymer is caused by insulating PS segments.
    Synthetic Metals 10/2012; 162(s 17–18):1531–1536. DOI:10.1016/j.synthmet.2012.07.022 · 2.25 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We report the first aqueous process fabrication of thick, flexible, and fully compressed lithium ion battery cathodes exceeding 200 mu m in thickness using an adhesive, elastomeric, and ionically conductive PEG-based copolymer binder. The binder was synthesized through the statistical copolymerization of poly(ethylene glycol) methyl ether methacrylates (PEGMA), methyl methacrylate (MMA), and isobutyl vinyl ether (IBVE) in optimal proportions. Using standard LiCoO2 as active material, dense and flexible cathode films can withhold active mass loadings over 30 mg/cm(2) which deliver 4.53 mAh/cm(2) with 94% capacity retention at C/2-rate. Electrodes were fabricated by casting aqueous cathode slurries onto nickel foam, followed by drying and hard calendar compression at 10 tons/cm(2). Coordinating the binder with lithium salt plays a crucial role in activating the cathode.
    Journal of The Electrochemical Society 10/2012; 159(12):A1928-A1933. DOI:10.1149/2.035212jes · 3.27 Impact Factor
  • Matthew Mcinnis · Lei Zhai
    [Show abstract] [Hide abstract]
    ABSTRACT: This review surveys the research regarding dispersing and functionalizing carbon nanotubes using conjugated polymers and block copolymers and the applications of resultant composites. The factors that affect the assembling behavior of conjugated polymers on carbon nanotubes have been discussed by comparing theoretical and experimental studies. Conjugated block copolymers have been used to disperse pristine carbon nanotubes through non-invasive – interactions. The conjugated polymer/carbon nanotube composites have demonstrated interesting applications in efficient field-effect-transistors, coatings, and aerogels. The future research directions regarding understand the impact of the polymer structures, the polymer/carbon nanotube interactions on the polymer assembling behavior and future functionalization of conjugated block copolymer dispersed carbon nanotubes are presented.
    06/2012; 1(2):119-141. DOI:10.1166/rnn.2012.1008
  • [Show abstract] [Hide abstract]
    ABSTRACT: Multi-walled carbon nanotube (MWCNT)/MnO2 supercapacitor electrodes containing MnO2 nanoflakes in the MWCNT network are fabricated through the oxidation of manganese acetate with poly(4-styrenesulfonic acid) (PSS) dispersed MWCNTs. The structural evolution of the electrodes under charge/discharge (reduction/oxidation) cycles and its impact on the electrodes’ electrochemical properties are evaluated. Structural evolution involves the dissolution of MnO2 upon reduction, the diffusion of the reduced Mn species from the MWCNT network toward the electrolyte solution, and the deposition of MnO2 on the electrode surface upon oxidation. Electrode structural changes, including the electrode dissolution and the growth of the MnO2 crystals, are scan rate dependent and have deteriorating effect on the electrode's electrochemical properties including the specific capacitance and cyclic stability
    Electrochimica Acta 01/2012; 59. DOI:10.1016/j.electacta.2011.11.017 · 4.50 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Polymer-derived amorphous SiBCN ceramics are synthesized through a simple dehydrocoupling and hydroboration reaction of an oligosilazane containing amine and vinyl groups and BH3·Me2S, followed by pyrolysis. Two types of ceramics, denoted as Si2B1 and Si4B1, are produced from preceramic polymers with Si/B ratios of 2/1 and 4/1, respectively. The structural evolution of these ceramics with respect to the pyrolysis temperature and boron concentration is investigated using solid-state NMR, Raman, and EPR spectroscopy. Solid-state NMR suggests the presence of three major components in the ceramics: (i) hexagonal boron nitride (h-BN), (ii) turbostratic boron nitride (t-BN), and (iii) BN2C groups. Increasing pyrolysis temperature leads to the transformation of BN2C groups into BN3 and “free” carbon. A thermodynamic model is proposed to explain such transformation. Raman spectroscopy measurements reveal that the concentration of the “free” carbon cluster decreases with increasing pyrolysis temperature, and Si4B1 contains more “free” carbon cluster than Si2B1. EPR studies reveal that the carbon (C)-dangling bond content also decreases with increasing pyrolysis temperature. It appears that the complete decomposition of the metastable BN2C groups to the BN3 groups and the “free” carbon affects the crystallization of SiBCN, which leads to Si4B1 ceramics crystallized at 1500 °C, whereas Si2B1 ceramics crystallized at 1600 °C.
    The Journal of Physical Chemistry C 11/2011; 115(50). DOI:10.1021/jp203287h · 4.77 Impact Factor
  • ACS Applied Materials & Interfaces 06/2011; DOI:10.1021/am200438j · 6.72 Impact Factor

Publication Stats

2k Citations
360.77 Total Impact Points


  • 2007–2015
    • University of Central Florida
      • • Department of Chemistry
      • • NanoScience Technology Center
      • • Department of Mechanical and Aerospace Engineering
      Orlando, Florida, United States
  • 2001–2004
    • Carnegie Mellon University
      • Department of Chemistry
      Pittsburgh, Pennsylvania, United States