Jianfeng Zang

Flexible Zn2SnO4/MnO2 Core/Shell Nanocable - Carbon Microfiber Hybrid Composites for High Performance Supercapacitor Electrodes

We demonstrate the design and fabrication of a novel flexible nanoarchitecture by facile coating ultrathin (several nanometers thick) films of MnO2 to highly electrical conductive Zn2SnO4 (ZTO) nanowires grown radially on carbon microfibers (CMFs) to achieve high specific capacitance, high-energy density, high-power density, and long-term life for supercapacitor electrode applications. The crystalline ZTO nanowires grown on CMFs were uniquely served as highly conductive cores to support a highly electrolytic accessible surface area of redox active MnO2 shells and also provide reliable electrical connections to the MnO2 shells. The maximum specific capacitances of 621.6 F/g (based on pristine MnO2) by cyclic voltammetry (CV) at a scan rate of 2 mV/s and 642.4 F/g by chronopotentiometry at a current density of 1 A/g were achieved in 1 M Na2SO4 aqueous solution. The hybrid MnO2/ZTO/CMF hybrid composite also exhibited excellent rate capability with specific energy of 36.8 Wh/kg and specific power of 32 kW/kg at current density of 40 A/g, respectively, and good long-term cycling stability (only 1.2% loss of its initial specific capacitance after 1000 cycles). These results suggest that such MnO2/ZTO/CF hybrid composite architecture is very promising for next generation high-performance supercapacitors.

In situ synthesis of ultrafine β-MnO2/polypyrrole nanorod composites for high-performance supercapacitors

We report a remarkable observation that is at odds with the established notion that β-MnO2 was regarded as an undesirable candidate for supercapacitor applications. The specific capacitance of β-MnO2 can reach as high as 294 F g−1, which is comparable to the best crystallographic structure, like α-MnO2. The key is to substantially decrease the size of β-MnO2 powders to ultra small regime. We demonstrate a facile, simple, and effective approach to synthesizing ultrafine (<10 nm in diameter) β-MnO2/polypyrrole nanorod composite powders for high-performance supercapacitor electrodes. Our observation may encourage a revisit of the other good or even bad candidate active materials if we can decrease their size to extremely small scales. In addition, the proposed synthetic mechanism and the developed synthetic strategy may provide design guidelines in synthesizing other energy storage materials toward ultrafine 1D nanostructures.

Harnessing Localized Ridges for High-Aspect-Ratio Hierarchical Patterns with Dynamic Tunability and Multifunctionality

A simple method for fabricating high-aspect-ratio, hierarchical, and dynamically tunable surface patterns is invented by harnessing localized-ridge instabilities in gold nanofilms coated on elastomer substrates (a); a theoretical model to calculate the critical parameters (e.g., wavelength and amplitude) for designing the new patterns is developed (b); and novel applications of the patterns as super-hydrophobic coatings (c) and biomimetic cell-culture substrates (d) capable of on-demand tunability are demonstrated.

Electrochemical detection of ultratrace nitroaromatic explosives using ordered mesoporous carbon.

A sensitive electrochemical sensor has been fabricated to detect ultratrace nitroaromatic explosives using ordered mesoporous carbon (OMC). OMC was synthesized and characterized by scanning electron microscopy, transmission electron microscopy and nitrogen adsorption/desorption measurements. Glassy carbon electrodes functionalized with OMC show high sensitivity of 62.7 μA cm(-2) per ppb towards 2,4,6-trinitrotoluene (TNT). By comparison with other materials such as carbon nanotubes and ordered mesoporous silica, it is found that the high performance of OMC toward sensing TNT is attributed to its large specific surface area and fast electron transfer capability. As low as 0.2 ppb TNT, 1 ppb 2,4-dinitrotoluene and 1 ppb 1,3-dinitrobenzene can be detected on OMC based electrodes. This work renders new opportunities to detect ultratrace explosives for applications of environment protections and home securities against chemical warfare agents.

Reversible Sliding in Networks of Nanowires

This work demonstrates that metal nanowires in a percolating network can reversibly slide across one another. Reversible sliding allows networks of metal nanowires to maintain electrical contact while being stretched to strains greater than the fracture strain for individual nanowires. This phenomenon was demonstrated by using networks of nanowires as compliant electrodes for a dielectric elastomer actuator. Reversible nanowire sliding enabled actuation to a maximum area strain of 200% and repetitive cycling of the actuator to an area strain of 25% over 150 times. During actuation, the transmittance of the network increased 4.5 times, from 13% to 58%. Compared to carbon-based compliant electrodes, networks of metal nanowires can actuate across a broader range of optical transmittance. The widely tunable transmittance of nanowire-based actuators allows for their use as a light valve.

Dynamic electrostatic lithography: multiscale on-demand patterning on large-area curved surfaces.

Dynamic electrostatic lithography is invented to dynamically generate various patterns on large-area and curved polymer surfaces under the control of electrical voltages. The shape of the pattern can be tuned from random creases and craters to aligned creases, craters and lines, and the size of the pattern from millimeters to sub-micrometers.

Electrospinning fabrication, structural and mechanical characterization of rod-like virus-based composite nanofibers

Tobacco mosaic virus (TMV) was electrospun with polyvinyl alcohol (PVA) into continuous TMV–PVA composite nanofibers to form a biodegradable nonwoven fibrous mat as an extracellular matrix (ECM) mimetic. Morphological characterizations by electron microscopy showed that the addition of varying amounts of TMV resulted in homogeneous nanofibers without phase separation and did not change the diameter of the composite nanofibers. The orientation of TMV in as-spun fibers could be readily controlled and post-processing of the nonwoven TMV–PVA mat significantly improved its water resistance. In addition, tensile tests were performed on individual nanofibers, which revealed that the TMV–PVA composite nanofibers achieved a comparable Youngs modulus as PVA nanofibers. Since the modification of TMV is readily achieved via genetic or chemical methods, this process offers a facile way to incorporate a variety of functionalities into polymer nanofibers. As a demonstration of its potential as ECM mimetic, a mutant TMV containing RGD peptide was co-spun with PVA and the resulting fibrous substrates were used to promote cell growth.

Electrical self-healing of mechanically damaged zinc oxide nanobelts.

We report the observation of remarkable electrical self-healing in mechanically damaged ZnO nanobelts. Nanoindentation into intrinsically defect-free ZnO nanobelts induces deformation and crack damage, causing a dramatic electrical signal decrease. Two self-healing regimes in the nanoindented ZnO nanobelts are revealed. The physical mechanism for the observed phenomena is analyzed in terms of the nanoindentation-induced dislocations, the short-range atomic diffusion in nanostructures, and the local heating of the dislocation zone in the electrical measurement.

Electron Beam Irradiation Stiffens Zinc Tin Oxide Nanowires

We report a remarkable phenomenon that electron beam irradiation (EBI) significantly enhances the Youngs modulus of zinc tin oxide (ZTO) nanowires (NWs), up to a 40% increase compared with the pristine NWs. In situ uniaxial buckling tests on individual NWs were conducted using a nanomanipulator inside a scanning electron microscope. We propose that EBI results in substantial atomic bond contraction in ZTO NWs, accounting for the observed mechanically stiffening. This argument is supported by our experimental results that EBI also reduces the electrical conductivity of ZTO NWs.

Shape-controlled assembly of luminescent dumbbell-like CdTe?cystine nanocomposites

A shape perfect luminescent dumbbell with size up to several microns was prepared by incorporating CdTe quantum dots (QDs) into locally created L-cystine matrices, and the photoluminescence of the shaped dumbbells can be easily tailored by reaction time. The growth mechanism was thoroughly investigated. This work not only gives a potential application in optical devices, but also gives a deep insight on the assembly mechanism of nanomaterials into micron-size objects.