Meng-Fang Lin

Enhancing electrochemical reaction sites in nickel-cobalt layered double hydroxides on zinc tin oxide nanowires: a hybrid material for an asymmetric supercapacitor device.

Conducting nanowires are of particular interest in energy-related research on devices such as supercapacitors, batteries, water splitting electrodes and solar cells. Their direct electrode/current collector contact and highly conductive 1D structure enable conducting nanowires to provide ultrafast charge transportation. In this paper, we report the facile synthesis of nickel cobalt layered double hydroxides (LDHs) on conducting Zn(2)SnO(4) (ZTO) and the application of this material to a supercapacitor. This study also presents the first report of an enhancement of the active faradic reaction sites (electroactive sites) resulting from the heterostructure. This novel material demonstrates outstanding electrochemical performance with a high specific capacitance of 1805 F g(-1) at 0.5 A g(-1), and an excellent rate performance of 1275 F g(-1) can be achieved at 100 A g(-1). Furthermore, an asymmetric supercapacitor was successfully fabricated using active carbon as a negative electrode. This asymmetric device exhibits a high energy density of 23.7 W h kg(-1) at a power density of 284.2 W kg(-1). Meanwhile, a high power density of 5817.2 W kg(-1) can be achieved at an energy density of 9.7 W h kg(-1). More importantly, this device exhibits long-term cycling stability, with 92.7% capacity retention after 5000 cycles.

Polydopamine Spheres as Active Templates for Convenient Synthesis of Various Nanostructures

In this work, monodisperse polydopamine (PDA) spheres with tunable diameters have been synthesized through a facile and low cost method using a deionized water and alcohol mixed solvent. The PDA spheres possess surface functional groups (-OH, -NH(2)), exhibiting an extraordinary versatile active nature. It is demonstrated that the PDA spheres could serve as an active template for the convenient synthesis of various nanostructures, e.g., MnO(2) hollow spheres or PDA/Fe(3)O(4) and PDA/Ag core/shell nanostructures. No surface modification or special treatment is required for the synthesis of these nanostructures, which makes the fabrication process simple and very convenient. The novel application of PDA/Fe(3)O(4) spheres as fillers in nanocomposites for high-performance capacitors is demonstrated, indicating a promising practicality. The PDA spheres provide a new general platform not only for the facile assembly of nanostructures but also a green synthetic template for practical applications.

Surface functionalization of BaTiO3 nanoparticles and improved electrical properties of BaTiO3/polyvinylidene fluoride composite

Surface functionalization of BaTiO3 nanoparticles with dopamine was carried out using a reflux method to strongly bind dopamine on the BaTiO3 nanoparticle surface and improve its compatibility with the polyvinylidene fluoride (PVDF) polymer matrix. Fourier transform infrared spectra confirm the successful surface functionalization of BaTiO3 nanoparticles after immobilization with dopamine. Electrical properties of the resultant nanocomposite show that the dielectric constant can be enhanced up to 56.8 with low dielectric loss.

Dopant induced hollow BaTiO3 nanostructures for application in high performance capacitors

In this work, large-scale single crystalline Nd-doped BaTiO3 hollow nanoparticles have been synthesized via a simple hydrothermal method without the assistance of a surfactant or high temperature sintering. With unique hollow structures, the nanoparticles not only exhibit excellent compatibility with poly(vinylidene fluoride) (PVDF), but significantly enhanced the dielectric properties of the nanocomposites. We demonstrated that the dielectric constant of the nanocomposite reached up to 480.3 with dielectric loss of 0.6 at 102 Hz. Design and optimization of the synthesis method have been achieved through a systematic study of the effect of reaction conditions on the size and morphology evolution of the hollow nanoparticles. The formation of hollow nanostructures is proposed to follow a Kirkendall induced hollowing mechanism which is governed by the differences in diffusion rates of dopant ions, water molecules and core ions during the synthesis reaction.

Green aqueous modification of fluoropolymers for energy storage applications

Fluoropolymers are of prime interest as solution processable materials for electronic applications such as embedded capacitors, multilayer capacitors, and high-energy-density capacitors. Herein, for the first time, we investigated an environmentally friendly green aqueous modification of fluoropolymers, poly(vinylidene fluoride) (PVDF) for energy storage applications. The PVDF polymer was modified in aqueous medium by using bioinspired protein dopamine without any harmful toxic chemicals. Dopamine functionalization onto pre-irradiated PVDF polymer powder was carried out using a simple reflux method to strongly bind dopamine onto the PVDF surface. The resulting dopamine modified PVDF films exhibited excellent dielectric properties, when compared with the pristine PVDF polymer. The dielectric constant can be enhanced up to 32 with fairly low dielectric loss as compared to pristine PVDF. Furthermore, the modified films were found to have good flexibility; they could be curled as easily as pristine PVDF films. Since this method avoids the use of toxic chemicals, it may allow the application of modified PVDF not only for energy storage applications but also for other applications such as in biocompatible materials.

Polystyrene grafted polyvinylidenefluoride copolymers with high capacitive performance

Electroactive materials are of great interest for high performance capacitive behavior due to their relaxed ferroelectric properties. In this work, we studied the dielectric properties of poly(vinylidene fluoride) (PVDF) grafted with polystyrene (PS) by electron beam radiation induced free radical graft copolymerization reaction in solution. The dielectric constant of polystyrene grafted PVDF copolymers reaches about 90 at 100 Hz at room temperature representing more than seven times increment compared with the pristine PVDF matrix. The dielectric loss of 0.005 at 1 KHz can be achieved. Correlation of the dielectric properties with the graft copolymerization reaction mechanism was discussed. This route represents one of the most effective techniques to synthesize potential graft copolymers with desirable dielectric properties in a wide frequency range for energy storage applications.

Formation of PVDF-g-HEMA/BaTiO3 nanocomposites via in situ nanoparticle synthesis for high performance capacitor applications

PVDF-g-HEMA [poly(vinylidene fluoride)-graft-poly(2-hydroxyethylmethacrylate)]/Barium Titanate (BaTiO3) nanocomposites were prepared successfully via an in situ synthesis method without any catalyst or initiator. The in situ synthesis approach enables the formation of oxide nanoparticles in the presence of the grafted polymer with a hydroxyl functionalization group for direct coupling with oxide nanofillers. This elegant in situ nanoparticle synthesis method provides a facile, cost-effective and void-free dispersion of the nanoparticles in the matrix. The dielectric nanoparticle (BaTiO3) is well-attached onto the insulating polymer (PVDF) surface due to the surface anchoring linkage through hydrogen bonding between the two components, leading to the reduced aggregation in the resultant nanocomposites. The novel PVDF-g-HEMA/BaTiO3 nanocomposites are investigated as high energy density capacitor materials, achieving highest dielectric constant reaching up to 333, and a dielectric loss of 0.73 at 30 wt% BaTiO3 at 1 kHz.

Highly Transparent Conducting Nanopaper for Solid State Foldable Electrochromic Devices

It is of great challenge to develop a transparent solid state electrochromic device which is foldable at the device level. Such devices require delicate designs of every component to meet the stringent requirements for transparency, foldability, and deformation stability. Meanwhile, nanocellulose, a ubiquitous natural resource, is attracting escalating attention recently for foldable electronics due to its extreme flexibility, excellent mechanical strength, and outstanding transparency. In this article, transparent conductive nanopaper delivering the state-of-the-art electro-optical performance is achieved with a versatile nanopaper transfer method that facilitates junction fusing for high-quality electrodes. The highly compliant nanopaper electrode with excellent electrode quality, foldability, and mechanical robustness suits well for the solid state electrochromic device that maintains good performance through repeated folding, which is impossible for conventional flexible electrodes. A concept of camouflage wearables is demonstrated using gloves with embedded electrochromics. The discussed strategies here for foldable electrochromics serve as a platform technology for futuristic deformable electronics.

Direct Observation of Indium Conductive Filaments in Transparent, Flexible, and Transferable Resistive Switching Memory

Electronics with multifunctionalities such as transparency, portability, and flexibility are anticipated for future circuitry development. Flexible memory is one of the indispensable elements in a hybrid electronic integrated circuit as the information storage device. Herein, we demonstrate a transparent, flexible, and transferable hexagonal boron nitride (hBN)-based resistive switching memory with indium tin oxide (ITO) and graphene electrodes on soft polydimethylsiloxane (PDMS) substrate. The ITO/hBN/graphene/PDMS memory device not only exhibits excellent performance in terms of optical transmittance (∼85% in the visible wavelength), ON/OFF ratio (∼480), retention time (∼5 × 104 s) but also shows robust flexibility under bending conditions and stable operation on arbitrary substrates. More importantly, direct observation of indium filaments in an ITO/hBN/graphene device is found via ex situ transmission electron microscopy, which provides critical insight on the complex resistive switching mechanisms.

A copper-based reversible electrochemical mirror device with switchability between transparent, blue, and mirror states

Herein, a reversible electrochemical mirror (REM) device was electrochemically tuned to achieve dual transmittance and reflectance modulations in a single device. Conventional REM devices reversibly switch between transparent and mirror states. However, it is a significant challenge to maintain the mirror state of the REM devices due to the diffusion of anions into the metal film at the open-circuit state. In this study, we report a Cu-based REM device that offers reversible switching between transparent, blue, and mirror states via a judicious selection of electrolyte and controllable electrodeposition. The blue state can be obtained through the formation of copper(I) chloride (CuCl) when copper(II) chloride (CuCl2) undergoes electrochemical reduction. Moreover, the polymer host PVA (polyvinyl alcohol) plays an important role in reducing the surface roughness of the electrodeposited mirror film, improving film uniformity, and maintaining the mirror state of the device during the voltage-off state.