Zhongqiu Tong

Layered polyaniline/graphene film from sandwich-structured polyaniline/graphene/polyaniline nanosheets for high-performance pseudosupercapacitors

Binder-free layered graphene/polyaniline composite film was prepared by an environmentally friendly and facile two-step route for the first time. Firstly, a sandwich-structured PANI/graphene/PANI nanosheet was prepared in situ from aqueous solution, followed an electrophoretic deposition process. By observations of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM), it conforms that the graphene sheet is uniformly covered by an ultralthin PANI film (3.7 nm). Raman spectra, Fourier transform infrared (FT-IR) spectra and X-ray photoelectron spectroscopy (XPS) are jointly used to confirm strong π–π electron and hydrogen bond interaction in the nanosheets. The layered PANI/graphene composite film exhibits an excellent gravimetric capacitance of 384 F g−1 at 0.5 A g−1 which is much higher than many other hybrid supercapacitors reported to date. It maintains its capacity up to 84% over 1000 cycles at a current density of 2 A g−1. This preparation method may provide a promising strategy for preparation of graphene-based composites with other conducting polymers and binder-free film electrodes.

Improved electrochromic performance and lithium diffusion coefficient in three-dimensionally ordered macroporous V2O5 films

Three-dimensionally ordered macroporous (3DOM) vanadium pentoxide (V2O5) films with various pore diameters were prepared by anodic deposition into colloidal crystal templates. The influence of the 3DOM structure on lithium ion (Li+) diffusion coefficient was investigated for the first time. X-ray diffraction analysis and HRTEM measurements show that the skeleton walls are composed of crystallites and amorphous V2O5. The study of electrochromic properties indicates that the pore size has a significant impact on the electrochromic performance. Small pores in the film lead to higher optical contrast and faster switching response. A high transmittance modulation in the visible and near-infrared spectral regions (50% at λ = 650 nm and 47% at λ = 900 nm) with fast response time (1.7 s for coloration and 3.2 s for bleaching) is observed in the 3DOM V2O5 film with a pore size of 210 nm. Because of the fully interconnected macroporous network in the 3DOM structure, the transport and reaction of lithium ions and electrons both behave in an effective 3D model throughout the whole nanostructure. Additionally, due to their influence on the polarization of the electrode and surface defects, sharp nanoscale edges around pores and rough surfaces can further promote Li+ diffusion and intercalation/de-intercalation. The 3DOM V2O5 film with a pore size of 210 nm exhibits a very high Li+ diffusion coefficient of 3.78 × 10−9 cm2 s−1, which is higher than any coefficient ever reported for a V2O5 film.

Versatile displays based on a 3-dimensionally ordered macroporous vanadium oxide film for advanced electrochromic devices

Three-dimensionally ordered macroporous (3DOM) vanadium oxide film was fabricated by anodic deposition of vanadium oxide into colloidal crystal template. The as-prepared films were investigated by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). The electrochemical and electrochromic behaviors of the films were studied in 1.0 M LiClO4–propylene carbonate solution. Because of the larger surface area and shorter diffusion distance, the 3DOM film exhibited better electrochromic performance than the dense film prepared without the template. The 3DOM film exhibited multicolor changes (yellow, green and black) in the voltage window from +1 to −1 V with a high transmittance modulation of ca. 34% at 460 nm and high switching speed (1.5 s for coloration and 2.1 s for bleaching). Cyclic voltammetry (CV) and chronoamperometry measurements showed that the 3DOM structure is beneficial for Li+ diffusion in vanadium oxide films. An ITO/vanadia/gel/PEDOT:PSS/ITO electrochromic device was assembled, and the device showed multicolor changes with fast switching speed (3.5 s for anodic coloration and 3.4 s for cathodic coloration) and good cycling stability.

Novel morphology changes from 3D ordered macroporous structure to V2O5 nanofiber grassland and its application in electrochromism

Because vanadium pentoxide (V2O5) is the only oxide that shows both anodic and cathodic coloration electrochromism, the reversible lithium ion insertion/extraction processes in V2O5 lead to not only reversible optical parameter changes but also multicolor changes for esthetics. Because of the outstanding electrochemical properties of V2O5 nanofibers, they show great potential to enhance V2O5 electrochromism. However, the development and practical application of V2O5 nanofibers are still lacking, because traditional preparation approaches have several drawbacks, such as multiple processing steps, unsatisfactory electrical contact with the substrate, expensive equipment, and rigorous experimental conditions. Herein, we first report a novel and convenient strategy to prepare grass-like nanofiber-stacked V2O5 films by a simple annealing treatment of an amorphous, three-dimensionally ordered macroporous vanadia film. The V2O5 nanofiber grassland exhibits promising transmittance modulation, fast switching responses, and high color contrast because of the outstanding electrochemical properties of V2O5 nanofibers as well as the high Li-ion diffusion coefficients and good electrical contact with the substrate. Moreover, the morphology transformation mechanism is investigated in detail.

Recent advances in multifunctional electrochromic energy storage devices and photoelectrochromic devices

Multifunctional devices integrated with electrochromism and energy storage or energy production functions are attractive because these devices can be used as an effective approach to address the energy crisis and environmental pollution in society today. In this review, we explain the operation principles of electrochromic energy storage devices including electrochromic supercapacitors, electrochromic batteries, and the photoelectrochromic devices. Furthermore, the material candidates and structure types of these multifunctional devices are discussed in detail. The major challenges of these devices along with a further outlook are highlighted at the end.

Rational selection of amorphous or crystalline V2O5 cathode for sodium-ion batteries

Vanadium oxide (V2O5), as a potential positive electrode for sodium ion batteries (SIBs), has attracted considerable attention from researchers. Herein, amorphous and crystalline V2O5 cathodes on a graphite paper without a binder and conductive additives have been synthesized via facile anodic electrochemical deposition following different heat treatments. Both the amorphous V2O5 (a-V2O5) cathode and crystalline V2O5 (c-V2O5) cathode show good rate cycling performance and long cycling life. After five rate cycles, the reversible capacities of both the cathodes were almost unchanged at different current densities from 40 to 5120 mA g-1. Long cycling tests with 10 000 cycles were carried out and the two cathodes exhibit excellent cycling stability. The c-V2O5 cathode retains a high specific capacity of 54 mA h g-1 after 10 000 cycles at 2560 mA g-1 and can be charged within 80 s. Interestingly, the a-V2O5 cathode possesses higher reversible capacities than the c-V2O5 cathode at low current densities, whereas it is inversed at high current densities. The c-V2O5 cathode shows faster capacity recovery from 5120 to 40 mA g-1 than the a-V2O5 cathode. When discharged at 80 mA g-1 (long discharge time of 140 min) and charged at 640 mA g-1 (short charge time of 17 min), the a-V2O5 cathode shows a higher discharge capacity than its c-V2O5 counterpart. The different electrochemical performance of a-V2O5 and c-V2O5 cathodes during various electrochemical processes can provide a rational selection of amorphous or crystalline V2O5 cathode materials for SIBs in their practical applications to meet the variable requirements.

A rapid-response electrochromic device with significantly enhanced electrochromic performance

A novel electrochromic device (ECD) was constructed with two same-material electrochromic layers deposited on indium-tin oxide (ITO)-coated glass substrates, a double-sided ITO-coated glass substrate, and a gel electrolyte. The device exhibited fast coloration/bleaching response and significantly enhanced optical modulation and coloration efficiency compared to traditional ECDs.

Near-infrared and Multicolor Electrochromic Device Based on Polyaniline Derivative

Electroactive conducting copolymers of aniline (ANI) and diphenylamine (DPA) are prepared on indium tin oxide (ITO) surface from 1 mol/L H2SO4 aqueous solution with different feed ratios of ANI to DPA by using a potentiostatic method. FTIR spectra and SEM measurements are used to confirm the formation of copolymers. Due to the combination of the N,N′-diphenyl benzidine and aniline units in the molecular chain, the copolymer films exhibit improved electrochemical and electrochromic properties, compared to PANI and PDPA. The copolymer [marked as P(ANI9-co-DPA1)] film prepared at a ratio of 9:1 (ANI/DPA) exhibits novel transmittance modulation both in visible and near-infrared (NIR) region between −0.8 V and 0.8 V (52% and 67% respectively) and fast response time (3.6 s for coloration and 2.3 s for bleaching at 600 nm). An electrochromic device (ECD) based on P(ANI9-co-DPA1) and PEDOT:PSS is also fabricated and shows a multicolor electrochromic performance, with a good optical contrast (29% in visible region and 40% in NIR region), acceptable response time (8.3 s for coloration and 7.5 s for bleaching at 600 nm) and long-term stability. Clear color changes from transparent (−0.8 V), bright green (0 V), seagreen (0.4 V) to dark slate gray (0.8 V) are demonstrated.

Self-supported one-dimensional materials for enhanced electrochromism

A reversible, persistent electrochromic change in color or optical parameter controlled by a temporarily applied electrical voltage is attractive because of its enormous display and energy-related applications. Due to the electrochemical and structural advantages, electrodes based on self-supported one-dimensional (1D) nanostructured materials have become increasingly important, and their impacts are particularly significant when considering the ease of assembly of electrochromic devices. This review describes recent advances in the development of self-supported 1D nanostructured materials as electrodes for enhanced electrochromism. Current strategies for the design and morphology control of self-supported electrodes fabricated using templates, anodization, vapor deposition, and solution techniques are outlined along with demonstrating the influences of nanostructures and components on the electrochemical redox kinetics and electrochromic performance. The applications of self-supported 1D nanomaterials in the emerging bifunctional devices are further illustrated.

Three dimensional hierarchically porous crystalline MnO2 structure design for a high rate performance lithium-ion battery anode

A reasonably designed anode of hierarchically porous crystalline manganese dioxide on nickel foam has been successfully synthesized by facile anodic electrochemical deposition in combination with heat treatment. The three dimensional structure avoids the application of binder and conductive additives. The Ni foam provides a highly electronically conductive network in conjunction with a large surface area to support well contacted MnO2 nanoparticles and effectively increases the mechanical strength of the MnO2 anode as well as suppresses the aggregation of MnO2 nanoparticles during discharge/charge processes. The hierarchical pores composed of a large amount of macropores and mesopores can not only accommodate the volume change of MnO2 nanoparticles during Li ion insertion/extraction, but also accelerate the penetration of electrolyte and promise fast transport and intercalation kinetics of Li ions. The crystalline MnO2 anode exhibits a higher electrochemical performance than the amorphous one. As a result, the hierarchically porous crystalline MnO2 anode shows a long cycling life of 778.0 mA h g−1 after 200 cycles at a current density of 0.4 A g−1 and high-rate capability of up to 82% capacity retention even after the current density increases 20 times from 0.1 to 2.0 A g−1.