Shengyuan Yang

Bottom-Up Fabrication of Activated Carbon Fiber for All-Solid-State Supercapacitor with Excellent Electrochemical Performance

Activated carbon (AC) is the most extensively used electrode material for commercial electric double layer capacitors (EDLC) given its high specific surface area (SSA) and moderate cost. However, AC is primarily used in the forms of powders, which remains a big challenge in developing AC powders into continuous fibers. If AC powders can be processed into fiber, then they may be scaled up for practical applications to supercapacitors (SCs) and satisfy the rapid development of flexible electronics. Herein, we report a bottom-up method to fabricate AC fiber employing graphene oxide (GO) as both dispersant and binder. After chemical reduction, the fiber has high electrical conductivity (185 S m(-1)), high specific surface area (1476.5 m(2) g(-1)), and good mechanical flexibility. An all solid-state flexible SC was constructed using the prepared fiber as electrode, which is free of binder, conducting additive, and additional current collector. The fiber-shaped SC shows high capacitance (27.6 F cm(-3) or 43.8 F g(-1), normalized to the two-electrode volume), superior cyclability (90.4% retention after 10u202f000 cycles), and good bendability (96.8% retention after bending 1000 times).

Controlled synergistic strategy to fabricate 3D-skeletal hetero-nanosponges with high performance for flexible energy storage applications

The simple combination of electrospinning and electrospraying has previously been studied by some researchers to fabricate novel nanomaterials for energy applications in batteries and supercapacitors. However, the performance of the resultant materials (especially electrodes) is not sufficient despite the collaboration of these two boundless methods. Herein, we report the best approach towards effective synergistic control of the two techniques to improve the electrochemical performance of the resultant electrode materials. Interestingly, the reported modified technique yielded unusual 3D-skeletal architectures with dissimilar but remarkable capacitance values. The current methodology is an easy and inexpensive approach to realizing 3D high-performance electroactive materials.

Design and synthesis of porous channel-rich carbon nanofibers for self-standing oxygen reduction reaction and hydrogen evolution reaction bifunctional catalysts in alkaline medium

Carbon-nanofiber-based (CNF-based) nonprecious catalysts and electrodes are essential components in next generation energy conversion and storage technologies. Moreover, porous architectures are highly desirable for active material embedded CNFs. Despite recent progress, controllable synthesis of porous CNFs with favorable mechanical properties is still challenging. Herein, we present a general and novel approach to prepare porous and channel-rich CNFs on a large scale through a free-surface electrospinning technique and subsequent carbonization of polyacrylonitrile (PAN)/cellulose acetate (CA) nanofibers. The resultant free-standing and flexible PAN/CA CNFs (CACNFs) possess abundant porous and channel-rich structures, which can be easily controlled by adjusting the weight ratio of PAN and CA. Based on the porous CACNFs, binder-free Fe3C embedded Fe/N doped CACNF films are successfully prepared. Combining the porous channel-rich structures and the high electrical conductivity of the carbon fibers, abundant accessible active sites and fast mass transport pathways are generated in the carbon fibers, leading to favorable catalytic activity and superior stability for ORR (half-wave potential 12 mV more positive than that of Pt/C) and HER (overpotential 440 mV@80 mV cm−2 and more than 100u2006000 s catalytic stability) in alkaline medium, demonstrating their promising potential for application in fuel cells, metal–air batteries and water splitting devices.

A novel stimuli-responsive fluorescent elastomer based on an AIE mechanism

In this paper, a facile approach for the synthesis of stimuli-responsive fluorescent elastomer was developed. Tetraphenylethylene (TPE) derivant was linked to flexible polydimethylsiloxane (PDMS) polymer chains by covalent bonding with a silane coupling agent, followed by condensation reaction with tetraethylorthosilicate (TEOS) as the curing agent via sol–gel reaction to obtain the fluorescent elastomer. 1HNMR and FTIR spectroscopy studies showed the degree of the reaction, and the homogeneous distribution of the TPE derivant in the elastomer was confirmed by SEM, XRD and PL spectra. Due to the hampered intramolecular rotation of the aryl rotors of the dye molecules with the intertwined polymer chains, the cured elastomers showed intense fluorescence emission. In addition, the elastomers exhibited stimuli-sensitive fluorescence against temperature, and their responsiveness was found to be reversible.

Hierarchically porous carbon black/graphene hybrid fibers for high performance flexible supercapacitors

To meet the rapid development of lightweight, flexible, and even wearable electronics, it is critically important to develop matchable, highly efficient energy-storage devices for their energy supply. Graphene fiber-based supercapacitors (SCs) are considered as one of the promising candidates because of the superior mechanical and electrical properties of graphene fibers. However, SCs based on neat graphene fibers generally suffer a low capacitance and poor rate performance, which largely restrict their potentially wide applications. Here, we report a simple, low cost and scalable wet-spinning method to fabricate porous carbon black/reduced graphene oxide (CB/rGO) hybrid fibers. The hybrid fibers possess very high surface area (254.6 m2 g−1) and a hierarchically porous nanostructure. A flexible solid-state SC was assembled using the hybrid fiber, which exhibited high capacitance (97.5 F cm−3), excellent cycling stability (95.9% capacitance retention over 2000 cycles), superior energy density (2.8 mW h cm−3) and ultrahigh power density (1200 mW cm−3). Its physical shape and electrochemical performance is also very well maintained under long-time periodic mechanical deformation that is particularly promising for wearable electronic devices.

Large Scale Production of Continuous Hydrogel Fibers with Anisotropic Swelling Behavior by Dynamic-Crosslinking-Spinning

Hydrogel microfibers have been considered as a potential biomaterial to spatiotemporally biomimic 1D native tissues such as nerves and muscles which are always assembled hierarchically and have anisotropic response to external stimuli. To produce facile hydrogel microfibers in a mathematical manner, a novel dynamic-crosslinking-spinning (DCS) method is demonstrated for direct fabrication of size-controllable fibers from poly(ethylene glycol diacrylate) oligomer in large scale, without microfluidic template and in a biofriendly environment. The diameter of fibers can be precisely controlled by adjusting the spinning parameters. Anisotropic swelling property is also dependent on inhomogeneous structure generated in spinning process. Comparing with bulk hydrogels, the resulting fibers exhibit superior rapid water adsorption property, which can be attributed to the large surface area/volume ratio of fiber. This novel DCS method is one-step technology suitable for large-scale production of anisotropic hydrogel fibers which has a promising application in the area such as biomaterials.

Systemic research of fluorescent emulsion systems and their polymerization process with a fluorescent probe by an AIE mechanism

In this paper, an AIE luminogen, which was used as a fluorescent probe, was synthesized and copolymerized with acrylate monomers to study the process of emulsion polymerization and properties of a fluorescent emulsion. At first, according to the changes in the fluorescence spectra, the emulsion polymerization process can be followed with real-time monitoring. Then, by varying the relative content of the AIE luminogen, the glass transition temperature of the synthesized emulsion, the size of the emulsion particle, the contents of the emulsion, and the detection temperature, etc., the relationship between the fluorescence properties and intrinsic properties of the emulsion was studied systematically. It should be pointed out that the microscopic motion of a segment of polymer can be studied by fluorescence spectra with the help of a fluorescent probe. Traditionally, AIE luminogens are applied in optoelectronics and biological domains as small organic molecules. When an AIE luminogen is connected with polymer chains by a chemical bond, a lot of interesting phenomena can be observed. The research results not only provide a new method to study the emulsion polymerization process and properties of emulsion, but also, the synthesized emulsion with properties of fluorescence may broaden the application of the AIE mechanism.

An attempt to adopt aggregation-induced emission to study organic–inorganic composite materials

Owing to the hybrid nature of organic–inorganic composite coatings, when applied, they can combine the merits of both components and thus make such coatings fit a wide range of applications. However, due to the property differences in these composites, the strategy to obtain well dispersed organic–inorganic coatings is not yet straightforward and it is of great importance for their implementation and to obtain advanced properties such as mechanical properties, corrosion-resistance, aging resistance performance, and others. In this regard, still, even the characterization and direct visualization of the making up the organic–inorganic composites are not easy tasks. Herein, a strategy to visual characterize organic–inorganic composite coatings via aggregation-induced emission (AIE) is reported. Briefly, the approach involved first designing and synthesizing a novel water dispersed AIEgen whose AIE effect was systematically analyzed. Then, inorganic Na+-montmorillonite (MMT) was introduced to the synthesized AIEgen via the ion exchange method in order to make the inorganic MMT adopt fluorescence properties. The modified MMT fluorescence property was beneficial for the imaging and characterization of the macro-dispersed MMT in the cured coatings. As an essential addition to the study, the responses of the modified MMT cured composite coatings to temperature and corrosive material erosion were studied in detail. An account of the responses demonstrated the possible application of such modified coatings in high-performance smart paints.

A bottom-up approach to design wearable and stretchable smart fibers with organic vapor sensing behaviors and energy storage properties

Realizing the best way to integrate electronics and textiles to develop smart wearable, functional apparel with multiple functionalities such as fibers with a unified capability to store and utilize energy is a significant topic of concern recently. Therefore, presenting a facile approach to obtain fibers with such unique properties in a continuous process is a forward contributing step towards the development of this field. Herein, a bottom-up approach to fabricate stretchable poly(styrene-butadiene-styrene)/few-layer graphene composite (SBS-G) fibers with unique organic vapor sensing behaviors and modified SBS-G fibers coated with electroactive carbon black (CB) nanofibers via modified electrospinning with excellent energy storage properties is presented. Unlike conventional conductive polymer composites (CPCs) that respond only to polar or non/low-polar organic vapors, the fabricated SBS-G composite fibers exhibited high sensitivity, excellent reversibility, and reproducibility as well as fast response to both polar and non/low-polar organic vapors. Moreover, the modified nanofiber-based SBS-G fibers demonstrated a high capacitive performance (78 F cm−3), energy and power density (6.6 mW h cm3 and 692 mW cm3) and excellent flexibility. This study provides guidelines for the fabrication of ideal organic vapor sensors based on polymer composite fibers and an approach to modify any “off-the-shelf fiber” for fiber-based power storage.

Studying a novel AIE coating and its handling process via fluorescence spectrum

For polymer materials, both their compositions and preparation process greatly influence their service performance. Thus, the sound understanding of the relationship between materials preparation processes and their properties is paramount. However, current research methods are partially limited due to the absence of a direct testing method to track the entire process, e.g. synthesizing, curing, ageing, and so on. With the ability for real-time sensitive characterization, fluorescence spectroscopy may be applied in testing polymer materials performance. Here, we synthesized a novel aggregation induced emission (AIE) resin named TPE–EPOXY resin and prepared an AIE coating based on it. According to restriction of intramolecular rotation (RIR) mechanism, the preparation, curing, and aging processes for the AIE polymer resins & coatings could be studied with real-time observation. In addition, their properties could also be studied systematically. The results in this paper pave a good way to understand the relationship between the internal structure and the properties of polymer materials. Moreover, the prepared AIE polymer resins has a potential to expand the application fields of the AIE mechanism.