"Dual Mediator System" Enables Efficient and Persistent Regulation toward Sulfur Redox Conversion in Lithium-Sulfur Batteries.

Li-S batteries present great potential to realize high-energy-density storage, but their practical implementation is severely hampered by the notorious polysulfide shuttling and the sluggish redox kinetics. While rationally designed redox mediators can optimize polysulfide conversion, the efficiency and stability of such a mediation process still remain formidable challenges. Herein, a strategy of constructing a "dual mediator system" is proposed for achieving efficient and durable modulation of polysulfide conversion kinetics by coupling well-selected solid and electrolyte-soluble mediators. Theoretical prediction and detailed electrochemical analysis reveal the structure-activity relationships of the two mediators in synergistically optimizing the redox conversions of sulfur species, thus achieving a deeper mechanistic understanding of a function-supporting mediator system design toward sulfur electrochemistry promotion. Specifically, such a dual mediator system realizes the bridging of full-range "electrochemical catalysis" and strengthened "chemical reduction" processes of sulfur species as well as greatly suppressed mediator deactivation/loss due to the beneficial interactions between each mediator component. Attributed to these advantageous features, the Li-S batteries enable a slow capacity decay of 0.026% per cycle over 1200 cycles and a desirable capacity of 8.8 mAh cm-2 with 8.2 mg cm-2 sulfur loading and lean electrolyte condition. This work not only proposes an effective mediator system design strategy for promoting Li-S battery performance but also inspires its potential utilization facing other analogous sophisticated electrochemical conversion processes.

Double-Layered Conductive Network Design of Flexible Strain Sensors for High Sensitivity and Wide Working Range.

For flexible strain sensors, the optimization between sensitivity and working range is a significant challenge due to the fact that high sensitivity and high working range are usually difficult to obtain at the same time. Herein, a breathable flexible strain sensor with a double-layered conductive network structure was designed and developed, which consists of a thermoplastic polyurethane (TPU)/carbon nanotube (CNT) layer (as a substrate layer) and a Ag nanowire (AgNW) layer. The TPU/CNT layer is made of electrospinning TPU with CNTs deposited onto the surface of TPU fibers, and the flexible TPU/CNT mat guarantees the integrity of the conductive path under a large strain. The AgNW layer was prepared by depositing different amounts of AgNWs on the surface of the TPU/CNT layer, and the high-conductivity AgNWs offer a low initial resistance. Benefitting from the synergistic two-layer structure, the as-obtained flexible strain sensor exhibits a very high sensitivity (up to 1477.7) and a very wide working range (up to 150%). Besides, the fabricated sensor exhibits fast response (88 ms), excellent dynamical stability (7000 cycles), and excellent breathability. The working mechanism of the strain sensor was further investigated using various techniques (microscopy, equivalent circuit, and thermal effects of current). Furthermore, the as-fabricated flexible strain sensors accurately detect the omnidirectional human motions, including subtle and large human motions. This work provides an efficient approach to achieve the optimization between high sensitivity and large working range of strain sensors, which may have great potential applications in health monitoring, body motion detection, and human-machine interactions.

One-step electrospinning cellulose nanofibers with superhydrophilicity and superoleophobicity underwater for high-efficiency oil-water separation.

Cellulose nanofibers have been widely applied in many fields because of its unique advantages. However, it is a challenge to prepare cellulose nanofibers by electrospinning directly owing to the special molecular structure of cellulose. This limits the practical applications of cellulose nanofibers. In this work, cellulose nanofibers were successfully prepared directly by design of new electrospinning receiving device and optimization of process parameters. The as-prepared cellulose nanofibers exhibit good oil-water separation performances. Driven solely by gravity, the separation flux of the cellulose nanofibers for mixture of oil and water reaches 34,300.6 L m-2 h-1, and the separation flux and efficiency for surfactant-stabilized emulsion of oil and water reach 2503.7 L m-2 h-1 and over 98.3%, respectively. The as-prepared cellulose nanofibers also exhibit good mechanical properties and reusability. The breaking strength of the cellulose nanofibers can reach 148.2 cN. The separation fluxes of cellulose nanofibers for mixtures and emulsions of oil and water can be maintained 99.7% and 86.3% of the initial value after being used for 20 times. Furthermore, the as-prepared cellulose nanofibers have good degradability. These properties render as-prepared cellulose nanofibers as promising materials with potential applications in oil-water separation.

Morphologies and Properties of PET Nano Porous Luminescence Fiber: Oil Absorption and Fluorescence-Indicating Functions.

A polyethylene terephthalate nano porous luminescence fiber (PNPLF) was prepared through electrospun technology. The SEM and TEM images show that the surfaces of the fibers are covered with pores. The diameter of the fiber is 250-500 nm, and the diameter of the pores is 20-180 nm. The water and oil contact angles of PNPLF are 135° and 27°, respectively. The oil absorption value of the as-prepared PNPLF achieves 135 g/g and has a good oil absorption function. The as-prepared PNPLF has good luminescence properties and fluorescent-indicating function. Even trace amounts of oil can also cause obvious change of fluorescence intensity of PNPLF which has a good stability from 20 °C to 70 °C. The breaking stress of yarn of PNPLF reaches 117cN. Furthermore, the good mechanical properties and thermal properties of PNPLF provide important basic conditions for their wide applications.

Synthesis and characterization of bright green terbium coordination complex derived from 1,4-bis(carbonylmethyl)terephthalate: Structure and luminescence properties.

A photoluminescent terbium (Tb) complex involving a novel benzoic-acid compound with a unique coordinated structure, namely 1,4-bis(carbonylmethyl)terephthalate (BCMT), has been designed and synthesized. The new coordinate structure and energy-transfer mechanism between the ligand and Tb(III) ions were investigated in detail. The results demonstrated that the BCMT-Tb(III) complex shows strong fluorescence intensity (4×106a.u.) and long fluorescence lifetime (1.302ms), owing to the favorable degree of energy matching between the triplet excited level of the ligand and the resonant level of Tb(III) ions. Based on the analysis of three-dimensional luminescence spectra, the as-prepared Tb(III) complex can be effectively excited in the range of 250-310nm, and it shows high color purity, with a bright green appearance.

Fabrication and characterization of dual-functional ultrafine composite fibers with phase-change energy storage and luminescence properties.

Ultrafine composite fibers consisting of a thermoplastic polyurethane solid-solid phase-change material and organic lanthanide luminescent materials were prepared through a parallel electrospinning technique as an innovative type of ultrafine, dual-functional fibers containing phase-change and luminescent properties. The morphology and structure, thermal energy storage, and luminescent properties of parallel electrospun ultrafine fibers were investigated. Scanning electron microscopy (SEM) images showed that the parallel electrospun ultrafine fibers possessed the desired morphologies with smaller average fiber diameters than those of traditional mixed electrospun ultrafine fibers. Transmission electron microscopy (TEM) images revealed that the parallel electrospun ultrafine fibers were composed of two parts. Polymeric phase-change materials, which can be directly produced and spun, were used to provide temperature stability, while a mixture of polymethyl methacrylate and an organic lanthanide complex acted as the luminescent unit. Differential scanning calorimetry (DSC) and luminescence measurements indicated that the unique structure of the parallel electrospun ultrafine fibers provides the products with good thermal energy storage and luminescence properties. The fluorescence intensity and the phase-change enthalpy values of the ultrafine fibers prepared by parallel electrospinning were respectively 1.6 and 2.1 times those of ultrafine fibers prepared by mixed electrospinning.