Jianhua Yan

Rechargeable lithium–sulfur (Li–S) batteries are receiving ever‐increasing attention due to their high theoretical energy density and inexpensive raw sulfur materials. However, their rapid capacity fade has been one of the key barriers for their further improvement. It is well accepted that the major degradation mechanisms of S‐cathodes include low electrical conductivity of S and sulfides, precipitation of nonconductive Li 2 S 2 and Li 2 S, and poly‐shuttle effects. To determine these degradation factors, a comprehensive study of sulfur cathodes with different amounts of electrolytes is presented here. A survey of the fundamentals of Li–S chemistry with respect to capacity fade is first conducted; then, the parameters obtained through electrochemical performance and characterization are used to determine the key causes of capacity fade in Li–S batteries. It is confirmed that the formation and accumulation of nonconductive Li 2 S 2 /Li 2 S films on sulfur cathode surfaces are the major parameters contributing to the rapid capacity fade of Li–S batteries.

Abstract Designing stable and efficient electrocatalysts for both oxygen reduction and evolution reactions (ORR/OER) at low‐cost is challenging. Here, a carbon‐based bifunctional catalyst of magnetic catalytic nanocages that can direct enhance the oxygen catalytic activity by simply applying a moderate (350 mT) magnetic field is reported. The catalysts, with high porosity of 90% and conductivity of 905 S m −1 , are created by in situ doping metallic cobalt nanodots (≈10 nm) into macroporous carbon nanofibers with a facile electrospinning method. An external magnetic field makes the cobalt magnetized into nanomagnets with high spin polarization, which promote the adsorption of oxygen‐intermediates and electron transfer, significantly improving the catalytic efficiency. Impressively, the half wave‐potential is increased by 20 mV for ORR, and the overpotential at 10 mA cm −2 is decreased by 15 mV for OER. Compared with the commercial Pt/C+IrO 2 catalysts, the magnetic catalyzed Zn–air batteries deliver 2.5‐fold of capacities and exhibit much longer durability over 155 h. The findings point out a very promising strategy of using electromagnetic induction to boost oxygen catalytic activity.

Abstract Fiber materials are highly desirable for wearable electronics that are expected to be flexible and stretchable. Compared with rigid and planar electronic devices, fiber-based wearable electronics provide significant advantages in terms of flexibility, stretchability and breathability, and they are considered as the pioneers in the new generation of soft wearables. The convergence of textile science, electronic engineering and nanotechnology has made it feasible to build electronic functions on fibers and maintain them during wear. Over the last few years, fiber-shaped wearable electronics with desired designability and integration features have been intensively explored and developed. As an indispensable part and cornerstone of flexible wearable devices, fibers are of great significance. Herein, the research progress of advanced fiber materials is reviewed, which mainly includes various material preparations, fabrication technologies and representative studies on different wearable applications. Finally, key challenges and future directions of fiber materials and wearable electronics are examined along with an analysis of possible solutions. Graphical abstract

Abstract Conductive porous carbon nanofibers are promising for environmental, energy, and catalysis applications. However, increasing their porosity and conductivity simultaneously remains challenging. Here we report chemical crosslinking electrospinning, a macro–micro dual-phase separation method, to synthesize continuous porous carbon nanofibers with ultrahigh porosity of >80% and outstanding conductivity of 980 S cm −1 . With boric acid as the crosslinking agent, poly(tetrafluoroethylene) and poly(vinyl alcohol) are crosslinked together to form water-sol webs, which are then electrospun into fibrous films. After oxidation and pyrolysis, the as-spun fibers are converted into B-F-N triply doped porous carbon nanofibers with well-controlled macro–meso–micro pores and large surface areas of ~750 m 2 g −1 . The sponge-like porous carbon nanofibers with substantially reduced mass transfer resistances exhibit multifunction in terms of gas adsorption, sewage disposal, liquid storage, supercapacitors, and batteries. The reported approach allows green synthesis of high-performance porous carbon nanofibers as a new platform material for numerous applications.