With the rapid development of flexible and wearable electronic devices, research on high-sensitivity strain sensors has been attracting much attention. Here, glutaraldehyde is used as a cross-linking reagent to precross-link poly(vinyl alcohol); then FeCl 3 •6H 2 O is added into the precross-linked poly(vinyl alcohol) to obtain composite films of FeCl 3 @PVA after gelatinization and freeze drying. Elastic conductive films of polypyrrole@poly(vinyl alcohol) (PPy@PVA) are prepared by immersing FeCl 3 @PVA into a solution of pyrrole in acetonitrile and water to complete the polymerization in situ. The effects of the concentrations of glutaraldehyde and FeCl 3 •6H 2 O on the film's structure and properties have been studied in detail; the results show that the strain sensor prepared from the optimized film has excellent stretchability (strain up to 309.5%), mechanical property (tensile strength of 32.8 MPa), and relatively high sensitivity (gauge factor can reach 5.07 under 1.0% strain). It can be used to detect various tiny physiological signals, for example, detecting the number of pulse beats, bending of the knuckles at different frequencies, and recognizing the pronunciation of different words by vocal cord vibration. These good properties mean that this kind of PPy@PVA strain sensor has great application prospects in physiological monitoring.

The rapid development of flexible electronic devices has caused a boom in researching flexible sensors based on hydrogels, but most of the flexible sensors can only work at room temperature, and they are difficult to adapt to extremely cold or dry environments. Here, the flexible hydrogel fibers (PEDOT:PSS@ PVA) with excellent resistance to extreme environments have been prepared by adding glycerin (GL) to the mixture of poly(vinyl alcohol) (PVA) and poly 3,4-dioxyethylene thiophene:polystyrene sulfonic acid (PEDOT:PSS) because GL molecules can form dynamic hydrogen bonds with an elastic matrix of PVA molecules. It is found that the prepared sensor exhibits very good flexibility and mechanical strength, and the ultimate tensile strength can reach up to 13.76 MPa when the elongation at break is 519.9%. Furthermore, the hydrogel fibers possess excellent water retention performance and low-temperature resistance. After being placed in the atmospheric environment for 1 year, the sensor still shows good flexibility. At a low temperature of −60 °C, the sensor can stably endure 1000 repeated stretches and shrinks (10% elongation). In addition to the response to a large strain, this fiber sensor can also detect extremely small strains as low as 0.01%. It is proved that complex human movements such as knuckle bending, vocalization, pulse, and others can be monitored perfectly by this fiber sensor. The above results mean that the PEDOT:PSS@PVA fiber sensor has great application prospects in physiological monitoring.

Hierarchically porous carbons (HPCs) have attracted much attention because of their potential application in carbonbased supercapacitors. Here, we list a facile and green method to obtain HPCs by annealing a coal tar pitch with sodium bicarbonate. The produced gases and sodium carbonate template can guide the formation of carbon products with a multiscale pore structure. Further activation by KOH endows HPC with a surface area of 2851.7 m 2 g −1 and a total pore volume of 2.4 cm 3 g −1 . Accordingly, such an HPC electrode achieves a specific capacitance of 321.5 F g −1 (0.5 A g −1 ) and retains 230.0 F g −1 (100.0 A g −1 ). Moreover, the HPC-based symmetric supercapacitor exhibits superior cyclic stability (1.1% capacity decay after 30,000 cycles) in an aqueous electrolyte. In the TEABF 4 /acetonitrile electrolyte, the assembled device displays a high energy density of 53.0 Wh kg −1 and still retains 77.9% even when the power density is increased from 750.0 to 15,000.0 W kg −1 . We believe that the salt-assisted synthesis strategy for HPC paves a green way to developing high-performance supercapacitors.