Conductive polymer hydrogels are receiving considerable attention in applications such as soft robots and human-machine interfaces. Herein, a transparent and highly ionically conductive hydrogel that integrates sensing, UV-filtering, water-retaining, and anti-freezing performances is achieved by the organic combination of tannic acid-coated hydroxyapatite nanowires (TA@HAP NWs), polyvinyl alcohol (PVA) chains, ethylene glycol (EG), and metal ions. The highly ionic conductivity of the hydrogel enables tensile strain, pressure, and temperature sensing capabilities. In particular, in terms of the hydrogel strain sensors based on ionic conduction, it has high sensitivity (GF = 2.84) within a wide strain range (350%), high linearity (R 2 = 0.99003), fast response (≈50 ms) and excellent cycle stability. In addition, the incorporated TA@HAP NWs act as a nano-reinforced filler to improve the mechanical properties and confer a UV-shielding ability upon the hydrogel due to its size effect and the characteristics of absorbing ultraviolet light waves, which can reflect and absorb short ultraviolet rays and transmit visible light. Meanwhile, owing to the water-locking effect between EG and water molecules, the hydrogel exhibits freezing resistance at low temperatures and moisture retention at high temperatures. This biocompatible and multifunctional conductive hydrogel provides new ideas for the design of novel ionic skin devices.

The rational design of excellent electrocatalysts is significant for triggering the slow kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in rechargeable metal–air batteries. Hereby, we report a bifunctional catalytic material with core–shell structure constructed by Co3O4 nanowire arrays as cores and ultrathin NiFe-layered double hydroxides (NiFe LDHs) as shells (Co3O4@NiFe LDHs). The introduction of Co3O4 nanowires could provide abundant active sites for NiFe LDH nanosheets. Most importantly, the deposition of NiFe LDHs on the surface of Co3O4 can modulate the surface chemical valences of Co, Ni, and Fe species via changing the electron donor and/or electron absorption effects, finally achieving the balance and optimization of ORR and OER properties. By this core–shell design, the maximum ORR current densities of Co3O4@NiFe LDHs increase to 3–7 mA cm–2, almost an order of magnitude increases compared to pure NiFe LDH (0.45 mA cm–2). Significantly, an OER overpotential as low as 226 mV (35 mA cm–2) is achieved in the designed core–shell catalyst, which is comparable to and/or even better than those of commercial Ir/C. Hence, the primary zinc–air battery employing Co3O4@NiFe LDH as an air electrode achieves a high specific capacity (667.5 mA h g–1) and first-class energy density (797.6 W h kg–1); the rechargeable battery can show superior reversibility, excellent stability, and voltage gaps of ∼0.8 V (∼60% of round-trip efficiency) in >1200 continuous cycles. Furthermore, the flexible quasi-solid-state zinc–air battery with bendable ability holds practical potential in portable and wearable electronic devices.

Electrically conductive polypyrrole is very attractive for tissue engineering because of its potential to modulate cellular activities through electrical stimulation. However, its in vivo behaviors have not been fully studied. This paper investigates the in vivo biocompatibility and biostability of PPy-coated polyester fabrics. Three PPy-coated fabrics were prepared using phosphonylation (PPy-Phos), plasma activation (PPy-Plas), and plasma activation plus heparin treatment (PPy-Plas-HE). Virgin and fluoropassivated fabrics (F-PET) were controls. The specimens were implanted subcutaneously in the back of rats for 3-90 days, then harvested and processed for enzymatic, histological, and morphological analyses. A noninvasive MRI method was used to continuously monitor the inflammation. The level of acid and alkaline phosphatase showed a similar or a less intensive cellular reaction by the PPy-coated fabrics, when compared to the controls. Histology supported the enzymatic results and showed a fast collagen infiltration at 28 days for the PPy-Phos fabric. MRI reported an overall decrease of inflammation over time, with the PPy-coated fabrics showing a similar or mild inflammation in contrast to the non-coated fabrics. PPy clusters and excessive PPy laminary coating on the PPy-Plas and PPy-Plas-HE were lost with the implantation. This experiment suggests a similar in vivo biocompatibility of the PPy-coated and noncoated polyester fabrics and the importance of achieving a thin, uniform PPy coating.

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Exploring high performance solid electrolytes is essential for the practical application of solid-state lithium–metal batteries. Here, graphene oxide (GO) is employed to improve the electrochemical performance, thermal stability, and mechanical strength of the poly­(ethylene oxide) (PEO) based electrolyte. The ionic conductivity of the hybrid electrolyte containing 1 wt % GO reaches 1.54 × 10–5 S cm–1 at 24 °C, which is 7 times that of the electrolyte without GO, and the activation energy decreases from 1.01 to 0.64 eV. It is found that GO can suppress the formation of crystalline nuclei of PEO, thus increase the amorphous regions, and improve the movement ability of the PEO segments. Importantly, GO-modified PEO electrolyte not only has a wide electrochemical window (∼5 V) but also increases the lithium ion migration number to 0.42. Taking advantage of the decent GO–PEO solid electrolyte, the symmetric Li/Li cell can stably cycle for 600 h with a very small overpotential (27 mV) at 0.1 mA cm–2, showing excellent performance in inhibiting lithium dendrites. Most importantly, the LiFePO4//GO–PEO//Li full battery also delivers superior cycle and rate properties, with an initial discharge capacity of 142 mAh g–1 at 0.5 C and 91% capacity retention after 100 cycles. Moreover, the full battery can stably cycle for more than 450 charge–discharge cycles at 1 C. It is anticipated that PEO polymer electrolyte modified by GO has great practical application potential.

The development of highly sensitive wearable and foldable pressure sensors is one of the central topics in artificial intelligence, human motion monitoring, and health care monitors. However, current pressure sensors with high sensitivity and good durability in low, medium, and high applied strains are rather limited. Herein, a flexible pressure sensor based on hierarchical three-dimensional and porous reduced graphene oxide (rGO) fiber fabrics as the key sensing element is presented. The internal conductive structural network is formed by the rGO fibers which are mutually contacted by interfused or noninterfused fiber-to-fiber interfaces. Thanks to the unique structures, the sensor can show an excellent sensitivity from low to high applied strains (0.24−70.0%), a high gauge factor (1668.48) at an applied compression of 66.0%, a good durability in a wide range of frequencies, a low detection limit (1.17 Pa), and anultrafast response time (30 ms). The dominated mechanism is that under compression, the slide of the graphene fibers through the polydimethylsiloxane matrix reduces the connection points between the fibers, causing a surge in electrical resistance. In addition, because graphene fibers are porous and defective, the change in geometry of the fibers also causes a change in the electrical resistance of the composite under compression. Furthermore, the interfused fiber-to-fiber interfaces can strengthen the mechanical stability under 0.01−1.0 Hz loadings and high applied strains, and the wrinkles on the surface of the rGO fibers increased the sensitivity under tiny loadings. In addition, the noninterfused fiber-to-fiber interfaces can produce a highly sensitive contact resistance, leading to a higher sensitivity at low applied strains.

HIGHLIGHTS • Layered SnS 2 nanosheets/reduced graphene fiber (SnS 2 @rGF) hybrid fabrics were fabricated as binder-free electrodes. • Ultralight rGF fabrics could increase the active materials loading to a high level of 67.2 wt% in the whole electrode, which is much higher than that of traditional slurry coating electrodes by using Cu or Al foil as current collectors. • The practical capacity based on the weight of electrode could increase to as high as ~ 538 mAh g −1 exceeding to the slurry coating electrodes. ABSTRACT Generally, the practical capacity of an electrode should include the weight of non-active components such as current collector, polymer binder, and conductive additives, which were as high as 70 wt% in current reported works, seriously limiting the practical capacity. This work pioneered the usage of ultralight reduced graphene fiber (rGF)

The biostability of a series of polypyrrole (PPy)-coated polyester fabrics was investigated in an in vitro model. PPy-coated sample fabrics were incubated in saline at 37 degrees C for 1 and 2 weeks. After each period of incubation, the surface electrical resistivity of the sample fabrics was measured to monitor the changes caused by the incubation. Redoping was then performed by immersing the sample fabrics in a 1N HCl solution at room temperature for 30 min, which was followed by another measurement of the surface resistivity. The surface morphology of the sample fabrics was observed by scanning electron microscopy. The surface chemical composition of the fabrics and the oxidation of nitrogen in PPy were measured with X-ray photoelectron spectroscopy. The surface electrical resistivity of the PPy-coated fabrics was found to increase with the progress of incubation, which was mainly caused by dedoping and uptake of oxygen. This increase was nonlinear and accelerated with time. The surface resistivity of most of the samples was retained in the range of 10(3)-10(4) Omega/square after 1 week of incubation, which was considered suitable for short-term electrical stimulation applications. Physical deterioration represented by the cracking and delamination of the PPy coating was occasionally observed on the sample fabrics showing the most significant increase of resistivity. Further improvement of the stability of conductivity is highly desirable.