Synergistic Interaction of Dual-Polymer Networks Containing Viologens-Anchored Poly(ionic liquid)s Enabling Long-Life and Large-Area Electrochromic Organogels.

Viologens-based electrochromic (EC) devices with multiple color changes, rapid response time, and simple all-in-one architecture have aroused much attention, yet suffer from poor redox stability caused by the irreversible aggregation of free radical viologens. Herein, the semi-interpenetrating dual-polymer network (DPN) organogels are introduced to improve the cycling stability of viologens-based EC devices. The primary cross-linked poly(ionic liquid)s (PILs) covalently anchored with viologens can suppress irreversible face-to-face contact between radical viologens. The secondary poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) chains with strong polar groups of -F can not only synergistically confine the viologens by the strong electrostatic effect, but also improve the mechanical performance of the organogels. Consequently, the DPN organogels show excellent cycling stability (87.5% retention after 10 000 cycles) and mechanical flexibility (strength of 3.67 MPa and elongation of 280%). Three types of alkenyl viologens are designed to obtain blue, green, and magenta colors, demonstrating the universality of the DPN strategy. Large-area EC devices (20 × 30 cm) and EC fibers based on organogels are assembled to demonstrate promising applications in green and energy-saving buildings and wearable electronics.

Stretchable, Electrochemically-Stable Electrochromic Devices Based on Semi-Embedded Ag@Au Nanowire Network.

Stretchable electrochromic (EC) devices that can adapt the irregular and dynamic human surfaces show promising applications in wearable display, adaptive camouflage, and visual sensation. However, challenges exist in lacking transparent conductive electrodes with both tensile and electrochemical stability to assemble the complex device structure and endure harsh electrochemical redox reactions. Herein, a wrinkled, semi-embedded Ag@Au nanowire (NW) networks are constructed on elastomer substrates to fabricate stretchable, electrochemically-stable conductive electrodes. The stretchable EC devices are then fabricated by sandwiching a viologen-based gel electrolyte between two conductive electrodes with the semi-embedded Ag@Au NW network. Because the inert Au layer inhibits the oxidation of Ag NWs, the EC device exhibits much more stable color changes between yellow and green than those with pure Ag NW networks. In addition, since the wrinkled semi-embedded structure is deformable and reversibly stretched without serious fractures, the EC devices still maintain excellent color-changing stability under 40% stretching/releasing cycles.

Preparation of cellulose acetate derived carbon nanofibers by ZnCl2 activation as a supercapacitor electrode.

Porous carbon nanofibers are fabricated by one-step carbonization and activation of electrospun cellulose acetate (CA) nanofibres. Electrospun CA nanofibers were obtained by the electrospinning of a CA/DMAC/acetone solution, followed by deacetylation in NaOH/ethanol solution. One-step carbonization and activation was achieved by dipping the as-spun fibers in ZnCl2 solution, followed by one-step high temperature treatment. The effects of the concentration of the dipping solution on the microstructure of the CA-based carbon nanofibers (CACNFs), including the morphology, crystal structure, porous structure, specific surface area and surface chemical properties, have been investigated. The coating of ZnCl2 effectively improves the thermal stability of electrospun CA nanofibers and obviously enhances the oxygen-containing surface groups of the CACNFs. The CACNFs have a norrow pore size distribution (0.6-1.2 nm) and a high specific surface area (∼1188 m2 g-1). Electrochemical performances of the CACNFs were evaluated as supercapacitor electrodes in 6 M KOH solution. The CACNFs demonstrate high specific capacitance (202 F g-1 at 0.1 A g-1) and excellent rate capability (61% of the retention from 0.1 to 20 A g-1). After 5000 cycles of the electrode, the capacitance is maintained at 92%, and the coulombic efficiency is close to 100%, showing high electrochemical stability and reversibility. The renewable features and excellent performance make CACNFs quite a promising alternative to efficient supercapacitor electrodes for energy storage applications.