Morphology and Photocatalytic Property of Hierarchical Polyimide/ZnO Fibers Prepared via a Direct Ion-exchange Process

A simple and efficient method has been developed for preparing hierarchical nanostructures of polyimide (PI)/ZnO fibers by combining electrospinning and direct ion-exchange process. Poly­(amic acid) (PAA) nanofibers are first prepared by electrospinning, and then, the electrospun PAA fibers are immersed into ZnCl₂ solution. After a subsequent thermal treatment, imidization of PAA and formation of ZnO nanoparticles can be simultaneously achieved in one step to obtain PI/ZnO composite fibers. SEM images show that ZnO nanoparticles are densely and uniformly immobilized on the surface of electrospun PI fibers. Furthermore, the morphology of ZnO can be tuned from nanoplatelets to nanorods by changing the initial concentration of ZnCl₂ solution. Photocatalytic degradation tests show an efficient degradation ability of PI/ZnO composite membranes toward organic dyes. Meanwhile, the free-standing membrane is highly flexible, easy to handle, and easy to retrieve, which enables its use in water treatment. This simple and inexpensive approach can also be applied to fabricating other hierarchically nanostructured composites

Electrically Conductive Polyaniline/Polyimide Nanofiber Membranes Prepared via a Combination of Electrospinning and Subsequent In situ Polymerization Growth

Highly aligned polyimide (PI) nanofiber membranes have been prepared by electrospinning equipped with a high speed rotating collector. As the electrospun polyimide nanofiber membranes possess large surface area, they can be used as the template for in situ growth of polyaniline (PANi) by using FeCl₃ as the oxidant. It is found that PANi nanoparticles can be uniformly distributed on the surface of highly aligned PI nanofibers due to the low oxidization/reduction potential of FeCl₃ and the active nucleation sites of the functionalized PI nanofibers. The as-prepared PANi/PI composite membranes not only possess excellent thermal and mechanical properties but also show good electrical conductivity, pH sensitivity and significantly improved electromagnetic impedance properties. This is a facile method for fabricating high-performance and multifunctional composites that can find potential applications in electrical and aerospace fields

Nitrogen-Doped Carbon Nanofiber/Molybdenum Disulfide Nanocomposites Derived from Bacterial Cellulose for High-Efficiency Electrocatalytic Hydrogen Evolution Reaction

To remit energy crisis and environmental deterioration, non-noble metal nanocomposites have attracted extensive attention, acting as a fresh kind of cost-effective electrocatalysts for hydrogen evolution reaction (HER). In this work, hierarchically organized nitrogen-doped carbon nanofiber/molybdenum disulfide (pBC-N/MoS₂) nanocomposites were successfully prepared via the combination of in situ polymerization, high-temperature carbonization process, and hydrothermal reaction. Attributing to the uniform coating of polyaniline on the surface of bacterial cellulose, the nitrogen-doped carbon nanofiber network acts as an excellent three-dimensional template for hydrothermal growth of MoS₂ nanosheets. The obtained hierarchical pBC-N/MoS₂ nanocomposites exhibit excellent electrocatalytic activity for HER with small overpotential of 108 mV, high current density of 8.7 mA cm^–2 at η = 200 mV, low Tafel slope of 61 mV dec^–1, and even excellent stability. The greatly improved performance is benefiting from the highly exposed active edge sites of MoS₂ nanosheets, the intimate connection between MoS₂ nanosheets and the highly conductive nitrogen-doped carbon nanofibers and the three-dimensional networks thus formed. Therefore, this work provides a novel strategy for design and application of bacterial cellulose and MoS₂-based nanocomposites as cost-effective HER eletrocatalysts

Flexible Hybrid Membranes of NiCo₂O₄‑Doped Carbon Nanofiber@MnO₂ Core–Sheath Nanostructures for High-Performance Supercapacitors

Construction of MnO₂-based hybrid nanostructures with carbonaceous materials has been considered as one of the most efficient strategies to overcome excessive aggregations of MnO₂ particles. Here, a facile approach of growing δ-phase and γ-phase MnO₂ with distinctly different morphologies on highly conductive NiCo₂O₄-doped carbon nanofibers (NCCNFs) through the combination of electrospinning, solution codeposition, and redox deposition methods is presented to form NCCNF@MnO₂ nanosheet (or nanorod) core–sheath nanostructures. The obtained two kinds of flexible hybrid membranes with hierarchical nanostructures are both evaluated as electrodes for high-performance supercapacitors. The greatly improved specific surface areas for ionic adsorption, significantly enhanced conductivity of NCCNF, and an open three-dimensional network for rapid electron transportation during the electrochemical processes jointly lead to remarkably enhanced specific capacitances of 918 and 827 F g^–1 (based on the active materials) at a scan rate of 2 mV s^–1 and good cycling ability with 83.3% and 87.6% retention after 2000 cycles for NCCNF@MnO₂ nanosheet and NCCNF@MnO₂ nanorod hybrid membranes, respectively. Therefore, this work suggests a novel strategy for design and potential application of MnO₂ hybrid materials in high-performance supercapacitors

Asymmetric Sodiophilic Host Based on a Ag-Modified Carbon Fiber Framework for Dendrite-Free Sodium Metal Anodes

Sodium (Na) metal is considered a promising anode material for high-energy Na batteries due to its high theoretical capacity and abundant resources. However, uncontrollable dendrite growth during the repeated Na plating/stripping process leads to the issues of low Coulombic efficiency and short circuits, impeding the practical applications of Na metal anodes. Herein, we propose a silver-modified carbon nanofiber (CNF@Ag) host with asymmetric sodiophilic features to effectively improve the deposition behavior of Na metal. Both density functional theory (DFT) calculations and experiment results demonstrate that Na metal can preferentially nucleate on the sodiophilic surface with Ag nanoparticles and uniformly deposit on the whole CNF@Ag host with a “bottom-up growth” mode, thus preventing unsafe dendrite growth at the anode/separator interface. The optimized CNF@Ag framework exhibits an excellent average Coulombic efficiency of 99.9% for 500 cycles during Na plating/stripping at 1 mA cm–2 for 1 mAh cm–2. Moreover, the CNF@Ag-Na symmetric cell displays stable cycling for 500 h with a low voltage hysteresis at 2 mA cm–2. The CNF@Ag-Na//Na3V2(PO4)3 full cell also presents a high reversible specific capacity of 102.7 mAh g–1 for over 200 cycles at 1 C. Therefore, asymmetric sodiophilic engineering presents a facile and efficient approach for developing high-performance Na batteries with high safety and stable cycling performance

Flexible Hybrid Membranes with Ni(OH)₂ Nanoplatelets Vertically Grown on Electrospun Carbon Nanofibers for High-Performance Supercapacitors

The practical applications of transition metal oxides and hydroxides for supercapacitors are restricted by their intrinsic poor conductivity, large volumetric expansion, and rapid capacitance fading upon cycling, which can be solved by optimizing these materials to nanostructures and confining them within conductive carbonaceous frameworks. In this work, flexible hybrid membranes with ultrathin Ni­(OH)₂ nanoplatelets vertically and uniformly anchored on the electrospun carbon nanofibers (CNF) have been facilely prepared as electrode materials for supercapacitors. The Ni­(OH)₂/CNF hybrid membranes with three-dimensional macroporous architectures as well as hierarchical nanostructures can provide open and continuous channels for rapid diffusion of electrolyte to access the electrochemically active Ni­(OH)₂ nanoplatelets. Moreover, the carbon nanofiber can act both as a conductive core to provide efficient transport of electrons for fast Faradaic redox reactions of the Ni­(OH)₂ sheath, and as a buffering matrix to mitigate the local volumetric expansion/contraction upon long-term cycling. As a consequence, the optimized Ni­(OH)₂/CNF hybrid membrane exhibits a high specific capacitance of 2523 F g^–1 (based on the mass of Ni­(OH)₂, that is 701 F g^–1 based on the total mass) at a scan rate of 5 mV s^–1. The Ni­(OH)₂/CNF hybrid membranes with high mechanical flexibility, superior electrical conductivity, and remarkably improved electrochemical capacitance are condsidered as promising flexible electrode materials for high-performance supercapacitors

Ni-Doped Graphene/Carbon Cryogels and Their Applications As Versatile Sorbents for Water Purification

Ni-doped graphene/carbon cryogels (NGCC) have been prepared by adding resorcinol and formaldehyde to suspension of graphene oxide (GO), using Ni²⁺ ions as catalysts for the gelation process to substitute the usually used alkaline carbonates. The metal ions of Ni²⁺ have elevated the cross-linking between GO and RF skeletons, thus strengthening the whole cryogel. The as-formed three-dimensional (3D) interconnected structures, which can be well-maintained after freeze-drying of the hydrogel precursor and subsequent carbonization under an inert atmosphere, exhibit good mechanical properties. During the carbonization process, Ni²⁺ ions are converted into Ni nanoparticles and thus embedded in the interconnected structures. The unique porosity within the interconnected structures endows the cryogels with good capability for the extraction of oils and some organic solvents while the bulk form enables its recycling use. When ground into powders, they can be used as adsorbents for dyestuffs. Therefore, the as-obtained cryogels may find potential applications as versatile candidates for the removal of pollutants from water

Highly Stretchable, Soft, Low-Hysteresis, and Self-Healable Ionic Conductive Elastomers Enabled by Long, Functional Cross-Linkers

Herein, a novel strategy has been developed for the preparation of high-performance conductive elastomers featuring long functional polymer cross-linkers. The macromolecular cross-linkers containing multi boronic ester bonds in the backbone were designed via thiol/acrylate reactions between poly(ethylene glycol) diacrylate (PEGDA) and a dithiol-containing boronic ester (BDB). The obtained PEG–BDB was copolymerized with n-butyl acrylate (n-BA) to provide PBA/PEG–BDB elastomers. The resultant elastomers exhibit combined desirable properties of high stretchability, low Young’s modulus, low hysteresis, and self-healing performance, simultaneously. To demonstrate their practical applications, sensors based on PBA/PEG–BDB were successfully attached onto diverse joints (wrist, elbow, and finger) of the puppet for real-time motion detection. What is more, the elastomer sensors could well recognize other human activities like writing. This work offers a new design strategy for flexible sensors by optimizing the cross-linked dimension with long functional polymer chains as cross-linkers

Visible-Light Transparent, Ultrastretchable, and Self-Healable Semicrystalline Fluorinated Ionogels for Underwater Strain Sensing

The development of ultrastretchable ionogels with a combination of high transparency and unique waterproofness is central to the development of emerging skin-inspired sensors. In this study, an ultrastretchable semicrystalline fluorinated ionogel (SFIG) with visible-light transparency and underwater stability is prepared through one-pot copolymerization of acrylic acid and fluorinated acrylate monomers in a mixed solution of poly(ethylene oxide) (PEO) and fluorinated ionic liquids. Benefiting from the formation of the PEO-chain semicrystalline microstructures and the abundant noncovalent interactions (reversible hydrogen bonds and ion–dipole interactions) in an ionogel, SFIG is rendered with room-temperature stable cross-linking structures, providing high mechanical elasticity as well as high chain segment dynamics for self-healing and efficient energy absorption during the deformation. The resultant SFIG exhibits excellent stretchability (>2500%), improved mechanical toughness (7.4 MJ m–3), and room-temperature self-healability. Due to the high compatibility and abundance of hydrophobic fluorinated moieties in the ionogel, the SFIG demonstrates high visible-light transparency (>97%) and excellent waterproofness. Due to these unique advantages, the as-prepared SFIG is capable of working as an ultrastretchable ionic conductor in capacitive-type strain sensors, demonstrating excellent underwater strain-sensing performances with high sensitivity, large detecting range, and exceptional durability. This work might provide a straightforward and efficient method for obtaining waterproof ionogel elastomers for application in next-generation underwater sensors and communications