Novel Synthesis,Coating, and Networking of Curved Copper Nanowires for Flexible Transparent Conductive Electrodes

In this work, a whole manufacturing process of the curved copper nanowires (CCNs) based flexible transparent conductive electrode (FTCE) is reported with all solution processes, including synthesis, coating, and networking. The CCNs with high purity and good quality are designed and synthesized by a binary polyol coreduction method. In this reaction, volume ratio and reaction time are the significant factors for the successful synthesis. These nanowires have an average 50 nm in width and 25–40 μm range in length with curved structure and high softness. Furthermore, a meniscus‐dragging deposition (MDD) method is used to uniformly coat the well‐dispersed CCNs on the glass or polyethylene terephthalate substrate with a simple process. The optoelectrical property of the CCNs thin films is precisely controlled by applying the MDD method. The FTCE is fabricated by networking of CCNs using solvent‐dipped annealing method with vacuum‐free, transfer‐free, and low‐temperature conditions. To remove the natural oxide layer, the CCNs thin films are reduced by glycerol or NaBH₄ solution at low temperature. As a highly robust FTCE, the CCNs thin film exhibits excellent optoelectrical performance (T = 86.62%, R _s = 99.14 Ω ^?1), flexibility, and durability (R/R ₀ < 1.05 at 2000 bending, 5 mm of bending radius).     

Characterization of conductive composite films based on TEMPO-oxidized cellulose nanofibers and polypyrrole

Abstract  

In this article, conductive composite films based on TEMPO-oxidized cellulose nanofibers (TOCN) and polypyrrole (PPy) were synthesized in situ by a Chemical Polymerization Induced Adsorption Process of pyrrole on the surface of TOCN in aqueous medium. Resulting composite films were investigated by X-ray photoelectron spectroscopy, scanning, and transmission electron microscopy, N₂ gas adsorption analysis, thermogravimetric analysis, mechanical tests, and conductivity measurements in the ambient air. Our results showed a stable, flexible, and highly electrically conductive composite film in which PPy nanoparticles coated the surface of the TOCN network. In addition, the advantage in using the famous material, TOCN, is clearly due to the presence of carboxylate (COOH/COO⁻Na⁺) and hydroxyl (OH) moieties on the surface of TOCN. These reactive moieties could enhance the adsorption process of positively charged PPy backbone during polymerization. TEM observations demonstrated the formation of a PPy coat along the surface of the cellulose nanofibers having a diameter of about 90 nm which is relatively higher compared to the initial diameter of pure TOCN (~9 nm). Despite the physical and chemical treatment of TOCN during polymerization, the micrometric length of the cellulosic nanomaterial was maintained. In addition, the incorporation of polyvinyl alcohol as an additive in the TOCN/PPy composite seems to enhance the flexibility of composite films (bent up to 180°) without losing the high electrical conductivity. Finally, because of the high conductivity and good mechanical properties of the TOCN/PPy composite films obtained in this work, they can be used as a promising material in applications of sensors, flexible electrodes, and other fields requiring electrically conductive flexible films.     

Fabrication of silica/platinum core-shell particles by electroless metal plating

An electroless metal plating method was used to form Pt shells on sub-micrometer-sized silica (SiO₂) particles fabricated by a sol-gel method. The electroless metal plating method was comprised of three steps: (1) surface-modification of SiO₂ particles with polyvinylpyrrolidone (PVP) (SiO₂/PVP) or poly-diallyldimethylammonium chloride (PDADMAC) (SiO₂/PDADMAC), (2) pre-deposition of Pt nuclei or Pt fine particles on the SiO₂ particles by reducing Pt ions in the presence of SiO₂/PVP particles (SiO₂/PVP-Pt) or SiO₂/PDADMAC particles (SiO₂/PDADMAC-Pt), and (3) growth of the pre-deposited Pt by immersing the SiO₂/PVP-Pt or SiO₂/PDADMAC-Pt particles in a Pt-plating solution. The pre-deposition of Pt nanoparticles was successfully performed for the surface-modified SiO₂ particles since the surface modification possibly strengthened the affinity between the SiO₂ particle surfaces and Pt ions. The Pt nanoparticles were pre-deposited more uniformly in the case of PVP because the pre-deposition took place more slowly for the PVP, which provided uniform surface-modification followed by the uniform pre-deposition of Pt nanoparticles. The formation of Pt shells was successfully performed on the SiO₂/PVP-Pt particles in the electroless metal plating process because Pt nuclei were generated by the reduction of H₂PtCl₆ and then further deposited on the Pt particle surfaces on the SiO₂/PVP-Pt particles.     

Boosting High‐Rate Sodium Storage Performance of N‐Doped Carbon‐Encapsulated Na3V2(PO4)3 Nanoparticles Anchoring on Carbon Cloth

The further development of high‐power sodium‐ion batteries faces the severe challenge of achieving high‐rate cathode materials. Here, an integrated flexible electrode is constructed by smart combination of a conductive carbon cloth fiber skeleton and N‐doped carbon (NC) shell on Na₃V₂(PO₄)₃ (NVP) nanoparticles via a simple impregnation method. In addition to the great electronic conductivity and high flexibility of carbon cloth, the NC shell also promotes ion/electron transport in the electrode. The flexible NVP@NC electrode renders preeminent rate capacities (80.7 mAh g^?1 at 50 C for cathode; 48 mAh g^?1 at 30 C for anode) and superior cycle performance. A flexible symmetric NVP@NC//NVP@NC full cell is endowed with fairly excellent rate performance as well as good cycle stability. The results demonstrate a powerful polybasic strategy design for fabricating electrodes with optimal performance.     

Green synthesis of micron-sized silver flakes and their application in conductive ink

A facile, green method for fabrication of conductive ink composed of Ag flakes was developed for use in flexible printed electronics. The Ag flakes were prepared using AgNO₃, nontoxic l-ascorbic acid (Vc) and polyvinylpyrrolidone (PVP) serving as a metal salt, reducing agent and capping agent, respectively. The prepared Ag flakes were characterized by XRD, SEM, and TGA. The combination of PVP and FeCl₃ was found to be critical for the formation of the Ag flakes, and reaction activity was affected by temperature. Samples obtained at 140 °C were composed of Ag flakes with an average size of 0.94 ± 0.3 μm. A new fabrication method for producing conductive patterns was designed using a syringe with varying dispersion areas, allowing the ink (Ag flakes and organic solvent) to be applied directly onto a flexible photo paper. The conductivity and flexibility of the pattern were experimentally tested under varying reaction temperatures and bending cycles. Increasing contact area and packing density between Ag flakes resulted in an improved conductivity of the bending pattern. After more than 5000 bending cycles, the patterns were sintered at 160 °C and the resistivity increased from 4.6 ± 0.6 to 22.4 ± 0.8 μΩ cm, acceptable values for practical applications. Sample conductive lines drawn by the Ag flake ink exhibited excellent conductive performance and mechanical integrity, demonstrating a promising method for the formation of flexible microelectrodes or electronic devices.     

Palladium nanoparticle deposition via precipitation: a new method to functionalize macroporous silicon

We present an original two-step method for the deposition via precipitation of Pd nanoparticles into macroporous silicon. The method consists in immersing a macroporous silicon sample in a PdCl₂/DMSO solution and then in annealing the sample at a high temperature. The impact of composition and concentration of the solution and annealing time on the nanoparticle characteristics is investigated. This method is compared to electroless plating, which is a standard method for the deposition of Pd nanoparticles. Scanning electron microscopy and computerized image processing are used to evaluate size, shape, surface density and deposition homogeneity of the Pd nanoparticles on the pore walls. Energy-dispersive x-ray spectroscopy (EDX) and x-ray photoelectron spectroscopy (XPS) analyses are used to evaluate the composition of the deposited nanoparticles. In contrast to electroless plating, the proposed method leads to homogeneously distributed Pd nanoparticles along the macropores depth with a surface density that increases proportionally with the PdCl₂ concentration. Moreover EDX and XPS analysis showed that the nanoparticles are composed of Pd in its metallic state, while nanoparticles deposited by electroless plating are composed of both metallic Pd and PdO_x.     

Metal Chelation Assisted In Situ Migration and Functionalization of Catalysts on Peapod‐Like Hollow SnO2 toward a Superior Chemical Sensor

Rational design of nanostructures and efficient catalyst functionalization methods are critical to the realization of highly sensitive gas sensors. In order to solve these issues, two types of strategies are reported, i.e., (i) synthesis of peapod‐like hollow SnO₂ nanostructures (hollow 0D‐1D SnO₂) by using fluid dynamics of liquid Sn metal and (ii) metal–protein chelate driven uniform catalyst functionalization. The hollow 0D‐1D SnO₂ nanostructures have advantages in enhanced gas accessibility and higher surface areas. In addition to structural benefits, protein encapsulated catalytic nanoparticles result in the uniform catalyst functionalization on both hollow SnO₂ spheres and SnO₂ nanotubes due to their dynamic migration properties. The migration of catalysts with liquid Sn metal is induced by selective location of catalysts around Sn. On the basis of these structural and uniform functionalization of catalyst benefits, biomarker chemical sensors are developed, which deliver highly selective detection capability toward acetone and toluene, respectively. Pt or Pd loaded multidimensional SnO₂ nanostructures exhibit outstanding acetone (R _air/R _gas = 93.55 @ 350 °C, 5 ppm) and toluene (R _air/R _gas = 9.25 @ 350 °C, 5 ppm) sensing properties, respectively. These results demonstrate that unique nanostructuring and novel catalyst loading method enable sensors to selectively detect biomarkers for exhaled breath sensors.     

Construction of Large‐Area Ultrathin Conductive Metal–Organic Framework Films through Vapor‐Induced Conversion

On account of unique characteristics, the integration of metal–organic frameworks as active materials in electronic devices attracts more and more attention. The film thickness, uniformity, area, and roughness are all fatal factors limiting the development of electrical and optoelectronic applications. However, research focused on ultrathin free‐standing films is in its infancy. Herein, a new method, vapor‐induced method, is designed to construct centimeter‐sized Ni₃(HITP)₂ films with well‐controlled thickness (7, 40, and 92 nm) and conductivity (0.85, 2.23, and 22.83 S m^?1). Further, traditional transfer methods are tactfully applied to metal–organic graphene analogue (MOGA) films. In order to maintain the integrity of films, substrates are raised up from bottom of water to hold up films. The stripping method greatly improves the surface roughness R_q (root mean square roughness) without loss of conductivity and endows the film with excellent elasticity and flexibility. After 1000 buckling cycles, the conductance shows no obvious decrease. Therefore, the work may open up a new avenue for flexible electronic and magnetic devices based on MOGA.     

Electrodeposition of silver (Ag) nanoparticles on MnO<Subscript>2</Subscript> nanorods for fabrication of highly conductive and flexible paper electrodes for energy storage application

Metal oxide based electrodes are attractive for energy storage applications with limited characteristics of flexibility due to inherent rigid structure. However, incorporation of flexible insulating matrix within metal oxide composites result in poor electrically conductive and energy storage characteristics. This study presents the fabrication of flexible MnO₂ based composite electrodes prepared by incorporation of lignocelluloses (LC) fibers, directly collected from a self-growing plant, Monochoria Vaginalis. Furthermore electrodeposition of silver (Ag) nanoparticles was performed on LC/MnO₂ in potentiostatic mode to address the electrically conductive characteristics. Morphology, structural, conductive and energy storage properties of fabricated electrodes are analyzed by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), impedance analyzer and potentiostat, respectively. SEM images clearly indicate the deposition of Ag nanoparticles on MnO₂ nanorods embedded in LC fibers whereas FTIR results confirm the bonding of the functional groups. Cyclic voltammetry measurements showed efficient kinetics of LC/MnO₂ after electrodeposition of Ag nanoparticles. The effects on electrical properties associated with blending MnO₂ nanorods in lignocelluloses fibers and Ag deposition on MnO₂ in LC/MnO₂ are explored in wide frequency range between 10 Hz and 5 MHz. However, deposition of Ag nanoparticles on MnO₂ nanorods surfaces acts as a conductive path and reduces the associated resistance. Incorporated flexibility in rigid structure of MnO₂ and further improvements in conductive and energy storage characteristics will open the possibilities to be used as electrode in modern bendable energy storage devices.     

Adaptive Fabrication of a Flexible Electrode by Optically Self‐Selected Interfacial Adhesion and Its Application to Highly Transparent and Conductive Film

A novel adaptive electrode fabrication method using optically self‐selected interfacial adhesion between a laser‐processed metal layer and polymer film is introduced to fabricate cost‐effectively a high‐resolution arbitrary electrode with high conductivity. The quality is close to that from vacuum deposition on a highly heat sensitive polymer film, with active response to various design requirements. A highly conductive metal film (resistivity: 3.6 μΩ cm) below a 5 μm line width with a uniform stepwise profile and mirror surface quality (R_rms: 5–6 nm) is fabricated on a cheap polymer film with a heat resistance limit of below 100 °C. Severe durability tests are successfully completed without using any adhesion promoters. Finally, a highly transparent and conductive electrode with a transparency above 95% and sheet resistance of less than 10 Ω sq^?1 is fabricated on a polymer film and on glass by using this method. These results can help realize a potential high‐throughput, low‐cost, solution‐processable replacement for transparent conductive oxides.     

Binary Synergistic Sensitivity Strengthening of Bioinspired Hierarchical Architectures based on Fragmentized Reduced Graphene Oxide Sponge and Silver Nanoparticles for Strain Sensors and Beyond

Recently, stretchable electronics have been highly desirable in the Internet of Things and electronic skins. Herein, an innovative and cost‐efficient strategy is demonstrated to fabricate highly sensitive, stretchable, and conductive strain‐sensing platforms inspired by the geometries of a spiders slit organ and a lobsters shell. The electrically conductive composites are fabricated via embedding the 3D percolation networks of fragmentized graphene sponges (FGS) in poly(styrene‐block‐butadiene‐block‐styrene) (SBS) matrix, followed by an iterative process of silver precursor absorption and reduction. The slit‐ and scale‐like structures and hybrid conductive blocks of FGS and Ag nanoparticles (NPs) provide the obtained FGS–Ag‐NP‐embedded composites with superior electrical conductivity of 1521 S cm^?1, high break elongation of 680%, a wide sensing range of up to 120% strain, high sensitivity of ≈10⁷ at a strain of 120%, fast response time of ≈20 ms, as well as excellent reliability and stability of 2000 cycles. This huge stretchability and sensitivity is attributed to the combination of high stretchability of SBS and the binary synergistic effects of designed FGS architectures and Ag NPs. Moreover, the FGS/SBS/Ag composites can be employed as wearable sensors to detect the modes of finger motions successfully, and patterned conductive interconnects for flexible arrays of light‐emitting diodes.     

Facile electroless copper plating on diamond particles without conventional sensitization and activation

Conventional electroless plating of copper on diamond particles needs SnCl₂ sensitization and PdCl₂ activation pretreatments, which needs noble metal and consumes a large amount of reducing agent. In this paper, metallic tungsten coatings were first plated onto diamond particles by microwave-heating salt-bath plating (MHSBP) method, and then copper layer was directly plated onto the out surface of the tungsten layer by an electroless plating method with no need of SnCl₂ sensitization and PdCl₂ activation pretreatments. Composition and morphology of the coatings was analyzed by XRD, SEM, and EDS. The results show that the copper coating on the diamond surfaces can be adjusted by control the concentration of CuSO₄·5H₂O and plating temperature, and a full copper coating is achieved with content of CuSO₄·5H₂O of 19.6 g/L in the plating solution at 60 °C. The bending strength of the coated diamond/Cu composites is as high as 630 MPa, which increases 93.3% than the uncoated composites. This work presents an electroless plating of copper can directly on the surfaces of diamond particles with no need of conventional sensitization and activation, and a strong interface combination between coated diamond and copper.     

Oxygen Evolution Assisted Fabrication of Highly Loaded Carbon Nanotube/MnO2 Hybrid Films for High‐Performance Flexible Pseudosupercapacitors

To date, it has been a great challenge to design high‐performance flexible energy storage devices for sufficient loading of redox species in the electrode assemblies, with well‐maintained mechanical robustness and enhanced electron/ionic transport during charge/discharge cycles. An electrochemical activation strategy is demonstrated for the facile regeneration of carbon nanotube (CNT) film prepared via floating catalyst chemical vapor deposition strategy into a flexible, robust, and highly conductive hydrogel‐like film, which is promising as electrode matrix for efficient loading of redox species and the fabrication of high‐performance flexible pseudosupercapacitors. The strong and conductive CNT films can be effectively expanded and activated by electrochemical anodic oxygen evolution reaction, presenting greatly enhanced internal space and surface wettability with well‐maintained strength, flexibility, and conductivity. The as‐formed hydrogel‐like film is quite favorable for electrochemical deposition of manganese dioxide (MnO₂) with loading mass up to 93 wt% and electrode capacitance kept around 300 F g^?1 (areal capacitance of 1.2 F cm^?2). This hybrid film was further used to assemble a flexible symmetric pseudosupercapacitor without using any other current collectors and conductive additives. The assembled flexible supercapacitors exhibited good rate performance, with the areal capacitance of more than 300 mF cm^?2, much superior to other reported MnO₂ based flexible thin‐film supercapacitors.     

A Crosslinked Polytetrahydrofuran‐Borate‐Based Polymer Electrolyte Enabling Wide‐Working‐Temperature‐Range Rechargeable Magnesium Batteries

A polymer‐based magnesium (Mg) electrolyte is vital for boosting the development of high‐safety and flexible Mg batteries by virtue of its enormous advantages, such as significantly improved safety, potentially high energy density, ease of fabrication, and structural flexibility. Herein, a novel polytetrahydrofuran‐borate‐based gel polymer electrolyte coupling with glass fiber is synthesized via an in situ crosslinking reaction of magnesium borohydride [Mg(BH₄)₂] and hydroxyl‐terminated polytetrahydrofuran. This gel polymer electrolyte exhibits reversible Mg plating/stripping performance, high Mg‐ion conductivity, and remarkable Mg‐ion transfer number. The Mo₆S₈/Mg batteries assembled with this gel polymer electrolyte not only work well at wide temperature range (?20 to 60 °C) but also display unprecedented improvements in safety issues without suffering from internal short‐circuit failure even after a cutting test. This in situ crosslinking approach toward exploiting the Mg‐polymer electrolyte provides a promising strategy for achieving large‐scale application of Mg‐metal batteries.     

Fabrication of hollow core–shell conductive nanoparticles based on nanocrystalline cellulose for conductive adhesive

A novel environmentally friendly method was developed to fabricate hollow core–shell conductive nanoparticles using a natural and nontoxic material, nanocrystalline cellulose (NCC), as the template. The NCC used in this study has nano-scale rod-like structure. After the oxidization to dialdehyde cellulose, the insulated NCC was functionalized by poly(dopamine) (PDA) in weakly alkaline conditions through Schiff base reaction and self-polymerization. The Schiff base can be hydrolyzed in an aqueous acetone solution via ultraviolet radiation so that the hollow structure constructed. This structure not only strengthened the mechanical properties but also provided more active sites for silver deposition. Utilizing the chelating ability of the catechol groups in PDA, electroless plating method was used to form the silver coating layer. Scanning electron microscope and Dynamic Light Scattering measurements indicated that these nanoparticles (NPs) had well-defined morphology and a mean diameter of 100–120 nm. Moreover, these prepared Ag–DA–NCC₀ NPs exhibited excellent conductivity. Their electrical resistivity reached 0.2 mΩ·cm, which is much higher than that of many other conductive particles used in conductive adhesive.     

Liquid Metal Droplet and Graphene Co‐Fillers for Electrically Conductive Flexible Composites

Colloidal liquid metal alloys of gallium, with melting points below room temperature, are potential candidates for creating electrically conductive and flexible composites. However, inclusion of liquid metal micro‐ and nanodroplets into soft polymeric matrices requires a harsh auxiliary mechanical pressing to rupture the droplets to establish continuous pathways for high electrical conductivity. However, such a destructive strategy reduces the integrity of the composites. Here, this problem is solved by incorporating small loading of nonfunctionalized graphene flakes into the composites. The flakes introduce cavities that are filled with liquid metal after only relatively mild press‐rolling (<0.1 MPa) to form electrically conductive continuous pathways within the polymeric matrix, while maintaining the integrity and flexibility of the composites. The composites are characterized to show that even very low graphene loadings (≈0.6 wt%) can achieve high electrical conductivity. The electrical conductance remains nearly constant, with changes less than 0.5%, even under a relatively high applied pressure of >30 kPa. The composites are used for forming flexible electrically‐conductive tracks in electronic circuits with a self‐healing property. The demonstrated application of co‐fillers, together with liquid metal droplets, can be used for establishing electrically‐conductive printable‐composite tracks for future large‐area flexible electronics.     

RuO2 Particles Anchored on Brush‐Like 3D Carbon Cloth Guide Homogenous Li/Na Nucleation Framework for Stable Li/Na Anode

Lithium (sodium)‐metal batteries are the most promising batteries for next‐generation electrical energy storage due to their high volumetric energy density and gravimetric energy density. However, their applications have been prevented by uncontrollable dendrite growth and large volume expansion during the stripping/plating process. To address this issue, the key strategy is to realize uniform lithium (sodium) deposition during the stripping/plating process. Herein, a thin lithiophilic layer consisting of RuO₂ particles anchored on brush‐like 3D carbon cloth (RuO₂@CC) is prepared by a simple solution‐based method. After infusion of Li, the RuO₂@CC transfers to Li‐Ru@CC. Ru nanoparticles not only play a role in leading Li⁺ (Na⁺) to plate on the 3D carbon framework, but also lower local current density because of the good electrical conductivity. Furthermore, density functional theory calculations demonstrate that Ru metal, the reaction product of alkali metal and Ru, can lead Li⁺ to plate evenly around carbon fiber owing to the strong binding energy with Li⁺. The Li‐Ru@CC anode shows ultralong cycle life (1500 h at 5 mA cm^?2). The full cell of Li‐Ru@CC|LiFePO₄ exhibits lower polarization (90% capacity retention after 650 cycles). In addition, sodium metal batteries based on Na‐Ru@CC anodes can achieve similar improvement.     

Preparation of copper nanoparticles on carbon nanotubes by electroless plating method

Densely distributed copper nanoparticles have been deposited on the surface of carbon nanotubes with a size of ∼10 nm by the electroless plating method. It has been found that the pretreatment of the carbon nanotubes is very important to obtain the copper nanoparticles on the carbon nanotubes; in our experiments, one-step pretreatment of mixed HNO₃ and H₂SO₄ was found effective. In order to attain nanosized copper particles, the electroless plating parameters should be closely controlled; e.g., the pH value of the plating solution, the temperature, and the concentration and titrating speed of HCOH were critical.     

Double‐Layer Polymer Electrolyte for High‐Voltage All‐Solid‐State Rechargeable Batteries

No single polymer or liquid electrolyte has a large enough energy gap between the empty and occupied electronic states for both dendrite‐free plating of a lithium‐metal anode and a Li⁺ extraction from an oxide host cathode without electrolyte oxidation in a high‐voltage cell during the charge process. Therefore, a double‐layer polymer electrolyte is investigated, in which one polymer provides dendrite‐free plating of a Li‐metal anode and the other allows a Li⁺ extraction from an oxide host cathode without oxidation of the electrolyte in a 4 V cell over a stable charge/discharge cycling at 65 °C; a poly(ethylene oxide) polymer contacts the lithium‐metal anode and a poly(N‐methyl‐malonic amide) contacts the cathode. All interfaces of the flexible, plastic electrolyte remain stable with no visible reduction of the Li⁺ conductivity on crossing the polymer/polymer interface.     

MXenes在柔性力敏传感器中的应用研究进展

随着可穿戴柔性电子技术的发展, 高灵敏度和宽感应范围的柔性力敏传感器的需求量逐渐增大, 如何选择兼具高导电性和良好柔性的材料作为传感器的敏感材料是获得高性能传感器的关键。近年来, MXene材料因其导电性好、柔韧性高、亲水性好以及合成可控等优点成为一种极具潜力的导电敏感材料。本文就MXene基柔性力敏传感器的类型、敏感材料的微结构设计方式、传感性能及传感机理等方面的研究进展进行了阐述和总结。