Fabrication Of Flexible Electrodes Research Articles

Laser-Assisted Photo-Thermal Reaction for Ultrafast Synthesis of Single-Walled Carbon Nanotube/Copper Nanoparticles Hybrid Films as Flexible Electrodes.

The hybridization of single-walled carbon nanotubes (SWCNTs) and Cu nanoparticles offers a promising strategy for creating highly conductive and mechanically stable fillers for flexible printed electronics. In this study, we report the ultrafast synthesis of SWCNT/Cu hybrid nanostructures and the fabrication of flexible electrodes under ambient conditions through a laser-induced photo-thermal reaction. Thermal energy generated from the nonradiative relaxation of the π-plasmon resonance of SWCNTs was utilized to reduce the Cu-complex (known as a metal-organic decomposition ink) into Cu nanoparticles. We systematically investigated the effects of SWCNT concentration and output laser power on the structural and electrical properties of the SWCNT/Cu hybrid electrodes. The SWCNT/Cu electrodes achieved a minimum electrical resistivity of 46 μohm·cm, comparable to that of the metal-based printed electrodes. Mechanical bending tests demonstrated that the SWCNT/Cu electrodes were highly stable and durable, with no significant deformation observed even after 1000 bending cycles. Additionally, the electrodes showed rapid temperature increases and stable Joule heating performance, reaching temperatures of nearly 80 °C at an applied voltage of less than 3.5 V.

High-conductivity and long-term stability strain sensor based on silk fibroin and polyvinyl alcohol hydrogels

Conductive hydrogels as promising candidates of wearable electronic have attracted considerable interest in health monitoring, multifunctional electronic skins, and human-machine interfaces. However, to simultaneously achieve excellent electrical properties, long-term stability, and water vapor permeability of conductive hydrogels remains a challenge. Herein, a highly conductive hydrogel (MPRS) with high breathability (5.90 mg∙cm−2∙h−1), excellent electrical conductivity (6.67 S/m), high elongation (315%), and remarkable water retention properties was prepared adopting cold freeze-thawing method. MXene, poly (3, 4-ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT: PSS), and reduced graphene oxide were used as conductive materials, while silk fibroin (SF) and polyvinyl alcohol (PVA) were used as the gel matrix. Lithium chloride solution was used as a solvent during the preparation process. The strain sensor based on this hydrogel demonstrates rapid response (0.33 s) and recovery ability (0.31 s) to strain stimuli. Upon 250 cycles of stretching at 35% strain, the output signal remains stable and highly repeatable, ensuring accurate detection of human joint movements and facial expressions. The fabrication of flexible electrodes using the hydrogel enabled real-time monitoring of human electromyography and electrocardiogram signals. The applications in a 2D sensor array and human-machine interaction interfaces also proved the excellent performance of this conductive hydrogels in wearable sensor.

Flexible, all-solid-state supercapacitors derived from waste polyurethane foams

Recently, flexible energy storage devices have attracted increasing interests for their promise in wearable electronic devices. In this study, the waste polyurethane foam (WPUF), a common polymeric waste having caused considerable environmental pollutions, is employed for the first time in the fabrication of flexible electrodes through wrapping carbon nanotubes (CNTs) and cellulose nanofibers (CNFs), pressing into thin foams with molds and in-situ growth of polyaniline (PANI). Within the hybrid foam, the CNT/CNF layer provides good electrical conductivity and hydrophilicity, while the highly porous structure still retained after appropriate hot pressing offers numerous pathways for efficient electrolyte ions transportation, and the loaded polyaniline is mainly responsible for the improved electrochemical capacitive properties. A symmetrical all-solid-state SC is assembled using the as-prepared WPUF-derived electrode, which displays superb physical and electrochemical performances, namely, excellent flexibility, high specific capacitance, and great stability at different bending angles. Interestingly, a flexible neat polyurethane membrane can also be easily prepared from WPUF via hot pressing, which is then applied to encapsulate SC to form a novel all-WPUF-based energy wristband to power an electronic watch. This study demonstrates a facile and scalable strategy for the fabrication of high-performance electrodes for wearable electronic devices, using the abundant polymeric wastes as the raw materials.

A reusable wet-transfer printing technique for manufacturing of flexible silver nanowire film-based electrodes

To explore a simple and efficient way to fabricate thin film electrodes on flexible substrates is highly desired because of its high promising application in optoelectronics. Transfer printing technique plays a key role in the fabrication of flexible electrodes from conventional substrates to flexible substrates. Unfortunately, a simple, room temperature, environmental-friendly and reusable transfer printing technique still remains challenging. Here we demonstrated a novel water-based wet-transfer printing technique that is simple, room temperature, environmental-friendly and reusable by taking advantage of the adjustment of the intermolecular hydrogen bonding between thin film and substrates. This effective and practical transfer technique may provide an effective route to develop electronic flexible devices with high performance.

Fabrication of Flexible Electrode with Sub-Tenth Micron Thickness Using Heat-Induced Peelable Pressure-Sensitive Adhesive Containing Amide Groups.

In response to the increasing demand for flexible devices, there is increasing effort to manufacture flexible electrodes. However, the difficulty of handling a thin film is an obstacle to the production of flexible electrodes. In this study, a heat-induced peelable pressure-sensitive adhesive (h-PSA) was fabricated and used to manufacture a flexible electrode with sub-tenth micron thickness. Unlike the control PSA, the incorporation of amide groups made the h-PSA fail through adhesive failure at temperatures ranging from 20 to 80 °C. Compared to the peeling adhesion (1719 gf/in) of h-PSA measured at 20 °C, the value (171 gf/in) measured at 80 °C was decreased by one order of magnitude. Next, the 8 μm thick polyethylene terephthalate (PET) film was attached on a thick substrate (50 μm) via h-PSA, and Mo/Al/Mol patterns were fabricated on the PET film through sputtering, photolithography, and wet-etching processes. The thick substrate alleviated the difficulty of handling the thin PET film during the electrode fabrication process. Thanks to the low peel force and clean separation of the h-PSA at 80 °C, the flexible electrode of metal patterns on the PET (8 μm) film was isolated from the substrate with little change (<1%) in electrical conductivity. Finally, the mechanical durability of the flexible electrode was evaluated by a U-shape folding test, and no cracking or delamination was observed after 10,000 test cycles.

Recent Advances in Design of Flexible Electrodes for Miniaturized Supercapacitors

AbstractThe increasing demands of portable, flexible, and wearable electronics have greatly stimulated the development of miniaturized supercapacitors (MSCs) with features of high flexibility, low weight, long lifespan, and safety. The techniques which can effectively incorporate functional nanomaterials into flexible electrodes are extremely important for future wide‐spread applications of MSCs, and thus are identified as the research focus in the field. Herein, this review focuses on recent advances in the fabrication of flexible electrodes and their applications in MSCs. In particular, the principles of the newly developed fiber spinning techniques and their utilization in designing microstructures and resulting electrochemical properties of fibrous electrodes are first described. Second, a few novel approaches to prepare planar MSCs and their special advantages are introduced, and third, the state‐of‐the‐art research in 3D stereo MSCs based on 3D printing and morphing technologies are discussed. In the end, the prospects and key challenges based on the considerations of performance improvement, device design, and system integration are outlined.

Atomic layer deposition-induced integration of N-doped carbon particles on carbon foam for flexible supercapacitor

Flexible devices have attracted abundant attention in energy storage systems. In this paper, we presented a novel approach for fabricating flexible supercapacitor based on metal organic frameworks-derived material. In this approach, a uniform zeolitic imidazolate frameworks-8 layer with a high mass loading was deposited on a flexible carbon foam (CF) skeleton efficiently by the induction of a uniform ZnO nanomembrane prepared via an atomic layer deposition technique. A flexible N-doped carbon particle-carbon foam (N-CP-CF) composite with a hierarchically porous structure and a large specific surface area (i.e., 538 m2 g−1) was obtained in a subsequent pyrolysis process. The resultant materials have the excellent electrochemical performance (i.e., a high specific capacitance of 300 F g−1 and a high energy density of 20.8 W h kg−1). The N-CP-CF composite can provide a stable capacitance (i.e., 250 F g−1) and an energy density (i.e., 17.36 W h kg−1) under large deformation (25% of original thickness). This work could propose a promising strategy in fabrication of flexible electrode with a large potential towards energy storage applications in the future.

Hierarchical FeCo2O4@NiCo layered double hydroxide core/shell nanowires for high performance flexible all-solid-state asymmetric supercapacitors

Flexible supercapacitors are important energy storage devices used for wearable and smart electronics. The key to fabricating flexible supercapacitors lies in the acquirement of flexible electrodes. However, design and fabrication of flexible electrodes with both high energy and power densities as well as long cycling life is still a challenge work. Herein, a novel flexible supercapacitor electrode composed of hierarchical FeCo2O4@NiCo-LDH core/shell heterostructures on carbon cloth is reported by a facile and cost-effective method. The electrode exhibits a remarkable specific capacitance of 2426 F g−1 at 1 A g−1, and ultrahigh rate capability with 72.5% capacitance retention at 20 A g−1, as well as excellent cycling stability with a capacitance retention of 91.6% after 5000 cycles. Furthermore, the FeCo2O4@NiCo-LDH/CC as the positive electrode, active carbon as the negative electrode, and PVA-KOH gel as both the solid state electrolyte and separator were assembled into flexible all-solid-state asymmetric supercapacitor. The resulting FeCo2O4@NiCo-LDH//AC ASC device exhibits a maximum energy density of 94.9 Wh kg−1, and a favorable energy density of 66.5 Wh kg−1 is still achieved at a high power density of 1.6 kW kg−1, as well as excellent cycling stability of 88.2% after 5000 cycles. Moreover, the ASC device exhibits outstanding flexible and reliability with no degradation under large twisting, which can light one red LED indicators efficiently. The work presented herein hold promise in energy storage for future portable and wearable electronic devices.

Effects of Flexible Dry Electrode Design on Electrodermal Activity Stimulus Response Detection.

The focus of this research is to evaluate the effects of design parameters including surface area, distance between and geometry of dry flexible electrodes on electrodermal activity (EDA) stimulus response detection. EDA is a result of the autonomic nervous system being stimulated, which causes sweat and changes the electrical characteristics of the skin. Standard silver/silver chloride (Ag/AgCl) EDA electrodes are rigid and lack conformability in contact with skin. In this study, flexible dry Ag/AgCl EDA electrodes were fabricated on a compliant substrate, used to monitor EDA stimulus responses and compared to results simultaneously collected by rigid dry Ag/AgCl electrodes. A repeatable fabrication process for flexible Ag/AgCl electrodes has been established. Surface area, distance between and geometry of electrodes are shown to affect the detectability of the EDA response and the minimum number of sweat glands to be covered by the electrodes has been estimated at 140, or more, in order to maintain functionality. The optimal flexible EDA electrode is a serpentine design with a 0.15cm2 surface area and a 0.20cm distance with an average Pearson correlation coefficient of . Fabrication of flexible electrodes is described and an understanding of the effects of electrode designs on the EDA stimulus response detection has been established and is potentially related to the coverage of sweat glands. This work presents a novel systematic approach to understand the effects of electrode designs on monitoring EDA which is of importance for the design of wearable EDA monitoring devices.

Introduction of a Chemical-Free Metal PDMS Thermal Bonding for Fabrication of Flexible Electrode by Metal Transfer onto PDMS.

Polydimethylsiloxane (PDMS) is a flexible and biocompatible material widely used in the fabrication of microfluidic devices, and is often studied for the fabrication of flexible electrodes. The most popular method of fabricating a flexible electrode using PDMS is done by transferring a metal electrode onto said PDMS. However, the transfer process is difficult and the transferred metal layer is easily damaged due to inherently weak adhesion forces between the metal and PDMS, thus requiring a chemical treatment or sacrificial layer between the two. The fabrication process using a chemical treatment or sacrificial layer is complicated and expensive, which is the major limitation of using PDMS in the fabrication of flexible electrodes. This paper discusses the findings of a possible solution to create strong bonding between PDMS and various metals (copper, nickel and silver) using a chemical-free metal to PDMS thermal bonding technique. This method is the same as the PDMS curing process, but with a variation in the curing condition. The condition required to create strong bonding was studied by observing copper transferred by various PDMS curing conditions, including the standard condition. The condition creating the strong bonding was baking PDMS (5:1 = base polymer: curing agent) at 150 °C for 20 min. Experimentation showed that the optimum thickness of the transferred metal shows that the optimum thickness is approximately 500 nm, which allows for a higher resistance to stresses. The successful transfer of copper, nickel and silver layers onto PDMS with a stronger adhesion force opens up many new applications dealing with the fabrication of flexible electrodes, sensors, and flexible soft magnets.

Design of micro, flexible light-emitting diode arrays and fabrication of flexible electrodes

In this study, we design micro, flexible light-emitting diode (LED) array devices. Using theoretical calculations and finite element simulations, we analyze the deformation of the conventional single electrode bar. Through structure optimization, we obtain a three-dimensional (3D), chain-shaped electrode structure, which has a greater bending degree. The optimized electrodes not only have a bigger bend but can also be made to spin. When the supporting body is made of polydimethylsiloxane (PDMS), the maximum bending degree of the micro, flexible LED arrays (4 × 1 arrays) was approximately 230 µm; this was obtained using the finite element method. The device (4 × 1 arrays) can stretch to 15%. This paper describes the fabrication of micro, flexible LED arrays using microelectromechancial (MEMS) technology combined with electroplating technology. Specifically, the isolated grooves are made by dry etching which can isolate and protect the light-emitting units. A combination of MEMS technology and wet etching is used to fabricate the large size spacing.

유연 복합재료 전극 제조 및 표면조도에 따른 접착 특성에 대한 연구

The fabrication of flexible electrodes coated on the surface of a dielectric elastomer film, which is a type of electroactive polymer (EAP), was carried out. Controlled amounts of Xylitol powder were added (10, 30, 50 and 70 wt%) to the commercial conductive polymer (PEDOT:PSS) to enhance resilience of the electrode. To check resilience of the fabricated composite electrodes, tensile tests were carried out using silicone films coated with the polymer electrodes. From the test results, it was found that 70 wt% Xylitol containing conductive polymer had excellent elongation and high failure strains. Furthermore, surface of the silicone film was uniformly polished with various abrading papers to enhance the wettability of the conductive polymers on the surface of the silicone film. It was found that the silicone film polished with #120 abrading paper had the best wettability and guaranteed excellent bonding behavior.

Interconnected carbon nanotube/graphene nanosphere scaffolds as free-standing paper electrode for high-rate and ultra-stable lithium–sulfur batteries

The rational design and fabrication of flexible electrodes with high capacity, high rate capability, and high cycling stability is of urgent need for bendable, wearable, and implantable electronic devices. The integration of conductive nanocarbon as flexible scaffolds is an efficient and effective route toward flexible high-energy-density lithium–sulfur batteries. Herein, a free-standing paper electrode was constructed by rational integration of high conductive super-long carbon nanotubes (CNTs) and nano-sized hollow graphene spheres (GSs) through a room-temperature solution-processable method for lithium–sulfur batteries. The hollow GSs afforded close space to accommodate sulfur species, sustain the volume fluctuation during cycling, and retard the dissolution of polysulfides and parasitic shuttle. The graphene walls of GSs and super-long CNTs synergistically constructed hierarchical short-/long-range electron/ion pathways. Consequently, the as-obtained flexible paper electrode was with a high sulfur utilization of 81% (corresponding to 1346mAhg−1) at a current density of 0.17Ag−1 (0.19mAcm−2), a high-rate capacity retention of 40% when the current density increased to supreme 16.7Ag−1 (18.4mAcm−2), and a superior capacity retention of 89.0% over 500 cycles. This proof-of-concept research indicated the well hybridization of graphene and CNTs holds promise in the efficient use as flexible electrodes for future flexible electronics.