High performance fiber-shaped flexible asymmetric supercapacitor based on MnO2 nanostructure composited with CuO nanowires and carbon nanotubes

The demand for wearable electronics has greatly promoted the development of flexible supercapacitors. Herein, we develop a series of approaches to fabricate a fiber-shaped supercapacitor with flexibility. In the device, CuO@MnO₂, carbon nanotube (CNT)@MnO₂ and PVA-KOH are respectively used as inner electrode, outer electrode and gel electrolyte. The approaches including in-situ growth of CNTs, in-situ etching removal of SiO₂ template and in-situ filling of gel electrolyte via hydrothermal process are explored to protect the device from structure damage caused by external forces and to maximize effective contact areas between active electrode materials and gel electrolyte. The optimized supercapacitor of copper wire@CuO@MnO₂//PVA-KOH//CNT@MnO₂ demonstrates a good capacitive performance (5.97 F cm^?3) and exhibits a high energy density (0.38 mWh cm^?3) at a power density of 25.5 mW cm^?3. In addition, it has perfect cycling stability (77% after 2000 cycles) with excellent flexibility. Therefore, this work will provide desirable processes to construct fiber-shaped supercapacitors as flexible and wearable energy storage devices.     

Fabrication of paper based carbon/graphene/ZnO aerogel composite decorated by polyaniline nanostructure: Investigation of electrochemical properties

The cellulose derived carbon/graphene/ZnO aerogel composite was prepared as an electrode in order to investigate the electrochemical properties. Carbon aerogel was synthesized using paper as an available cellulose source, and the composite was obtained through a new and simple preparation method including the immersion of monolithic carbon aerogel in graphene oxide/Zn²⁺ suspension and subsequent chemical reduction and freeze drying. The morphology, functional groups and crystalline structure of the samples were studied with Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction Spectroscopy (XRD), respectively. Electrochemical performance of the prepared binder free electrodes was examined using Cyclic Voltammetry (CV), Galvanostatic Charge-Discharge (GCD) and Electrochemical Impedance Spectroscopy (EIS). The data revealed that flexible carbon/graphene/ZnO composite resulted in a low density (0.035 g cm⁻³) electrode with the capacitance of 900 mF cm⁻² at a high current density of 10 mA cm⁻², lower IR drop and high cyclic stability (capacitance retention of 96%) after 1000 cycles, at 10 mA cm⁻². These features were due to the presence of 3D porous conductive network, highly reduced graphene oxide, and the formation of ZnO nanoparticles on graphene sheets. Moreover, polyaniline (PANI) was introduced to carbon/graphene/ZnO composite electrode using electro-oxidation method at different reaction time and aniline concentration in order to achieve remarkably improved capacitance of 2500 mF cm⁻² (at 10 mA cm⁻²) and low charge transfer resistance. Also, after the supercapacitor device assembly, the capacitance was retained. Based on the results, the synthesized composite is a promising material for new generation of lightweight freestanding electrodes with the high electrochemical performance.     

纤维状柔性超级电容器的研究进展

随着智能可穿戴设备的快速发展,对柔性能量储存设备提出了更高的要求.纤维状超级电容器具有柔性、轻质、功率密度高、循环寿命长、快速充放电的优势,在可穿戴领域展现出广泛的应用潜力.碳纳米管纤维、石墨烯纤维和碳纤维具有较高的电导率,可以满足超级电容器电导率的要求,被认为是理想的纤维状超级电容器的电极材料.主要综述了碳纳米管纤维、石墨烯纤维和碳纤维基超级电容器的制备方法、电化学性能和纤维状超级电容器的应用,重点介绍了一些国内外代表性的研究工作.最后分析了纤维状超级电容器研究中存在的问题,并对未来的研究方向和发展趋势进行了预测和展望.     

Rational design of nickel cobalt sulfide/oxide core-shell nanocolumn arrays for high-performance flexible all-solid-state asymmetric supercapacitors

The development of wearable electronics has created a surge of interest in designing flexible energy storage device with high energy density and long lifespan. In this work, we have successfully fabricated a flexible asymmetric supercapacitor (ASC) based on the NiCo₂S₄@NiCo₂O₄ nanocolumn arrays (NCAs). The nickel cobalt sulfide/oxide core-shell nanostructures were rationally synthesized through a facile stepwise approach. The NiCo₂S₄@NiCo₂O₄ NCAs based electrode delivered a high specific capacitance of 2258.9 F g⁻¹ at a current density of 0.5 A g⁻¹. The as-assembled flexible ASC device exhibited a high energy density of 44.06 Wh kg⁻¹, a high power density of 6.4 kW kg⁻¹, and excellent cycling stability by retaining 92.5% after 6000 cycles. Excitingly, the electrochemical property of the ASC device could be maintained under severe bending, indicating superior flexibility and mechanical stability. The NiCo₂S₄@NiCo₂O₄ core-shell NCAs possess enormous potential for future wearable electronic applications.     

Electrochemical kinetics of 2D-MoS2 sputtered over stainless-steel mesh: Insights into the Na+ ions storage for flexible supercapacitors

Direct growth of layered MoS₂ nanoworms on low-cost bendable SSM has been physically achieved for flexible supercapacitor utilization. The homogeneously grown MoS₂@SSM electrode demonstrates several electroactive cavities, facilitating the swift diffusion and additional pathways for Na⁺-ion intercalation. The structural and morphological features of MoS₂ thin film grown at optimized substrate temperature (300 °C) revealed the formation of the porous array of intermixed nanoworms. The advanced electrode delivers a specific capacitance of 214.90 F/g at a scan rate of 5 mV/s. The specific energy of 28.05 Wh/kg is obtained at 0.26 kW/kg, further elucidating the rich electrochemical response. A wide voltage window of 1.2 V with elongated cycling (retains ～88% capacitance after 3000 cycles) has been achieved by MoS₂@SSM electrode (dimensions 1 × 1 cm²). Moreover, Dunn's technique has gauged the origin of dual contribution in charge storage mechanism and considerable dominance of capacitive contribution over faradic one. The synthesized electrode has been investigated at a bending angle of 180° (retains ～92%), signifying better mechanical stability and pliability. As practical applicability in the flexible supercapacitor, the contemporary route yields a cathode of enormous potential, which may enable new possibilities in wearable hands-on electronics and demonstrate a framework to manifest its real practical application.     

Mechanically strong high performance layered polypyrrole nano fibre/graphene film for flexible solid state supercapacitor

Paper like flexible electrode becomes one of the most important research objects recently in request of the fast expanding market of portable electronics. Flexible solid state supercapacitors are shortlisted as one of the most promising energy devices to power electronics with medium to high power density requirements. In this work, we developed a simple but effective way to produce a mechanically strong and electrochemically active RGO/polypyrrole (PPy) fibre paper. A well-bedded microstructure was created with interlaced polypyrrole fibres evenly distributed between the graphene layers. Such microstructure can create enormous amount of pores and therefore provides larger interfaces for charge carrier storage/release. The effects of polypyrrole fibres on the film’s morphologies, mechanical properties and electrochemical performance were discussed. A solid state supercapacitor was demonstrated using such paper electrodes and a gel type electrolyte – phosphate acid (H₃PO₄) infused polyvinyl alcohol (PVA). It showed a high capacitance (345 F g⁻¹) and an excellent cycling stability (9.4% drop after 1000 cycles).     

Preparation of on chip,flexible supercapacitor with high performance based on electrophoretic deposition of reduced graphene oxide/polypyrrole composites

A new concept is introduced to fabricate flexible, on-chip supercapacitors by electrophoretically depositing highly dispersed reduced graphene oxide/polypyrrole on interdigital-like electrodes. By the unique method, the deposited films could construct on the substrate facilely and uniformly. The prepared all-solid-state device demonstrates high volumetric capacitance (about 147.9 F cm⁻³), high energy density (13.15 mWh cm⁻³ at a power density of 1300 mW cm⁻³) and excellent cycling stability (approximately 71.7% of the initial capacitance retained after 5000 cycles). Compared with other supercapacitor, the device demonstrated here is lightweight, flexible and inexpensive.     

Fabrication of PANI@Ti3C2Tx/PVA hydrogel composite as flexible supercapacitor electrode with good electrochemical performance

Developing a new strategy to effectively prevent the restacking of MXene nanosheets will have significant impacts on designing flexible supercapacitor electrodes. Herein, a novel Ti₃C₂T_x/polyvinyl alcohol (PVA) porous sponge with 3D interconnected structures is prepared by sol-gel and freeze-dried methods. This Ti₃C₂T_x/PVA porous sponge is used as the template of in-situ polyaniline (PANI) polymerization, and the fabricated PANI@Ti₃C₂T_x/PVA hydrogel composite is applied as flexible supercapacitors electrodes. 1D conductive polymer chains PVA could increase the interlayer spacing of Ti₃C₂T_x nanosheets, which is beneficial to expose more electrochemical active sites. The supercapacitor based on PANI@Ti₃C₂T_x/PVA hydrogel composite exhibits the coexistence of double-layer capacitance and pseudocapacitance behavior. This supercapacitor shows a maximum areal specific capacitance of 103.8 mF cm^?2 at 2 A m^?2, and it also exhibits a maximum energy density of 9.2 μWh·cm^?2 and an optimum power density of 800 μW cm^?2. The capacitance of this supercapacitor is almost not change under different bending angles. Moreover, 99% capacitance retention is achieved after 10 000 charge/discharge cycles of the supercapacitor. The synergistic effect between PANI and Ti₃C₂T_x/PVA composite may improve the number of reactive sites and provide efficient channels for ion diffusion/electron transport.     

Enhanced electrochemical performance of hybrid composite microstructure of CuCo2O4 microflowers-NiO nanosheets on 3D Ni foam as positive electrode for stable hybrid supercapacitors

Self-assembled composite porous structures comprising CuCo₂O₄ microflowers and NiO hexagonal nanosheets were synthesized on a conducting 3D Ni foam surface [CCO/NO] using a simple hydrothermal method. This unique composite assembly was further characterized and electrochemically evaluated as a binder-free positive electrode for hybrid supercapacitor application. The study showed that the CCO/NO exhibited a maximum areal capacitance of 1444 mF cm^?2, significantly higher than the parent CuCo₂O₄ and NiO electrodes, with remarkable stability of 88.5% for 10,000 galvanostatic charge-discharge cycles. Key features for the enhanced electrochemical performance of CCO/NO can be related to a lowered diffusion resistance because the hybrid nanocomposite porous assembly generates short diffusion paths for electrolyte ions and more active sites for reversible faradaic transition for charge storage. The hybrid supercapacitor was assembled using activated carbon as a negative electrode and CCO/NO as a positive electrode in alkaline electrolyte, performed at an improved potential of 1.6 V. Device showed a maximum areal capacitance of 122 mF cm^?2, a maximum areal energy density of 43 μWh cm^?2, and a maximum areal power density of 5.1 mW cm^?2. This hybrid supercapacitor showed remarkable cyclic stability up to 98% for 10,000 cycles. This study encourages the development of low-cost, high-performance, durable electrode designs using hybrid composite for next-generation energy storage systems.     

Lead-free BiFeO3 film on glass fiber fabric: Wearable hybrid piezoelectric-triboelectric nanogenerator

Constructing hybrid nanogenerators (NGs) based on triboelectric effect and piezoelectric effect can combine the merits of the individual type of NG thus have drawn great attention in flexible wearable electronics. Herein, we prepared flexible BiFeO₃ (BFO) film in a simple and cost-effective way, which was used to fabricate a wearable hybrid piezoelectric-triboelectric nanogenerator (H–P/TENG) with silk fiber. By optimizing the experimental conditions, the highest open-circuit voltage of 110 V and short-circuit current density of 3.67 μA/cm² were achieved under 1 Hz contact-separation movement. The device also showed the best output power density of 151.42 μW/cm² with load resistance of 250 MΩ. Stimulating by moving body, the fabricated H–P/TENG successively realized the harvest and conversion of mechanical energy into electric energy, demonstrating great potential to monitor posture and establish a self-powered system. Moreover, the proposed H–P/TENG exhibited great stable output after 1800 contact-separation cycles, indicating the outstanding structure stability and fatigue resistance. This work will provide not only a facile and viable way to realize the application of ferroelectric materials in H–P/TENG but also new opportunities for developing monitor posture and self-powered systems.     

2D/2D SnS2/MoS2 layered heterojunction for enhanced supercapacitor performance

Two-dimensional (2D) SnS₂/MoS₂ heterojunction with a 2D/2D novel structure was used as electrode material for enhanced supercapacitor performance. Compared with the sole SnS₂, the as-prepared 2D/2D SnS₂/MoS₂ layered heterojunction has exhibited great improvement in supercapacitor properties. This novel structure can effectively prevent agglomeration and stacking in electrochemical process, and 2D/2D structure is beneficial to intercalation and desorption of ions in electrochemical processes. The experiment result shows that MoSn₅ (samples with 5% MoSn5 mole ratios) display a specific capacitance of 466.6 F/g at the current density of 1 A/g in 0.5 mol/L potassium hydroxide solution, an impressive cycling stability with 88.2% capacitance retention at current density of 4 A/g. In addition, the as-fabricated symmetric supercapacitor exhibited high energy density of 115 Wh kg⁻¹ at the power density of 2230 Wh kg⁻¹. This work provides a fundamental investigation of 2D/2D layered material synergistic effect on the electrochemical process.     

Facile synthesis of flexible and free-standing cotton covered by graphene/MoO2 for lithium-ions batteries

It is necessary to build flexible and free-standing materials for flexible/wearable electronics in high-performance lithium-ions batteries. Herein, we design and fabricate a flexible and free-standing 3 D carbon/MoO₂ composite through a facile immersing method followed by an annealing process. The carbon framework is supported by non-woven cotton totally covered by graphene sheets. The nanosized MoO₂ particles were uniformly anchored on cotton fibers and graphene sheets. The structure has several advantages, such as an interconnected 3D electronically conductive network, plenty of channels for electrolyte solution cross, and more active points for the electrode reaction. Compared with cotton/MoO₂ (C/MoO₂) without graphene sheets, the CGN/MoO₂ composite (cotton covered by graphene/MoO₂) showed much better thermal stability and excellent cycling performance. The proposed synthesis process paves a new way as promising electrode materials for high power battery applications such as roll-up displays and wearable devices.     

Recent Advances in Electrochemical Performances of Graphene Composite (Graphene-Polyaniline/Polypyrrole/Activated Carbon/Carbon Nanotube) Electrode Materials for Supercapacitor: A Review

The latest trend in the direction of miniaturized portable electronic devices has brought up necessitate for rechargeable energy sources. Among the various non conventional energy devices, the supercapacitor is the promising candidate for gleaning the energy. Supercapacitor, as a new energy device that colligates the gap between conventional capacitors and batteries, it has attracted more attention due to its high power density and long cycle life. Many researchers work on, synthesizing new electrode material for the development of supercapacitor. The electrode material possesses salient structure and electrochemical properties exhibit the efficient performance of the supercapacitor. Graphene has high carrier mobility, thermal conductivity, elasticity and stiffness and also has a theoretical specific capacitance of 2630 m²g^??1 corresponds to a specific capacitance of 550 Fg^??1. This article summarizes and reviews the electrochemical performance and applications of various graphene composite materials such as graphene/polyaniline, graphene/polypyrrole, graphene/metal oxide, graphene/activated carbon, graphene/carbon nanotube as an electrode materials towards highly efficient supercapacitors and also dealt with symmetric, asymmetric and hybrid nature of the graphene based supercapacitor.     

Novel one-step synthesis for 3-D four-pointed micro-star of quaternary metal (Mo–V–Mn–Ag) oxide electrode for asymmetric supercapacitor

An intention of the present work is to synthesize a quaternary metal oxide by a simple and cost-effective method. MoVMnAg-oxide@Ni-foam is synthesised by one-step hydrothermal method. The as-deposited MoVMnAg-oxide sample is systematically examined through XRD, FESEM, EDS-mapping, and TEM analysis. The electrochemical performance of an MoVMnAg@Ni-foam electrode is tested using CV, GCD, and EIS techniques. MoVMnAg-oxide@Ni-foam has a considerable high areal capacitance of 651 mFcm^?2 with 0.13 mWhcm^?2 energy at 1.8 mWcm^?2 power density in 1 M KOH electrolyte calculated from GCD curves. Also, the electrode shows a diffusion coefficient of 1.52 × 10^?7 cm²s^?1 along with 91 % of diffusive-controlled contribution and a b-value of 0.51, which depicts faradaic charge storage mechanism. An assembled asymmetric supercapacitor device (MoVMnAg@Ni-foam//AC) delivers an areal capacitance of 312 mFcm^?2 with 0.37 mWcm^?2 power density at 1 mAcm^?2 current density within 0 – 1.5 V voltage window. The asymmetric device showed cyclability and coulombic efficiency of 80.3% and 95% respectively measured up to 10,000 GCD cycles. These results demonstrate the deposition of quaternary metal oxide directly on Ni-foam showing highly competitive electrochemical performance so that they can be utilized in energy storage applications.     

Self-standing manganese dioxide/graphene carbon nanotubes film electrode for symmetric supercapacitor with high energy density and superior long cycling stability

The low capacitance utilization and capacitance fading of manganese dioxide (MnO₂) is mainly due to poor electro-conductivity and irreversible phase transform. This work proposes a new method of designing hierarchical and binder-free electrode based on MnO₂ material for stable supercapacitor with high specific capacitance. Herein, we fabricated the self-standing electrode of MnO₂ on nitrogen-doped graphene and single wall carbon nanotubes (SWCNTs) self-standing film (NGCF) by electrochemical deposition. As a result, as-prepared MnO₂/NGCF cathode showed excellent electrochemical performance of 489.7 F g^-1 at 1 A g^-1. Assembled symmetric aqueous supercapacitor (SC) manifests high voltage of 2.4 V and presents excellent high energy density of 106.7 Wh kg^-1 at 1200 W kg^-1 and outstanding long-life stability without no decay after 10 000 charge-discharge circuits. This work proposes a new view of designing hierarchical and binder-free electrode with high energy density and long cycling stability based on MnO₂ material for stable symmetric supercapacitor.     

Flexible,self-powered Bi2O2Se/Graphene photoeletrochemical photodetector based on solid-state electrolytes

Flexible photodetectors have attracted great attention in fields such as display screens, aerospace, and civil engineering due to their wearable and large-area foldable advantages. Therefore, the hybrid structure of Bismuth oxyselenide(Bi₂O₂Se)/Graphene was successfully synthesized in this work through mechanical compound method. In addition, we constructed a photodetector based on solid-state electrolyte, which has the advantage of small size, light weight, and portability. Photoelectrochemical tests show that the Bi₂O₂Se/graphene photodetector based on solid-state electrolyte has excellent photoresponse characteristics under 0 V, and its photocurrent density is 400 nA/cm² when the optical power is 120 mW/cm². In addition, the Bi₂O₂Se/graphene photodetector exhibits superb flexibility. After different bending angles and bending times, the photocurrent slightly decreases, which may be due to small cracks in the bending process. Finally, the tested Bi₂O₂Se/graphene solid-state photodetector showed excellent stability. The photocurrent was only slightly reduced after 1000 s, which was 81% of the original value. The result shows that the hybrid structure of Bi₂O₂Se/Graphene has potential in the field of photodetectors with exceptional performance, excellent stability and mechanical properties.     

Nanoengineering of ZnCo2O4@CoMoO4 heterogeneous structures for supercapacitor and water splitting applications

A hybrid ZnCo₂O₄@CoMoO₄ heterogeneous structure deposited onto nickel foam was synthesized via a two-step hydrothermal process. The results demonstrate that the hybrid architecture exhibits excellent electrochemical performance, including the specific capacitance of 1040C g^?1 at 1 A g^?1 for hybrid structures, high energy density of 87.3 Wh kg^?1 at a power density of 2700 W kg^?1 for an as-assembled supercapacitor and excellent cycle stability with a capacity retention of 99% undergoing 8000 charge-discharge for the device. Moreover, it also shows favorable electrocatalytic activity with low overpotentials of 237 mV at 20 mA cm^?2 for oxygen evolution reaction and 114 mV at 10 mA cm^?2 for hydrogen evolution reaction, and low cell voltage of 1.54 V at 10 mA cm^?2 for overall water splitting. In addition, the stability maintains well for the long-term use of 13 h. We believe that this hybrid ZnCo₂O₄@CoMoO₄ heterogeneous structure could be a promising candidate for future energy storage and conversion.     

Core–Shell Structured Cellulose Nanofibers/Graphene@Polypyrrole Microfibers for All‐Solid‐State Wearable Supercapacitors with Enhanced Electrochemical Performance

Thanks to their considerable electrochemical and mechanical properties, fiber‐shaped supercapacitors have become the most potential energy storage devices for portable and wearable electronics in the future; however, challenges still exist in the pursuit of practical applications among them. In this work, ternary microfibers, which are composed of TEMPO‐oxidized cellulose nanofibers/reduced graphene oxide microfiber cores coated with polypyrrole shell layers, are successfully fabricated through industrializable and sustainable wet‐spinning and interfacial polymerization strategies. The prepared microfibers possess well‐defined microstructures and outstanding mechanical properties (559 MPa). When assembled into symmetrical all‐solid‐state fiber‐shaped supercapacitors (FSCs), they exhibit remarkable electrochemical properties (647 mF cm^?2, 14.37 µWh cm^?2 at 0.1 mA cm^?2), prominent cycling stability (92.5% capacitance retention and 92.6% coulomb efficiency after 10 000 cycles), and extraordinary flexibility (no significant decay in capacitance after 5000 bending cycles), which are superior to all the congeneric FSCs reported to date. The prominent performances are ascribed to the synergistic effect of the well‐designed ternary system and synergistic effects between interior components. The advantages in electrochemical, mechanical, and industrial properties of the ternary FSCs can provide reference and boost the development of flexible energy storage applications.     

3D nanostructured CuxO modified copper foam as a binder-free electrode for all-solid-state supercapacitor

Copper oxides (Cu_xO) play an active role in the field of binder-free electrodes for supercapacitors due to their own advantages, including high theoretical capacity, non-toxicity, low cost, etc. Developing mild and cheap process to prepare Cu_xO nanomaterials would broad its application in supercapacitors. In this paper, copper oxide is used as an active material and copper foam (CF) is chosen as a substrate to synthesize metal oxide-based electrodes by an in-situ oxidation method. Ingeniously, the availability of copper foam has a dual nature encompassing as a collector as well as a copper source. The as-obtained Cu_xO/CF-60 electrode possesses an area capacitance of 354.6 mF cm⁻² under 2 mA cm⁻². It also has superior cycle stability with 93.8 % of initial capacitance undergo 5000 charge-discharge cycles. Moreover, the all-solid-state asymmetric supercapacitor, combining Cu_xO/CF-60 and activated carbon (AC) pasted on nickel foam (NF) as the respective positive and negative electrodes, exhibits an energy density of 25 μWh cm⁻² when power density reaches 3 mW cm⁻². The Cu_xO/CF-60//AC/NF device displays better cycling stability as 80.2 % of initial capacitance after 5000 cycles. This work provides a simple way for designing Cu_xO based electrodes and lays the foundation for subsequent improvements in electrochemical performance.     

Corn Cob Lignin-based Porous Carbon Modified Reduced Graphene Oxide Film For Flexible Supercapacitor Electrode

Flexible supercapacitors (FSCs) have attracted widespread attention of many researchers as a type of portable energy storage devices. However, there are still challenges in preparing renewable and inexpensive electrode materials. Herein, we prepared the porous carbon (PC) by the two-step process involving hydrothermal method and low-temperature heat treatment using corn cob lignin as the carbon source, and different types for PC were obtained by changing the temperature of low temperature heat treatment (100?°C–300?°C). The flexible electrode film was prepared by combining the obtained corn cob lignin-based PC with reduced graphene oxide (RGO), in addition, we investigated the effect of PC obtained by different low-temperature heat treatment (100?°C, 150?°C, 200?°C, 250?°C, and 300?°C) on the electrochemical properties of the composite electrode. The optimal low-temperature heat treatment temperature (250?°C) was determined and the PC250/RGO film electrodes displayed a high area specific capacitance of 636 mF/cm² with a mass of 2.2?mg/cm² (specific capacitance of 289?F/g) at 0.2?mA/cm² and 82% of the capacitance was retained after 10,000 charge and discharge cycles at 5?mA/cm², at the same time on the electrode film flexibility test, the influence of different bending angle on the electrochemical properties can be ignored. The assembled supercapacitor had the advantages of flexible, lightweight, low price, and environment friendly, which can achieve area specific capacitance of 324.5 mF/cm² at 0.2?mA/cm² and 91.8% capacitance retention after 1000 charging/discharging cycles. These good electrochemical properties illustrate the application prospects of composite electrode materials in wearable and portable electronic devices.