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Laser-induced graphene (LIG) technology featuring low-cost, high-efficiency and scalability has presented great advantages in micro-supercapacitors (MSCs) fabrication. However, the limited capacitance of LIG based MSCs is still hindering their further development. Herein, we introduce joule heating as a critical in-situ treatment merged with the assembly of laser-induced graphene paper based MSCs (LIGP-MSCs) toward capacitive enhancement. By increasing heating-treatment temperature from ∼20 to 500 °C, the number of nanopores in LIGP continuously increases, attributed to the gradual decomposition of amorphous carbon components. The resulting joule-heated LIGP (J-LIGP) with improved specific surface area (160.97–533.49 m2/g) and pore volume (0.179–0.553 cm3/g) as well as superhydrophilic surface is highly suitable to be employed as J-LIGP-MSCs microelectrodes. By investigating process dependent performance, the J-LIGP-MSCs heated at 500 °C for 60 min delivers a significantly improved specific areal capacitance (CA) of 13.71 mF/cm2 at 10 mV/s, which is approximately six-fold higher than that of unheated LIGP-MSCs. By further exploring and optimizing the process efficiency, J-LIGP-MSCs with a CA of 12.61 mF/cm2 has been achieved by 550 °C heating for only 5 min. Along with superior mechanical flexibility, cyclability and structural modularity, the proposed in-situ joule heating treatment is finally proved to be a universal approach for consistently enhancing the CA of LIG based MSCs processed under various chemical modifications.

The construction of flexible electrochemical devices for energy storage and generation is of utmost importance in modern society. In this article, we report on the synthesis of flexible MoS2-based composite paper by high-energy shear force milling and simple vacuum filtration. This composite material combines high flexibility, mechanical strength and good chemical stability. Chronopotentiometric charge–discharge measurements were used to determine the capacitance of our paper material. The highest capacitance achieved was 33 mF·cm−2 at a current density of 1 mA·cm−2, demonstrating potential application in supercapacitors. We further used the material as a cathode for the hydrogen evolution reaction (HER) with an onset potential of approximately −0.2 V vs RHE. The onset potential was even lower (approximately −0.1 V vs RHE) after treatment with n-butyllithium, suggesting the introduction of new active sites. Finally, a potential use in lithium ion batteries (LIB) was examined. Our material can be used directly without any binder, additive carbon or copper current collector and delivers specific capacity of 740 mA·h·g−1 at a current density of 0.1 A·g−1. After 40 cycles at this current density the material still reached a capacity retention of 91%. Our findings show that this composite material could find application in electrochemical energy storage and generation devices where high flexibility and mechanical strength are desired.Keywords: flexible composites; hydrogen evolution reaction (HER); lithium ion batteries (LIBs); molybdenum disulfide; nanoarchitectonics; supercapacitors

In recent era of modern and bendable technology, energy dearth arises as a paramount subject around the globe with a dire demand of flexible and lightweight energy storage devices. This study targets fabrication of reduced graphene oxide (rGO) and utility of abundantly available, cost effective, and environment friendly lignocelluloses (LC) fibers extracted from Carica papaya source, as a binder to bind active material (rGO) as robust and compact paper sheet. Fabricated samples were analyzed by X-ray diffraction for crystallographic analysis, Scanning electron microscopy, Transmission electron microscope for morphology, Fourier transform infrared spectroscopy for structural bonding, and Raman spectroscopy for vibrational modes. Robust and bendable rGO/LC paper electrode was tested for energy storage application by employing in different characterizations, i.e., cyclic voltammetry for capacitive behavior, galvanostatic charge–discharge for symmetric EDLC, and electrochemical impedance spectroscopy for resistive charge kinetics, respectively. rGO/LC composite sheet employed as working electrode in 3-electrode CV measurements and revealed specific capacitance of 591 F/g at a scan rate of 5 mV/s by keeping the undistorted shape of voltammograms at higher scan rates which present it as a suitable candidate for modern flexible and energy storage devices. rGO/LC-based symmetric cell revealed the highest specific capacitance of 228 F/g at applied current density of 0.1 A/g, the energy density of 6.3 Wh/kg, and power density of 129 W/kg, respectively. rGO/LC-based symmetric cell confirmed the cycling stability by revealing capacitance retention of 82% after 200 cycles. It can conclude that biomass-based rGO paper sheet can be a potential candidate as environmentally safe with remarkable electrochemical activity in energy storage applications.

Fast supercapacitors that can be charged and discharged at tens of hertz high frequency are reported using binder-free electrodes of MoS2 nanosheets grown on plasma pyrolyzed cellulose microfiber (pCMF) paper. Rapid plasma pyrolysis was applied to obtain highly conductive carbon fiber sheet from conventional cellulose filter paper to be used as a scaffold, on which MoS2 nanosheets were grown vertically wrapped around carbon microfibers in a hydrothermal reaction. Such binder-free MoS2-pCMF electrode based supercapacitor demonstrated fast-rate performance in an aqueous electrolyte with a cutoff frequency of 103 Hz. A large specific capacitance density of 125 mF cm−2 was also measured. The organic electrolyte cell of these electrodes exhibited a power density of 12.05 W cm-3 at a rate of 15 V s−1. These MoS2-pCMF electrodes were highly stable. In a cycling test at a current density of 10 mA cm−2, the cell maintained its capacitance with trivial degradation in 50,000 cycles.

Flexible energy storage devices have received great interest due to the increasing demand for wearable and flexible electronic devices with high-power energy sources. Herein, a novel hybrid flexible hexagonal boron nitride integrated graphene paper (BN/GrP) is fabricated from 2D hexagonal boron nitride (h-BN) nanosheets integrated with graphene sheets dispersion via a simple vacuum filtration method. FE-SEM indicated that layered graphene nanosheets tightly confined with h-BN nanosheets. Further, the Raman spectroscopy confirmed successful integration of BN with graphene. As-prepared BN/GrP free-standing flexible conductive paper showed high electrical conductivity of 5.36 × 104 S m−1 with the sheet resistance of 8.87 Ω sq−1. However, after 1000 continuous bending cycles, the BN/GrP sheet resistance increased just about 8.7% which indicated good flexibility of the paper. Furthermore, as-prepared BN/GrP showed excellent specific capacitance of 321.95 F g−1 at current density of 0.5 A g−1. In addition, the power and energy densities were obtained as 3588.3 W kg−1, and 44.7 W h kg−1, respectively. The stability of the prepared flexible electrode was tested in galvanostatic charge/discharge cycles, where the results showed the 96.3% retention even after 6000 cycles. These results exhibited that the proposed BN/GrP may be useful to prepare flexible energy-storage systems.

Paper-based microfluidic devices have the potential of being a low-cost platform for diagnostic devices. Electrical circuit analogy (ECA) model has been used to model the wicking process in paper-based microfluidic devices. However, material characteristics such as absorption capacity cannot be included in the previous ECA models. This paper proposes a new model to describe the wicking process with liquid absorption in a paper strip. We observed that the fluid continues to flow in a paper strip, even after the fluid reservoir has been removed. This phenomenon is caused by the ability of the paper to store liquid in its matrix. The model presented in this paper is derived from the analogy to the current response of an electric circuit with a capacitance. All coefficients in the model are fitted with data of capillary rise experiments and compared with direct measurement of the absorption capacity. The theoretical data of the model agrees well with experimental data and the conventional Washburn model. Considering liquid absorption capacity as a capacitance helps to explain the relationship between material characteristics and the wicking mechanism.

Made available in DSpace on 2020-12-10T19:54:25Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-03-04 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) We present a capacitive smart sensor based on printed circuit board (PCB) technology to measure the amount of water content in a paper pulp at the wet end of a paper machine. The developed sensor incorporates in the same PCB the signal processing circuits. It is a handheld portable device, and its output is sent to the reading equipment using a Bluetooth wireless connection, providing to the sensor's operator ease of mobility around the wet end of a paper machine. The prototype was tested in a laboratory, using a wire mesh to emulate the end of a paper machine, and we were able to measure and easily detect when it reaches the water content in the range of 90% to 92%, as required in the paper fabrication process. Standard deviation of the capacitance measurements at various moisture levels is four orders of magnitude smaller than the mean. The smart sensor was tested in the 20 degrees C to 40 degrees C temperature range, in a paper pulp with a gravimetric water content of 91%. Since the variation of capacitance with temperature is practically linear, we propose a simple linear compensation equation to correct the observed sensitivity with the temperature. To keep the signal processing circuits small, low cost, simple, and robust, a novel direct interface sensor to microcontroller circuit technique was used to make the capacitive measurement, allowing for measuring small capacitance deviations without high-frequency oscillators. It was shown that it is possible to integrate the signal processing circuits in the top layer of the PCB interdigitated sensor without adding noise or degrading the performance of the capacitive sensor. Sao Paulo State Univ Julio de Mesquita Filho, Fac Sci & Engn, Tupa, SP, Brazil Parana Fed Univ Technol UTFPR, Cornelio Procopio, PR, Brazil FEEC UNICAMP, Dept Semicond Instrumentat & Photon, Campinas, SP, Brazil Uninove Campus Vergueiro, Sao Paulo, SP, Brazil Sao Paulo State Univ Julio de Mesquita Filho, Fac Sci & Engn, Tupa, SP, Brazil CAPES: 001

Highlights The superior conductivity and unique porous electrode structure in the TiN paper enable fast charging by simultaneously providing efficient ion diffusion and electron transport. The TiN paper-based supercapacitors exhibit charging/discharging at an ultrahigh scan rate of 100 V s−1 in a wide voltage window of 1.5 V in Na2SO4 neutral electrolyte and show zero capacitance loss after 200,000 cycles. Electronic supplementary material The online version of this article (10.1007/s40820-019-0340-7) contains supplementary material, which is available to authorized users., Ultrafast-charging energy storage devices are attractive for powering personal electronics and electric vehicles. Most ultrafast-charging devices are made of carbonaceous materials such as chemically converted graphene and carbon nanotubes. Yet, their relatively low electrical conductivity may restrict their performance at ultrahigh charging rate. Here, we report the fabrication of a porous titanium nitride (TiN) paper as an alternative electrode material for ultrafast-charging devices. The TiN paper shows an excellent conductivity of 3.67 × 104 S m−1, which is considerably higher than most carbon-based electrodes. The paper-like structure also contains a combination of large pores between interconnected nanobelts and mesopores within the nanobelts. This unique electrode enables fast charging by simultaneously providing efficient ion diffusion and electron transport. The supercapacitors (SCs) made of TiN paper enable charging/discharging at an ultrahigh scan rate of 100 V s−1 in a wide voltage window of 1.5 V in Na2SO4 neutral electrolyte. It has an outstanding response time with a characteristic time constant of 4 ms. Significantly, the TiN paper-based SCs also show zero capacitance loss after 200,000 cycles, which is much better than the stability performance reported for other metal nitride SCs. Furthermore, the device shows great promise in scalability. The filtration method enables good control of the thickness and mass loading of TiN electrodes and devices. Electronic supplementary material The online version of this article (10.1007/s40820-019-0340-7) contains supplementary material, which is available to authorized users.

As a critical component of a high-voltage direct current (HVDC) transmission system, resin impregnated paper (RIP) wall bushing has become a weak point because of its surface charge accumulation. This paper studies a model RIP wall bushing core designed by the equal capacitance method. The stationary resistive field along the gas–solid interface of the RIP wall bushing core is investigated theoretically by a gas model, which considers the non-linearly field-dependent volume conductivity. The results show that the gas conductivity along the core surface tends to be an arched distribution from the high-voltage conductor to the end shielding screen. The surface charge mainly accumulates at the turning point of the radius, which may threaten the core’s insulation. Then, the surface charge is obtained through a measurement system, where the experimental results are highly consistent with the simulation results. Considering the time constant of charge dissipation is nearly 15 min, it would be better to measure the surface charge on one axial direction of RIP wall bushing core after each voltage application. The simulation and experimental results of this paper can guide the design of a RIP wall bushing core.

This paper demonstrates a facile strategy for the development of nanosilver decorated polyaniline coated (PAg) paper-based electrodes for the fabrication of solid-state symmetrical supercapacitors. PAg based printing paper was developed through a two-step process involving initial silver nucleation and growth on the paper followed by aniline polymerization. The developed electrically conductive paper exhibited a highly porous structure and excellent mechanical stability. Further symmetrical supercapacitors having the configuration PAg/electrolyte/PAg were fabricated and evaluated for electrochemical performance such as specific capacitance (483 F g−1 and 613 F g−1 in aqueous 1 M H2SO4 and PVA–H2SO4 gel electrolytes respectively), energy density (69.56 and 85.13 W h kg−1), and power density (243.44 and 405.375 W kg−1) and cycling stability (90% of its capacitance retention even after 2000 cycles), exhibiting excellent performance under various bending conditions. All these exciting results suggest that the developed paper-based flexible solid-state energy device can serve as an efficient, sustainable, and low-cost energy storage system for portable microelectronic devices which are expected to revolutionize the perception of energy-storage devices in the electronics industry.

A flexible filter paper based composite electrode was prepared via the convenient one-step synthesis of silver doped graphene for the first time, followed by in-situ polymerization of aniline monomers. Using L-ascorbic acid for simultaneous reduction of grapheme oxide and silver nitrate, we provided a new and green method to prepare graphene hybrid sheets without toxicity. It was found that the as-fabricated hybrid electrode formed a three-dimensional porous architecture, which not only increased the specific surface area of composite, but also facilitated the ion diffusion of the electrolyte. In addition, according to the tests of electrochemical performances, the flexible hybrid electrode subsequently exhibited exceptional specific capacitance of 437.3 F/g, energy density of 1133.5 W&middot, h/kg and power density of 88.8 kW/kg, respectively. Meanwhile, the as-prepared hybrid demonstrated a good cycling stability with only 10.99% specific capacitance deterioration after 5000 times of cycling. This preparation technology presented here shows great potential for the development and application of wearable and portable energy storage devices, particularly for flexible supercapacitors. Moreover, this study puts forward a general, simple and low-cost route of fabricating a novel flexible electrode on a large scale, eventually for environmental protection.

The oil impregnated paper capacitance graded transformer bushings serves as the external connection device of the transformer to support and connect the insulation, and its insulation state is related to the safe and stable operation of substation equipment.In this paper, a simulation model of 110kV oil impregnated paper capacitance graded transformer bushings is constructed on the commercial finite element software platform based on the actual size of the bushing and the principle of equal capacitance and steps. The paper calculate the potential and radial electric field distribution of the bushing under the normal working voltage, and analyze the influence of the aluminum plate on the radial electric field distribution of the bushing, verifying the rationality of the design principle based on equal capacitance and steps.

Flexible In2O3 nanowire transistors gated by microporous SiO2-based solid electrolytes are fabricated on paper substrates at room temperature. Low-voltage (1.0 V) operation of these devices is realized owing to the large electric-double-layer capacitance of (1.73 μF/cm2 at 20 Hz) of the microporous SiO2 solid electrolytes, which were deposited at room temperature. The subthreshold swing, current on/off ratio, and field-effect mobility of the paper-based nanowire transistors are estimated to be 74 mV/decade, 1.7×106, and 218.3 cm2/V·s, respectively. These low-voltage paper-based nanowire transistors show promise for use in portable flexible paper electronics and low-cost portable sensors.

This paper presents the design, fabrication, and characterization results of a paper-based, low-cost, easy-to-use, comfortable and wearable tactile sensor array for human health monitoring applications. Paper substrate and spray-deposited metallic electrodes and traces are employed to achieve a low fabrication cost. Capacitive sensing scheme employing a deformable triangular PDMS sensing membrane is chosen due to its high sensitivity and zero DC power dissipation. Trade-offs among different sensor array designs are investigated to achieve an optimal design, which consists of a $1\times 5$ sensor array occupying an area of 10 mm $\times10$ mm. Each sensor in the array achieves a nominal capacitance value and sensitivity of approximately 1 pF and 30 fF/mmHg, respectively. Fabricated sensor array can be comfortably attached to an individual’s temporal region and ankle area to monitor real-time blood pressure (BP) pulse waveform with high fidelity, from which heart rate and heart rate variability information can be accurately obtained. In addition, the prototype sensor array demonstrates its capability of detecting atrial fibrillation (AFib) from BP pulse waveform measured from an AFib patient. [2020-0179]

Here we developed a free-standing reduced graphene oxide (rGO)-polypyrrole (PPy) hybrid paper via electropolymerization on a paper-like graphene gel. This flexible hybrid paper displayed a uniform layered structure with PPy coated onto the graphene layers. A high areal mass of 2.7 mg cm−2 could be obtained. It delivered a greatly enhanced areal capacitance of 440 mF cm−2 at 0.5 A g−1, in contrast to that 151∼198.5 mF cm−2 previously reported for graphene paper or polypyrrole-graphene paper. It can retain ∼81% of the initial capacitance at a high current density of 6 A g−1. The combined high flexibility with outstanding electrochemical performance, makes such novel hybrid paper a promising electrode for flexible supercapacitors.

This paper presents research results of the loss factor of high voltage insulation samples made of aramid paper impregnated with various types of insulating oil. The analysis was carried out in the high frequency domain in the range of 50 Hz to 1 MHz. The experiments were carried out for three impregnation types: mineral oil, synthetic ester and natural ester. The influence of temperature in the range of 20 &deg, C to 100 &deg, C, which is typical when using this type of insulation in power transformers, was taken into account. In addition, the process of influence of initial aging of aramid paper was simulated by heat soaking the samples before their impregnation at a temperature of 250 &deg, C in multiple time intervals. Based on the analyses of dispersion characteristics of insulation sample loss factors, conclusions and recommendations for further diagnostics of aramid-oil insulations using the method described were delineated.

In this paper, using a low-cost paper fiber (PF) as a substrate, eigenstate polyaniline–coated PFs with graphene (GO/PANI/PF) ternary materials were synthesized by using the chemical oxidative polymerization method. Electrochemical measurements showed that the GO/PANI/PF electrode exhibited an excellent electrochemical performance compared with the PANI electrode. By adjusting the ratio of PANI and PF, the as-prepared GO/PANI/PF–2.5% electrode exhibited the highest specific capacitance 937 F g−1 at current density 1 A g−1 in a 0.5 M H2SO4 aqueous solution, and 74.5% retention of initial capacitance after 2000 charge–discharge cycles at 5 A g−1. The symmetric capacitor on the basis of GO/PANI/PF nanocomposite delivers a superior energy density of 10.12 Wh kg−1 at 456 W kg−1 at a current density of 1 A g−1.

Made available in DSpace on 2019-10-04T12:39:06Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-07-15 Japan Society for the Promotion of Science, Japan JSPS KAKENHI Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) This article presents results of a pulsed UV laser method for the simultaneous reduction of graphite oxide (GO) and patterning of reduced graphene oxide (rGO). This direct laser writing method was applied to the fabrication of graphene-based, in-plane interdigitated micro-supercapacitors (mu-SCs), prepared on free-standing GO paper (10 mu m thick). The electrochemical performance of mu-SCs was studied using two different electrolytes (KOH and NaCl). The results from cyclic voltammetry measurements exhibited typical electrical double layer behavior, with specific capacitances of 9.3 mu F/cm(2) and 13.8 mu F/cm(2) (at a scan rate of 10 mV/s) for KOH and NaCl electrolytes, respectively. The mu-SCs exhibited good performance, with retention of 95% of the original capacitance values after 3400 charge-discharge cycles. When compared to devices obtained by conventional lithographic techniques, the laser fabrication of planar mu-SCs is faster, cost-effective and scalable. We believe this one-step and environmentally friendly laser-assisted method to be a good alternative for the fabrication of flexible energy storage devices. (C) 2019 Elsevier Ltd. All rights reserved. Toyohashi Univ Technol, Dept Elect & Elect Informat Engn, 1-1 Hibarigaoka,Tempaku Cho, Toyohashi, Aichi 4418580, Japan Ctr Informat Technol Renato Archer CTI, BR-13069901 Campinas, SP, Brazil Univ Campinas UNICAMP, Ctr Semicond Components & Nanotechnol CCS Nano, BR-13083870 Campinas, SP, Brazil Sao Paulo State Univ, Dept Phys, Fac Sci & Technol, BR-19060900 Presidente Prudente, SP, Brazil CUHP, Sch Phys & Mat Sci, Dharamshala 176215, HP, India Univ Campinas UNICAMP, Inst Chem, Dept Analyt Chem, POB 6154, BR-13084974 Campinas, SP, Brazil Sao Paulo State Univ, Dept Phys, Fac Sci & Technol, BR-19060900 Presidente Prudente, SP, Brazil Japan Society for the Promotion of Science, Japan: P18063 JSPS KAKENHI: 18H03841 JSPS KAKENHI: 18F18063 FAPESP: 2017/22186-0 FAPESP: 2013/14262-7

Accurate measurement and monitoring of respiration is vital in patients affected by severe acute respiratory syndrome coronavirus - 2 (SARS-CoV-2). Patients with severe chronic diseases and pneumonia need continuous respiration monitoring and oxygenation support. Existing respiratory sensing techniques require direct contact with the human body along with expensive and heavy Holter monitors for continuous real-time monitoring. In this work, we propose a low-cost, non-invasive and reliable paper-based wearable screen printed sensor for human respiration monitoring as an effective alternative of existing sensing systems. The proposed sensor was fabricated using traditional screen printing of multi-walled carbon nanotubes (MWCNTs) and polydimethylsiloxane (PDMS) composite based interdigitated electrodes on paper substrate. The paper substrate was used as humidity sensing material of the sensor. The hygroscopic nature of paper during inhalation and exhalation causes a change in dielectric constant, which in turn changes the capacitance of the sensor. The composite interdigitated electrode configuration exhibited better response times with a rise time of 1.178s being recorded during exhalation and fall time of 0.88s during inhalation periods. The respiration rate of sensor was successfully examined under various breathing conditions such as normal breathing, deep breathing, workout, oral breathing, nasal breathing, fast breathing and slow breathing by employing it in a wearable mask, a mandatory wearable product during the current COVID-19 pandemic situation.Thus, the above proposed sensor may hold tremendous potential in wearable/flexible healthcare technology with good sensitivity, stability, biodegradability and flexibility at this time of need.

Rapid and accurate clinical assessment of hemostasis is essential for managing patients who undergo invasive procedures, experience hemorrhages, or receive antithrombotic therapies. Hemostasis encompasses an ensemble of interactions between the cellular and non-cellular blood components, but current devices assess only partial aspects of this complex process. In this work, we describe the development of a new approach to simultaneously evaluate coagulation function, platelet count or function, and hematocrit using a carbon nanotube-paper composite (CPC) capacitance sensor. CPC capacitance response to blood clotting at 1.3 MHz provided three sensing parameters with distinctive sensitivities towards multiple clotting elements. Whole blood-based hemostasis assessments were conducted to demonstrate the potential utility of the developed sensor for various hemostatic conditions, including pathological conditions, such as hemophilia and thrombocytopenia. Results showed good agreements when compared to a conventional thromboelastography. Overall, the presented CPC capacitance sensor is a promising new biomedical device for convenient non-contact whole-blood based comprehensive hemostasis evaluation.

Hierarchical composites (CFP–PANI) of carbon fiber papers (CFP) and polyaniline (PANI) have been facilely prepared by in-situ polymerization of aniline monomers on the surface of CFP films, which were simply obtained by low-cost carbonization of widely used filter paper. The wood–celluloses, which serve as the main component and the backbone of filter paper, are key raw materials for fabricating energy-related devices. Carbon fibers with porous structure were formed after the cellulose fibers were carbonized at high temperature. And cross-linked conductive networks have been achieved with the carbon fibers connected with each other. Different amounts of aniline monomer were in-situ polymerized on the surface of CFP, resulting in the formation of three-dimensional (3D) free-standing composite paper of CFP–PANI. Compared with pristine CFP and pure PANI, greatly enhanced electrochemical performance of CFP–PANI composite has been successfully achieved, including high specific capacitance (334 F g −1 ), good cycling stability as well as excellent rate capability. These superior electrochemical properties of CFP–PANI composite paper can be ascribed to the hierarchical structure of CFP, strong interaction between CFP and PANI, as well as the synergistic capacitance performance of CFP films and PANI nanoparticles, suggesting CFP–PANI composite paper thus simply prepared is good candidate for applications in high performance energy storage fields.

Current collectors are an important component of electrodes, functioning as conductive media by collecting currents from active materials and then exporting them to the external circuit. Common current collectors for graphene hydrogel (GH)-based supercapacitors are nickel foams or metal foils (platinum, gold, and aluminium, etc.). Here, hydrothermally synthesized GH was directly pressed on carbon paper and used as electrodes (denoted as GHE) for supercapacitors. With a mass loading of 2.7 mg&middot, cm&minus, 2 at an active area of 0.64 cm2, the GHE-based supercapacitors revealed a high gravimetric capacitance of 294 F&middot, g&minus, 1 at a current density of 1.18 A&middot, 1. When increasing the current density to 28.24 A&middot, 1, 66% (193 F&middot, 1) of the initial capacitance was maintained for the GHE-based supercapacitors. High performance for GHE-based supercapacitors was attributed to large specific surface area and good electrical conductivity of GH, and its intimate contact with carbon paper.

To facilitate better interpretation of dielectric response measurements—thereby directing numerical evidence for condition assessments of oil-paper-insulated equipment in high-voltage alternating current (HVAC) transmission systems—a novel approach is presented to estimate the parameters in the extended Debye model (EDM) using wideband frequency domain spectroscopy (FDS). A syncretic algorithm that integrates a genetic algorithm (GA) and the Levenberg-Marquardt (L-M) algorithm is introduced in the present study to parameterize EDM using the FDS measurements of a real-life 126 kV oil-impregnated paper (OIP) bushing under different controlled temperatures. As for the uncertainty of the EDM structure due to variable branch quantity, Akaike’s information criterion (AIC) is employed to determine the model orders. For verification, comparative analysis of FDS reconstruction and results of FDS transformation to polarization–depolarization current (PDC)/return voltage measurement (RVM) are presented. The comparison demonstrates good agreement between the measured and reconstructed spectroscopies of complex capacitance and tan δ over the full tested frequency band (10−4 Hz–103 Hz) with goodness of fit over 0.99. Deviations between the tested and modelled PDC/RVM from FDS are then discussed. Compared with the previous studies to parameterize the model using time domain dielectric responses, the proposed method solves the problematic matching between EDM and FDS especially in a wide frequency band, and therefore assures a basis for quantitative insulation condition assessment of OIP-insulated apparatus in energy systems.

Flexible paper electrodes for supercapacitors were prepared with partially-exfoliated graphite and polypyrrole as the active materials. Graphite was coated on paper with pencil drawing and then electrochemically exfoliated using the cyclic voltammetry (CV) technique to obtain the exfoliated graphite (EG)-coated paper (EG-paper). Polypyrrole (PPy) doped with β-naphthalene sulfonate anions was deposited on EG-paper through in-situ polymerization, leading to the formation of PPy-EG-paper. The as-prepared PPy-EG-paper showed a high electrical conductivity of 10.0 S·cm−1 and could be directly used as supercapacitor electrodes. The PPy-EG-paper electrodes gave a remarkably larger specific capacitance of 2148 F∙g−1 at a current density of 0.8 mA∙cm−2, compared to PPy-graphite-paper (848 F∙g−1). The capacitance value of PPy-EG-paper could be preserved by 80.4% after 1000 charge/discharge cycles. In addition, the PPy-EG-paper electrodes demonstrated a good rate capability and a high energy density of 110.3 Wh∙kg−1 at a power density of 121.9 W∙kg−1. This work will pave the way for the discovery of efficient paper-based electrode materials.

This article presents a sensor for detecting the distribution of forces on a surface. The device with nine buttons consisted of an elastomer-based layer as a touch interface resting on a substrate of patterned metallized paper. The elastomer-based layer included a three-by-three array of deformable, hemispherical elements/reliefs, facing down toward an array of interdigitated capacitive sensing units on patterned metallized paper. Each hemispherical element is 20 mm in diameter and 8 mm in height. When a user applied pressure to the elastomer-based layer, the contact area between the hemispherical elements and the interdigitated capacitive sensing units increased with the deformation of the hemispherical elements. To enhance the sensitivity of the sensors, embedded particles of hydrogel in the elastomer-based layer increased the measured electrical responses. The measured capacitance increased because the effective dielectric permittivity of the hydrogel was greater than that of air. Electromechanical characterization verified that the hydrogel-filled elastomer was more sensitive to force at a low range of loads (23.4 pF/N) than elastomer alone without embedded hydrogel (3.4 pF/N), as the hydrogel reduced the effective elastic modulus of the composite material by a factor of seven. A simple demonstration suggests that the force-sensing array has the potential to contribute to wearable and soft robotic devices.

Hybrid Sn–Co binary oxide with different Sn/Co feeding molar ratios on carbon paper are successfully obtained using a facile hydrothermal method followed by a post-annealing procedure. The results of electrochemical tests show that the electrode with a feeding molar ratio of 1:4 (named as Sn1Co4) has better electrochemical performance than that of the others. The specific capacitance can achieve 937.4 F g−1at 5 mV s−1 (580.8 F g−1 at 1 A g−1), as well as the capacitance retention is 97.5% after the galvanostatic charge-discharge for 20000 cycles at 30 A g−1. These results demonstrate that the Sn1Co4 can be considered as a potential electrode material for the next generation supercapacitor.

A novel porous graphene paper is prepared via freeze drying a wet graphene oxide gel, followed by thermal and chemical reduction. The macroscopic structure of the formed graphene paper can be tuned by the water content in the gel precursor. With 92% water content, an interconnected macroporous network can be formed. This porous graphene (PG) paper exhibits excellent electrochemical properties. It can deliver a high discharge capacity of 420 mA h g−1 at a current density of 2000 mA g−1 when used as binder-free lithium ion battery anode. PG paper exhibits a specific capacitance of 137 F g−1 at 1 A g−1 in a flexible all-solid-state supercapacitor with PVA/H2SO4 electrolyte. It can maintain 94% of its capacitance under bending. This electrochemical performance and mechanical flexibility makes it an excellent material for flexible energy storage devices.

A novel method of producing flexible graphene-based paper (GBP) electrodes through the direct hydrothermal reduction of graphene oxide based paper is developed. On the basis of an electrostatic attraction mechanism or pH-enhanced π–π attraction mechanism, a delicate balance between integrity, flexibility and porosity of GBPs is maintained during the hydrothermal treatment process, providing them with excellent compositional, microstructural and supercapacitive characteristics. Furthermore, the insertion of CNT into the graphene interlayer spaces immensely improves the specific capacitance (up to 195 F g−1) and rate capability (10 A g−1) of the supercapacitors assembled with these GBPs. In addition, the facile and simple preparation procedures and arbitrarily controlled area and thickness of the GBPs predict their promising industrialization potential.

The superior mechanical flexibility, mechanical strength, electrical conductivity, high specific surface area, and a special two-dimensional crystalline structure make graphene a very promising building block material for flexible electromechanical actuators. However, graphene papers have exhibited limited electromechanical actuation strain in aqueous electrolyte solution. In this paper, we show an easy approach to significantly improve the electromechanical actuation of reduced graphene oxide (rGO) papers via fine tuning the oxygen functional groups in rGO sheets, which was achieved by careful control of quantity of the reduction agent used in the chemical reduction process of graphene oxide. The actuation strains are enhanced up to 0.2% at an applied voltage of −1 V, which is more than a 2 fold increase compared to the regular pristine rGO paper. Further theoretical and experimental analyses reveal that the change of the capacitance and the stiffness of the rGO papers are two key factors responsible for the observed improvement.

Flexible micro-supercapacitors (FMSCs) are promising candidates for portable and on-chip energy storage due to their miniaturization, lightweight and high-security. Till now, FMSCs still suffer from several limitations, such as complex fabricating process, low areal energy storage, and short cycling lifetime, badly inhibiting its wider on-chip integrated applications. Here, we directly employ an easy-processing spray coating of the Ti3C2Tx MXene conductive inks to massively fabricate the paper-based all-solid-state FMSCs. Instead of traditional noble metals Au as current collector, the sprayable and highly conductive Ti3C2Tx MXene interdigitated electrodes serve the dual function of the active materials and current collection. Based on it, we develop an all-solid-state FMSC by employing polyvinyl alcohol & H2SO4 gel-like solid-state electrolyte and self-flowed polydimethylsiloxane encapsulated layer. With further optimizing the geometric configurations of interdigitated electrodes, the as-prepared FMSCs exhibit high areal capacitance of 23.4 mF cm−2 and excellent rate-capability of 81.4%. Moreover, these paper-based FMSCs also demonstrate outstanding cyclic capability of 92.4% capacitance retention after 5000 cycles, along with remarkable flexibility. Consequently, we believe that this innovative strategy will open new avenues for easily and largely fabricating various FMSCs to further promote the integration of portable and on-chip energy storage systems.

Paper based humidity sensors are low-cost, flexible, and biodegradable. However, the previously reported paper based humidity sensors exhibit poor repeatability, low sensitivity, high drift, and slow response. Here, we reported a new strategy to monolithically fabricate humidity sensor based on porous paper (PPHS) using robust and precise screen and gravure printings. PPHS is highly sensitive, with the maximum 1480% change at 1 kHz and the maximum 411.4% change at 10 kHz in capacitance, respectively. PPHS is highly repeatable (a 1.05% standard derivation in sensitivity for 3 continuous runs) and is stable and insensitive to a mild temperature change (15-30 °C). PPHS rapidly responds (0.8 s) and recovers (0.78 s). PPHS is also highly foldable and twistable. The high repeatability, high sensitivity, quick response/recovery, high foldability/twistability, and good stability of PPHS could be attributable to the combined effects of the high specific surface area of porous paper and the robust and precise printings. By comparison, PPHS is more sensitive than the previously reported paper-based humidity sensors and several humidity sensors fabricated using different substrates, materials, and printings. Due to these unique features, PPHS shows great potential applications in the humidity sensing, the breath detection, the proximity detection, and non-touch switch.

In this study, three-type paper supercapacitors based on the polyvinylidene fluoride (PVDF) and polyvinyl alcohol (PVA)/phosphoric acid (H3PO4) gel electrolytes and graphite nanoparticles (GNPs) electrodes have been fabricated. The gel electrolytes and electrodes films have been coated on the paper using push coating and then characterized by scanning electron microscopy (SEM). In two types of the paper supercapacitors, on the PVDF gel electrolyte film, a layer of PVA/water and BaTiO3 as a gel separator film has been coated. The specific capacitance of the paper supercapacitors using cyclic voltammetry (CV) and galvanostatic (charge–discharge) methods at the scan rates 20 and 150 mV s−1 have been investigated. The paper supercapacitor based on the BaTiO3 separator film showed higher specific capacitance (312 F g−1) compared to other samples. Also, using electrochemical impedance spectroscopy (EIS), the Nyquist and Bode curves of paper supercapacitors have been measured. For the paper supercapacitors based on the PVDF gel electrolyte film and BaTiO3 separator film using the Nyquist curves, the equivalent series resistance (ESR) was 306 Ω and 125 Ω, respectively. The paper supercapacitor based on BaTiO3 gel separator structure represents a new type of flexible supercapacitor with high performance that can be applied to electronic devices.

Measurements of capacitors made with paper sheets reveal a significant decrease in capacitance with increasing frequency from 10 to 100,000 Hz, offering a simple demonstration of complex dielectric phenomena using common equipment., 3 pages, 2 figures

A facile template approach is developed to prepare highly conductive and flexible reduced graphene oxide (rGO) paper with hierarchical porous structures. When used as an electrode for a capacitor, these porous carbon layers demonstrate an enhanced electrochemical performance due to their large ion-accessible surface area and efficient electrolyte-ion transport pathways. The porous rGO electrode delivers a specific capacity of 173.5 F g−1, almost 1.8 times higher than 95.1 F g−1 of packed rGO. More importantly, the porous electrode also exhibits a good electrochemical performance with an energy density of 28.5 W h kg−1 and power density of 4000 W kg−1, as well as excellent cycling stability with 101.5% of its initial capacitance after 2000 charge–discharge cycles at a current density of 5 A g−1.

Graphene/carbon paper is prepared by pyrolyzing graphene modified cellulose filter paper and directly used as a binder-free electrode to assemble a supercapacitor (SC) with a redox active electrolyte, containing a Fe3+/Fe2+ additive. By the graphene incorporation and the carbonization of the cellulose fibers, both the microstructure and the electrical conductivity of the carbon paper are promoted greatly. The filter paper derived carbon (FPC) electrode exhibits a specific capacitance (Cs) of 2832 F&middot, g&minus, 1 in a 1 M H2SO4 + 0.5 M Fe3+/Fe2+ electrolyte at 1 A&middot, 1, which is about 81 times that in a normal H2SO4 electrolyte. With the modification of graphene, the capacitive performance of the SC is enhanced further and a remarkable Cs of 3396 F&middot, 1 at 1 A&middot, 1 is achieved for a graphene modified filter paper carbon (GFPC) electrode, which remains at ~632 F&middot, 1 at 10 A&middot, 1. The free standing GFPC electrode also exhibits good cycling stability (93.8% of capacitance retention after 2000 cycles) and an energy density of 118 Wh&middot, kg&minus, 1 at a power density of 500.35 W&middot, 1, all of which are much higher than those of FPC. These encouraging results suggest that the graphene modification of electrode materials combined with a Fe3+/Fe2+ redox active electrolyte is a prospective measure to fabricate SC with an ultrahigh performance.

Here we describe an aqueous asymmetric supercapacitor assembled using Co(OH)F nanorods on Ni foam (Co(OH)F@NF) as the positive electrode and layered Ti3C2Tx paper on Ni foam (Ti3C2Tx@NF) as the negative electrode. The Co(OH)F@NF was fabricated by a facile hydrothermal process. The nanorods were constructed as three-dimensional networks with stable structures and good durability in electrochemical reactions. As expected, the Co(OH)F@NF exhibited excellent capacitance (1265 mF cm−2 at 1 mA cm−2) and wonderful rate performance (90% from 1 to 10 mA cm−2). The Co(OH)F@NF//Ti3C2Tx@NF asymmetric supercapacitor devices showed high capacitance of 376 mF cm−2 and excellent rate capacity of 91% retention. When the two Co(OH)F@NF//Ti3C2Tx@NF devices were combined in series, a red led bulb could be lit for 12 minutes, further corroborating the possibility of the devices being used for practical applications.

Research, design, fabrication and results of various screen printed capacitive humidity sensors is presented in this paper. Two types of capacitive humidity sensors have been designed and fabricated via screen printing on recycled paper and cardboard, obtained from the regional paper and cardboard industry. As printing ink, commercially available silver nanoparticle-based conductive ink was used. A considerable amount of work has been devoted to the humidity measurement methods using paper as a dielectric material. Performances of different structures have been tested in a humidity chamber. Relative humidity in the chamber was varied in the range of 35%–80% relative humidity (RH) at a constant temperature of 23 °C. Parameters of interest were capacitance and conductance of each sensor material, as well as long term behaviour. Process reversibility has also been considered. The results obtained show a mainly logarithmic response of the paper sensors, with the only exception being cardboard-based sensors. Recycled paper-based sensors exhibit a change in value of three orders of magnitude, whereas cardboard-based sensors have a change in value of few 10s over the entire scope of relative humidity range (RH 35%–90%). Two different types of capacitor sensors have been investigated: lateral (comb) type sensors and modified, perforated flat plate type sensors. The objective of the present work was to identify the most important factors affecting the material performances with humidity, and to contribute to the development of a sensor system supported with a Radio Frequency Identification (RFID) chip directly on the material, for use in smart packaging applications. Therefore, the authors built a passive and a battery-supported wireless module based on SL900A smart sensory tag’s IC to achieve UHF-RFID functionality with data logging capability.

In this work, we fabricated a lightweight (1.25 g cm−3) N doped reduced graphene (N-RGO) paper through a combined method of vacuum filtration and thermal treatment under an ammonia atmosphere. 0.48% of N has been uniformly incorporated into the graphene sheets, which results in an inherent improvement in conductivity. Simultaneously, the as-fabricated N-RGO paper possesses excellent flexibility without any effect on its electronic properties. Furthermore, the good performance of N-RGO as a supercapacitor electrode was also demonstrated with a high specific capacitance of 280 F g−1 at 5 mV s−1. The N-RGO electrode also exhibited a remarkable long-term cycling stability with 99.4% capacitance retention after 40000 cycles. This work constitutes the first attempt of applying N-doping to improve the electronic properties and electrochemical performance for graphene paper.

Graphene-based microsupercapacitors (mSCs) as important micro-power sources for miniaturized electronic devices have been a fascinating research topic. However, the large specific surface area of graphene is not fully exhibited due to the π-π stacking of graphene nanosheet in these graphene-based mSCs system fabricated by previously reported methods. Here, we propose a new method to fabricate the compact, flexible and all-solid-state graphene hydrogel-based mSC (GH-mSC) by combing paper chip with selective vacuum filtration, which allows the fabrication of mSCs with different sizes and shapes. The stack capacitance value of GH-mSC is 2.51 F cm−3 and the CV curve still keep quasi-rectangular even at a very high scan rate of 50000 mV s−1. The GH-mSC delivers acceptable energy densities of 0.223 mW h cm−3 and power densities of 0.024 W cm−3, which is better than electrolytic capacitor. Further, the GH-mSCs exhibit superior long-time cycling stability and good flexibility. More importantly, the mSC on paper chips allows easy scaling up of capacitance and output voltage by simply fabricating several mSCs on a plane or both sides of a paper and then connecting in parallel or series. These characteristics suggest that GH-mSCs are promising as power sources.

Paper-based flexible supercapacitors (SCs) show advantages due to the improved adhesion between paper and active materials, the simplified printing process and the lower cost, compared to other substrates such as plastics. Here we report the fabrication of solid-state yet flexible SCs by inkjet-printing a hybrid ink consisting of carbon quantum dots (CQDs) and graphene oxide (GO) platelets, followed by casting of polyvinyl alcohol (PVA)/sulfuric acid (H2SO4) gel electrolyte. The SC obtained from 100-time-printing of the hybrid ink shows a specific capacitance of ~1.0 mF cm−2 at a scan rate of 100 mV s−1, which is enhanced by nearly 150%; the whole device including paper substrate, gel electrolyte and active material demonstrates an energy density of 0.078 mW h cm−3 at a power density of 0.28 mW cm−3. In addition, the excellent mechanical strength of GO platelets ensures the good flexibility and mechanical robustness of the printed SCs, which show a retention of 98% in capacitance after being bended for 1,000 cycles at a bending radius of 7.6 mm. This study demonstrates a promising strategy for the large-scale preparation of low-cost, lightweight, and flexible/wearable energy storage devices based on carbon-based ink and paper substrate.

A novel redox-mediated gel polymer electrolyte (GPE) including polyvinyl alcohol, phosphoric acid and phosphomolybdic acid (PVA-H3PO4-PMo12) and symmetric graphite carbon paper electrodes was applied to construct a solid-state carbon paper supercapacitor. The ionic conductivity increased from 3.85 mS cm−1 for PVA-H3PO4 GPE to 5.45 mS cm−1 for PVA-H3PO4-PMo12 GPE with optimal PMo12/H3PO4 mass ratio of 0.5, presenting the improved ionic transportation. The specific capacitance of carbon paper supercapacitors obviously increased from 12.16 mF cm−2 (or 296.6 mF cm3) for PVA-H3PO4 GPE to 28.65 mF cm−2 (or 698.8 mF cm−3) for PVA-H3PO4-PMo12 GPE at a current density of 0.2 mA cm−2, presenting highly improved capacitance performance. The capacity retention of carbon paper supercapacitors was also enhanced from 21.4% for PVA-H3PO4 GPE to 45.9% for PVA-H3PO4 -PMo12 GPE when the current density increased from 0.2 to 2.0 mA cm−2, presenting highly improved rate capability. The PMo12 with redox activity could contribute to the pseudocapacitance through fast and reversible multi-electron transfer process at the interface of carbon paper electrode and GPE electrolyte. However, the capacitance retention obviously decreased from almost above 100% for PVA-H3PO4 GPE-based supercapacitor to 50% for PVA-H3PO4-PMo12 GPE-based supercapacitor after 2000 charge−discharge cycles at 0.5 mA cm−2. The gradually descended reversibility of PMo12 transformed products mostly caused a lowered cycling stability for PVA-H3PO4-PMo12 GPE in long-term cycling redox process. Accordingly, PMo12 could act as a potential redox mediator in GPE electrolyte to improve the capacitance performance of the carbon paper supercapacitors.

An easily-operated and inexpensive strategy (pencil-drawing–electrodeposition–electro-oxidation) is proposed to synthesize a novel class of multilayer core–shell structured composite paper electrode, which consists of copper, cuprous oxide and graphite assembled on cellulose fibers. This interesting electrode structure plays a pivotal role in providing more active sites for electrochemical reactions, facilitating ion and electron transport and shorting their diffusion pathways. This electrode demonstrates excellent electrochemical properties with a high specific capacitance of 601 F g−1 at 2 A g−1 and retains 83% of this capacitance when operated at an ultrahigh current density of 100 A g−1. In addition, a high energy density of 13.4 W h kg−1 at the power density of 0.40 kW kg−1 and a favorable cycling stability (95.3%, 8000 cycles) were achieved for this electrode. When this electrode was assembled into an asymmetric supercapacitor with carbon paper as negative electrode, the device displays remarkable electrochemical performances with a large areal capacitances (122 mF cm−2 at 1 mA cm−2), high areal energy density (10.8 μW h cm−2 at 402.5 μW cm−2) and outstanding cycling stability (91.5%, 5000 cycles). These results unveil the potential of this composite electrode as a high-performance electrode material for supercapacitors.

Insulators or bushings are one of the most common cause of transformer failures especially those with fire and collateral damage. This can be prevented by application of off-line and on-line monitoring, especially by measuring of capacitance C and dielectric dissipation factor tanδ, but current physical understanding of these parameters should be improved. A complex research of temperature dependence of C and tanδ, which is based on measurements on a specially designed oil impregnated paper bushing models with different moisture contents in the insulation and during artificial ageing, is presented in the paper. Useful relationships, which enable calculation of tanδ as a function of observed influencing parameters, are also presented.

PEDOT:PSS has been widely used as the electrode materials for supercapacitors. However, processing PEDOT:PSS bulk films with good flexibility and mechanical stability is still challenging. The present study is aimed at providing a facile and low-cost strategy for the preparation of mechanically strong and conductive PEDOT:PSS based bulk films by using Cellulose nanofibrils (CNF) as building blocks. PEDOT:PSS/CNF suspension was firstly prepared via a simple in situ polymerization process. Afterwards, flexible and conductive PEDOT:PSS/CNF nanopaper (PEDOT:PSS/CNP) were prepared from the PEDOT:PSS/CNF suspension by vacuum filtration and Dimethyl sulfoxide (DMSO) post-treatment. Results showed that the optimized PEDOT:PSS/CNP exhibited excellent flexibility, high tensile strength (72 MPa), and high electrical conductivity (66.67 S/cm). Finally, a symmetric supercapacitor was assembled using the PEDOT:PSS/CNP as electrodes. The assembled supercapacitor could deliver the maximum areal specific capacitance of 854.4 mF cm−2 (corresponding to 122.1F cm−3) at 5 mV/s and offer the highest areal energy density of 30.86 μWh cm−2 (corresponding to 4.41 mWh cm−3), which are among the highest values reported for PEDOT:PSS based supercapacitors. More importantly, the assembled supercapacitor showed remarkable cycling stability with the capacitance retention of 95.8% after 10,000 charge/discharge cycles. Considering the good mechanical properties and excellent electrochemical performance, the PEDOT:PSS/CNP could be a promising electrode material for flexible supercapacitors.

In this study, CuCo2S4 directly grown on carbon fiber papers (CFP) were prepared by a low-cost hydrothermal method. We also studied the influence of two different sulfur sources on the morphology and performance of CuCo2S4. Compared to TAA as sulfur source, the performance and morphology of CuCo2S4 by Na2S·9H2O are better. The CuCo2S4–Na2S nanotubes possess irregular diameters from 100 to 200 nm. An electrode made of the synthesized CuCo2S4–Na2S nanotubes/CFP composite exhibits a maximum specific capacitance of 456 F g−1 at 1 A g−1 and 83% of capacitance retention after 5000 cycles at 5 A g−1. The synthesized CuCo2S4–Na2S/CFP is used to construct an all-solid-state asymmetric supercapacitor (ASC) as the positive electrode, while and the negative electrode is made of a Fe2O3/reduced graphene oxide (rGO) composite on Ni foam. This asymmetric device has delivered an energy density of 50 W h kg−1 and a power density of 700 W kg−1 at an operating voltage of 1.5 V. It retains a long cycling life—78.2% capacity retention ratio after 5000 cycles. This work demonstrates the feasibility of the CuCo2S4–Na2S nanotubes in the applications of high-performance supercapacitors.

Keeping in view the huge demands of green and flexible supercapacitors to further digitalize and electrify human community, it is imperative to develop cost-effective and eco-friendly solutions. Herein, we report a sequential protocol to fabricate flexible, lightweight and inexpensive cellulose fiber thin film electrode based on vertically aligned polyaniline (PANI) nano-dendrites@fiber for supercapacitors. In this process, the mechanical shearing not only induces the branched architecture on cellulose fibers, but also promotes the subsequent growth of vertically aligned nano-dendrites of PANI on the cellulose fibers with increased PANI loading. The high fibrillation caused by mechanical shearing and the well-ordered growth of vertically aligned PANI dendrites on cellulose fibers make the resultant PANI@Paper hierarchically porous with high specific surface area, conductivity, mechanical strength and flexibility. The PANI@Paper based supercapacitor demonstrates excellent specific capacitance of 296 Fg-1 at 1 Ag-1 and areal capacitance of 5017 mF cm−2 at 10 mA cm−2. Furthermore, a solid-state supercapacitor based on PANI@Paper demonstrates excellent capacitance (282 Fg-1 at 1 Ag-1), high energy density (2.5 Wh kg−1) and power density of (0.3 kW kg−1). Impressively, all-paper supercapacitor fabricated with PANI@Paper and commercial paper shows remarkable capacitance (271 Fg-1 at 1 Ag-1) and flexibility while maintaining the electrochemical stability.

Flexible all-solid-state supercapacitors (FASSCs) have attracted much attention as power supplies for portable and wearable electronic products. Herein, we report the fabrication of a foldable, extra lightweight, flexible chopped carbon fiber paper (CFP) with a porous network structure prepared via wet-mold papermaking that can serve as a conductive substrate. The conductivity and pseudocapacitance of the electrode were improved by controlling the growth of 3D Cu(OH)2 nanorod arrays on CFP substrate. The Cu(OH)2@CFP electrode has a high specific capacitance of 421.8 mF cm−2 at a current density of 0.5 mA cm−2 with capacitance retention of 82.98% at a current density of 10 mA cm−2 after 5000 charge-discharge cycles. The FASSC manifested not only a large capacitance of 196.1 mF cm−2 at 2 mA cm−2, as well as energy and power densities of 6.97 × 10−2 mWh cm−2 and 1.6 mW cm−2, respectively, but also excellent stability of 80.3% over 5000 cycles at 5 mA cm−2. In addition, we confirmed that the FASSC has a large bending angle and can be twisted into various shapes, thereby indicating its applicability in portable and wearable electronic devices.