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Wearable electronic devices have emerged which require compact, flexible power storage devices such as batteries and supercapacitors. Recently, energy storage devices have been developed based on supercapacitor threads. However, current supercapacitor energy storage threads which use electrolytes based on aqueous gels have a 1 V potential window. This is much lower than the voltage required by most electronic devices. This current contribution presents an approach for fabricating a multilayer supercapacitor working as a circuit unit, in which series combinations of the multiple layer structures can achieve a higher potential window, which can better meet the needs of wearable electronic devices.

Two-capacitive layer thread supercapacitors were fabricated using a semi-automatic dip coating method by coating two capacitive layers sequentially on a 50 μm stainless steel core wire, each capacitive layer includes ink, aqueous-based gel electrolyte and silver conductive paint layers.

Two capacitive layers of the single thread supercapacitor can work independently, or as combination circuits – parallel and series. Cyclic voltammograms showed that all flexible circuits have high electrochemical stability. For the case of series circuit configuration, with H₃PO-polyvinyl alcohol (PVA) gel electrolyte, a working potential window of 2 V was achieved.

A flexible single thread supercapacitor of multilayer structure, with working voltage above 1 V in H₃PO₄-PVA gel electrolyte, has not been reported before. A semi-automatic dip coating setup used to process the thread supercapacitor has high potential for transfer to an industrial environment for mass production.

The purpose of this paper is to show how to obtain a supercapacitor with high specific power (P) and high specific energy (E_p) simultaneously.

The carbon aerogels are obtained by ambient pressure drying method instead of supercritical drying method and carbon aerogels/Ni(OH)₂ composites are prepared by in situ polymerisation. A series of asymmetric supercapacitors based on carbon aerogels/Ni(OH)₂ composites as positive electrode and activated carbon as negative electrode, respectively, are assembled. The electrochemical performances of carbon aerogels/Ni(OH)₂ composites and supercapacitors are studied.

The results show that the specific capacitance (C_P) of carbon aerogels/Ni(OH)₂ composites is 584 F/m². The working potential of supercapacitors could be increased to 1.6V. When the mass ratio of carbon aerogels and Ni(OH)₂ is 3:7, the mass ratio of positive electrode and negative electrode is 1:1, the E_P and P of the supercapacitor is higher than 10.5 Wh/kg and 578 W/kg, respectively, when the current varies from 50 mA to 100 mA and the attenuation ratio of C_P is only 8.3 per cent after 10,000 cycles at 100 mA.

The supercapacitors can be used in the field of automobile engineering and can solve the problems of energy shortage and environmental pollutions.

The supercapacitor based on carbon aerogels/Ni(OH)₂ composites as positive electrode and activated carbon as negative electrode is novel and the synthetic properties of the supercapacitor are excellent.

The purpose of this paper is to report on the feasibility of the manufacture of printed rechargeable power sources incorporating, in the first instance, electrode structures from the previous study, and moving on to improved electrode structures fabricated, via flexographic printing, using commercially available inks. It has been shown previously that offset lithography, a common printing technique, can be used to make electrodes for energy storage devices such as primary cells.

A pair of the original Ag/C electrodes, printed via offset lithography, were sandwiched together with a PVA-KOH gel electrolyte and then sealed. The resultant structures were characterised using electrochemical techniques and the performance as supercapacitors assessed. Following these studies, electrode structures of the same dimensions, consisting of two layers, a silver-based current collector covered with a high surface area carbon layer, were printed flexographically, using inks, on a melinex substrate. The characterisation and assessment of these structures, as supercapacitors, was determined.

It was found that the supercapacitors constructed using the offset lithographic electrodes exhibited a capacitance of 0.72 mF/cm2 and had an equivalent series resistance of 3.96 Ω. The structures fabricated via flexography exhibited a capacitance of 4 mF/cm2 and had an equivalent series resistance of 1.25 Ω The supercapacitor structures were subjected to bending and rolling tests to determine device performance under deformation and stress. It was found that supercapacitor performance was not significantly reduced by bending or rolling.

This paper provides insight into the use of printed silver/carbon electrodes within supercapacitor structures and compares the performance of devices fabricated using inks for offset lithographic printing presses and those made using commercially available inks for flexographic printing. The potential viability of such structures for low-end and cheap energy storage devices is demonstrated.

Non-linear power–voltage characteristics of solar cell and frequently changing output due to variation in solar irradiance caused by movement of clouds are the major issues need to be considered in photovoltaic (PV) penetration to maintain the power quality of the grid. It is important for a PV module to always function at its maximum available power point to increase the efficiency and to maintain the grid stability. A possible solution to mitigate these generation fluctuations is the use of an electric double-layer capacitor or supercapacitor energy storage device, which is an efficient storage device for power smoothing applications. This study aims to propose a power smoothing control approach to smoothen out the output power variations of a solar PV system using a supercapacitor energy storage device.

To extract the maximum possible power from a PV panel, there are several maximum power points tracking (MPPT) algorithms developed in literature. Fuzzy logic controller-MPPT method is used in this work as it is a very efficient and popular technique which responds quickly under varying ecological conditions, reduced computational complexity and does not depend on any system constraints. Fuzzy logic-based MPPT controller by Boost DC–DC converter is developed for operating the PV panels at available maximum power point. Fuzzy logic-proportional integral (PI) charge controller is implemented by Buck–Boost converter to provide the constant current and suitable voltage for supercapacitor and to achieve better power smoothing. PI charge controller is preferred in this work as it offers better outcomes and is very easy to implement.

Simulation results conclude that the proposed power smoothing control approach can efficiently smooth out the power variations under variable irradiance and temperature situations. To confirm the accurateness of the proposed system, it is validated for poly-crystalline PV module and comparison of results is done by using different case study with and without the use of an energy storage system under change in irradiance condition. The proposed system is developed and examined on MATLAB/Simulink environment.

The performance comparison between PV power output with and without the use of a supercapacitor energy storage device under different Case Studies shows that the improved performance in smoothing of power output was achieved with the use of a supercapacitor energy storage device.

The purpose of this paper is to develop nitrogen-enriched carbon (NC) with high conductivity and specific capacitance as electrode materials for supercapacitors.

Graphene oxide (GO) was synthesized by the modified Hummers–Offeman method. NC was synthesized by carbonization of melamine formaldehyde resin/graphene oxide (MF/GO) composites. Supercapacitors based on Ni(OH)2/Co(OH)2 composites as the positive electrode and NC as the negative electrode were assembled. The electrochemical performances of NC and supercapacitors are studied.

The results show that obtained NC has high nitrogen content. Compared to NC-GO0 without GO, high conductivity and specific capacitance were obtained for NC with GO due to the introduction of layered GO. The presence of pseudocapacitive interactions between potassium cations and the nitrogen atoms of NC was also proposed. When the weight ratio of GO to MF is 0.013:1, the obtained NC-GO3 has the highest specific capacitance of 154.07 F/g due to GO and its highest content of N-6. When the P of the asymmetric supercapacitor with NC-GO3 as the negative electrode is 1,326.70 W/kg, its Cps and Ep are still 23.84 F/g and 8.48 Wh/Kg, respectively. There is only 4.4 per cent decay in Cps of the supercapacitor over 1,000 cycles.

NC is a suitable electrode material for supercapacitors. The supercapacitors can be used in the field of automobiles and can solve the problems of energy shortage and environmental pollutions.

NC based on MF/GO composites with high nitrogen content and conductivity was novel and its electrochemical properties were excellent.

The purpose of this paper is to develop feasible composite electrodes with a long cycle life and large specific capacitance and to investigate optimal ratio between aniline and activated carbon materials.

PANI/AC composite electrode materials were synthesised by in situ polymerisation of aniline on activated carbon with ammonium persulphate as oxidant. Hybrid supercapacitors are assembled by putting Ni‐MH battery separator between positive and negative electrodes. The electrochemical performances of PANI/AC composite electrode materials and supercapacitors are studied.

The results show that the optimal ratio between aniline and activated carbon is 1:1.08. The specific capacitance of polyaniline electrode materials is 956 F g⁻¹. The specific capacitance of supercapacitors is 159.37 F g⁻¹. This result could be attributed to the pseudocapacitive effect of Ni(OH)₂. What's more, the activated carbon addition reduced the resistance of polymer electrode materials thus improving the cyclic life.

The supercapacitors can be used in the field of automobiles and can solve the problems of energy shortage and environmental pollutions.

A hybrid supercapacitor, which was immersed in alkaline solution, was assembled by putting Ni‐MH battery separator between two electrodes Ni(OH)₂ as positive electrode and polyaniline composites as negative electrode. In the case of alkaline solution, the capacitive performance of hybrid supercapacitor was improved and excellent.

The purpose of this paper is to prepare a spherical modifier-modified activated carbon fiber of high specific capacitance intended for electrode materials of supercapacitor.

In this study, phenolic-based microspheres are taken as modifiers to prepare PAN-based fiber composites by electrospinning, pre-oxidation and carbonization. Pearl-chain structures appear in RFC/ACF composites, and pure polyacrylonitrile fibers show a dense network. The shape and cross-linking degree are large. After the addition of the phenolic-based microspheres, the composite material exhibits a layered pearlite chain structure with a large porosity, and the RFC/ACF composite material is derived because of the existence of a large number of bead chain structures in the composite material. The density increases, the volume declines and the mass after being assembled into a supercapacitor as a positive electrode material decreases. The specific surface area of RFC/ACF composites is increased as compared to pure fibers. The increase in specific surface area could facilitate the diffusion of electrolyte ions in the material. Owing to the large number of bead chains, plenty of pore channels are provided for the diffusion of electrolyte ions, which is conducive to enhancing the electrochemical performance of the composite and improving the RFC/ACF composite and the specific capacitance of the material. The methods of electrochemical testing on symmetric supercapacitors (as positive electrodes) are three-electrode cyclic voltammetry, alternating current impedance and cycle stability.

The specific capacitance value of the composite material was found to be 389.2 F/g, and the specific capacitance of the electrode operating at a higher current density of 20 mA/cm2 was 11.87 F/g (the amount of the microsphere modifier added was 0.3 g). Using this material as a positive electrode to assemble into asymmetrical supercapacitor, after 2,000 cycles, the specific capacitance retention rate was 87.46 per cent, indicating excellent cycle stability performance. This result can be attributed to the fact that the modifier embedded in the fiber changes the porosity between the fibers, while improving the utilization of the carbon fibers and making it easier for electrolyte ions to enter the interior of the composites, thereby increasing the capacitance of the composites.

The modified PAN-based activated carbon fibers in the study had high specific surface area and significantly high specific capacitance, which makes it applicable as an efficient and environment-friendly absorbent, as well as an advanced electrode material for supercapacitor.

The purpose of this paper is to develop porous nitrogen-enriched carbon (NC-U) with high nitrogen concentration and high specific capacitance (Cpe) as the electrode material for supercapacitors.

NC-U was obtained by carbonization of polyvinylpyrrolidone/melamine formaldehyde resin (PVP/MF) with different contents of urea. In comparison, NC-K was also prepared by the KOH activation method. A series of asymmetric supercapacitors with NC as a negative electrode was assembled. The composition, microstructure and electrochemical properties of NC and their supercapacitors were studied.

The results show that NC-U shows irregular particles with a porous honeycomb structure. High Cpe was obtained for urea-treated NC-U because of the improvement of nitrogen, conductivity and specific surface area (S _BET ). NC-U50 with 13.15 per cent at nitrogen has the highest Cpe of 148.53 F/g because of the highest concentration of N-6 and N-5. NC-K with higher S _BET has lower Cpe than NC-U50 because of its lower nitrogen concentration. When the specific power of the supercapacitor with NC-U50 as a negative electrode is 1,565.56 W/kg, its specific energy is still 4.35 Wh/kg. There is only 5.9 per cent decay in Cpe over 1,000 cycles.

NC-U is a suitable electrode material for supercapacitors, which can be used in the field of electric vehicles to solve the problems of energy shortage and environmental pollutions.

Porous NC-U based on PVP/MF/urea composites with high nitrogen concentration and Cpe is novel, and it owns good electrochemical properties.

The overall purpose of this research paper largely depends on developing an easy method to synthesis a material suitable for supercapacitor application. This paper includes the synthesis of, α-Co(OH)₂, its structural, elemental and morphological properties and its supercapacitor properties.

Firstly, the electrolyte is prepared using binder free method, then electrodeposition is used to synthesize α-Co(OH)₂ at 2 V. X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and scanning electron microscope (SEM) are used to study the structural, elemental and morphological characteristics. The supercapacitor properties are investigated by using cyclic voltammetry, charging-discharging graph, stability test and electrochemical impedance spectroscopy (EIS).

Synthesis of α-Co(OH)₂ is a tedious job as the temperature and use of weak base plays an important role. However, throughout electrodeposition, temperature is maintained using a water bath and weak base as the precursor. The presence of nitrate anions shows more interlayer space than that of ß-Co(OH)₂ because of which free diffusion of the electrolyte is possible. Sheets structures are more visible in SEM images. Nanosheet like structure is observed in the film and such kind of structure provide higher surface area and higher specific capacitance. Usually, the surface morphology of cobalt hydroxide shows flower-like, spherical and nanocubes particles. The cross-section of the deposited film and it is found to be approximately 100 µm. In the forward and backward scan, oxidation and reduction peaks are clearly visible. However, such a behavior is reported as stable because of no further peaks of oxidation.

XRD and EDS confirms the growth of α-Co(OH)₂. SEM images shows the porous nature of the film. Specific capacitance and energy density has been estimated at 5 mV s⁻¹ is 780 F g⁻¹ and 82 W h kg⁻¹, respectively. The film was stable for 600 cycles showing 75 per cent capacitance retention. The voltage drop is 0.02 V for 0.5 A cm⁻², indicating low resistance and good conductivity of the film. The specific power is estimated to be 15 W kg⁻¹ for 1 A cm⁻². The value of R_ESR, R_CT, C_DL and W is 4.83 Ohm, 1.273 Ohm, 0.00233 C and 0.717, respectively. Thus indicating α-Co(OH)₂ to be better candidate for supercapacitor applications.

The purpose of this paper is to prepare a new modified activated carbon fibers (ACFs) of high specific capacitance used for electrode material of supercapacitor.

In this study, the specific capacitance of ACF was significantly increased by using the phenolic resin microspheres and melamine as modifiers to prepare modified PAN-based activated carbon fibers (MACFs) via electrospinning, pre-oxidation and carbonization. The symmetrical supercapacitor (using MACF as electrode) and hybrid supercapacitor (using MACF and activated carbon as electrodes) were tested in term of electrochemical properties by cyclic voltammetry, AC impedance and cycle stability test.

It was found that the specific capacitance value of the modified fibers were increased to 167 Fg^-1 by adding modifiers (i.e. 20 wt.% microspheres and 15 wt.% melamine) compared to that of unmodified fibers (86.17 Fg^-1). Specific capacitance of modified electrode material had little degradation over 10,000 cycles. This result can be attributed to that the modifiers embedded into the fibers changed the original morphology and enhanced the specific surface area of the fibers.

The modified ACFs in our study had high specific surface area and significantly high specific capacitance, which can be applied as efficient and environmental absorbent, and advanced electrode material of supercapacitor.