Supercapacitors (Chemistry) Research Papers - Academia.edu (original) (raw)

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- Materials Science, Renewable Energy, Energy and Environment, Supercapacitors (Chemistry)

High surface area carbon materials have high double layer capacitances because of their enhanced internal surface area and hence are attractive materials for supercapacitor applications. In this work, we demonstrate that utilizing a simple shaking experiment, hydroquinone can be physisorbed inside the pores of activated charcoal and the material can be used as a supercapacitor having a highest specific capacitance of ~200 F/g in 1 M H2SO4. Nearly 40% of the specific capacitances were pseudocapacitance in nature because of the observed reversible redox chemistry of hydroquinone/benzoquinone couples where hydroquinone underwent proton-coupled electron transfer (2H+/2e-) to form benzoquinone. The redox chemistry of hydroquinone/quinone is chemically irreversible but the same chemistry has been found to be chemically reversible and fast electron transfer kinetics at the electrode surface was observed in this study presumably because of proton-coupled electron transfers that were catalyzed by oxide sites present on the activated charcoal. Due to the observed reversible electrochemistry, the material also showed excellent capacitance retention in the long term cyclic tests. The approach presented in this study conceptually brings a new dimension to improve the chemistry of energy storage systems by simultaneous introduction of physisorption and proton-coupled electron transfer.

- by chanderpratap singh and +1
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- Supercapacitors (Chemistry), Proton Coupled Electron Transfer, Activated Charcoal, Physisorption

Biomass pyrolysis is a promising renewable sustainable source of fuels and petrochemical substitutes. It may help in compensating the progressive consumption of fossil-fuel reserves. The present article outlines biomass pyrolysis. Various types of biomass used for pyrolysis are encompassed, e.g., wood, agricultural residues, sewage. Categories of pyrolysis are outlined, e.g., flash, fast, and slow. Emphasis is laid on current and future trends in biomass pyrolysis, e.g., microwave pyrolysis, solar pyrolysis, plasma pyrolysis, hydrogen production via biomass pyrolysis, co-pyrolysis of biomass with synthetic polymers and sewage, selective preparation of high-valued chemicals, pyrolysis of exotic biomass (coffee grounds and cotton shells), comparison between algal and terrestrial biomass pyrolysis. Specific future prospects are investigated, e.g., preparation of supercapacitor biochar materials by one-pot one-step pyrolysis of biomass with other ingredients, and fabricating metallic catalysts embedded on biochar for removal of environmental contaminants. The authors predict that combining solar pyrolysis with hydrogen production would be the eco-friendliest and most energetically feasible process in the future. Since hydrogen is an ideal clean fuel, this process may share in limiting climate changes due to CO 2 emissions.
Keywords Sustainable and renewable energy source; Fossil-fuel alternatives; Biomass pyrolysis; Biofuel (bio-oil, biogas, biochar); Charcoal (activated carbon); Hydrogen fuel

- by Prof Dr Yehia Fahmy and +2
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- Environmental Engineering, Environmental Science, Development Economics, Environmental Economics

Supercapacitors are known for their rapid energy charge–discharge properties, often ten to a hundred times faster than batteries. However, there is still a demand for supercapacitors with even faster charge–discharge characteristics to fulfill the requirements of emerging technologies. The power and rate capabilities of supercapacitors are highly dependent on the morphology of their electrode materials. An electrically conductive 3D porous structure possessing a high surface area for ions to access is ideal. Using a flash of light, a method to produce highly interconnected 3D graphene architectures with high surface area and good conductivity is developed. The flash converted graphene is synthesized by reducing freeze-dried graphene oxide using an ordinary camera flash as a photothermal source. The flash converted graphene is used in coin cell supercapacitors to investigate its electrode materials properties. The electrodes are fabricated using either a precoating flash conversion or a postcoating flash conversion of graphene oxide. Both techniques produce supercapacitors possessing ultra-high power (5–7 × 105 W kg−1). Furthermore, optimized supercapacitors retain >50% of their capacitance when operated at an ultrahigh current density up to 220 A g−1.

- by Anne Hathaway and +5
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- Materials Science, Electronics, Graphene, Supercapacitors (Chemistry)

Nickel doped zinc oxide (Ni/ZnO) nanostructures have the potential to improve the performance of electrochemical capacitors. This study investigates the preparation of Ni/ZnO nanomaterials by facile co-precipitation (CPM) and hydrothermal (HTM) methods. The effect of the synthesis methods on the optical, structural, chemical and morphological properties on ZnO products is investigated using ultra violet (UV)-visible spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray spectrometry (EDX), room temperature photoluminescence (PL), Fourier transform infrared (FTIR) and Raman spectroscopy. Finally, the electrochemical performance of the synthesized nanorods were examined by fabrication of a supercapacitor using standard three electrode cell configuration and tested with a cyclic voltammogram (CV) and galvanostatic charge-discharge (GCD) measurements. The results shown that the samples synthesized by HTM exhibited improved electrochemical capacitance performance with higher current density. The discharge curves are linear in the total range of potential with constant slopes, showing perfect capacitance. In conclusion, Ni/ZnO nanoparticles synthesized by this method with further optimization have the potential to lead to a high-efficiency supercapacitors.

- by Joshua Pearce and +1
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- Materials Engineering, Materials Science, Chemistry, Thin Films and Coatings

With every moving day, the aspect that is going to be the most important for modern science and technology is the means to supply sufficient energy for all the scientific applications. As the resource of fossil fuel is draining out fast, an alternative is always required to satisfy the needs of the future world. Limited resources also force to innovate something that can utilize the resource more efficiently. This work is based on a simple synthesis route of biomass-derived hard carbon and to exploring the possibility of using it as electrochemical supercapacitors. A cheap, eco-friendly and easily synthesized carbon material is utilized as electrode for electrochemical energy-storage. Four diferent hard carbons
were synthesized from KOH activated banana stem (KHC), phosphoric acid treated banana stem derived carbons (PHC), corn-cob derived hard carbon (CHC) and potato starch derived hard carbons
(SHC) and tested as supercapacitor electrodes. KOH-activated hard carbon has provided 479.23F/g specific capacitance as calculated from its cycle voltammograms. A detailed analysis is done to correlate
the results obtained with the material property. Overall, this work provides an in depth analysis of the science behind the components of an electrochemical energy-storage system as well as why the
diferent characterization techniques are required to assess the quality and reliability of the material for electrochemical supercapacitor applications.

At present world facing major problems of rapid growth of population and global economy due to this demand for energy consumption has been considerably increased. Supercapacitor devices are emerging as one of the promising energy devices for the future energy technology. In this regards, the transition metal oxides are suitable electrode materials for pseudocapacitors due to different oxidation states and different ions. In this review article, we focused on the pure nickel oxide based materials synthesizing by various synthetic methods. Nowadays nickel oxide is emerging electrode material for energy storage application due to its thermal stability, high chemical stability, high theoretical specific capacity, low price, naturally abundant and environment friendliness. There are three important factors on which performance of supercapacitor mainly depends on namely electrochemical properties of the electrode material, electrolyte and voltage range. In this review paper, storage mechanism of supercapacitors with their types, characteristics of the electrode material, different synthesis methods of nickel oxide
electrode material and different electrolyte materials have been reported.

- by Suraj khalate
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- Catalysis, Solar Cell, Photonics, Supercapacitors (Chemistry)

Since its discovery a decade ago, dozens of potential uses for graphene have been proposed, from faster computer chips and flexible touchscreens to hyper-efficient solar cells and desalination membranes. One exciting property that has sparked significant interest is its ability to store electrical charge. A single sheet of graphene sufficient in size to cover an entire American football field would weigh just a fraction of a gram. This huge surface area associated with this small amount of graphene can be squeezed inside an AA battery, enabling the design of new energy-storage devices with the ability to store massive amounts of charge. In this Review, we discuss the inherent properties of graphene and what it has to offer for energy storage. Much of the Review covers the synthesis and assembly of graphene into macrostructures that exploit the unique features of individual graphene sheets to build new materials for various applications. Particular attention is paid to the processing of graphene into electrodes, which is an essential step in the production of devices. Graphene can be useful by itself, but it is also promising — as we discuss — for composites with superior performance compared with existing materials. Currently, graphene is the most studied material for charge storage and the results from many laboratories confirm its potential to change today's energy-storage landscape. Specifically, graphene could present several new features for energy-storage devices, such as smaller capacitors, completely flexible and even rollable energy-storage devices, transparent batteries, and high-capacity and fast-charging devices. These and other features are explored in this Review. Despite notable progress, the future of graphene in the energy-storage market is uncertain because of several challenges. We discuss and propose solutions to these challenges and also briefly discuss the potential of other emerging 2D materials for energy-storage applications. Graphene for energy storage The fundamental properties of graphene make it promising for a multitude of applications. In particular, graphene has attracted great interest for supercapacitors because of its extraordinarily high surface area of up to 2,630 m 2 g −1. Recently, the intrinsic capacitance of single-layer graphene was reported to be ~21 μF cm −2 ; this value sets the upper limit for electric double-layer (EDL) capac-itance for all carbon-based materials 1. Thus, supercapac-itors based on graphene could, in principle, achieve an EDL capacitance as high as ~550 F g −1 if the entire surface area can be fully utilized. However, to understand the limits of graphene in supercapacitors, it is important to know the energy density of a fully packaged cell and not just the capacitance of the active material. In addition to the capacitance of graphene, the maximum energy density of graphene-based supercapacitors depends on several other parameters, such as the thickness and density of the graphene film and other cell components, including the current collector and the separator, the nature and density of the electrolyte, the operating voltage window of the cell and the packaging efficiency. As illustrated in FIG. 1, when using a standard current collector, separator and acetonitrile-based electrolyte, the two key parameters that control the energy density of graphene supercapacitors are the density of the graphene film and the voltage of the cell. For an electrochemical cell using 200-μm-thick graphene electrodes with a density of 1.5 g cm −3 and an operating voltage of 4 V, the maximum theoretical energy density is ~169 Wh kg −1 Abstract | Graphene has recently enabled the dramatic improvement of portable electronics and electric vehicles by providing better means for storing electricity. In this Review, we discuss the current status of graphene in energy storage and highlight ongoing research activities, with specific emphasis placed on the processing of graphene into electrodes, which is an essential step in the production of devices. We calculate the maximum energy density of graphene supercapacitors and outline ways for future improvements. We also discuss the synthesis and assembly of graphene into macrostructures, ranging from 0D quantum dots, 1D wires, 2D sheets and 3D frameworks, to potentially 4D self-folding materials that allow the design of batteries and supercapacitors with many new features that do not exist in current technology. NATURE REVIEWS | MATERIALS ADVANCE ONLINE PUBLICATION | 1 REVIEWS © 2 0 1 6 M a c m i l l a n P u b l i s h e r s L i m i t e d. A l l r i g h t s r e s e r v e d .

- by Yuanlong Shao and +1
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- Materials Science, Graphene, Nanotechnology, Supercapacitors (Chemistry)

The hybrid approach allows for a reinforcing combination of properties of dissimilar components in synergic combinations. From hybrid materials to hybrid devices the approach offers opportunities to tackle much needed improvements in the performance of energy storage devices. This paper reviews
the different approaches and scales of hybrids, materials, electrodes and devices striving to advance
along the diagonal of Ragone plots, providing enhanced energy and power densities by combining
battery and supercapacitor materials and storage mechanisms. Furthermore, some theoretical aspects
are considered regarding the possible hybrid combinations and tactics for the fabrication of optimized
final devices. All of it aiming at enhancing the electrochemical performance of energy storage systems

The demand for flexible/wearable electronic devices that have aesthetic appeal and multi-functionality has stimulated the rapid development of flexible supercapacitors with enhanced electrochemical performance and mechanical flexibility. After a brief introduction to flexible supercapacitors, we summarize current progress made with graphene-based electrodes. Two recently proposed prototypes for flexible supercapacitors, known as micro-supercapacitors and fiber-type supercapacitors, are then discussed. We also present our perspective on the development of graphene-based electrodes for flexible supercapacitors.

- by Anne Hathaway and +1
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- Graphene, Nanotechnology, Supercapacitors (Chemistry), Capacitors, Supercapacitors, Energy storage devices
- by Jinbo Pang
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- Energy, Supercapacitors (Chemistry), Lithium-Ion Battery, Phosphorene

Transition metal carbides and nitrides (MXenes), a family of two-dimensional (2D) inorganic compounds, are materials composed of a few atomic layers of transition metal carbides, nitrides, or carbonitrides. Ti 3 C 2 , the first 2D layered MXene, was isolated in 2011. This material, which is a layered bulk material analogous to graphite, was derived from its 3D phase, Ti 3 AlC 2 MAX. Since then, material scientists have either determined or predicted the stable phases of 4200 different MXenes based on combinations of various transition metals such as Ti, Mo, V, Cr, and their alloys with C and N. Extensive experimental and theoretical studies have shown their exciting potential for energy conversion and electro-chemical storage. To this end, we comprehensively summarize the current advances in MXene research. We begin by reviewing the structure types and morphologies and their fabrication routes. The review then discusses the mechanical, electrical, optical, and electrochemical properties of MXenes. The focus then turns to their exciting potential in energy storage and conversion. Energy storage applications include electrodes in rechargeable lithium-and sodium-ion batteries, lithium–sulfur batteries, and supercapacitors. In terms of energy conversion, photocatalytic fuel production, such as hydrogen evolution from water splitting, and carbon dioxide reduction are presented. The potential of MXenes for the photocatalytic degradation of organic pollutants in water, such as dye waste, is also addressed, along with their promise as catalysts for ammonium synthesis from nitrogen. Finally, their application potential is summarized.

- by Jinbo Pang and +1
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- Renewable Energy, Energy, Supercapacitors (Chemistry), Lithium-Ion Battery

Transition metal chalcogenides (TMCs) embedded with a carbon network are gaining much attention because of their high power capability, which can be easily integrated to portable electronic devices. Facile chemical route has been explored to synthesize hexagonal structured VS 2 nanoparticles onto multiwalled carbon nanotubes (MWCNTs) matrix. Such surface-modified VS 2 /MWCNTs electrode has boosted the electro-chemical performance to reach high capacitance to 830 F/g and excellent stability to 95.9% over 10 000 cycles. Designed flexible solid-state symmetric supercapacitor device (FSSD) with a wide voltage window of 1.6 V exhibited maximum gain in specific capacitance value of 182 F/g at scan rate of 2 mV/ s along with specific energy of 42 Wh/kg and a superb stability of 93.2% over 5000 cycles. As a practical approach, FSSD has lightened up " VNIT " panel consisting of 21 red LEDs.

- by Bidhan Pandit
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- Supercapacitors (Chemistry)

Traditional printing methods offer the advantage of well-matured technology, high accuracy of depositing inks over flexible substrates at high web speeds, and low cost of fabrication. The components of a battery—the current collectors, active layers, and separator—can all be deposited using convention- al printing techniques by designing suitable inks. A combination of low thickness of printed electrodes, flexible packaging, battery architecture, and material properties makes printed batteries flexible. In this paper, we will discuss mate- rial challenges and mechanical limits of flexible printed batteries. We will review several printing techniques and present examples of batteries printed using these methods. In addition, we will briefly discuss other novel non-printed compliant batteries that have unique mechanical form.

- by Abhinav Gaikwad
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- Lithium Batteries, 3D printing, Supercapacitors (Chemistry), Batteries

Electrochemical impedance spectroscopy (EIS) is an experimental method for characterizing electrochemical
systems. This method measures the impedance of the concerned electrochemical system over
a range of frequencies, and therefore the frequency response of the system is determined, including
the energy storage and dissipation properties. The aim of this article is to review articles focusing on
electrochemical impedance spectroscopic studies and equivalent electrical circuits of conducting polymers,
such as polypyrrole, polycarbazole, polyaniline, polythiophene and their derivatives, on carbon
surfaces. First, the conducting polymers are introduced. Second, the electrochemical impedance spectroscopic
method is explained. Third, the results of EIS applications using equivalent electrical circuits for
conducting polymers taken from the literature are reviewed.

- by Murat Ateş
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- Polymer Chemistry, Polymer science, Carbon Nanotubes, Conducting Polymers

Metal cobaltites have promising electrochemical properties for their application as an energy storage
medium.In this paper, usefulness of MgCo2O4
as a supercapacitor electrode is demonstrated and
compared its performance with two other cobaltites, MnCo2O4
and CuCo2O4. The materials are synthesized
using molten salt method and characterized by X-ray diffraction, scanning electron microscopy,
BET surface area, cyclic voltammetry, galvanostatic charge–discharge cycling, and electrochemical
impedance spectroscopy techniques. The MgCo2O4 electrodes show superior charge storage
properties in 3 M LiOH among a diverse choice of electrolytes. The MgCo2O4 show higher theoretical (3122 F/g) and practically achieved capacitance (320 F/g), larger coulombic efﬁciency, and cycling stability than the other two; therefore, it could be developed as a low-cost energy storage
medium.

- by syam g krishnan Krishnan and +2
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- Supercapacitors (Chemistry)

Supercapacitors are increasingly used for energy conversion and storage systems in sustainable nanotechnologies. Graphite is a conventional electrode utilized in Li-ion-based batteries, yet its specific capacitance of 372 mA h g −1 is not adequate for supercapacitor applications. Interest in supercapacitors is due to their high-energy capacity, storage for a shorter period and longer lifetime. This review compares the following materials used to fabricate supercapacitors: spinel ferrites, e.g., MFe 2 O 4 , MMoO 4 and MCo 2 O 4 where M denotes a transition metal ion; perovskite oxides; transition metals sulfides; carbon materials; and conducting polymers. The application window of perovskite can be controlled by cations in sublattice sites. Cations increase the specific capacitance because cations possess large orbital valence electrons which grow the oxygen vacancies. Electrodes made of transition metal sulfides, e.g., ZnCo 2 S 4 , display a high specific capacitance of 1269 F g −1 , which is four times higher than those of transition metals oxides, e.g., Zn-Co ferrite, of 296 F g −1. This is explained by the low charge-transfer resistance and the high ion diffusion rate of transition metals sulfides. Composites made of magnetic oxides or transition metal sulfides with conducting polymers or carbon materials have the highest capacitance activity and cyclic stability. This is attributed to oxygen and sulfur active sites which foster electrolyte penetration during cycling, and, in turn, create new active sites.

- by AhMed Ibrahim and +1
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- Conducting Polymers, Supercapacitors (Chemistry), Batteries, Energy efficiency

A catastrophic outage of the U.S. electric grid could seriously jeopardize national security; threaten critical, life-sustaining services and, consequently, the health of millions of people; and cost trillions of dollars in lost revenue. This study identifies proactive, cost-effective solutions that could be implemented promptly to protect utility communication and control systems from solar storms and electromagnetic pulses caused by nuclear detonations in the atmosphere. It also identifies possible sources of federal grants and methods of cost recovery to encourage utilities to invest in grid resiliency. Protecting electric grid communications and its power sources could facilitate rapid recovery and prevent extended outages caused by natural or deliberate EMP events.

Galvanostatic deposition of tartrate–doped polypyrrole (PPy) is carried out on platinum foil in acetonitrile solution with tartaric acid, tetrabutylammonium tetrafluoroborate and Triton-X 100 for supercapacitor studies. The effect of substrate is studied by comparing the results obtained by using platinum, stainless steel and pencil graphite electrodes. The capacitive performance of the coatings are evaluated in an H2SO4/water medium by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge–discharge methods. Based on the charge–discharge results obtained, the tartrate–doped PPy coatings represent a high specific capacitance of 794 F g -1 (areal capacitance of 238 mF cm-2) and a high energy density of 105 Wh kg-1 on pencil graphite electrode, and a high power density of 36.3 kW kg-1 on 316Ti stainless steel electrode. High values may be attributed to the incorporation of tartaric acid via hydrogen bonding, and/or tartrate anion as dopant together with the tetrafluoroborate anion. Besides, Triton X100 provides high porosity and therefore high surface area.

- by Erhan Karaca
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- Polymer Chemistry, Polymer science, Electrochemistry, Energy

Carbon materials are widely used in supercapacitors because of their high surface area, controlled porosity and ease of processing into electrodes. The combination of carbon with metal oxides results in hybrid electrodes with higher specific capacitance than pure carbon electrodes, which has so far limited the energy density of supercapacitors currently available commercially. However, the preparation and processing of carbon/metal oxide electrodes into supercapacitors of different structures and configurations, especially for miniaturized electronics, has been challenging. Here, we demonstrate a simple one-step process for the synthesis and processing of laser-scribed graphene/RuO2 nanocomposites into electrodes that exhibit ultrahigh energy and power densities. Hydrous RuO2 nanoparticles were successfully anchored to graphene surfaces through a redox reaction of the precursors, graphene oxide, and RuCl3 using a consumer grade LightScribe DVD burner with a 788 nm laser. This binder-free, metal current collector-free graphene/RuO2 film was then used directly as a hybrid electrochemical capacitor electrode, demonstrating much-improved cycling stability and rate-capability with a specific capacitance up to 1139 F g−1. We employed these hybrid electrodes for building aqueous-based symmetric and asymmetric cells that can deliver energy densities up to 55.3 Wh kg−1, placing them among the best performing hybrid electrochemical capacitors. Furthermore, this technique was used for the direct writing of interdigitated hybrid micro-supercapacitors in a single step for the first time, with great potential for miniaturized electronics. This simple approach provides a general strategy for making a wide range of composite materials for a variety of applications.

- by Anne Hathaway and +3
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- Materials Science, Graphene, Nanomaterials, Nanotechnology

In present investigation, microflowers like hydrous cobalt phosphate is prepared via a facile single-step hydrothermal method on stainless steel substrate. The microflowers like morphology of hydrous cobalt phosphate thin film consists of microplates and further microplates converted to flakes, by means of a change in length, width and thickness, with urea variation.
Hydrous cobalt phosphate thin film electrode demonstrates a high specific capacitance of 800 F g-1
at 2 mA cm-2 with 33.62 Wh kg-1 energy density and 3.12 kW kg-1 power density. By taking advantages of hydrous cobalt phosphate thin film (as a cathode electrode) and copper sulfide thin film (as an anode electrode), the asymmetric devices (aqueous/all-solid-state) are fabricated. Aqueous asymmetric device shows a high specific capacitance of 163 F g-1 at 2 mA cm-2 with an energy density of 58.12 Wh kg-1 and power density of 3.52 kW kg-1. Moreover, all-solid-state
asymmetric supercapacitor device delivers a high specific capacitance of 70 F g-1 at 2 mA cm-2 with 24.91 Wh kg-1 energy density and 2.63 kW kg-1 power density in PVA-KOH gel electrolyte. The long-term cyclic stability (94 % after 3000 cycles) and actual practical demonstration (lightning 65 red LEDs) suggesting an industrial application of all-solid-state asymmetric device.

- by Suraj khalate and +1
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- Chemical Engineering, Supercapacitors (Chemistry), Batteries, Transition-Metal Oxides

Great attention has been drawn to flexible and portable electronic devices,
so it is important to develop flexible energy-storage devices. In this study, the porous
Ni-Co-N nanosheets on flexible graphene paper (GP) are prepared by surface
nitridation of NiCo 2 O 4 nanosheets. Compared with NiCo 2 O 4 /GP, Ni 3 N/GP and
CoN/GP, Ni-Co-N/GP shows superior performance in terms of specific capacitance of
960 F/g (48.1 mF/cm 2 ) at 4 A/g, rate performance (86% capacitance retention) and
cycle life (the capacitance retention reaches 95% over 5000 cycles). The paper-based
all-solid-state asymmetric supercapacitors (SCs) are manufactured based on
Ni-Co-N/GP and chemical oxidized GP (graphene oxide paper, GOP), which exhibits
excellent bendable, flexible, scalable and lightweight. The flexible energy device
shows an outstanding specific energy of 4.78 mWh/cm 3 and excellent cycle life (89%capacitance retention after 8000 cycles)

The global supercapacitor market has been growing rapidly during the past decade. Today, virtually all commercial devices use activated carbon. In this work, it is shown that laser treatment of activated carbon electrodes results in the formation of microchannels that can connect the internal pores of activated carbon with the surrounding electrolyte. These microchannels serve as electrolyte reservoirs that in turn shorten the ion diffusion distance and enable better interaction between the electrode surfaces and electrolyte ions. The capacitance can be further increased through fast and reversible redox reactions on the electrode surface using a redox-active electrolyte, enabling the operation of a symmetric device at 2.0 V, much higher than the thermodynamic decomposition voltage of water. This simple approach can alleviate the low energy density of supercapacitors which has limited the widespread use of this technology. This work represents a clear advancement in the processing of activated carbon electrodes toward the next-generation of low-cost supercapacitors.

- by Anne Hathaway and +1
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- Renewable Energy, Nanomaterials, Nanoparticles, Energy Storage (in Engineering)

For practical deployment of supercapacitors characterized by high energy density, power density and long cycle life, they must be realized using low cost and environmentally benign materials. Titanium dioxide (TiO 2) is largely abundant in the earth's crust; however, they show inferior supercapacitive electrochemical properties in most electrolytes for practical deployment. In this paper, we show that nickel doped TiO 2 (Ni:TiO 2) nanowires developed by electrospinning showed five times larger capaci-tance (~200 F g À1) than the undoped analogue (~40 F g À1). Electrochemical measurements show that the Ni:TiO 2 nanowires have 100% coulombic efficiency. The electrodes showed no appreciable capacitance degradation for over 5000 cycles. The superior charge storage capability of the Ni:TiO 2 could be due to its high electrical conductivity that resulted in five orders of magnitude higher ion diffusion as determined by cyclic voltammetry and electrochemical impedance spectroscopy measurements.

- by syam g krishnan Krishnan
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- Energy Economics, Energy, Supercapacitors (Chemistry), Batteries

The increasing demand for energy has triggered tremendous research efforts for the development of lightweight and durable energy storage devices. Herein, we report a simple, yet effective, strategy for high-performance supercapacitors by building three-dimensional pseudocapacitive CuO frameworks with highly ordered and interconnected bimodal nanopores, nanosized walls (∼4 nm) and large specific surface area of 149 m2 g–1. This interesting electrode structure plays a key role in providing facilitated ion transport, short ion and electron diffusion pathways and more active sites for electrochemical reactions. This electrode demonstrates excellent electrochemical performance with a specific capacitance of 431 F g–1 (1.51 F cm–2) at 3.5 mA cm–2 and retains over 70% of this capacitance when operated at an ultrafast rate of 70 mA cm–2. When this highly ordered CuO electrode is assembled in an asymmetric cell with an activated carbon electrode, the as-fabricated device demonstrates remarkable performance with an energy density of 19.7 W h kg–1, power density of 7 kW kg–1, and excellent cycle life. This work presents a new platform for high-performance asymmetric supercapacitors for the next generation of portable electronics and electric vehicles.

Most methods for improving supercapacitor performance are based on developments of electrode materials to optimally exploit their storage mechanisms, namely electrical double layer capacitance and pseudocapacitance. In such cases, the electrolyte is supposed to be electrochemically as inert as possible so that a wide potential window can be achieved. Interestingly, in recent years, there has been a growing interest in the investigation of supercapacitors with an electrolyte that can offer redox activity. Such redox electrolytes have been shown to offer increased charge storage capacity, and possibly other benefits. There are however some confusions, for example, on the nature of contributions of the redox electrolyte to the increased storage capacity in comparison with pseudocapacitance, or by
expression of the overall increased charge storage capacity as capacitance. This report intends to provide a brief but critical review on the pros and cons of the application of such redox electrolytes in supercapacitors, and to advocate development of the relevant research into a new electrochemical energy storage device in parallel with, but not the same as that of supercapacitors.

- by George Z . Chen and +2
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- Supercapacitors (Chemistry), Energy Storage, Redox Electrolytes

A simple and scalable approach has been reported for V 2 O 5 encapsulation over interconnected multi-walled carbon nanotubes (MWCNTs) network using chemical bath deposition method. Chemically synthesized V 2 O 5 /MWCNTs electrode exhibited excellent charge-discharge capability with extraordinary cycling retention of 93% over 4000 cycles in liquid-electrolyte. Electrochemical investigations have been performed to evaluate the origin of capacitive behavior from dual contribution of surface-controlled and diffusion-controlled charge components. Furthermore, a complete flexible solid-state, flexible symmetric supercapacitor (FSS-SSC) device was assembled with V 2 O 5 /MWCNTs electrodes which yield remarkable values of specific power and energy densities along with enhanced cyclic stability over liquid configuration. As a practical demonstration, the constructed device was used to lit the 'VNIT' acronym assembled using 21 LED's. One dimensional (1D) carbon nanotubes (CNTs) are well-suited for supercapacitor applications due to their great conductive nature, porous surface area, and high aspect ratio. However, improved performances could be gained by encapsulating its surface with other electroactive materials, like transition metal oxides (TMOs). The resulting hybrid electrodes can feature dual supercapacitive behavior, as electric double layer along with pseudocapacitive from TMOs. Furthermore, TMOs possess an unmatched combination of properties like unique morphology and stability at wider temperature range that brand them superior to polymers towards supercapacitor application 1,2. Amongst metal oxides, ruthenium oxide (RuO 2) got much attention in past decades because of its reversible oxidation states and great electrical conductivity. Zhang et al. 3 were able to attain a high specific capacitance of 860 F g −1 for tubular ruthenium oxide. On the other hand, RuO 2 is rare, expensive and most importantly toxic, which deters as supercapacitor material 4 and hence, research on alternative TMOs electrode materials is of great importance. Layered V 2 O 5 has gained much interest due to its multiple valance states responsible to deliver high specific energy based on intercalation/deintercalation of electrolyte ions 5 , but its final performance differs greatly depending on the synthetic route and the phase obtained. Sol-gel derived nanoporous V 2 O 5 attains capacitance of 214 F g −1 in 2 M KCl 6 whereas the same electrolyte at the same concentration through co-precipitation method yields 349 F g −1 specific capacitance 7,8. Instead of using just the metal oxide, nanocomposites with MWCNTs will further boost the electrochemical properties of the resulting electrodes. A series of different metal oxide/ MWCNTs composites have been used as electrode. Many strategies are auctioned to trigger the supercapacitor performance of V 2 O 5 with the tools such as synthesis method, morphology and so forth. Kim et al. 9 improved

This work manifests the synthesis of reduced graphene oxide nanosheets through in situ solvothermal reduction of graphene oxide. The as-synthesized reduced graphene oxide nanosheets are utilized as a supercapacitor electrode. A series of structural and morphological investigations evince that graphene oxide can be successfully reduced through solvothermal strategy in absolute ethanol as solvent. Fourier transform infrared spectroscopy results showed that reduced graphene oxide displayed very low-intensity bands related to oxygenated functional groups, implying a high reduction degree. Besides that, it shows good electrochemical characteristics such as high specific capacitance of 183 F g-1 is obtained in 5 M KOH at 0.25 A g-1 and low internal and charges transfer resistances which are 430 and 64 mΩ, respectively. The findings confirm that graphene oxide can be reduced through solvothermal reduction strategy. Further, the as-prepared reduced graphene oxide nanosheets is a good candidate for supercapacitors application.

- by Mohammad R. Thalji
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- Graphene, Supercapacitors (Chemistry), Graphene Oxide, Solvothermal Synthesis

Silver (Ag) nanoparticles were synthesized through an electroless deposition providing high surface coverage of porous material. The structural and morphological characteristics were investigated along with electrochemical studies to evaluate the charge storage performance. The nanoparticle morphology provides more active sites and diffusion paths for the electrolyte ions resulting in maximum utilization of active electrode material. Ag nanoparticles based electrode not only exhibited a maximum specific capacitance of 452 F/g (at scan rate of 2 mV/s) and specific energy of 27.8 Wh/kg, but also achieved a tremendous gain over cyclic stability by retrieving 63% capacitance after 10,000 cycles. Such attractive electrochemical behavior of the formed electrode is suitable for the manufacturing of the good quality supercapacitors by utilizing a roll-to-roll industrial production technology.

- by Bidhan Pandit and +1
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- Supercapacitors (Chemistry)

g r a p h i c a l a b s t r a c t Electrochemical approach of chemically synthesized MWCNT/HgS composite towards high performance supercapacitor application. a b s t r a c t Supercapacitors as one of the most important energy storage devices have been receiving worldwide attention due to their high capacitance, power density, long cycle life, and rapid charge/discharge rates as compared to conventional electrolytic capacitors and rechargeable batteries. A nanocomposite has been prepared using mercury sulfide (HgS) and multiwalled carbon nanotubes (MWCNTs) via novel, simple , and low-cost 'dip and dry' process followed by successive ionic layer adsorption and reaction (SILAR) method. The association of HgS nanoparticles with high surface area reinforced MWCNTs nanonetwork boosts the electrochemical supercapacitive performance of nanocomposite compared to bare HgS and MWCNTs. This nanocomposite yields excellent specific capacitance of 946.43 F/g at scan rate of 2 mV/s and an outstanding rate capability of 93% retention over 4000 cycles with decent charge–discharge cycles. Moreover, the electrode exhibits maximum specific energy and power densities of 42.97 Wh/kg and 1.60 kW/kg, respectively. The promising capabilities of formed nanocomposite can explore the opportunities as alternative electrode material for energy storage applications.

- by Bidhan Pandit
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- Supercapacitors (Chemistry)

The electrochemical characteristics of supercapacitors consisting of molybdenum carbide derived carbon C(Mo2C) electrodes in 1M NaPF 6 solutions in various mixtures (0.5–5%) of vinylene carbonate (VC) with propylene carbonate (PC) and ethyl acetate (EA) (1:1 by volume) have been studied using cyclic voltammetry, constant current charging/discharging and electrochemical impedance spectroscopy methods. The specific capacitance and series resistance values dependencies on the used solvent mixture and applied temperature (from −40 • C to 60 • C) have been established. The region of ideal polarizability has been established for C(Mo 2 C) electrodes in all electrolytes and temperatures investigated, except at T ≥ 40 • C. Specific conductivity values have been measured and correlated with electrochemistry data. Limiting capacitance, calculated characteristic time constant and complex power values depend noticeably on the solvent mixture used in the electrolyte, i.e. on the viscosity and specific conductivity of the electrolyte solution. The studied electrolytes are potential candidates for low-temperature supercapacitors.

- by Ronald Väli and +2
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- Chemical Engineering, Renewable Energy, Electrochemistry, Energy Storage (in Engineering)

In this study, a simple and cost-effective method of fabricating hybrid transparent conductive electrodes (TCEs) based on embedded silver nanowires (Ag NWs)/PEDOT: PSS was developed with the addition of low-temperature synthesis of Ni(OH) 2 and polyethylenimine ethoxylated (PEIE) composites as a novel interlayer. The hybrid TCEs with a Ni(OH) 2-PEIE interlayer exhibit remarkable volumetric capacitance of 443 F cm −3 with transparency of 86%, which is one of the highest values reported to date in the transparent supercapacitor. The fabricated bifunctional solid-state electrochromic-supercapacitor device with a transparency of 80% shows stable cyclic stability up to 10,000 charge/discharge cycles, extremely high coloration efficiency of 517 cm 2 C −1 at 633 nm, and a fast switching speed (< 0.6 s). The noted improvement is mainly caused by the Ni(OH) 2-PEIE interlayer influence the pore density of PEDOT: PSS which provides high surface area, thus resulting in efficient charge transfer pathways and fast ion diffusion. Moreover, a capacitance retention of 90% is achieved even after 8000 bending cycles at a bending radius of 1 mm and 15 times of crumpling is tolerated without noticeable degradation, implying excellent mechanical robustness and flexibility. The results present the significant potential of transparent hybrid electrodes for efficient energy storage and electrochromicity with stable trans-mittance changes, even during fast charge/discharge processes, demonstrating their potential as smart wearable energy storage devices.

Nanowires of a composite, Mn 2 O 3-SnO 2 , are synthesized at 100 g scale. The composite nanowires showed beneficial properties of the constituents. They showed significantly high charge storability and cyclability than the constituents. The superior charge storage are attributed to lower characteristic resistances. a b s t r a c t Large scale production of electrochemical materials in non-conventional morphologies such as nanowires has been a challenging issue. Besides, functional materials for a given application do not often offer all properties required for ideal performance; therefore, a composite is the most sought remedy. In this paper, we report large scale production of a composite nanowire, viz. Mn 2 O 3-SnO 2 , and their constituent binary nanowires by a large scale electrospinning pilot plant consisting of 100 needles. Electrochemical characterization of thus produced composite nanowires showed nearly threefold increase in the discharge capacity compared to their single component counterparts: Mn 2 O 3-SnO 2 53mAhgAˋ1(specificcapacitance,CS53 mA h g À1 (specific capacitance, C S 53mAhgAˋ1(specificcapacitance,CS384 F g À1); Mn 2 O 3 18mAhgAˋ1(CS18 mA h g À1 (C S 18mAhgAˋ1(CS164 F g À1); and SnO 2 14mAhgAˋ1(CS14 mA h g À1 (C S 14mAhgAˋ1(CS128 F g À1) at 1 A g À1 in 6 M KOH. The EIS studies showed that the characteristic resistances and time of the composite electrode are appreciably lower than their constituents. Owing to the scalability of the synthesis processes and promising capacitive properties achieved would lead the composite material as a competitive low-cost and high-performance supercapacitor electrode.

- by syam g krishnan Krishnan and +1
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- Nanocomposites, Energy Storage (in Engineering), Supercapacitors (Chemistry), Batteries

In the present study, molybdenum diselenide/reduced graphene oxide (MoSe 2 /rGO) nanosheets were synthesized via a facile hydrothermal process and the electrochemical performance of the nanosheets was evaluated for supercapacitor applications. The MoSe 2 nanosheets were uniformly distributed on the surface of the rGO matrix. The MoSe 2 /rGO nanosheet electrode exhibited an enhanced specific capaci-tance (211 F g −1) with excellent cycling stability, compared with pristine MoSe 2. The enhanced electro-chemical performance of the MoSe 2 /rGO nanosheet electrode is mainly attributed to the improved electron and ion transfer mechanism involving the synergistic effects of pseudocapacitance (from the MoSe 2 nanosheets) and the electric double layer charge (EDLC, from the rGO nanosheets) storage behavior. These results demonstrate that the enhanced electrochemical performance of MoSe 2 /rGO nanosheets could be obtained via a facile and scalable approach.

Orange by-products e.g. orange peel and the extract of orange juice are used as sources for biological anti-oxidants such as ascorbic acid, flavonoids, phenolic compounds and pectins. In this study these antioxidants were successfully used to prepare nanosized materials of α-MnO 2 by cost effective and eco-friendly green chemistry method. The prepared oxides of MnO 2 which have unique properties as a storage cathode material were tested as a pseudocapacitor electrode materials in this study. X-ray powder diffraction (XRD) confirmed the structure of α-MnO 2 for the prepared samples. Thermal behavior of prepared oxides was tested using thermo-gravimetric analysis (TGA). Transmission electron microscopy (TEM) showed the nanosized nature of the prepared oxides. N 2-adsorption-desorption isotherms and pore-size distributions of prepared oxides showed that the surface areas are 5.63 and 8.40 m 2. g −1 for sample prepared from the extract of orange juice (OJ-MnO 2) and that prepared from the extract of orange peel (OP-MnO 2), respectively. Better electrochemical properties are obtained for OP-MnO 2 , the capacitance of OP-MnO 2 (139 F/g) is more than two times and half that obtained for OJ-MnO 2 (50 F/g) at the current density 0.5 A/g.

- by Safaa A Elsherif and +1
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- Supercapacitors (Chemistry)

Supercapacitors are evolving into an important component in energy storage technology with the capability for storing and discharging energy very quickly and effectively. State-of-the-art supercapacitors feature activated carbon electrodes impregnated with a non-aqueous electrolyte (typically acetonitrile) that operate at voltages between 2.2–2.7 V. Unfortunately, activated carbons have low specific capaci-tance (100–120 F g −1) in organic electrolytes which severely limits the energy density of supercapacitors. In addition, organic solvents are often flammable leading to safety and environmental concerns. Aqueous electrolytes, on the other hand, are safer, cheaper and have higher ionic conductivity, promising higher capacitance electrodes. However, the low voltage window enforced by the low decomposition voltage of water around 1.23 V is a major challenge. Here, we demonstrate symmetric supercapacitors operating at an ultrahigh voltage of 1.8 V that can provide specific electrode capacitances up to 716 F g −1 , which is higher than traditional activated carbon electrodes. This is possible through designing both the electrode and electrolyte to work synergistically towards improving not only the capacitance of the electrodes, but also the voltage and cycling stability of the supercapacitor. We also demonstrate by using a simple laser technique the possibility of fabricating micro-supercapacitors with great potential for miniaturized electronics. This work provides an effective strategy for designing and fabricating aqueous supercapacitors that hold promise for a sustainable energy future.

- by Anne Hathaway
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- Graphene, Nanotechnology, Supercapacitors (Chemistry), Nanoscience

Electrochemical double layer capacitors (EDLCs) are investigated with activated carbon electrodes and a lithium-ion electrolyte, in anticipation of potential future applications in hybridised battery-supercapacitor devices and lithium ion capacitors. An experimental study of a symmetric electrochemical double layer capacitor (EDLC) with activated carbon (AC) electrodes on aluminium foil current collectors and electrolyte 1 M LiPF6 in EC:EMC 50:50 v/v concludes a stability window to a maximum potential of 3 V, an equivalent in series resistance of 48 Ω for 1 cm² cell area (including the contact resistance between electrode and current collector) and an average specific electrode capacitance of 50.5 F g⁻¹. Three AC electrode materials are assessed via computer simulations based on a continuum ion and charge transport model with volume-averaged equations, considering the pore size distribution for each electrode material and, depending on pore size, transport of tetrahedral solvated or flat solvated Li⁺ ions and solvated or desolvated PF6⁻ ions. The computer simulations demonstrate that the best electrode material is an AC coating electrode with a hierarchical pore size distribution measured in the range of 0.5–180 nm and bimodal shape, and specific surface area BET = 808 m² g⁻¹.

- by Foivos Markoulidis
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- Lithium, Consumer Behavior, Carbon Nanotubes, Nanomaterials

Chromium aluminum oxide (AlCrO3) is a promising material for deep-ultraviolet optical masks.1-3 Its moderate band gap and moderate dielectric features are useful for optoelectronics and other applications. To improve the optoelectronic properties, a liquid precursor assisted sol-gel synthesis method is often used because it provides a precise control over size and morphology of oxides. Considering these points, in this investigation, we report synthesis of AlCrO3 of small crystallites by a soft chemistry involving a hydrogel. A liquid precursor was obtained of Al(NO3)3·9H2O, CrO3 and C6H8O7.H2O dissolved in water by stirring at 60 C for 24 h. After 24 hours of a continuous thermal agitation, the sample has been converted into a dark blue “hydrogel”. A gel so obtained was dried by heating it in air at 120 °C for 8 h. A ceramic powder so obtained was annealed at three different temperatures 500 °C, 700°C and 1000 °C respectively for 30 min each in microwave furnace in order to get a final product AlCrO3 of small crystallites. X-ray diffraction pattern confirms the formation of a phase pure AlCrO3 of a rhombohedral
crystal structure. The microstructure analyzed with SEM images describes small crystallites
which appear in self-assemblies of 200 nm average size. The TGA-DTA analysis of the as-prepared sample depicts a three-step thermal desorption in the range of 50-900 °C, while the DSC thermogram shows two distinct endothermic peaks at 86 °C and 506 °C followed by a weak exothermic peak at 448 °C. Band gaps of the AlCrO3 nanopowders annealed at 500 °C, 700 °C and 1000°C were estimated to be 4.3, 4.6 and 4.7 eV respectively by the light absorption spectra. The optical properties of these samples AlCrO3 confirmed that these can be good light-emitting ceramics, which can be applied in developing verities of optical and gas sensors, color pigments, and optical devices. Keywords: Deep ultra-violet masks, Optical materials, Synthesis, Nanomaterials.
Bibliography
1. E. Kim et al., Jpn. J. Appl. Phys. 39 (2000) 4820.
2. Y. Choi et al., Jpn. J. Appl. Phys. 41 (2002) 5805.
3. J. Kri`an et al., Acta Chim. Slov. 59 (2012) 163.

- by Akshay Jain
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- Supercapacitors (Chemistry), Activated Carbon, Hydrothermal Synthesis

This paper presents a control algorithm for utilizing a polymer electrolyte membrane fuel cell (PEMFC) as a main power source and storage devices (batteries and supercapacitors) for dc distributed system, particularly for future FC vehicle applications. This strategy is based on a standard dc bus voltage regulation, which takes into account the slowest dynamics of a fuel cell (FC) and the fastest dynamics of a supercapacitor bank. The principle is based on frequency approach that the FC dynamics are limited to avoid fuel starvation problems and the battery dynamics are also limited to reduce its stress. Its originality lies in using only the supercapacitor for supplying the energy required to achieve the dc bus voltage regulation, the battery for supplying the energy to keep the supercapacitor charged, and the FC for supplying the energy to keep the battery charged. To validate the proposed principle, a hardware system is realized by analog circuits and numerical calculations by dSPACE. Experimental results with small-scale devices (a PEMFC: 500-W, 50-A; a battery bank: 68-Ah, 24-V; and a supercapacitor bank: 292-F, 30-V) authenticate the excellent control algorithm during motor drive cycle.

- by Phatiphat Thounthong
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- Fuel Cells, Supercapacitors (Chemistry), Supercapacitors, Battery

Prussian blue-polypyrrole (PB-PPy) nanocomposite was deposited directly on glassy carbon electrode (GCE) by self-assembly (SA) based on multiple sequential adsorption of FeCl 3-K 3 [Fe(CN) 6 ] and pyrrole. This approach offers easy preparation of electrodes, which allows control of its electrochemical behaviour and sensitivity towards hydrogen peroxide (H 2 O 2). PB-PPy nanocomposite was also electrodeposited in one-pot aqueous solution for the comparison purpose in terms of morphology and its electrochemical and electrocatalytic behaviours. Field-emission scanning microscope (FESEM) presented the morphology SA PB-PPy nanocomposites was irregular whereas electrodeposited PB-PPy was in nanocubic framework. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed to study the electrochemical behaviour of fabricated PB-PPy films. The SA PB-PPy electrode with 10 deposition cycles demonstrated good sensing behaviour towards H 2 O 2 with good selectivity whereas capacitive property was observed when the deposition cycles increased to 20.

- by Pui Kee Lee and +1
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- Electrochemistry, Self Assembly, Electrochemical Sensors, Supercapacitors (Chemistry)

This paper reports the synthesis of continuous nanobelts, whose thickness is less than half of its pore diameter, of a material hybrid composing of nanograins of nickel oxide and cobalt oxide by electrospinning technique and their capacitive charge storage properties. While the constituent binary metal oxides (NiO and Co 3 O 4) formed solid cylindrical nanofibers the hybrid and a stoichiometric compound in the Ni-CoO system, i.e., spinel-type NiCo 2 O 4 , formed as thin nanobelts due to the magnetic interaction between nickel and cobalt ions. The nanobelts showed six-fold larger surface area, wider pores, and impressive charge storage capabilities compared to the cylindrical fibres. The hybrid nanobelts showed high specific capacitance (C S ~ 1250 F g −1 at 10 A g −1 in 6 M KOH) with high capacity retention, which is appreciably larger than found for the stoichiometric compound (~970 F g −1 at 10 A g −1). It is shown that the hybrid nanobelts have lower internal resistance (1.3 Ω), higher diffusion coefficient (4.6 × 10 −13 cm 2 s −1) and smaller relaxation time (0.03 s) than the benchmark materials studied here.

- by Midhun Harilal
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- Supercapacitors (Chemistry), Energy Storage

To fulfill the increasing energy demand, it is necessary to develop such an electrode material for pseudocapacitors having a high energy density, better cycle life, and potential for commercialization. Herein, we report an electrocodeposition technique to fabricate a high-performance V 2 O 5-PANi composite deposited on the metallic Nickel foam substrate as an electrode for pseudocapacitors. Ni foam serves as a porous and conductive framework and therefore shortens the ions diffusion pathway. Composite shows good performance than pure V 2 O 5 and PANi due to their synergistic effect. X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) analysis have confirmed the successful incorporation of metal oxide into the polymer backbone. Moreover, V 2 O 5-PANi composite exhibited a very wide voltage window of 2.5V (between-1 and 1.5V vs. SCE), the highest specific capacitance of 1115 F/g, and less charge transfer resistance. The ability to prepare composite electrodes with high performance via a binder-free electro-codeposition technique could open up new prospects for high energy density pseudocapacitors.

- by Zia-Ur-Rehman Qau
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- Materials Chemistry, Supercapacitors (Chemistry)

Herein, we delineate the one-pot preparation of nickel cobalt telluride nanorods (NiCoTe NRs) by the hydrothermal method using cetyltrimethylammonium bromide and ascorbic acid as reducing agents. The Ni 0.7 Co 0.3 Te NRs (NCT-1 NRs) were investigated with different characterization techniques, such as X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. Magnetic measurement shows the paramagnetic behavior of the prepared samples with the saturation magnetization. The NCT-1 NR-modified electrode is employed into the electrochemical hydrogen evolution reaction and hybrid supercapacitor applications. NCT-1 is demonstrated as a good electrocatalyst for the hydrogen evolution reaction at the onset potential of 244 mV versus reversible hydrogen electrode and delivered a high current density of 1 mA/cm 2. NCT-1 displays a specific capacity of 433 C/g at 0.5 A/g current density and 100% capacity retention, even after 5000 cycles. Furthermore, a hybrid asymmetric supercapacitor device was fabricated on the basis of NCT-1 as a positive electrode and orange-peel-derived activated carbon (OPC-700) as a negative electrode. It delivered a high energy density of 43 Wh/kg and a power density of 905 W/kg with long cyclic stability of 91% after 25 000 cycles.

- by Manikandan M
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- Supercapacitors (Chemistry), Water Splitting, Vsm (magnetic Properties)

This study presents an original control algorithm for a hybrid energy system with a renewable energy source, namely, a polymer electrolyte membrane fuel cell (PEMFC) and a photovoltaic (PV) array. A single storage device, i.e., a supercapacitor (ultracapacitor) module, is in the proposed structure. The main weak point of fuel cells (FCs) is slow dynamics because the power slope is limited to prevent fuel starvation problems, improve performance and increase lifetime. The very fast power response and high specific power of a supercapacitor complements the slower power output of the main source to produce the compatibility and performance characteristics needed in a load. The energy in the system is balanced by d.c.-bus energy regulation (or indirect voltage regulation). A supercapacitor module functions by supplying energy to regulate the d.c.-bus energy. The fuel cell, as a slow dynamic source in this system, supplies energy to the supercapacitor module in order to keep it charged. The photovoltaic array assists the fuel cell during daytime. To verify the proposed principle, a hardware system is realized with analog circuits for the fuel cell, solar cell and supercapacitor current control loops, and with numerical calculation (dSPACE) for the energy control loops. Experimental results with small-scale devices, namely, a PEMFC (1200 W, 46 A) manufactured by the Ballard Power System Company, a photovoltaic array (800 W, 31 A) manufactured by the Ekarat Solar Company and a supercapacitor module (100 F, 32 V) manufactured by the Maxwell Technologies Company, illustrate the excellent energy-management scheme during load cycles.

- by Phatiphat Thounthong
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- Photovoltaics, Fuel Cells, Supercapacitors (Chemistry), Fuel Cell

A B S T R A C T While the market for supercapacitors is rapidly growing due to their high power density, their low energy density compared to batteries represents a great barrier for the future of this technology. The poorly understood chemistry of electrode-electrolyte interfaces implies that there is substantial room for improvement through a careful design of the materials involved. Here we present a unique approach for improving the energy density of supercapacitors through redox additive-assisted electrocatalytic in situ regeneration of the electrode active materials. By utilizing a quinone-based redox electrolyte and a nanostructured conjugated polyaniline electrode, we continually regenerate the reactants, resulting in a redox supercapacitor having an extremely high energy density of 1091 Wh kg −1 (based on the total mass of the electrode active materials and the redox additive) and a high power density up to 196 kW kg −1. Considering the other outstanding properties of the polyaniline-naph-thoquinone system, such as extreme flexibility (96% capacity retention after bending at an angle of 180° for 1000 cycles), non-flammability, and excellent cycling stability (84% capacity retention after 7000 cycles at 35 A g −1), such a well designed in situ regeneration of the electrode active materials makes this method a very promising approach towards the development of state-of-the-art energy storage devices.

- by Anne Hathaway
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- Conducting Polymers, Nanotechnology, Supercapacitors (Chemistry), Nanoscience