Materials For Electrochemical Capacitors Research Articles

Novel electroactive nanocomposite of POAP for highly efficient energy storage and electrocatalyst: Electrosynthesis and electrochemical performance

In this work, we presented facile route for fabrication of poly ortho aminophenol (POAP) POAP and POAP/ZnO nanocomposite on the surface of the working electrode. The fractal dimension of nanocomposite films in the presence of counter ions was investigated. Surface morphology of the composite film was studied by surface microscopy techniques (SEM). The presence of ZnO in the films was confirmed by EDS analysis. The results indicate that a strong interaction exist at the interface of POAP and nano-ZnO. Different electrochemical methods including galvanostatic charge discharge experiments and cyclic voltammetry have been applied to study the system performance. This work introduces new nanocomposite materials for electrochemical redox capacitors with such advantages as the ease of synthesis, high active surface area and stability in an aqueous electrolyte. Furthermore, comparison with a Ni-POAP the Ni-POAP/ZnO electrode shows a better catalytic performance for the electrocatalytic oxidation of methanol in alkaline solution. It is observed that the in the presence of ZnO nanoparticles current density of electro-oxidation of methanol is almost constant in 400 cycles due to the stability of electrocatalyst in this cycle number and indicating that methanol reacted with the surface and no poisoning effect on the surface was observed.

Pulse electrosynthesis of novel wormlike gadolinium oxide nanostructure and its nanocomposite with conjugated electroactive polymer as a hybrid and high efficient electrode material for energy storage device

An effective approach for increasing the life cycle of pure p-type conductive polymers is combining conventional conductive polymers and nanomaterials to fabricate hybrid electrodes. In this paper, Gadolinium oxide (Gd2O3) has first been synthesized using pulse electrochemical approach. Hybrid POAP/Gd2O3 films have then been fabricated by POAP electropolymerization in the presence of Gd2O3 nanoparticles as active electrodes for electrochemical supercapacitors. Surface and electrochemical analyses have been used for characterization of Gd2O3 and POAP/Gd2O3 composite films. Different electrochemical methods including galvanostatic charge discharge experiments, cyclic voltammetry and electrochemical impedance spectroscopy have been applied to study the system performance. Specific capacitance, specific energy and specific power of the composite film are calculated 300F·g−1, 41.66Wh·kg−1 and 833.22W·kg−1 respectively. This work introduces new nanocomposite materials for electrochemical redox capacitors with such advantages as the ease of synthesis, high active surface area and stability in an aqueous electrolyte.

Facile preparation of MnO2@C composite nanorods for high-performance supercapacitors

Novel MnO2@C composite nanorods were successfully prepared by a facile solvothermal method. The results showed that a uniform carbon layer was formed around the MnO2 nanorods. The carbon layer provided a highly conductive pathway to boost the charge transport involved during the capacitance generation. The electrochemical properties of MnO2@C composite nanorods were investigated by cyclic voltammetry and galvanostatic charge–discharge. The composites as electrode materials of supercapacitors exhibited high specific capacitance (295 F/g) compared with MnO2 nanorods (149 F/g) with a wide operation window (0–1.0 V). The electrochemical impedance spectroscopic studies showed the charge-transfer resistance (Rct) of the MnO2@C composite nanorods (1.10 Ω) was much lower than that of pure MnO2 (2.53 Ω). Moreover, the MnO2@C composite nanorods exhibited excellent cycling behavior with no more than 5 % capacitance loss after 2000 cycles. These results indicated that the MnO2@C composite nanorods could be a promising electrode material for high-performance electrochemical capacitors.

Vanadium based materials as electrode materials for high performance supercapacitors

Abstract As a kind of supercapacitors, pseudocapacitors have attracted wide attention in recent years. The capacitance of the electrochemical capacitors based on pseudocapacitance arises mainly from redox reactions between electrolytes and active materials. These materials usually have several oxidation states for oxidation and reduction. Many research teams have focused on the development of an alternative material for electrochemical capacitors. Many transition metal oxides have been shown to be suitable as electrode materials of electrochemical capacitors. Among them, vanadium based materials are being developed for this purpose. Vanadium based materials are known as one of the best active materials for high power/energy density electrochemical capacitors due to its outstanding specific capacitance and long cycle life, high conductivity and good electrochemical reversibility. There are different kinds of synthetic methods such as sol-gel hydrothermal/solvothermal method, template method, electrospinning method, atomic layer deposition, and electrodeposition method that have been successfully applied to prepare vanadium based electrode materials. In our review, we give an overall summary and evaluation of the recent progress in the research of vanadium based materials for electrochemical capacitors that include synthesis methods, the electrochemical performances of the electrode materials and the devices.

Microstructural characterization of the cycling behavior of electrodeposited manganese oxide supercapacitors using 3D electron tomography

Manganese oxide has been investigated extensively as an electrochemical capacitor or supercapacitor electrode material. Manganese oxide is inexpensive to fabricate and exhibits relatively high capacitance values, i.e., in excess of 200 F g−1 in many cases; the actual value depends very much on the fabrication method and test conditions. The cycling behavior of Mn oxide, fabricated using anodic electrodeposition, is investigated using slice and view techniques, via a dual scanning electron microscope (SEM) and focused ion beam (FIB) instrument to generate three-dimensional (3D) images, coupled with electrochemical characterization. The initial as-fabricated electrode has a rod-like appearance, with a fine-scale, sheet-like morphology within the rods. The rod-like structure remains after cycling, but there are significant morphological changes. These include partial dissolution of Mn oxide followed by redeposition of Mn oxide in regions close to the substrate. The redeposited material has a finer morphology than the original as-fabricated Mn oxide. The Mn oxide coverage is also better near the substrate. These effects result in an increase in the specific capacitance.

Silica decorated on porous activated carbon nanofiber composites for high-performance supercapacitors

Abstract A hybrid of silica decorated on porous activated carbon nanofibers (ACNFs) is fabricated in the form of a web via electrospinning and an activation process as an electrode material for electrochemical capacitors in an organic electrolyte. The introduction of PhSiH 3 (PS) into the polyacrylonitrile (PAN) solution induces a porous ACNF structure containing silica nanoparticles (NPs) via the spontaneous sol-gel process of PS by steam in the subsequent physical activation process. These inorganic-organic hybrid composites of porous ACNF containing silica NPs show superior specific capacitance and energy density in electrochemical tests, along with good rate capability and excellent cycle life in an organic electrolyte, which is attributed to the combination of ACNF's high surface area and silica's hydrophilicity. The electrochemical performance decreases with increasing PS concentration, and this trend is consistent with the specific surface area results, which reveal the rapid formation of a double layer.

Nitrogen-doped hollow carbon spheres for supercapacitors application

Highly monodispersed nitrogen-doped hollow mesoporous carbon spheres (N-HMCSs) are prepared through a “silica-assisted” synthetic strategy with cetyltrimethylammonium bromide as cationic surfactant, 3-aminophenol/formaldehyde as carbon and nitrogen sources, tetraethyl orthosilicate as the structure-assistant agent. The particle sizes and shell thicknesses of the N-HMCSs can be easily tuned in the range of 130–290 nm and 17–42 nm, respectively, by simply modifying the ethanol-water volume ratio. The obtained N-HMCSs have high surface areas (750–1006 m2 g−1), large pore volumes (1.01–1.41 cm3 g−1), uniform mesoporous size of ∼3 nm, and high nitrogen loading content of 6.86 wt%. Due to these characteristics, the N-HMCSs exhibit a specific capacitance of 170 F g−1 at a current density of 1.0 A g−1 in 6 M KOH aqueous electrolyte. Besides, the capacitance still remains 94% after 5000 charge/discharge cycle, suggesting excellent cycling stability. The N-HMCSs may show promising prospects as electrode materials for electrochemical capacitors.

Effectively Improving Capacitive Performance of Three‐Dimensional Iron(III) Oxide Nanotube Arrays by Rationally Filling Mesopores with Polypyrrole

AbstractFe2O3 is a promising electrode material for electrochemical capacitors, but challenges remain in enhancing its capacitive performance. Herein, we effectively improved the capacitive properties of 3D Fe2O3 nanotube arrays by partly filling their mesopores with polypyrrole (PPy) through vapor‐phase polymerization. Although the filled PPy was only 9.7 wt %, the resulting hybrid Fe2O3/PPy arrays tripled the specific capacitance to 367 F g−1 at 1.0 A g−1, doubled their high rate capability (106 F g−1 at 10 A g−1), and exhibited good cycling stability at high current density. The capacitive performances of the hybrid arrays are among the best for Fe2O3‐based electrodes. It is believed that the partly filled mesopores not only increase the electronic conductivity and electroactivity of each hybrid nanotube but also avoid blocking the ion‐diffusion path. All the features allow the arrays to exhibit synergetic pseudocapacitive properties and to maintain stable and fast electrochemical kinetics. Our findings provide an efficient strategy to boost the electrochemical performances of transition‐metal oxide nanomaterials by rationally filling their mesopores with a small amount of a conductive polymer.

The Influence of Modification of the Surface of Nanoporous Carbon Material by the Oxides of Metals

Nitrogen containing carbon materials with metal of oxides (Fe, Ni, Co) prepared by thechemical precipitation method have been shown to be outstanding novel materials forelectrochemical capacitors. The electrochemical properties of the electrodes have been studied byconsidering the effect of the mole ratio of metals. Cyclic voltammetric measurements indicate thatnickel, cobalt and iron oxides increase specific capacity of electrochemical capacitors up to 260 F/gin 30% KOH electrolyte. Impedance studies show that the enhanced electrical properties and highfrequency response are attributed to the presence of Fe oxides.

Designed Formation of MnO2@NiO/NiMoO4 Nanowires@Nanosheets Hierarchical Structures with Enhanced Pseudocapacitive Properties

AbstractAlthough the preparation of hierarchical structures of transition‐metal oxides (TMOs) has been intensively studied in recent years, it is still a great challenge to synthesize hierarchical multicomponent TMOs. Herein, we report a versatile method to fabricate three‐component TMOs, namely MnO2@NiO/NiMoO4 nanowires@nanosheets hierarchical porous composite structures (HPCSs). Through a combination of a chemical‐solution‐based route and subsequent calcination, the as‐prepared MnOOH@NiMo precursor is topotactically transformed to MnO2@NiO/NiMoO4 HPCSs without notable structural variation. Ultrathin NiO/NiMoO4 nanosheets become interconnected into a honeycomb analogue with plentiful mesopores. Comparative results demonstrate the vital role of hexamethylenetetramine (HMT), and the solvent system in the formation of the MnOOH@NiMo precursor. When examined as electrode materials for electrochemical capacitors, MnO2@NiO/NiMoO4 HPCSs, with an areal mass loading as high as 5 mg cm−2, deliver a specific capacitance of 918 F g−1 at a current density of 1.0 A g−1 and maintain good cycling stability, which displays better electrochemical performance than electrodes composed of a single component. Note that a high‐voltage asymmetric supercapacitor is configured with MnO2@NiO/NiMoO4 HPCSs (still as high as 2 mg cm−2) against activated carbon, and exhibits outstanding cycling stability with a high energy density of 26.5 Wh kg−1 and a power density of 401 W kg−1. These analytical and experimental results clearly confirm the advantages of distinctive 3D multicomponent hierarchical architectures for engineering high‐performance electrochemical capacitors.

MnO2 decorated on electrospun carbon nanofiber/graphene composites as supercapacitor electrode materials

Composites made of MnO2 well-decorated on hierarchical porous carbon nanofiber/graphene (MnO2/HPCNF/G) have been successfully prepared through one-step electrospinning and thermal process as an electrode material for electrochemical capacitors. The presence of graphene in the MnO2/HPCNF/G composite fibers aids the uniform dispersion of the MnO2 particles and thus prevents their agglomeration. A graphene concentration of 5wt% offers larger accessible specific surface area and good conductivity due to the well-dispersed graphene in the composites, which increases their electrochemical properties by rapid ion transport and low resistance for charge diffusion in the electrolyte. The supercapacitor electrode prepared with 5wt% graphene shows high specific capacitance (210Fg−1 at a current density of 1mAcm−2), good rate capability (170Fg−1 retained at a high current density of 20mAcm−2), and high energy density (24–19Whkg−1, at power densities ranging from 400 to 10,000Wkg−1) in a 6M KOH aqueous solution. This enhanced electrochemical performance is ascribed to the synergistic effect between the double-layer capacitance of CNF/graphene and the high electrical conductivity and pseudocapacitive effect of the MnO2 particles.

Carbon Electrode Materials for Electrochemical Capacitors (review)

The known methods of synthesis of carbon materials for electric symmetric electrochemical capacitors are considered. Particular attention is drawn to the methods of exo- and endotemplate synthesis of carbon materials. It is concluded that further improving of the electrochemical properties of the electrodes will be connected with the search for qualitatively new ways of carbon materials activation that provide microcrystallites a graphite-likestate and affinity of their surface to the electrolytes.

Electrochemical behavior of pitch-based activated carbon fibers for electrochemical capacitors

In the present study, electrode materials for electrochemical capacitors were developed using pitch-based activated carbon fibers with steam activation. The surface and structural characteristics of activated carbon fibers were observed using scanning electron microscopy and X-ray diffraction, respectively. Pore characteristics were investigated using N2/77K adsorption isotherms. The activated carbon fibers were applied as electrodes for electrical double-layer capacitors and analyzed in relation to the activation time. The specific surface area and total pore volume of the activated carbon fibers were determined to be 1520–3230m2/g and 0.61–1.87cm3/g, respectively. In addition, when the electrochemical characteristics were analyzed, the specific capacitance was confirmed to have increased from 1.1F/g to 22.5F/g. From these results, it is clear that the pore characteristics of pitch-based activated carbon fibers changed considerably in relation to steam activation and charge/discharge cycle; therefore, it was possible to improve the electrochemical characteristics of the activated carbon fibers.

Rational design of new electrolyte materials for electrochemical double layer capacitors

Abstract The development of new electrolytes is a centerpiece of many strategies to improve electrochemical double layer capacitor (EDLC) devices. We present here a computational screening-based rational design approach to find new electrolyte materials. As an example application, the known chemical space of almost 70 million compounds is investigated in search of electrochemically more stable solvents. Cyano esters are identified as especially promising new compound class. Theoretical predictions are validated with subsequent experimental studies on a selected case. These studies show that based on theoretical predictions only, a previously untested, but very well performing compound class was identified. We thus find that our rational design strategy is indeed able to successfully identify completely new materials with substantially improved properties.

Biomass-Derived Carbonaceous Cathodes for Sustainable Lithium-Ion Storage

Biomass derived carbonaceous materials have been widely used as active electrode materials for electrochemical double layer capacitors (EDLCs) or hybrid capacitors. However, redox-active properties of these carbonaceous materials have not been explored. Here, for the first time, we demonstrated that carbonaceous materials from earth-abundant glucose via a hydrothermal carbonization (HTC) process have redox-active properties with lithium ions. Morphologies of the carbon materials can be controlled from spheres to sheets by using graphene oxide as a template. When used as cathodes in lithium ion cells, both the carbon spheres and sheets showed high redox potentials in the voltage range of 2.2 - 3.7 V vs. Li. Freestanding, flexible composite electrodes consisting of the hydrothermal carbon materials and few-walled carbon nanotubes delivered high specific capacities up to ~155 mAh/gelectrode for carbon spheres and ~176 mAh/gelectrode for carbon sheets, respectively. These carbon materials exhibited no obvious capacity fade up to 10,000 cycles, proposing to be promising cathodes for lithium-ion batteries or capacitors. The simple, scalable HTC process converting earth-abundant biomass source into high performance cathode materials enables the development of high-performance lithium-ion storage systems, which can provide a sustainable solution towards clean and renewable energy storage.

Enhanced performance of HRGO-RuO2 solid state flexible supercapacitors fabricated by electrophoretic deposition

Ruthenium oxide (RuO2) nanomaterials exist as excellent materials for electrochemical capacitors. However, they tend to suffer from low mechanical flexibility when cast into films, which makes them unsuitable for flexible device applications. Herein, we report an environmentally friendly and solution-processable approach to fabricate RuO2-based composite electrodes for flexible solid state supercapacitors. The composites were produced by anchoring RuO2 nanoparticles onto holey reduced graphene oxide (HRGO) via a sol-gel method, followed by the electrophoretic deposition (EPD) of the material into thin films. The uniform anchoring of ultra-small RuO2 nanoparticles on the two-dimensional HRGO sheets resulted in HRGO-RuO2 hybrid sheets with excellent mechanical flexibility of HRGO. EPD induced a layer-by-layer assembly mechanism for the HRGO-RuO2 hybrid sheets, which resulted in a binder-free, flexible electrode. The obtained HRGO-RuO2 flexible supercapacitors exhibited excellent electrochemical capacitive performance in a PVA-H2SO4 gel electrolyte with a specific capacitance of 418 F g−1 and superior cycling stability of 88.5% capacitance retention after 10,000 cycles. In addition, these supercapacitors exhibited high rate performance with capacitance retention of 85% by increasing the current density from 1.0 to 20.0 A g−1, and excellent mechanical flexibility with only 4.9% decay in the performance when bent 180°.

Nanocomposite of p-type conductive polymer/functionalized graphene oxide nanosheets as novel and hybrid electrodes for highly capacitive pseudocapacitors

An effective approach for increasing the life cycle of poly ortho aminophenol (POAP) as a p-type conductive polymers is combining conventional conductive polymers and nanomaterials to fabricate hybrid electrodes. In this paper, functionalized graphene oxide (FGO) has first been synthesized using a chemical approach. Hybrid POAP/FGO films have then been fabricated by POAP electropolymerization in the presence of FGO nanoparticles as active electrodes for electrochemical supercapacitors. Based on the atomic scale study results, it seems that H3PO4− oxygen atoms and terminal pyridine ring nitrogen atoms play a crucial role in the intramolecular charge and energy transfer in the FGO molecular systems. Theoretical studies, surface and electrochemical analyses have been used for characterization of POAP/FGO composite films. Different electrochemical methods including galvanostatic charge discharge experiments, cyclic voltammetry and electrochemical impedance spectroscopy have been applied to study the system performance. This work introduces new nanocomposite materials for electrochemical redox capacitors with such advantages as the ease of synthesis, high active surface area and stability in an aqueous electrolyte.

Recent progress in flexible energy storage materials for lithium-ion batteries and electrochemical capacitors: A review

Abstract

Anion-Exchange Formation of Hollow NiCo2 S4 Nanoboxes from Mesocrystalline Nickel Cobalt Carbonate Nanocubes towards Enhanced Pseudocapacitive Properties.

An efficient anion-exchange protocol was investigated for the controllable fabrication of hollow NiCo2 S4 nanoboxes (NBs) from mesocrystalline nickel cobalt carbonate nanocubes as promising pseudocapacitive materials for electrochemical capacitors. The underlying processes of the formation of the hollow architecture were systematically investigated. Originating from the unique structural and compositional advantages, the resultant hollow NiCo2 S4 NB electrode with a loading of 5 mg cm2 delivered a large specific capacitance of 777 F g-1 at a high rate of 4 A g-1 in a three-electrode configuration with 6 m KOH as electrolyte. Furthermore, an asymmetric device constructed with the hollow NBs and activated carbon (AC) as positive and negative electrodes, respectively, showed extraordinary supercapacitance within an electrochemically operating voltage window from 0.0 to 1.5 V. The unique AC//NiCo2 S4 NB hybrid capacitor exhibited a large specific energy density (active mass normalized) of approximately 17.1 W h kg-1 at a high power density of 2250 W kg-1 , and desirable cycling durability with approximately 75 % specific capacitance retention after 5000 consecutive cycles at a current rate of 2 A g-1 . These electrochemical investigations strongly indicated that the as-fabricated hollow NiCo2 S4 NBs can be elegantly utilized as powerful candidates for advanced electrode platforms.

Enhanced supercapacitive performance of manganese oxides doped two-dimensional titanium carbide nanocomposite in alkaline electrolyte

Two-dimensional transition metal carbides MXenes, one of promising electrode materials for electrochemical capacitors (ECs), process unique layered structure, high surface area, remarkable chemical stability, and electrical conductivity for energy storage. However, the low capacity of MXene electrodes limits their further application in ECs. Herein, with excellent electrochemical performance of MnO2, Ti3C2 nanosheets decorated with MnO2 nanoparticles were synthesized through a simple liquid phase precipitation method and heat treatment process, and were subsequently employed to the electrode for ECs. TEM and XRD results demonstrate that MnO2 nanoparticles, about 20–40 nm in diameter size, have been homogeneously inserted into the interlamination of Ti3C2 matrix for cation intercalation. Due to the synergistic effect between MnO2 and Ti3C2 matrix, the nanocomposite exhibits a superior areal capacitances of 377 mF cm−2 at scan rate of 5 mV s−1, which is significantly higher than that of Ti3C2 (306 mF cm−2), and shows excellent cycling stability with capacitance retaining 95% after 5000 cycles. Even at a high scan rate of 200 mV s−1 (310 mF cm−2), MnO2–Ti3C2 nanocomposite displays a high rate capability of 83%. These results demonstrate that MnO2–Ti3C2 nanocomposites offer fascinating potential for high-performance ECs.