Use In Electrochemical Capacitors Research Articles

Ion Intercalation into 2D Titanium Carbide Based MXenes: Applications for Electrochemical Capacitors

We recently produced a new 2-D material, viz. Ti3C2, by selectively etching aluminium from a MAX phase Ti3AlC2 and labelled it MXene. MXenes represents a large family of transition metal carbides and carbonitrides, not just a single phase. Unlike graphene, whose chemistry is restricted to carbon, MXenes allow a variety of chemical compositions and are establishing themselves as a new class of two-dimensional materials. MXenes possess good in-plane conductivity, which in combination with the rich surface chemistry makes them attractive for electrical energy storage applications. However while potential of MXenes as anode materials for Li-ion batteries has already been shown, their use in electrochemical capacitors has not been explored.Herein, we report on the intercalation of Li+, Na+, Mg2+, K+, NH4 +, and Al3+ ions between the 2D Ti3C2Tx layers. In most cases, the cations intercalated spontaneously. The intercalation of some ions, notably Al3+, can be promoted electrochemically. We also report on intercalation-induced high volumetric capacitance of flexible Ti3C2Tx paper electrodes. This study provides a basis for exploring a large family of 2D carbides and carbonitrides in electrochemical energy storage applications using single- and multivalent ions.References.Lukatskaya, M.R., et al., Cation Intercalation and High Volumetric Capacitance of Two-Dimensional Titanium Carbide. Science, 2013. 341(6153): p. 1502-1505.

Surface modified carbon cloth for use in electrochemical capacitor

The paper reports enhanced power densities for electrochemical capacitor through grafting carbon nanotubes (CNTs) onto the surface of activated carbon cloth (ACC). The surface-modified ACCs were first examined for their material properties and then evaluated for their electrode performance such as capacitance, equivalent series resistance, energy density, and power density. Improved electrochemical performance was obtained due to the surface modification by CNTs. In particular, the CNTs lower the contact resistance and therefore increase the power density of the electrochemical capacitor. Furthermore, we show that through such a surface modification, the specific capacitance can be increased from 108 to 117F/g, i.e., an 8.3% increase, the energy density can be increased from 16.7 to 17.64Wh/kg, i.e., a 5.4% increase, or the power density can be increased from 4.8 to 11.3kW/kg, i.e., a 135% increase. To our best knowledge, the energy density and power density of a electrochemical capacitor having CNT-grafted ACC electrode have not been reported. Also, a 70% retention at a scan rate of 500mVs−1 and a long cycle life of 20,000 cycles at a scan rate of 200mVs−1 are demonstrated.

Mass Transport Properties of Manganese Dioxide Phases for Use in Electrochemical Capacitors: Structural Effects on Solid State Diffusion

The solid state mass transport characteristics of various manganese dioxide phases has been examined with a focus on their use in electrochemical capacitors. The phases examined included γ-MnO2 (electrolytic manganese dioxide), β-MnO2 (Pyrolusite), Ramsdellite, δ-MnO2 (Birnessite), α-MnO2 (Cryptomelane) and λ-MnO2. Diffusion within each phase was examined using electrochemical impedance spectroscopy (EIS) and step potential electrochemical spectroscopy (SPECS). A√D (where A is surface area and D is the diffusion coefficient) decreases with depth of discharge, and is also affected by the phase of manganese dioxide studied, with γ-MnO2 exhibiting the highest A√D value. Overall, values of A√D varied between 3 × 10−8 – 2 × 10−10 m3/s1/2/g, which is comparable with literature data. These results also provide information on the kinetics of lattice expansion and contraction which occurring during cycling. High surface area phases such as γ-MnO2, Ramsdellite and Cryptomelane, showed significant hysteresis in lattice contraction which is attributed to the diffusion of protons through surface domains. Low surface area phases (Pyrolusite and λ-MnO2) did not display this hysteresis, suggesting that proton diffusion occurs predominantly in the bulk of the material. No direct correlation between mass transport and specific capacitance is observed, suggesting that other material properties contribute to specific capacitance.

Microporous carbons finely-tuned by cyclic high-pressure low-temperature oxidation and their use in electrochemical capacitors

Microporous carbons with a finely controlled porosity have been prepared from non-porous chars by cyclic oxidation/thermal desorption and further used in supercapacitor electrodes working in organic medium. The described activation method is shown to be effective for at least two types of non-porous carbons derived from sucrose and cellulose. The low temperature oxidation is realized by H2O2 at 200°C and followed by thermal desorption of the surface functional groups at 900°C under nitrogen flow. The porosity-forming procedure involves 4–5 oxidation/decomposition cycles, thus allowing a gradual adjustment of average pore size to that of ions making up the standard organic electrolyte −1molL−1 TEA+ BF4− in acetonitrile. The build-up of pore volume during the initial cycles proceeds essentially through the opening/formation and deepening of narrow micropores (L0≈0.8nm), whereas a slight pore widening appears to be the main outcome of further cycles. Due to the low burn-off of the overall process, the carbons are shown to form much denser coatings (0.71gcm−3) than a steam-activated carbon used in industrial supercapacitors (0.52gcm−3).

New application and electrochemical characterization of a nickel-doped mesoporous carbon for supercapacitors

A novel electrode of nickel-doped mesoporous carbon (NMC) is prepared from furfuryl alcohol and firstly developed for use in electrochemical capacitors. The electrochemical performance of NMC/AC capacitor is systematically investigated and characterized by BET and BJH methods for determining surface area and pore size distribution, respectively. This new NMC/AC shows a high specific capacitance, high energy and power density due to its large surface area and bulk conductivity. Its electrochemical characteristics are investigated through cyclic voltammetry (CV), electrochemical impedance spectroscopy and charge–discharge (C/D) tests. The NMC/AC has a specific capacitance of 144.3 Fg −1, higher than that of a pure activated carbon (AC)-based EDLC (ca. 105 Fg −1). It can be a promising candidate for a new energy storage material for supercapacitor.

MnO2/TiN heterogeneous nanostructure design for electrochemical energy storage

MnO(2)/TiN nanotubes are fabricated using facile deposition techniques to maximize the surface area of the electroactive material for use in electrochemical capacitors. Atomic layer deposition is used to deposit conformal nanotubes within an anodic aluminium oxide template. After template removal, the inner and outer surfaces of the TiN nanotubes are exposed for electrochemical deposition of manganese oxide. Electron microscopy shows that the MnO(2) is deposited on both the inside and outside of TiN nanotubes, forming the MnO(2)/TiN nanotubes. Cyclic voltammetry and galvanostatic charge-discharge curves are used to characterize the electrochemical properties of the MnO(2)/TiN nanotubes. Due to the close proximity of MnO(2) with the highly conductive TiN as well as the overall high surface area, the nanotubes show very high specific capacitance (662 F g(-1) reported at 45 A g(-1)) as a supercapacitor electrode material. The highly conductive and mechanically stable TiN greatly enhances the flow of electrons to the MnO(2) material, while the high aspect ratio nanostructure of TiN creates a large surface area for short diffusion paths for cations thus improving high power. Combining the favourable structural, electrical and energy properties of MnO(2) and TiN into one system allows for a promising electrode material for supercapacitors.

Biomolecule-assisted hydrothermal approach towards synthesis of ultra-thin nanoporous α-Co(OH)2 mesocrystal nanosheets for electrochemical capacitors

We describe here a novel biomolecule-assisted hydrothermal strategy for the synthesis of two-dimensional ultra-thin α-Co(OH)2 mesocrystal nanosheets. These unique ultra-thin α-Co(OH)2 mesocrystal nanosheets have good electrical conductivity and are highly attractive for application in electrochemical capacitors due to many of their properties, such as high crystallinity with small particle size, large specific surface area, high porosity as well as good handling. Impressively, a specific capacitance (SC) of 506 F g−1 can be achieved by the nanoporous α-Co(OH)2 mesocrystals at 10 mA cm−2 (ca. 1.33 A g−1), and even 427 F g−1 at 40 mA cm−2 (ca. 5.33 A g−1), indicating their great ability to deliver a large SC and high electrochemical utilization at high rates. Moreover, a low SC degradation of ca. 3% after 2000 continuous charge–discharge cycles at a current density of 5.33 A g−1 reveals their good electrochemical stability at high rates, which is of great importance for their practical application. The synthesis strategy reported here is a simple and cost-effective means of performing the large-scale production of α-Co(OH)2 mesocrystal nanosheets with good electrochemical capacitance, and is expected to be applied in the preparation of other metal hydroxides or oxides with similar microstructures and electrochemical properties for use in electrochemical capacitors or even for use in Li-ion batteries.

Mesoporous carbons derived from citrates for use in electrochemical capacitors

Mesoporous carbons derived from citrates for use in electrochemical capacitors

Mesoporous carbons derived from citrates for use in electrochemical capacitors

Two mesoporous carbons were prepared by simple pyrolysis of commercial magnesium or barium citrate and tested as electrode materials for electrochemical double-layer capacitors (EDLCs), denoted MgC and BaC, respectively. The as-prepared carbon materials were characterized by N 2 adsorption, scanning electron microscopy and Fourier transform infrared spectrometry. Nitrogen adsorption measurements demonstrated that the porosity of the prepared carbons was related to the type of metal cation. BaC possesses a typical bimodal pore size distribution (PSD) at 3.8 and about 15 nm, while MgC was between small-size mesoporous and microporous. The carbons were tested as electrode materials using different electrochemical means such as cyclic voltammetry and constant current charge-discharge. Very high specific capacitance (180 F·g −1 for MgC and 171 F·g −1 for BaC) was achieved in an ionic liquid electrolyte. BaC proved to be an excellent electrode material with a high rate performance for EDLC application and exhibited an energy density up to 53.3 Wh·kg −1 and a high maximum specific power density of 20 kW·kg −1 in IL electrolyte. The good capacitive performance of BaC is attributed to its bimodal PSD and hydrophilic surface properties.

Cycle stability of birnessite manganese dioxide for electrochemical capacitors

A combination of step potential electrochemical spectroscopy (SPECS) and electrochemical impedance spectroscopy (EIS) has been used to examine the electrochemical cycling behaviour of a well-characterized birnessite-phase manganese dioxide sample for use in electrochemical capacitors. The resistance and interfacial properties of the macroscopic electrode were found to be irreversible with cycling. However, the corresponding properties for the individual particles were more reversible, although they did show substantial hysteresis in their behaviour during cycling. This behaviour was discussed in terms of the structural, conductivity and morphological characteristics of the birnessite at different depths of discharge.

Enhanced actuation of PPy/CNT hybrid fibers using porous structured DNA hydrogel

A high-surface-area material has recently attracted interest in actuator systems. We report on improved performance of the simultaneous electrochemical linear actuation of conducting polymer (CP)/carbon nanotube (CNT) hybrid fibers using porous structured deoxyribonucleic acid (DNA) hydrogels. It was deduced that individual DNA-wrapped CNTs had efficiently doped the PPy on its inner and outer surface through the association of PPy with the DNA via a supramolecular interaction. To assess the potential of the PPy/DNA/CNT hybrid fibers for use in electrochemical capacitors and actuators, we showed that the redox response of the hybrid fibers was improved by the addition of DNA to the PPy/CNT film. The values of the measured electrochemical capacitance (∼371 F/g in a lithium bis(trifluoromethylsulfonyl)imide aqueous solution, where the joint mass of PPy, DNA, and CNT was considered) were higher than those of previous CNT/PPy composite films with a controlled pore size (∼250 F/g). The fibers showed actuation stability with an expansion and contraction of ∼4.41% under a low potential (±1 V). DNA/PPy/CNT hybrid fibers will form the basis for new intelligent materials for applications such as bio-artificial muscles.

Synthesis and Characterization of Cryptomelane for use in Electrochemical Capacitors

Cryptomelane was synthesized by a solid state with low temperature technique and tested as active material for an electrochemical capacitor. X-ray diffraction peaks are in good agreement with the standard pattern of tetragonal cryptomelane. Surface area and pore sized distribution shows 292 m2/g and 6.12nm respectively which show a mesopore structure. Two different aqueous electrolytes were tested K2SO4 0.1M and Na2SO4 0.1M both of them present an ideal capacitive behavior, being more interesting capacitance values with Na2SO4 0.1M electrolyte. Further testing using this electrolyte with different scan rates presents capacitor behavior under 5mV/s.

Manganese Oxides Prepared by Ultrasonication and Their Use in Electrochemical Capacitors

not Available.

R&D considerations for the performance and application of electrochemical capacitors

Research and development (R&D) of electrochemical capacitors is discussed in terms of material characteristics and device performance and testing. Various chemistries and technologies being developed are identified and the status of and problems associated with each of the technologies are discussed. The technologies considered include those using various types of carbon and pseudo-capacitive materials such as metal oxides. What is needed to make the various electrochemical capacitor technologies cost competitive with batteries for different applications and markets is also considered. Electrochemical capacitors (especially double-layer capacitors) are intrinsically high power devices of limited energy storage capability and long cycle life; batteries are basically energy storage devices, which can be designed and used as relatively high power devices with a sacrifice in useable energy storage capacity. Both electrochemical capacitors and high power batteries are designed with thin electrodes, materials having nano-scale characteristics, and a minimum resistance. Much of the research on electrochemical capacitors is concerned with increasing their energy density with the minimum sacrifice in power capability and cycle life for deep discharges. Of special interest has been the development of advanced carbons with specific capacitance (F/g) significantly greater than the present values of 150–200 F/g in aqueous electrolytes and 80–120 F/g in organic electrolytes. Cost continues to be a major obstacle to the development of large markets for electrochemical capacitors particularly for vehicle applications. The development of lower cost carbons appropriate for use in electrochemical capacitors is underway by several speciality carbon suppliers. The goal is to reduce the cost of the carbon to $10–15/kg.

In Situ Mn K-edge X-ray Absorption Spectroscopy Studies of Electrodeposited Manganese Oxide Films for Electrochemical Capacitors

In situ Mn K-edge fluorescence X-ray absorption spectroscopy (XAS) was used to analyze the manganese oxides electrodeposited on a porous carbon paper substrate for use in electrochemical capacitors in order to determine the local and electronic structural changes in the material as a function of the applied potential in a neutral electrolyte. Within the potential range from +0.1 to +0.8 V vs SCE (reversible region), the cyclic voltammogram (CV) showed ideal capacitive characteristics. On the other hand, large current tails were observed at near both ends of the potential window in the CV when the upper and lower potential limits were expanded to +1.0 and −0.3 V vs SCE (irreversible region), which is indicative of an irreversible reaction. According to the in situ X-ray absorption near-edge structure (XANES) results, the capacitive currents of the manganese oxides in 2 M KCl in the reversible region originated from the Faradaic pseudocapacitance. The average oxidation state and local structure of the manga...

Electrochemical characteristics and impedance spectroscopy studies of nano-cobalt silicate hydroxide for supercapacitor

Cobalt silicate hydroxide (Co 3[Si 2O 5] 2[OH] 2) was prepared by chemical method for use in electrochemical capacitors. X-ray diffraction (XRD) and transmission electron microscopy (TEM) tests indicate that the material was pure hexagonal phase with uniform nanometer size distribution. Cyclic voltammeter (CV) and galvanostatic charge/discharge measurements show that the cobalt silicate hydroxide-based electrode has stable electrochemical capacitor properties between potential range of 0.1–0.55 V with a maximum specific capacitance of 237 F g −1 in alkaline solution and 95% of capacity efficiency was reached after 150 cycles. Electrochemical impedance spectra (EIS) investigation illustrates that the capacitance of the test electrode was mainly consisted of pseudo-capacitance, which was caused by underpotential deposition of H 3O + at the electrode surface.

Manganese Oxide Film Electrodes Prepared by Electrostatic Spray Deposition for Electrochemical Capacitors

Porous manganese oxide thin film electrodes were prepared for use in electrochemical capacitors by electrostatic spray deposition. The as-prepared manganese oxide film showed ideal capacitive behavior after potential cycling within the range of to 0.9 V (vs saturated calomel electrode) in a 0.1 M electrolyte. Analysis of the X-ray diffraction, X-ray absorption spectroscopy, and Raman scattering data during the cycling showed that the as-prepared crystalline film was electrochemically oxidized to pseudocapacitive amorphous film by the potential cycling. The effects of the film thickness and heat treatment temperature of the as-prepared manganese oxide films on the electrochemical properties were also investigated. The specific capacitance of the electrochemically oxidized amorphous films was dependent on the film thickness, rather than on the heat treatment of the as-prepared oxide films. The specific capacitance decreased from 330 to as the mass (i.e., thickness) of the oxide was increased from 18 to .

Preparation of lead ruthenium oxide and its use in electrochemical capacitor

Lead ruthenium oxide, Pb 2Ru 2O 6.5 was formed by solid-state reaction method at elevated temperature. The Pb 2Ru 2O 6.5 was examined with X-ray diffraction (XRD), scanning electron microscopy (SEM), thermo gravimetric analysis (TGA), and Brunauer, Emmett and Teller (BET) techniques. The lead ruthenium oxide calcined at and above 400 °C shows crystalline Pb 2Ru 2O 6.5 phase. Using methods of cyclic voltammetry and charge–discharge in a solution of 0.5 M H 2SO 4, we obtained a maximum specific capacitance of 160 F g −1 for lead ruthenium oxide calcined at 400 °C. This value is higher than the value obtained with chemical precipitation method of Pb 2Ru 2O 6.5 electrode

Preparation of lead ruthenium oxide and its use in electrochemical capacitor

Preparation of lead ruthenium oxide and its use in electrochemical capacitor

NiO-based composite electrode with RuO 2 for electrochemical capacitors

NiO/RuO 2 composite materials were prepared for use in electrochemical capacitors (ECs) by co-precipitation method followed by heat treatment. X-ray diffraction (XRD) spectra indicated that no new structural materials were formed and ruthenium oxide particles were coated by NiO particles. RuO 2 partly introduced into NiO-based electrode had improved its electrochemical performance and capacitive properties by using electrochemical measurements. A maximum specific capacitance of 210 F/g was obtained for NiO-based composite electrode with 10 wt.% RuO 2 in the voltage range from −0.4 to 0.5 V in 1 mol/l KOH solution. By comparison of effect of modified modes on the specific capacitance, chemically modified composite electrodes had more stable cycling properties than those of physically modified electrodes. After 200 cycles, specific capacitance of NiO-based chemical composite electrode with 5 wt.% RuO 2 kept 95% above, while that of physical electrode was only 79% of initial specific capacitance.