Active Material For Supercapacitors Research Articles

Insights into the Influence of Key Preparation Parameters on the Performance of MoS2/Graphene Oxide Composites as Active Materials in Supercapacitors

Advances in energy storage and energy conversion play an essential role nowadays because the energy demands are becoming greater than ever. To overcome the actual performances of the materials used to build supercapacitors, a combination of transition metal dichalcogenides (TMDCs) and graphene oxide (GO) or reduced graphene oxide (rGO) as graphene-based structures are often studied for their excellent properties, such as high specific area and good electrical conductivity. Nevertheless, synthesis pathways and parameters play key roles in obtaining better materials as components for supercapacitors with higher technical performances. Driven by the desire to understand the influence of the structural and morphological particularities on the performances of supercapacitors based on MoS2/graphene oxide (GO) composites, a survey of the literature was performed by pointing out the alterations induced by different synthesis pathways and key parameters to the above-mentioned particularities.

Investigation of the electrochemical behavior of ZIF-67 @ carbon nanotube and graphene oxide as potential electrode active materials for supercapacitors

Investigation of the electrochemical behavior of ZIF-67 @ carbon nanotube and graphene oxide as potential electrode active materials for supercapacitors

Quantum Capacitance through Molecular Infiltration of 7,7,8,8-Tetracyanoquinodimethane in Metal-Organic Framework/Covalent Organic Framework Hybrids.

Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) have been extensively investigated during the last two decades. More recently, a family of hybrid materials (i.e., MOF@COF) has emerged as particularly appealing for gas separation and storage, catalysis, sensing, and drug delivery. MOF@COF hybrids combine the unique characteristics of both MOF and COF components and exhibit peculiar properties including high porosity and large surface area. In this work, we show that the infiltration of redox-active 7,7,8,8-tetracyanoquinodimethane (TCNQ) molecules into the pores of MOF@COF greatly improves the characteristics of the latter, thereby attaining high-performance energy storage devices. Density functional theory (DFT) calculations were employed to guide the design of a MOF@COF-TCNQ hybrid with the TCNQ functional units incorporated in the pores of MOF@COF. To demonstrate potential application of our hybrids, the as-synthesized MOF@COF-TCNQ hybrid has been employed as an active material in supercapacitors. Electrochemical energy storage analysis revealed outstanding supercapacitor performance, as evidenced by a specific areal capacitance of 78.36 mF cm-2 and a high stack volumetric energy density of 4.46 F cm-3, with a capacitance retention of 86.4% after 2000 cycles completed at 0.2 A cm-2. DFT calculation results strongly indicate that the high capacitance of MOF@COF-TCNQ has a quantum capacitance origin. Our liquid-phase infiltration protocol of MOF@COF hybrids with redox-active molecules represents a efficacious approach to design functional porous hybrids.

Synthesis of graphene-like porous carbon from biomass for electrochemical energy storage applications

Graphene-like porous carbon (GLC) was synthesized from walnut shell (WSh) by carbonization and thermochemical activation process. The obtained samples of graphene-like porous carbon based on walnut shell (GLC-WSh) were characterized by physicochemical analysis in order to optimize the synthesis process. The optimum condition of GLC-WSh synthesis was determined to meet the basic requirements for various applications such as an active material for supercapacitors, lithium-ion battery, as energy-intensive additives in order to increase the efficiency of high-energy rocket fuels, and as a membrane for desalination of seawater. The Raman spectra confirmed the presence of few-layer graphene in GLC-WSh with on average number of 5–7 graphene layers. The specific surface area (SSA) was determined using nitrogen adsorption/desorption analysis. The SSA is 2800 m2 g−1 according to Brunauer-Emmett-Teller method. The mass yield of GLC-WSh from the initial mass of the WSh was 21%. The synthesized GLC-WSh powder was applied as an active material for an electrochemical double layer capacitor. Electrochemical characterization showed a high specific capacitance value of 263 F/ g and columbic efficiency of 99.4% at a gravimetric current density of 1000 mA/ g.

N, Se doped flower-shaped hollow carbon spheres to enhance performance in supercapacitor

Designing energy storage devices assembled with precious metal-free active materials is the key to developing a low-carbon economy and sustainable energy supply. Therefore, we take Se as the guest and porous nitrogen-modified flower-shaped hollow carbon spheres (NFHC) as the main body to form Se-NFHC. The performance as an active material in supercapacitors is explored. The results show that the specific capacitance of the material reaches 774 F g−1, and after 6000 constant current charge–discharge tests, it can still maintain 95.4% specific capacitance, which provides selectivity for materials in the field of energy storage.

Solution Processing of Topochemically Converted Layered WO3 for Multifunctional Applications

Solution processing of nanomaterials is a promising technique to utilize in various applications owing to its simplicity and scalability. However, the studies on liquid phase exfoliation (LPE) of tungsten oxide (WO3) are limited, unlike others due to lack of commercial availability of bulk WO3 with layered structures. Herein, we report a one-step topochemical synthesis approach to obtain bulk layered WO3 from commercially available layered tungsten disulfide (WS2) by optimizing various parameters like reaction time and temperature. Detailed microscopic and spectroscopic techniques have confirmed the conversion process. Further, LPE has been carried out on topochemically converted bulk layered WO3 in twenty-two different solvents, and among studied solvents isopropyl alcohol-water (1:1) co-solvent system appears to be the best. This indicates that the possible values of surface tension and Hansen solubility parameters for bulk WO3 could be close to that of co-solvent system. The obtained WO3 dispersions in a low boiling point solvent enable to fabricate thin films with varying thickness using spray deposition method. The obtained thin films are used as active materials in supercapacitors without any conductive additives/binders and exhibited an areal capacitance of 31.7 mF cm-2 at 5 mV s-1. The photoelectrochemical measurements reveal that these thin films can also be used as photoanodes for photoelectrochemical water oxidation.

Systematic synthesis of ZIF-67 derived Co3O4 and N-doped carbon composite for supercapacitors via successive oxidation and carbonization

Zeolitic imidazolate framework-67 (ZIF67) composed of cobalt metal and 2-methylimidazole is one of the attractive metal organic frameworks for energy storage, due to the possible formation of cobalt oxide and N-doped graphite via oxidation and carbonization processes. It is the first time to develop cobalt oxide and N-doped graphite in one ZIF67 derivative as active material for supercapacitor (SC), which stores charges via redox reactions and electric double-layered behaviors. Six active materials with careful designs are constructed, including carbonized ZIF67 (C67), oxidized C67 (C67/O), oxidized ZIF67-covered C67 (C67/O67), oxidized ZIF67 (O67), carbonized O67 (O67/C), and carbonized ZIF67-covered O67 (O67/C). Detailed formation process and mechanism of these active materials are provided. The highest areal capacitance (CA) of 332.3 mF/cm2 at 20 mV/s is obtained for C67/O electrode, due to the suitable composition of Co3O4 and N-doped graphite as well as the particle-assembled polyhedron structure with high porosity. The asymmetric SC composed of C67/O electrodes shows a potential window of 1.0 V and the maximum energy density of 0.87 Wh/kg at power density of 150 W/kg. Excellent cycling stability with CA retention of 100% and Coulombic efficiency of 100% after 4000 times repeatedly charge/discharge process is also achieved for this asymmetric SC.

Liquid-Exfoliated Molybdenum Telluride Nanosheets for High-Performance Supercapacitors

Two-dimensional (2D) MoTe2 nanomaterials have emerged as a promising candidate for constructing excellent supercapacitors due to their high capacitive performance. Recent studies have revealed that MoTe2 has broad prospects as an active material in supercapacitors, although its strict requirements in terms of the external environment and complex preparation process remain serious obstacles to its practical application. Toward this end, MoTe2 nanosheets (NSs) were prepared by a facile and inexpensive liquid-phase exfoliation approach for the fabrication of MoTe2 electrodes. The results show that the MoTe2 NSs exhibit significantly improved electrochemical performance, with a specific capacitance (859 F g−1) more than three times that of bulk MoTe2 (271 F g−1) at a current density of 1 A g−1. In addition, the MoTe2-based electrode showed excellent cycle stability and maintained excellent specific capacitance (92.7% of the initial value) after 1000 cycles under the working condition of a current density of 10 A g−1. This study describes a fundamental investigation on the energy storage and conversion properties of 2D layered materials.

Efficient pore engineering in carbonized zeolitic imidazolate Framework-8 via chemical and physical methods as active materials for supercapacitors

Pore structure of active material plays important roles on energy storage of supercapacitor (SC), since charges are accumulated in and released from pores during charge/discharge process. Carbonized zeolitic imidazolate framework-8 (ZIF-8) with high surface area and electrical conductivity is widely applied as active material. Easy removal of Zn and ZnO simplifies pore engineering of carbonized ZIF-8. It is the first time using chemical and physical methods to create pores in carbonized ZIF-8. Chemical method is removing ZnO and Zn using HCl treatment, and physical method is evaporating Zn at 1000 °C. Due to larger size of ZnO and lower annealing temperature without Zn evaporation, carbonized ZIF-8 synthesized using 800 °C shows the highest specific capacitance (CF) of 186.79 F/g at 20 mV/s, while that prepared using physical method merely presents CF value of 43.82 F/g. With HNO3 and H2SO4 treatments, carbonized ZIF-8 shows reduced electrochemical performance due to serious structure damage. Symmetric SC composed of optimized carbonized ZIF-8 electrodes presents CF value of 214.8 F/g at 20 mV/s and maximum energy density of 10.71 Wh/kg at power density of 800 W/kg. Excellent charge/discharge cycling stability is achieved with CF retention of 83% and Coulombic efficiency of 90% after 8000 times charge/discharge process.

Bifuctional indigocarmin­intercalated Ni­Al layered double hydroxide: investigation of characteristics for pigment and supercapacitor application

In the modern world, one promising direction is the production and use of multifunction compounds. Ni-Al layered double hydroxide is widely used as the active material in supercapacitors. Nickel compounds are also colored and can be used as pigments. The characteristics of bi-functional indigo carmine intercalated Ni-Al (Ni:Al=4:1) hydroxides, synthesized at an equilibrium рН and рН=14 have been studied. The crystal structure of the prepared samples was studied by means of X-ray diffraction analysis and thermogravimetry, pigment characteristics – by measuring and calculating color characteristics in CIELab and XYZ systems, electrochemical characteristics – cyclic voltammetry and galvanostatic charge-discharge cycling. Comparative analysis of the electrochemical characteristics of Ni-Al-indigo carmine and Ni-Al-carbonate hydroxides has been conducted. Using XRD and thermogravimetry analysis methods, it was found that Ni-Al–indigo carmine hydroxide is a layered double hydroxide with the structure of α-Ni(OH)2 with average (synthesis at рН=14 and low (synthesis at equilibrium рН) crystallinity. It was found that synthesized Ni-Al-indigo carmine LDH had color bordering between light and blue (color tone 483–485 nm) with the lightness of 40–50 % and average color purity. It was found that the specific capacity of indigo carmine intercalated Ni-Al LDH (synthesis at рН=14 exceeded that of carbonate intercalated: the maximum specific capacity at full discharge was 1,007 F/g hydroxide and 2,996 F/h Ni, at discharge to 0 В –946 F/g. First, for Ni-Al-indigo carmine LDH, two discharge plateaus were observed, which correspond to the discharge of Ni3+ and indigo carmine

Nickel and cobalt metal-organic-frameworks-derived hollow microspheres porous carbon assembled from nanorods and nanospheres for outstanding supercapacitors

The development of efficient electrode materials is essential to promote the performance of energy storage equipment. Nowadays, metal organic frameworks (MOFs) have been widely regarded as active materials for supercapacitors mainly thanks to their adjustable structure and outstanding porosity. Here, highly optimized Nickel and Cobalt MOF-derived N-doped porous carbon (Ni/Co-MOF-NPC) are considered the best choice for electrode materials due to their unique structural properties and excellent electrochemical performance. Pure cobalt oxide rarely reaches a specific capacitance of 104.3 F g−1 when the current density is 1 A g−1, but the optimized Ni/Co-MOF-NPC-2:1 offers an ultra-high specific capacitance of 1214 F g−1, which is much higher than that of pure cobalt oxide in a three-electrode test system. When the current density is 10 A g−1, after 6000 cycles, the capacitance can still maintain 98.8% of the initial capacitance. Asymmetric supercapacitors were assembled using the prepared Ni/Co-MOF-NPC-2:1 as the positive electrode material, corrugated paper activated carbon (CPAC) as the negative electrode material, the prepared Ni/Co-MOF-NPC-2:1//CPAC exhibits an outstanding energy density of 55.4 Wh kg−1 at 758.5 W kg−1, and has a significant cycle stability of 75.2% retention after 20,000 cycles. This excellent MOF synthesis strategy reduced the gap between the experimental synthesis and practical application of MOF in fast energy storage.

Development of a new hybrid CNT-TEPA@poly(3,4-ethylenedioxythiophene-co-3-(pyrrol-1-methyl)pyridine) for application as electrode active material in supercapacitors

We report the synthesis of a CNT-TEPA@PEPy hybrid material by the copolymerization of EDOT and Py analogs units covalently bonded to TEPA modified carbon nanotubes (CNTs). The chemical structure and morphology of the hybrid were compared to those of the unmodified CNTs using FTIR, Raman and XPS spectroscopies. The hybrid was applied as the electrode active material in symmetric supercapacitors (SCs) which were evaluated in aqueous and organic (acetonitrile) electrolytes to study the versatility of the as-synthesized CNT-TEPA@PEPy. The capacitances values of the cells obtained from the hybrid-based SCs are 56% and 115% higher than those of the cells prepared with the unmodified CNT in organic and aqueous electrolytes, respectively. The full cells assembled with CNT-TEPA@PEPy exhibited excellent cyclability with 81.3% and 77.5% of capacitance retention after 5000 cycles in aqueous and organic media, respectively. The device properties indicate the feasibility of the applied synthetic approach, showing that the prepared hybrid is a promising material for use in highly cyclable supercapacitors.

A metallic-free materials supercapacitor with high energy density based on N-S-doped carbon hollow sphere electrode

There is an urgent need to develop means of greener synthesis strategies based on harmless activated chemical reagents, sustainable, economical and effective carbon precursors as active materials for supercapacitors. In this respect, the design and production of carbon-based electrode of supercapacitor with high catalytic activity is of great significance. The BET surface area of the N-S-doped carbon hollow sphere (N-S-CHS) is as large as 556 m2 g−1. The N-S-CHS electrode displays a high specific capacitance of 439.98 F g−1 at 1 A g−1, after 4000 cycles of constant current charge and discharge, the specific capacitance remains 92.3%. This work highlights the crucial role of metallic-free materials for applications in the energy storage and conversion.

Porous nanosheets-based carbon aerogel derived from sustainable rattan for supercapacitors application

Porous carbon materials with well distributed micro-mesopores from biomass resources for supercapacitors application have attracted considerable attention because of both the environmental issues caused by fossil and its great depletion. A novel porous nanposheets-based carbon aerogel was synthesized by a combined process of complete delignification, carbonization and chemical activation of a sustainable source of rattan. The biomass supramolecular structure changes and carbon formation were technically monitored by spectroscopy and thermochemistry. Based on the metabolic channels and preparation resulted pores, the nanposheets-based carbon aerogel shows a large number of and a wide range of miro-mesopores together with a large specific surface area (2436 m2 g−1). When used as an active material for supercapacitor, such rattan derived hierarchical porous carbon aerogel reveals an inspiring specific capacitance of 221 F g−1 at 0.5 A g−1 and an excellent rate capability of owing 80% capacitance retention at a current density of 20 A g−1. These promising characteristics provide a high-value solution for developing renewable rattan source into an active material for high-performance supercapacitors.

Polyaniline Based Ternary Hierarchical Microspheres for Supercapacitor Application

With rapid advancements in renewable energy harvesters and flexible electronics, there is a dire need to develop energy storage devices (EEDs) that respond well to these applications. Supercapacitors are a type of EEDs with higher energy and power densities. This, combined with their ultra high cycle life makes them an attractive candidate to be used both as a standalone or coupled with other EEDs. The active material in supercapacitors can be broadly classified into three types: carbonaceous, conductive polymer, and metal oxides. Each category of materials has its own advantages and drawbacks. It is reasonable to formulate a ternary composite such that the advantage of one material effectively suppresses the drawback of the other. Herein, a ternary hierarchical microsphere (TMS) composed of polyaniline nanofibers, CeO2 nanorods, and reduced graphene is obtained through a simple and highly scalable spray-drying technique. The synthesized TMS was physiochemically characterized using XRD, FTIR, SEM, XPS, and gas adsorption surface analysis. Electrochemical analysis revealed that the optimized TMS possess high specific capacity (685 F g-1), good rate performance and excellent cycle life (~90% capacitance retention after 6000 cycles). An asymmetric device constructed using the TMS and rGO revealed a high specific energy density (46.3 W h kg-1) at a power density of 850 W kg-1 with a very stable cyclic performance. Thus, we demonstrate a simple yet effective strategy to produce high-performance supercapacitor material, which is highly scalable for industrial-scale production.

In situ growth of manganese oxide nanosheets over titanium dioxide nanofibers and their performance as active material for supercapacitor

In recent years, electrochemical energy devices, i.e. batteries, fuel cells, solar cells, and supercapacitors, have attracted considerable attention of scientific community. The architecture of active materials plays a crucial role for improving supercapacitors performance. Herein, titanium dioxide (TiO2) nanofibers (1D) have been synthesized by electrospinning process and used as a backbone to manganese dioxide (MnO2) nanosheets (2D) growth through hydrothermal method. This strategy allows the obtaining of 1D/2D heterostructure architecture, which has demonstrated superior electrochemical performance in relation to pristine MnO2. The highest electrochemical performance is due to the synergic effect between the metal oxides, where TiO2 nanofibers provide electrochemical stability for active MnO2 phase. Thus, the designed TiO2@MnO2 structure can reach maximum specific capacitance of 525 F·g−1 at a current density of 0.25 A·g−1, and it demonstrates an excellent stability by retaining 81% of the initial capacitance with coulombic efficiency of 91%. Therefore, the novel architecture of TiO2@MnO2 based on nanofibers and nanosheets exhibits superior electrochemical properties to be used in supercapacitor applications.

Comparison of the free-standing flexible electrodes fabricated with metallic 1T or semiconducting 2H MoS2 nanosheets and high conductivity PEDOT:PSS

The improvement and promotion of the active materials in supercapacitors (SCs) have been gotten a lot of attention with the emergency awareness of environment protection and energy crisis. Herein, a free-standing flexible film was developed as the active electrodes of SCs, fabricated by mixing 1T or 2H MoS2 nanosheets with high electric conductivity poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) via vacuum filtration and H2SO4 post-treatment. The 2H MoS2–based hybrid electrodes with post-treatment and 10% mass ratio for 2H MoS2 to PEDOT:PSS exhibited highest specific capacitance of 89Fg−1 @ 0.1 A g−1. Through the comparison between 1T MoS2 and 2H MoS2-based hybrid electrodes, 2H MoS2–based hybrid electrodes presented higher capacitance properties than 1T MoS2–based hybrid electrodes at the mass ratio range of 5% to 20%, while the capacitance performance of 1T MoS2–based hybrid electrodes was higher at range of 30% to 40%. It was assumed that the conductivity and capacitance performance of hybrid films were enhanced with organic polar solution (N,N-dimethylformamide) and H2SO4 post-treatment under the mass ratio range of 5% to 20%. Also, the high intrinsic capacitance of 2H MoS2 nanosheets was not achieved due to the poor electric conductivity for the mass ratio range of 30% to 40%. Therefore, it was an effective strategy to fabricate free-standing flexible hybrid electrodes with stable 2H MoS2 nanosheets and high conductivity materials for flexible energy storage and conversion.

Anionic carbonate activation of layered (α+β) nickel hydroxide

Nickel hydroxide is widely used as the active material in supercapacitors. Samples of Ni(OH)2 with the (α+β) layered structure, synthesized in the slit-diaphragm electrolyzer, are the most active. The possibility of carbonate activation of layered (α+β) Ni(OH)2 was studied by the synthesis of samples in the slit-diaphragm electrolyzer using a mixture of sodium hydroxide and sodium carbonate as the electrolyte. The molar part of sodium carbonate in the NaOH+Na2CO3 mixture was controlled by acid titration in the presence of two indicators. The synthesis of nickel hydroxide samples was conducted at the molar part of carbonate from 0.16 (NaOH without the additional introduction of carbonate) to 0.83. The crystal structure of the samples was studied by means of X-ray diffraction analysis, electrochemical characteristic – by means of cyclic voltammetry and galvanostatic charge-discharge cycling in the accumulator regime. By means of XRD analysis, it was found that upon increasing the molar part of carbonate in the anolyte to 0.49, the crystallinity of the monophase layered (α+β) structure increases. It was found that a further increase of the carbonate part results in a more amorphous structure due to a partial breakdown of the hydroxide lattice with the formation of basic salts and formation of the bi-phase system. This conclusion is supported by cyclic voltammetry and discharge curves. The study of the electrochemical characteristics revealed, that for the molar part of carbonate below 0.39, carbonate activation of hydroxide occurs resulting in an improved specific capacity. Increasing the carbonate part to 0.49 results in a lower specific capacity, and even further increase results in the breakdown of hydroxide into basic salts and a significant drop in electrochemical activity. Thus, it was found, that to achieve the maximum activating effect, the optimal molar part of sodium carbonate (in a mixture with sodium hydroxide) should be about 40 %. The specific capacity of nickel hydroxide under this optimal condition is 234 mA·h/g, and this sample is found to be susceptible to activation with cobalt compounds, which further improved capacity to 254 mA·h/g.

High-performance supercapacitor electrodes based on NiMoO4 nanorods

Abstract

Cobalt-Porphyrin Modified Three-Dimensional Graphene Hydrogel Electrode for High Performance Asymmetric Supercapacitors

Three-dimensional (3D) graphene-based materials have attracted much attention in the field of supercapacitors for their large surface areas and fast electronic conductivity capability. Faradaic pseudo-capacitance materials inside the architecture can enlarge the electrochemical performance of the electrode. Additionally, metal porphyrins are negative electrode active materials for supercapacitors as they have potential high pseudo-capacitance, conductivity and N-doping. The design and preparation of the 3D cobalt-porphyrin modified graphene hydrogels (3D CoP/GHs) is an interesting topic. Here, we have fabricated the 3D CoP/GH by a two-step method. The composite electrode reaches a specific capacitance of 335[Formula: see text]F[Formula: see text]g[Formula: see text], twice that of pure GHs. At the same time, resistance of the electrode material decreases and the ion transfer is accelerated due to the addition of cobalt-porphyrin. After 10[Formula: see text]000 cycles, the 3D CoP/GH maintains its stable specific capacitance retention of 94.11% indicating its excellent cycle life. The cycle life is much better than that of a hydrogel that has not been doped (81.63%) according to our previous work. Then we fabricated an asymmetrical supercapacitor which uses both the 3D CoP/GH and GH as the two electrodes (3D CoP/GH[Formula: see text]GH), and reaches an outstanding energy density of 30.40[Formula: see text]Wh[Formula: see text]kg[Formula: see text] at a current density of 1[Formula: see text]A[Formula: see text]g[Formula: see text] while the power density is 749.5[Formula: see text]W[Formula: see text]kg[Formula: see text].