Electrochemical Capacitor Applications Research Articles

Nanostructured V2O5 and its nanohybrid with MXene as an efficient electrode material for electrochemical capacitor applications

Vanadium pentoxide (V 2 O 5 ) is an excellent electrode material for electrochemical capacitor (ECCs) applications, but its lower electrical conductivity is the primary obstacle that restricts its practical applications. This obstacle can be eliminated by forming its nanohybrid (NCs) with a highly capacitive and conductive matrix such as MXene. MXene is a new two-dimensional (2D) material with good electronic conductivity and a larger specific surface area, making it a very suitable substrate for composite formation. Unfortunately, the two-dimensional MXene sheets stacked quickly, limiting their specific surface area and charge/mass transport properties. Here we used the hydrothermal approach to fabricate V 2 O 5 nanowires (NWs) and form their nanohybrid with MXene via the ultrasound route. To assess electrochemical suitability, the fabricated samples were loaded onto a carbon cloth (CC) and used as a working electrode in the half-cell configuration. The nanohybrid (V 2 O 5 /MXene) sample showed a good specific capacity (C sp ) of 768 F/g (at 1 A/g) because of its greater surface area, hybrid composition, excellent electrical conductivity, and passive nanostructure. It also showed superior cyclic, electrochemical and mechanical capability and maintained a specific capacity of 93.3%, even after completion of 6000 GCD tests. In addition, the nanohybrid sample electrode also exhibits superb rate performance and lost only 14.4% of its initial specific capacity on increasing the applied current density from 1 to 5 A/g. There is no doubt that V 2 O 5 NWs inter-stack between MXene nanosheets to develop effective interface interaction and suppress their stacking.

Green synthesis of cobalt oxide thin films as an electrode material for electrochemical capacitor application

In this study, we report on the fabrication and characterization of cobalt oxide (Co3O4) thin film that is potentially important for electrochemical capacitor applications. For that purpose, the precursor powder of Co3O4 was prepared using the cost-effective sol-gel synthesis route and heat treatment at a relatively low temperature. A thin film of Co3O4 was prepared on a fluorine-doped tin oxide (FTO) substrate using a simple doctor-blade method. X-ray diffraction and Raman spectroscopy confirmed the formation of pure Co3O4 thin film on FTO, and scanning and transmission electron microscopy confirmed the nanoscale nature of the particles in the film. The electrochemical studies revealed a specific capacitance of 237 ​F ​g-1 for the Co3O4 electrode, with a remarkable cycling stability in 1 ​M NaOH electrolyte, and 77% capacity retention after 2000 cycles at 5 ​mA ​cm-2 current density (833 ​mA ​g-1); this demonstrates that Co3O4 is a promising material for electrochemical devices. Further, the electrochemical impedance measurements revealed an internal (solution) of 10 ​Ω, whereas the charge transfer resistance between the electrode and the electrolyte was roughly 40 ​Ω.

Cost Effective, Metal Free Reduced Graphene Oxide Sheet for High Performance Electrochemical Capacitor Application

Cost Effective, Metal Free Reduced Graphene Oxide Sheet for High Performance Electrochemical Capacitor Application

Hierarchical MnCo2O4@CuCo2O4 core-shell nanoarrays on carbon cloth as binder-free electrode for flexible all-solid-state asymmetry supercapacitors

Hierarchical core-shell nanowire arrays with a shell of CuCo2O4 nanosheets and a core of MnCo2O4 nanowires directly coated on the conductive carbon cloth (CC) are rationally designed and synthesized via a facile hydrothermal route with a post low-temperature thermal treatment in air. The binder-free MnCo2O4@CuCo2O4/CC composite material exhibits an enhanced performance (1241.0 C g−1 at 1 A g−1) compared with the MnCo2O4/CC (832.7 C g−1 at 1 A g−1) and CuCo2O4/CC (734.1 C g−1 at 1 A g−1). In addition, the MnCo2O4@CuCo2O4/CC electrode is assembled into a flexible all-solid-state asymmetric supercapacitor (ASC), which delivers a maximum specific energy of 62.0 Wh kg−1 at a specific power of 747.2 W kg−1 with 91.2% capacity retention after 10000 charge–discharge cycles at 8 A g−1. And the ASC device also exhibits 91.7% capacity retention at floating time over 200 h at 8 A g−1. Further, the MnCo2O4@CuCo2O4//AC device shows superior flexible performance while bending at various angles. These results make this MnCo2O4@CuCo2O4 core/shell composite to be a good candidate for flexible all-solid-state electrochemical capacitors applications.

Activated Carbon from Corncobs Doped with RuO2 as Biobased Electrode Material

Bio-based activated carbons with very high specific surface area of >3.000 m² g−1 (based on CO2 adsorption isotherms) and a high proportion of micropores (87% of total SSA) are produced by corncobs via pyrolysis and chemical activation with KOH. The activated carbon is further doped with different proportions of the highly pseudocapacitive transition metal oxide RuO2 to obtain enhanced electrochemical properties and tune the materials for the application in electrochemical double-layer capacitors (EDLC) (supercapacitors). The activated carbon and composites are extensively studied regarding their physico-chemical and electrochemical properties. The results show that the composite containing 40 wt.% RuO2 has an electric conductivity of 408 S m−1 and a specific capacitance of 360 Fg−1. SEM-EDX, XPS, and XRD analysis confirm the homogenous distribution of partly crystalline RuO2 particles on the carbon surface, which leads to a biobased composite material with enhanced electrochemical properties.

One-pot synthesis of ultrahigh performance nanorod structured Co3O4@Fe2O3 anchored on a resonating 2D-carbon with high potential window and surface area for supercapacitors application

Herein we illustrate a rational scheme to construct nanorod structured Co3O4@Fe2O3-2DC working electrode for electrochemical capacitor applications. When analyzed as a supercapacitor electrode material, Co3O4@Fe2O3-2DC at 5 A/g delivered an optimum capacity retention of 96.7%, and a high specific capacitance of 2657.1 F/g at a marginal current density of 1 A/g. Co3O4@Fe2O3-2DC unparalleled electrochemical performance can be accredited to its unique morphology consigned with a high specific surface area of 532.8 m2/g, and the effect of synergy between single-layer practically defect free graphene, and the anchored cobalt and iron metal oxides. The electrode operated within a wide potential window, almost at the limit for aqueous electrolyte system (1.23 V), which makes it merit a high over-potential caption. These results validate Co3O4@Fe2O3-2DC to be considered as a favorable electrode material, for application in next-generation excellent performance supercapacitors.

Boost of Charge Storage Performance of Graphene Nanowall Electrodes by Laser-Induced Crystallization of Metal Oxide Nanostructures.

Major research efforts are being carried out for the technological advancement to an energetically sustainable society. However, for the full commercial integration of electrochemical energy storage devices, not only materials with higher performance should be designed and manufactured but also more competitive production techniques need to be developed. The laser processing technology is well extended at the industrial sector for the versatile and high throughput modification of a wide range of materials. In this work, a method based on laser processing is presented for the fabrication of hybrid electrodes composed of graphene nanowalls (GNWs) coated with different transition-metal oxide nanostructures for electrochemical capacitor (EC) applications. GNW/stainless steel electrodes grown by plasma enhanced chemical vapor deposition were decorated with metal oxide nanostructures by means of their laser surface processing while immersed in aqueous organometallic solutions. The pseudocapacitive nature of the laser-induced crystallized oxide materials prompted an increase of the GNW electrodes' capacitance by 3 orders of magnitude, up to ca. 28 F/cm3 at 10 mV/s, at both the positive and negative voltages. Finally, asymmetric aqueous and solid-state ECs revealed excellent stability upon tens of thousands of charge-discharge cycles.

Renewable biomass‐derived carbons for electrochemical capacitor applications

AbstractBiomass is rich, renewable, sustainable, and green resources, thereby excellent raw material for the fabrication of carbon materials. The diversity in structure and morphology of biomass are relevant in obtaining carbon materials with different structures and performances. The inherent ordered porous structure of biomass also benefits the activation process to yield porous carbons with ultrahigh specific surface area and pore volume. Besides, obtained biomass‐derived carbons (BDCs) are hard carbon with porous morphology, stable structure, superior hardness/strength, and good cycling performances when used in electrochemical capacitors (ECs). The inherent N, S, P, and O elements in biomass yield naturally self‐doped N, S, P, and O BDCs with unique intrinsic structures. In this paper, the synthesis approaches and applications of BDCs in ECs are reviewed. It shows that BDCs electrochemical performances are highly determined by their pore structures, specific surface areas, heteroatoms doping, graphitization degree, defects, and morphologies. The electrochemical performances of BDCs can further be improved by compositing with other materials, such as graphene, carbon nanofibers/nanotubes, transition metal oxides or hydroxides, and conducting polymers. The future challenges and outlooks of BDCs are also provided.

Ionogels Obtained by Thiol-ene Photopolymerization-Physicochemical Characterization and Application in Electrochemical Capacitors.

Flexible ionogels with good mechanical properties were obtained in situ by thiol-ene photopolymerization of trimethylolpropane tris(3-mercaptopropionate) (TMPTP) and 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione (TATT) (with C=C: SH ratio 1:1) in four imidazolium ionic liquids (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide—EMImNTf2, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate-EMImOTf, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide-BMImNTf2, and 1-butyl-3-methylimidazolium trifluoromethanesulfonate—BMImOTf) used in the range 50 to 70 wt.%. The mechanical and electrochemical properties of obtained ionogels were examined. Ionogels with ionic liquids (ILs) with NTf2− anion are more puncture resistant than with OTf− anion. Moreover, ionogels with the NTF2− anion have better electrochemical properties than those with the OTf− anion. Although it should be noted that ionogels with the EMIm+ cation have a higher conductivity than the BMIm+. This is connected with intermolecular interactions between polymer matrix and IL related to the polarity of IL described by the Kamlet-Taft parameters. These parameters influence the morphology of the polymer matrix (as shown by the SEM micrograph), which is formed by interconnected polymer spheres.

Green Synthesis of Cobalt Oxide Thin Films as an Electrode Material for Electrochemical Capacitor Application

Green Synthesis of Cobalt Oxide Thin Films as an Electrode Material for Electrochemical Capacitor Application

Preparation of a high strength, rapid self-healing composite gel and its application in electrochemical capacitor

It is imperative to develop ideal self-healing material with intrinsic mechanical strength and mild self-healing conditions. Here, a rapid self-healing poly(vinyl alcohol) (PVA)/chitosan (CS) composite gel with multiple hydrogen bonds is designed. PVA/CS gel shows a particularly high strength of 0.266 MPa and can heal rapidly after completely broken. The self-healing performance can be ascribed to multiple hydrogen bonds provided by the PO/P–O⋯H groups of phytic acid. In particular, PVA/CS gel can be served as solid electrolyte. A flexible all-solid-state capacitor can be assembled based on the flexible polyaniline electrode and PVA/CS gel used as solid electrolyte. The capacitor exhibits a high specific capacitance of 390.6 mF/cm2 and high capacitance retention ratio after hundreds of bends. Additionally, the PVA/CS gel can reconnect the broken capacitor with partial capacitance retention. This work can contribute to the design and fabrication of rapid self-healing gel and flexible all-solid-state capacitor.

Influence of Surface Potential at Aqueous/TiO2 Thin-Film Interface on the Capacitance Performance

Electrochemical capacitors and capacitive deionization store energy through the interfacial layer formed between electrodes and electrolytes. TiO2 thin-film deposited on Si wafers was studied by ellipsometry under controlled humidity to explore the refractive index (dielectric constant) of pore water. The surface potential measured by electrophoretic mobility at different equilibrated pH and specific adsorbing ion concentrations influences the refractive index of pore water. The higher the surface potential, the higher the refractive index, the lowest refractive index occurring close to the isoelectric pH. The presence of the specific adsorbing ions on the nanopore walls increases the refractive index. Furthermore, galvanostatic charge/discharge measurements were performed using TiO2 thin films coated on platinized Ti coupons to obtain the capacitance of the aqueous TiO2 thin-film systems. The capacitance followed a similar trend as the surface potential and can be improved by specific adsorbing ion addition over the pH range of 5 to 9. In addition, the crystalline structure of TiO2 thin-film varied by different sintering temperatures also influences the surface potential, resulting a different capacitive performance. At elevated sintering temperature, TiO2 transfers from anatase to rutile with an increased surface potential. The electrochemical tests show that the electrode capacitance increases from 19.50 to 41.82 mF/cm2. The investigation of oxide materials in the application for electrochemical capacitors and capacitive deionization could be another possibility other than carbon materials.

Sonochemical synthesis of NiCo2O4/NRGO nanocomposite as a cathodic material for the electrochemical capacitor application

In this work, a novel nanocomposite consisting of NiCo2O4/N-doped reduced graphene oxide was prepared. In the first step, ultrafine NiCo2O4 nanoparticles (4.4 nm) were synthesized by the sonochemical method. In the second step, graphene oxide was synthesized by modified Hummer methods and then reduced and N-doped (NRGO) by a chemical method using a mixture of hydrazine and ammonia solution. NiCo2O4/NRGO nanocomposite was produced using the dispersion of NRGO nanosheets and NiCo2O4 nanoparticles under ultrasonic radiation for 30 min. The structure, morphology, and composition of various samples were investigated using an adequate analytical characterization method. Electrochemical tests such as cyclic voltammetry and galvanostatic charge–discharge studies were done in a three-electrode system with 1.0 M Na2SO4 solution as the electrolyte for supercapacitive study of the samples. The results confirmed the excellent supercapacitive behavior of the nanocomposite and good stability during the charge–discharge cycle. The specific capacitance for the nanocomposite was calculated using a galvanostatic charge–discharge experiment which 618 F.g−1 in current density of 4.0 A.g−1.

Compatible Solid Polymer Electrolyte Based on Methyl Cellulose for Energy Storage Application: Structural, Electrical, and Electrochemical Properties.

Compatible green polymer electrolytes based on methyl cellulose (MC) were prepared for energy storage electrochemical double-layer capacitor (EDLC) application. X-ray diffraction (XRD) was conducted for structural investigation. The reduction in the intensity of crystalline peaks of MC upon the addition of sodium iodide (NaI) salt discloses the growth of the amorphous area in solid polymer electrolytes (SPEs). Impedance plots show that the uppermost conducting electrolyte had a smaller bulk resistance. The highest attained direct current DC conductivity was 3.01 × 10−3 S/cm for the sample integrated with 50 wt.% of NaI. The dielectric analysis suggests that samples in this study showed non-Debye behavior. The electron transference number was found to be lower than the ion transference number, thus it can be concluded that ions are the primary charge carriers in the MC–NaI system. The addition of a relatively high concentration of salt into the MC matrix changed the ion transfer number from 0.75 to 0.93. From linear sweep voltammetry (LSV), the green polymer electrolyte in this work was actually stable up to 1.7 V. The consequence of the cyclic voltammetry (CV) plot suggests that the nature of charge storage at the electrode–electrolyte interfaces is a non-Faradaic process and specific capacitance is subjective by scan rates. The relatively high capacitance of 94.7 F/g at a sweep rate of 10 mV/s was achieved for EDLC assembly containing a MC–NaI system.

The Study of Electrical and Electrochemical Properties of Magnesium Ion Conducting CS: PVA Based Polymer Blend Electrolytes: Role of Lattice Energy of Magnesium Salts on EDLC Performance.

Plasticized magnesium ion conducting polymer blend electrolytes based on chitosan (CS): polyvinyl alcohol (PVA) was synthesized with a casting technique. The source of ions is magnesium triflate Mg(CF3SO3)2, and glycerol was used as a plasticizer. The electrical and electrochemical characteristics were examined. The outcome from X-ray diffraction (XRD) examination illustrates that the electrolyte with highest conductivity exhibits the minimum degree of crystallinity. The study of the dielectric relaxation has shown that the peak appearance obeys the non-Debye type of relaxation process. An enhancement in conductivity of ions of the electrolyte system was achieved by insertion of glycerol. The total conductivity is essentially ascribed to ions instead of electrons. The maximum DC ionic conductivity was measured to be 1.016 × 10−5 S cm−1 when 42 wt.% of plasticizer was added. Potential stability of the highest conducting electrolyte was found to be 2.4 V. The cyclic voltammetry (CV) response shows the behavior of the capacitor is non-Faradaic where no redox peaks appear. The shape of the CV response and EDLC specific capacitance are influenced by the scan rate. The specific capacitance values were 7.41 F/g and 32.69 F/g at 100 mV/s and 10 mV/s, respectively. Finally, the electrolyte with maximum conductivity value is obtained and used as electrodes separator in the electrochemical double-layer capacitor (EDLC) applications. The role of lattice energy of magnesium salts in energy storage performance is discussed in detail.

Three-Dimensional Architectures in Electrochemical Capacitor Applications – Insights, Opinions, and Perspectives

This review focuses on describing the current state-of-the-art in the synthesis of 3D carbon architectures for the electrochemical capacitor application. The selection is based on both template and non-template strategies. Particular attention has been paid to carbon materials because of their structural interconnection, which not only creates the desired hierarchical porous channels but also ensures high conductivity and mechanical stability. A comprehensive overview of electrode materials is presented here with a detailed discussion of composite solutions, including their advantages and disadvantages. Numerous examples from the literature are presented for individual solutions. The future challenges posed for this type of material are finally summarized.

Impact of phase segregation on optical and electrochemical property of BiPO4 nanostructures for energy storage applications

In the present paper, we report the influence of phase segregation (hexagonal and monoclinic phase) of facile microwave-assisted BPO (BiPO4) nanostructures on optical and electrochemical properties for supercapacitor applications. The XRD patterns reveal pure phase formation of both the samples of BiPO4 synthesized at 300 °C and 600 °C (JCPDS #15-0766 and JCPDS #43-0637). Phase transition of BiPO4 from hexagonal to monoclinic phase obtained by sintering the sample (BP600) at 600 °C. The FWHM values of the X-ray diffraction peaks observed to decrease with an increase in sintering temperature, which can be ascribed to the enhancement of the crystallite size. The synthesized samples of BiPO4 are in the nanometer dimension, which also revealed through FESEM examination. FTIR, Raman, and PL spectroscopy also revealed the crystal structure symmetry distinction among the hexagonal and monoclinic BiPO4 phase. Specific capacity calculated from GCD (galvanostatic charge and discharge) analysis for BP300 and BP600 samples is 1074 Cg−1 and 451 Cg−1, correspondingly, at the current density of 1 Ag−1. The investigation divulges that the phase segregation plays a considerable utility in tuning the electrochemical performance of BiPO4 nanostructures as active electrode material for next-generation electrochemical capacitors application.

Fabrication of binary transition metal hydroxides and their nanocomposite with CNTs for electrochemical capacitor applications

In this paper, we have prepared the flower-like nanoarchitecture of the Ni–Co binary metal layered hydroxides (Ni–Co-BMLHs) by urea assisted Solvothermal process and formed their nanocomposite with 5% CNTs via ultra-sonication approach. The physical characterizations of the prepared samples were carried out to obtain the compositional, structural, and morphological information. The influence of CNTs (5%) on the electronic conductivity of the nanocomposite was examined by current-voltage (I˗V) experiments. In nanocomposite, the effective interaction between the Ni–Co-BMLHs and CNTs results showed good electrical conductivity (1.52 × 10-2 S/m) that further facilitates the charge-transportation process during the electrochemical reactions. From electrochemical tests, the Ni–Co-BMLHs/CNTs based electrode showed excellent electrochemical activity with a specific capacitance (Cs) of 1305 F/g at 1 A/g. After 3000 CV cycles, the nanocomposite based electrode lossed 10.43% of its initial Cs, which reveals its desireable capacity retention. Moreover, the nanocomposite also exhibits superior rate capability as it lost just 8% capacitance by doubling the current density. The lower charge transfer resistance (Rct, 2.53 Ω) of the Ni–Co-BMLHs/CNTs than that of pure Ni–Co BMLH (3.92 Ω) during the EIS measurements also indicate that the CNTs additive in the nanocomposite lowers the internal resistance that facile electron transport during the faradaic reactions. The obtained results present the Ni–Co BMLHs/CNTs as unique electrode materials that have the potential for high-performance supercapacitors.

Activated Carbons From Winemaking Biowastes for Electrochemical Double-Layer Capacitors.

Revalorizing organic biowaste is critical to achieve a full circular economy, where waste is transformed into resources. One of the main strategies is to produce activated carbons and use them as functional materials for electrochemical energy storage. In this study, winemaking wastes, bagasse (BAG), and cluster stalks (CS) were recovered and used in the preparation of activated carbons by a hydrothermal process. Then, they were chemically activated using KOH and investigated for electrochemical capacitor applications. The activation treatment resulted in microporous structures, characterized by a type I isotherm for low partial pressures (P/P0), and a type IV for higher pressures, as observed by Brunauer–Emmett–Teller surface analysis, with specific surfaces of 1,861 and 2,662 m2·g−1 for BAG and CS, respectively. These microporous structures were also investigated by means of scanning electron microscopy, revealing a high porous degree. Micro-Raman spectroscopy and X-ray photoelectron spectroscopy measurements displayed bands associated to disorder of the structure of the carbonaceous material. The electrochemical performance of the resulting materials was investigated for electrochemical energy storage applications, as supercapacitor electrode, in 1 M KOH aqueous electrolyte. These biowaste-derived materials displayed electrochemical double-layer capacitance, with 129 F·g−1 at 10 A·g−1 in the 0.1 to −1.0 V vs. saturated calomel electrode. For that reason, they are pin-pointed as potential negative electrodes for electrochemical double-layer supercapacitors and hybrid or asymmetric supercapacitors.

Characteristics of EDLC device fabricated from plasticized chitosan:MgCl2 based polymer electrolyte

Chitosan (CS) based polymer electrolytes are prepared via a simple method called solution casting where the ionic source in this work is magnesium chloride (MgCl2). The plasticization method is implemented using glycerol. Through XRD it appears that amorphous phase enrich with increasing glycerol concentration. The impedance study is carried out to estimate the DC conductivity of the plasticized samples. The highest conducting (1.03 × 10−3 S/cm) plasticized electrolyte is used as electrode separator for electrochemical double-layer capacitor (EDLC) application. Ionic transference number in this work is 0.97 where it concludes that the ion is the main charge carrier. No obvious changes in current are detected as the voltage sweeps from 0 to 1.83 V, meaning that CS:MgCl2: glycerol system is potentially steady up to 1.83 V. The outcome of cyclic voltammetry (CV) indicates that no redox reaction is observed and specific capacitance is influenced by scan rates. The crucial parameters of the EDLC, e.g., specific capacitance, internal resistance, energy density, and power density at the 1st cycle are 117 F/g, 183 Ω, 13.1 Wh/kg and 550 W/kg, respectively.