Electric Double Layer Capacitance Research Articles

Activated Carbons as Nanoporous Electron-Ion-Exchangers

The electrochemical, ion-exchange, sorption, hydrophilic-hydrophobic properties of several types of electrodes based on activated carbon (AC) and its porous structure are studied. By the method of standard contact porosimetry it is found that AC exhibits both hydrophilic and hydrophobic porosity and has the high specific surface area (600–2600 m2/g) which explains its use in supercapacitors and for capacitive deionization (CDI) of water. A new phenomenon of superhydrophilicity caused by swelling of surface groups (SG) in water is observed. The measurements of the AC surface conductivity show that even in pure water AC exhibits considerable ionic conductivity, which makes possible its use in the production of pure water by CDI. AC is shown to be an electron-ion-exchanger which is its unique feature. It is found that in addition to the electric double layer capacitance, the pseudocapacitance of redox-reactions of surface groups makes a substantial contribution into its total capacitance. The deep cathodic charging to negative potentials vs. reversible hydrogen electrode (RHE) in concentrated H2SO4 allows reaching the specific preudocapacitance of AC of 1100 F/g mainly due to the high pseudocapacitance of the reaction of hydrogen intercalation into carbon. This corresponds to the formation of a new compound C6H. In pure water, the specific capacitance of AC reaches 66 F/g and does not increase with the increase in KCl concentration, which suggests that this capacitance is associated with surface groups.

Electrochemical Properties of CMC–PVA Polymer Blend Electrolyte for Solid State Electric Double Layer Capacitors

In this work, the electrochemical properties of polymer blend electrolyte (PBE) based CMC-PVA is presented for electrical double layer capacitance (EDLC) application. CMC-PVA PBE is incorporated in two different systems which contain an (1) ammonium nitrate (NH4NO3) ionic dopant (System I), and (2) ethylene carbonate (EC) plasticizer (System II). The ionic conductivity of PBE based on CMC (55 wt.%)–PVA (15 wt.%)–NH4NO3 (30 wt.%) and CMC (53 wt.%)–PVA (13 wt.%)–NH4NO3 (28 wt.%)–EC (6 wt.%) were optimized at room temperature with value of 1.70 × 10−3 S/cm and 3.92 × 10−3 S/cm, respectively. The ionic conduction for both systems shows Arrhenius behavior when tested at different temperatures. Electrochemical properties of the fabricated EDLC cell were analyzed for their electrochemical properties and System II showed higher specific capacitance than System I with values of 64.9 F/g and 89.1 F/g, respectively, based on a CV scan rate of 2 mV/s. Both fabricated EDLC show outstanding cycling stability over 10,000 cycles, which indicates that the present PBE based CMC–PVA has outstanding electrochemical performance and is a promising candidate for EDLC application.

Urchin‐like CoP nanomaterial as an electrocatalyst for efficient hydrogen evolution reaction

The morphology and structure of the electrocatalysts are important factors affecting their performance for electrochemical splitting water into hydrogen. Herein, the urchin-like CoP nanomaterials with the large specific surface area (SSA) were fabricated through the solvothermal process and the solid-gas reaction for hydrogen evolution reaction (HER). The resulting CoP nanomaterial with a diameter of approximately 4 μm was assembled by the nanowires with a length of about 10 nm. The excellent performance is accessible for HER with a small overpotential of 130 mV and a low Tafel slope of 52 mV/decade in a 0.5 M H2SO4 aqueous solution. Especially, the resulting urchin-like CoP nanomaterials with a large SSA and electric double-layer capacitance lower the electrochemical impedance and accelerate the electron transfer, endowing the excellent performance for HER process.

One‐step Preparation of Conducting Polymer/Metal Oxide Doped RGO Trinary Composite for Supercapacitor Applications

AbstractA naive one‐pot strategy developed to prepare high‐performance trinary based material as an energy storage material for supercapacitor. Herein, we have systematically studied and established an effortless and proficient synthetic method to formulate reduced graphene oxide (rGO)/polyaniline (PANI)/manganese dioxide (MnO2) (RPM) trinary material in one‐step without any additional oxidizing/polymerizing agent and acidic condition. The approach of “one arrow two targets” have employed to synthesize trinary based nanocomposite. For the first time, we have synthesized this trinary material in one step. Initially, in‐situ synthesized carbonic acid was consumed as a reducing agent to reduce the graphene oxide (GO) as well as it provided acidic condition for the formation of MnO2 and polymerization of aniline. Secondarily, MnO2 particles synthesized from KMnO4 precursor, which acted as an oxidizing agent to polymerize aniline in the presence of carbonic acid. The material reflected the electrical double layer capacitance as well as pseudocapacitance of RGO and PANI/MnO2. The material exhibited the maximum specific capacitance, 592 F/g at 1 A/g current density corresponds to excessive specific energy and specific power 66.6 Wh/kg, 1800 W/kg, respectively. This familiar route of direct production of graphene with the synergism of PANI‐MnO2 on carbon can be useful for large‐scale fabrication of nano‐carbon material for diverse applications including energy storage application.

Structural and thermodynamic properties of the electrical double layer in slit nanopores: A Monte Carlo study.

Grand canonical Monte Carlo (GCMC) simulation techniques at a constant electrode-electrolyte potential drop are employed to study the differential capacitance of a planar electric double layer in slit nanopores. According to the technique, a single randomly selected ion is exchanged between a simulation box and a reservoir. The probability of this step is given by the GCMC algorithm. To preserve the electroneutrality of the system after the ion exchange, the electrode charge is adequately modified, which produces electrode charge fluctuations. The charge fluctuations are used to calculate the differential capacitance of the double layer. Results for the ion distributions, electrode surface charge density, and differential capacitance in slit nanopores are reported for a symmetric system of +1:-1 ionic valences with a common ionic diameter of 0.4 nm at electrolyte concentrations of 0.2M, 1.0M, and 2.5M, pore widths of 0.6 nm, 0.8 nm, and 1.2 nm, a potential drop of 0.05 V, a relative permittivity of 78.5, and a temperature of 298.15 K. These results are compared with the corresponding data for a +1:-2 valence asymmetric system and a size asymmetric system with ionic diameters of 0.4 nm and 0.3 nm. The results show that with increasing electrolyte concentration, the range of confinement effects decreases. For divalent anions, the width dependence of electrode charge and differential capacitance reveals a maximum. The differential capacitance curves show a camel shape to bell shape transition as the electrolyte concentration increases. Asymmetry in both ionic valences and diameters leads to asymmetric capacitance curves.

Electrochemical Behavior of Cobalt Oxide/Boron-Incorporated Reduced Graphene Oxide Nanocomposite Electrode for Supercapacitor Applications

Electrodes from hydrothermally synthesized boron-incorporated reduced graphene oxide (B-rGO), Co3O4, and Co3O4/B-rGO nanocomposites are tested in 2 M KOH and NaOH electrolytes for supercapacitor applications. Structural characterization was done by x-ray diffraction and x-ray photoelectron spectroscopy. Cyclic voltammogram of B-rGO indicates partial electrical double-layer capacitance and pseudocapacitive behaviors. Co3O4, shows two reversible redox peaks, indicating diffusion-controlled (battery-like) process. Interestingly, Co3O4/B-rGO possesses both the pseudocapacitive and diffusion-controlled features. The specific capacitance (Csp) from galvanostatic charge/discharge experiments is higher in all the electrodes in KOH than in NaOH. Co3O4/B-rGO shows the highest Csp of 600 F g−1 (270 C g−1) at 0.1 A g−1 and 454 F g−1 (204 C g−1) at 10 A g−1 in KOH. Co3O4/B-rGO-KOH system retains 87.8% capacitance after 2000 cycles, demonstrating very good cyclic stability. Co3O4/B-rGO-KOH system yields, a remarkable, maximum power density of 2250 W kg−1 with an energy density of 12.77 W h kg−1 at 10 A g−1. The better performance in KOH is attributed to the low hydration sphere radius, high ionic conductivity of K+, low diffusive and charge transfer and electrode resistance, estimated from electrochemical impedance spectroscopy. The electrode–electrolyte combination is crucial for the overall performance as a supercapacitor electrode.

Heteroatoms-doped porous carbon electrodes with three-dimensional self-supporting structure derived from cotton fabric for high-performance wearable supercapacitors

In this work, converting cotton fabrics into high-performance flexible carbon electrodes are achieved successfully by using traditional dyeing, flame retardant finishing and carbonization processes for wearable supercapacitors. The optimal carbon electrode (CCF-SP) doped with O, N, P and S heteroatoms, exhibits high surface area (643.7 m2 g−1), porous structure and good hydrophilicity. Because of electric double layer capacitance provided by carbon materials and faradaic capacitance provided by heteroatoms, the specific capacitance of CCF-SP electrode is as high as 3079.8 ± 17.9 mF cm−2 at 2 mA cm−2. After 5000 cyclic tests, residual capacitance of CCF-SP is still 99.3% of the initial value, suggesting good rate property and coulombic efficiency. In addition, flexible supercapacitor (FSC) assembled by CCF-SP electrodes exhibits an excellent energy density of 9.4 mWh cm−3 at power density of 37.5 mW cm−3. This device can power electronic gadgets at bending situation without loss of capacitance. The stunning electrochemical properties of the created carbon electrodes and its FSCs indicate that the method of heteroatoms doping combined with carbonization treatments is cheap and easy to mass produce, which can be utilized to fabricate electrodes for wearable electronic devices in the future.

Porous Carbon-Based Supercapacitors Directly Derived from Metal-Organic Frameworks.

Numerously different porous carbons have been prepared and used in a wide range of practical applications. Porous carbons are also ideal electrode materials for efficient energy storage devices due to their large surface areas, capacious pore spaces, and superior chemical stability compared to other porous materials. Not only the electrical double-layer capacitance (EDLC)-based charge storage but also the pseudocapacitance driven by various dopants in the carbon matrix plays a significant role in enhancing the electrochemical supercapacitive performance of porous carbons. Since the electrochemical capacitive activities are primarily based on EDLC and further enhanced by pseudocapacitance, high-surface carbons are desirable for these applications. The porosity of carbons plays a crucial role in enhancing the performance as well. We have recently witnessed that metal–organic frameworks (MOFs) could be very effective self-sacrificing templates, or precursors, for new high-surface carbons for supercapacitors, or ultracapacitors. Many MOFs can be self-sacrificing precursors for carbonaceous porous materials in a simple yet effective direct carbonization to produce porous carbons. The constituent metal ions can be either completely removed during the carbonization or transformed into valuable redox-active centers for additional faradaic reactions to enhance the electrochemical performance of carbon electrodes. Some heteroatoms of the bridging ligands and solvate molecules can be easily incorporated into carbon matrices to generate heteroatom-doped carbons with pseudocapacitive behavior and good surface wettability. We categorized these MOF-derived porous carbons into three main types: (i) pure and heteroatom-doped carbons, (ii) metallic nanoparticle-containing carbons, and (iii) carbon-based composites with other carbon-based materials or redox-active metal species. Based on these cases summarized in this review, new MOF-derived porous carbons with much enhanced capacitive performance and stability will be envisioned.

Electrochemically Exfoliated Graphene/Manganese Dioxide Nanowire Composites as Electrode Materials for Flexible Supercapacitors

Flexible supercapacitors are of great significance for the development of intelligent electronic products and wearable devices. Herein, through reasonable design, self-supporting flexible film composites that can be used as supercapacitor electrodes, are synthesised by vacuum filtration. The composites are composed of electrochemically exfoliated graphene nanosheets and MnO2 nanowires, in which the graphene nanosheets mainly play the role of skeleton support, enhance conductivity, and provide electric double-layer capacitance, while the MnO2 nanowires mainly provide pseudocapacitance. Results show that the sample with 20% MnO2 possesses the best electrochemical performance due to the mass ratio which can give full play to the pseudocapacitive properties of MnO2 and the conductivity of graphene. The maximum mass specific capacitance reaches 106.2F g−1 at 0.5A g−1, and the areal specific capacitance is 767.0mF cm−2 at 1mA cm−2. The electrode also maintains 86.7% of the initial capacitance after 10000 cycles, indicating good cyclic stability. Furthermore, an asymmetric solid supercapacitor based on flexible thin films is assembled. The energy density is 20.7Wh kg−1, the power density is 1000W kg−1, and the capacitance remains 84.2% after 3000 cycles at 5.0A g−1. These results suggest that the as-prepared self-supporting material has the potential to be used to construct flexible supercapacitors for wearable equipment.

Hybrid supercapacitor based on graphene and Ni/Ni(OH)2 nanoparticles formed by a modified electrochemical exfoliation method

Hybrid supercapacitor combined with the merits of both the electric double layer capacitance and redox pseudocapacitance and thus have great potential. Here, hybrid materials of graphene and Ni/Ni(OH)2 nanoparticles were prepared through a modified electrochemical exfoliation method for using for supercapacitor. Large quantities of Ni/Ni(OH)2 nanoparticles with high redox pseudocapacitance were found to disperse either on the outer surface of the graphene or enclosed by the graphene with high electric double layer capacitance. The hybrid materials as-prepared show a capacitance as ultrahigh as 5715 mF/cm2 (1905 F/g) at 10 mA/cm2 and it remains 94.8% after 1000 cycles in 6 M KOH.

N-doped hierarchically porous carbon derived from grape marcs for high-performance supercapacitors

In this report, cost-effective nitrogen (N) -doped porous biocarbon was fabricated from grape marcs, and it demonstrated excellent capacitance, cyclic stability and rate performance as an electrode material for supercapacitors. By using urea as N-doping agent and KOH as activator, the as-prepared carbon material possessed suitable N-doping content (2.04 at%), well-developed porous structure and large specific surface area (2221.4 m2 g−1). As is clearly evidenced by the experimental results, the introduced N-containing functional groups could not only boost the electric double-layer capacitance (EDLC), but endow the material with considerable pseudo-capacitance under acidic conditions, thus resulting in distinct capacitances of the material under different electrolytes (446.0, 345.5 and 310.0 F g−1 at 0.5 A g−1 in 1 M H2SO4, 6 M KOH and 1 M Na2SO4, respectively). Moreover, the symmetrical supercapacitor device assembled based on this material also showed excellent performance by reaching an energy density of 16.3 Wh kg−1 with the power density of 348.3 W kg−1. All the results ensure that the biomass carbon derived from grape marcs can be used as a low cost, renewable and high-performance electrode material for supercapacitors.

Comparative Study of the Efficiency of New Technical Carbons СН210 and С40 in Electrosynthesis of Н2О2 from О2 in Gas-Diffusion Electrodes on Their Basis

The efficiency of new brands of technical carbon CH210 and C40 in the electrogeneration of Н2О2 from О2 in gas-diffusion electrodes (GDE) on their basis is studied in acidic solutions of the 0.5 М K2SO4 : 0.1 M H2SO4 (3 : 1) electrolyte. The textural characteristics of original materials and their mixtures with polytetrafluoroethylene used as the hydrophobizer are determined by low-temperature nitrogen adsorption as well as their electric double layer capacitance. For a comparison, similar studies are also carried out with technical carbon Vulcan XC-72. The rate constants for hydrogen peroxide decomposition on these materials in acidic solutions are determined. The data on the kinetics of hydrogen peroxide accumulation at the overall current density of 1500 А/m2 are as follows: the 6 h electrolysis produces the solution with Н2О2 concentration exceeding 2.5 М with the current efficiency higher than 70.0%. It is concluded that in this case, the surface area is not the determining factor. The technical carbons СН210 and С40 are comparable as regards their efficiency with the well-known technical carbon Vulcan XC-72 and can be used as electrocatalysts in GDE for electrosynthesis of Н2О2 from О2.

An integrated all-solid-state screen-printed potentiometric sensor based on a three-dimensional self-assembled graphene aerogel

An integrated all-solid-state screen-printed ion-selective potentiometric sensor for the determination of Cu2+ is proposed. The whole-cell potentiometric sensor incorporates a polymeric membrane copper ion-selective electrode (Cu2+-ISE) as an indicator electrode and an Ag/AgCl reference electrode with a polyvinyl butyral reference membrane. The three-dimensional (3D) self-assembled porous graphene aerogel (PGA) can be conveniently and rapidly electrodeposited on the electrode substrate surface. Due to its interior 3D interconnected porous structures, the PGA has a large electrical double layer capacitance and fast charge transfer capability, which make it promising to be used as solid contact for the fabrication of the Cu2+-ISE. The developed potentiometric sensor shows a good Nernstian response over a range from 10−6 to 10−3 M with a detection limit of 10−6.5 M. In addition, the sensor exhibits a stable potential response with the absence of an undesirable water layer at the ion-selective membrane/PGA interface.

Preparation of Polyaniline onto dl-Tartaric Acid Assembled MXene Surface as an Electrode Material for Supercapacitors

Polyaniline (PANI)/MXene composites have been widely studied for high performance supercapacitors because of the combination of the electric double layer capacitance and pseudocapacitance. In this ...

Scalable synthesis of zeolite-templated ordered microporous carbons without external carbon deposition for capacitive energy storage

Abstract Zeolite-templated carbons (ZTCs) have unique ordered microporous structures composed of 3-dimensionally connected graphene nanoribbons and buckybowl-like frameworks. ZTCs can exhibit extra-large surface areas, narrow micropore size distributions, and electrical conductivity, which make them promising for adsorption, catalysis, and energy storage. However, the synthesis of ZTCs still remains a great challenge when the synthesis scale is larger than just a few grams. Carbon deposition within narrow zeolite micropores is diffusion-limited, and unwanted dense carbon layers are often deposited at the external surface of zeolite, substantially diminishing ZTCs' structural properties and performances in various applications. In this study, we conducted the large-scale synthesis of ZTCs (>80 g) in a bubbling fluidized bed, which enables efficient mass/heat transfer. Compared to conventional synthesis in a fixed bed, ZTCs with superior structural properties could be synthesized in much shorter time. The resultant ZTCs showed ordered microporous structures with large surface areas (~3000 m2 g−1) and microporosity (~1.1 cm3 g−1). Most importantly, these ZTCs were free of undesirable external carbon deposition, which greatly diminishes the mass transfer of guest molecules (e.g., electrolytes) into the micropores. As a result, the ZTCs showed superior electrical double-layer capacitance compared to those synthesized in a typical fixed bed.

Facile flame deposition of carbon coating onto Ni foam and the study of the derived carbon foam with high capacitive performance

Porous carbon foam was directly synthesized in an ethanol vapor flame within only 1 min for the first time. Nickel foam served as both hard template and catalyst substrate for catalyzing deposition of carbon coating on its surface. Carbon foam modified with oxygen-containing organic groups was obtained after etching the metal substrate. The following thermal treatment endowed the carbon foam with corrugated strut surface, decreased thickness of carbon strut layer, and reduced hetero-atom doping level. Moreover, the electrical conductivity of the foam was enhanced by >3 orders of magnitude up to 59.3 S m−1. Additionally, the free-standing thermal-annealed carbon foam electrode exhibited a desirable electric double-layer capacitance of 172 F g−1 at 2 Ag−1 in a three-electrode half-cell configuration, which could be due to its unique porous structure, high electrical conductivity, rich defects and oxygen-doping of the carbon foam.

Effective carbon dioxide stabilization of nanofibers electrospun from raw coal tar and polyacrylonitrile

Non-fuel utilizations of coal for sustainable carbon materials production is certainly beneficial to the abatement of anthropogenic carbon dioxide emissions. Also, the technological uses of carbon dioxide are emergent to the earlier realization of the Paris Climate Agreement. This research was innovatively designed to produce carbon nanofibers from Wyoming Powder-River-Basin coal-derived supercritical extraction liquid (referred to raw coal tar) along with predetermined percentages of polyacrylonitrile by electrospinning, fiber stabilization with carbon dioxide, and subsequent carbonization treatment. The effects of raw coal tar additives to polyacrylonitrile nanofibers regarding the structural, textural and surface properties were investigated. Attenuated total reflection and diffuse reflectance infrared Fourier transform analyses reveal the difference in the dynamic evolution pathways of surface functional groups during the state-of-the-art oxygen-based and the new carbon dioxide-based fiber stabilization processes. In terms of mechanical properties, raw coal tar modifications give significant rise to the tensile strength of annealed polyacrylonitrile nanofibers, regardless of oxidative stabilization options. Additionally, the synergy of raw coal tar containing (30 wt %) polymeric precursor and carbon dioxide stabilization produces carbon nanofibers with a superior area-normalized electric double-layer capacitance of 1408.9 μF/cm2, which is approximately 4 times higher than the oxygen-stabilized pure polyacrylonitrile-derived ones.

Alternative coulometric signal readout based on a solid-contact ion-selective electrode for detection of nitrate

Traditional potentiometric NO3−-selective electrodes suffer from a fundamental limitation of the Nernst slope (59.1 mV/dec at 25 °C) due to the relationship between the potential and the logarithmic of ionic activity. Herein, a coulometric signal readout is proposed instead of the potentiometric response for detection of NO3− based on an ordered mesoporous carbon (OMC)-based solid-contact ion-selective electrode (ISE). The mechanism for obtaining the coulometric signal is based on the electrical double layer capacitance of OMC compensating the potential change at the ion-selective membrane/solution interface during the measurements under the control of a constant applied potential. Under the optimized conditions, the coulometric signal for the OMC-based solid-contact NO3−-ISE shows two linear responses in the activity range of 1.0 × 10−6-8.0 × 10−6 M and 8.0 × 10−6-8.0 × 10−4 M, and the detection limit is 4.0 × 10−7 M (3σ/s). The proposed coulometric response also shows excellent reproducibility and stability in the presence of O2 and CO2 and light on/off. Additionally, the coulometric response shows acceptable and reliable results for detection of NO3− in mineral water as compared to the traditional potentiometric response and the ion chromatography. This work provides a promising alternative signal readout for detection of ions by using solid-contact ion-selective electrodes.

Alternately Dipping Method to Prepare Graphene Fiber Electrodes for Ultra-high-Capacitance Fiber Supercapacitors.

SummaryFlexible fiber supercapacitors are promising candidate for power supply of wearable electronics. Fabrication of high-performance fibers is in progress yet challenging. The currently available graphene fibers made from wet-spinning or electro-deposition technologies are far away from practical applications due to their unsatisfactory capacitance. Here we report a facile alternately dipping (AD) method to coat graphene on wire-like substrates. The excellent mechanical properties of the substrate with greatly diverse choices can be carried over to the fiber supercapacitors. Under such guideline, the graphene fiber with a titanium core made by our AD method (AD:Ti@RGO) shows an ultra-high specific capacitance of up to 1,722.1 mF cm−2, which is ∼1,000 times that of wet-spinning- and electro-deposition-fabricated neat graphene fibers and presents the highest specific capacitance to date. With excellent mechanical properties and striking electrochemical performances, the AD:Ti@RGO-based supercapacitors light the path to the next-generation technologies for wearable devices.

MnO/few-layered-graphene composite as a high performance electrode material in aqueous supercapacitors

MnO nanonetwork decorated few layered graphene (FLG) composite was prepared using a completely solid state process and when tested as an electrode material in an aqueous supercapacitor it delivered an excellent specific capacitance (SC) of 778.5 F/g at a current density of 0.5 A/g and retained 93% of the SC even after 1000 charge-discharge cycles. Cyclic Voltammetry (CV) studies showed that the SC of the composite is the resultant of the combined electric double layer capacitance of FLG and pseudo-capacitance of MnO. The negligible change in the nature of CV curves recorded at different scan rates showed that the composite is electrochemically stable. Also, the high discharge capacitance is explained in terms of composite’s porosity, which shortens the cation path into the electrode matrix.