Electric Double Layer Capacitance Research Articles

Molecular Insights into Curvature Effects on the Capacitance of Electrical Double Layers in Tricationic Ionic Liquids with Carbon Nanotube Electrodes.

Ionic liquid (IL) electrolytes and carbon nanotube (CNT) electrodes have exhibited promising electrochemical performance in supercapacitors. Nevertheless, the adaptability of tricationic ILs (TILs) in CNT-based supercapacitors remains unknown. Herein, the performance of supercapacitors with (6,6), (8,8), (12,12), and (15,15) CNT electrodes in the TIL [C6(mim)3](Tf2N)3 was assessed via molecular dynamics simulations, paying attention to the electric double-layer (EDL) structures and the relations between the CNT curvature and capacitance. The results disclose that counterion and co-ion number densities near CNT electrodes have a marked reduction, compared with that of the graphene electrode. The capacitance of the EDL in the TIL increases significantly as the CNT curvature increases and the capacitance of the TIL/CNT systems is higher than that of the TIL/graphene system. Moreover, different EDL structures in the TIL and the monocationic IL (MIL) [C6mim][Tf2N] near CNT electrodes were revealed, showing higher-concentration anions [Tf2N]- at the CNT surfaces in the TIL. It is also verified that the TIL has a greater energy-storage ability under high potentials. Furthermore, the almost flat or weakly camel-like capacitance-voltage (C-V) curve of EDLs in the TIL turns into a bell shape in the MIL, because of the ion accumulation at the CNT surfaces and the associations between ions.

Capacitive Behavior of Aqueous Electrical Double Layer Based on Dipole Dimer Water Model.

The aim of the present paper is to investigate the possibility of using the dipole dimer as water model in describing the electrical double layer capacitor capacitance behaviors. Several points are confirmed. First, the use of the dipole dimer water model enables several experimental phenomena of aqueous electrical double layer capacitance to be achievable: suppress the differential capacitance values gravely overestimated by the hard sphere water model and continuum medium water model, respectively; reproduce the negative correlation effect between the differential capacitance and temperature, insensitivity of the differential capacitance to bulk electrolyte concentration, and camel-shaped capacitance-voltage curves; and more quantitatively describe the camel peak position of the capacitance-voltage curve and its dependence on the counter-ion size. Second, we fully illustrate that the electric dipole plays an irreplaceable role in reproducing the above experimentally confirmed capacitance behaviors and the previous hard sphere water model without considering the electric dipole is simply not competent. The novelty of the paper is that it shows the potential of the dipole dimer water model in helping reproduce experimentally verified aqueous electric double layer capacitance behaviors. One can expect to realize this potential by properly selecting parameters such as the dimer site size, neutral interaction, residual dielectric constant, etc.

Deep Eutectic Solvent (DES) for In Situ Templating Carbon Material: Carbon Characterization and Application in Supercapacitors Containing Multivalent Ions

The development of carbon materials with desirable textures and new aqueous electrolytes is the key strategy to improve the performance of supercapacitors. Herein, a deep eutectic solvent (DES) was used for in situ templating of a carbon material. A carbon material was characterized (XRD, N2-physisorption, FTIR, SEM and EDS) and used as an electrode material for the first time in multivalent-based supercapacitors. In situ templating of carbon was performed using a novel DES, which serves as a precursor for carbon and for in situ generation of MgO. The generation of MgO and its roles in templating of carbon were discussed. Templating of carbon with MgO lead to an increase in surface area and a microporous texture. The obtained carbon was tested in multivalent-ion (Al3+ and Mg2+) electrolytes and compared with H2SO4. The charge-storage mechanism was investigated and elaborated. The highest specific capacitance was obtained for the Al(NO3)3 electrolyte, while the operating voltage follows the order: Mg(NO3)2 > Al(NO3)3 > H2SO4. Electrical double-layer capacitance (versus pseudocapacitance) was dominant in all investigated electrolytes. The larger operating voltage in multivalent electrolytes is a consequence of the lower fraction of free water, which suppresses hydrogen evolution (when compared with H2SO4). The GCD was experimentally performed on the Al(NO3)3 electrolyte, which showed good cyclic stability, with an energy density of 22.3 Wh kg−1 at 65 W kg−1.

Capacitive deionization performance of asymmetric nanoengineered CoFe2O4 carbon nanomaterials composite.

Capacitive deionization (CDI) is a relatively new technique that uses electric double layer (EDL) effects, high-affinity chemical groups, redox-active materials, and membrane capacitive electrosorption principle for the desalination. In this paper, hydrothermal synthesis of cobalt ferric oxide (CFO) metal oxide nanoparticles (NPs) coupled with the vacuum filtration method, or the freeze-drying method is used to fabricate high-performance nanocomposites: CFO-graphene, CFO-CNTs, and CFO-3DrGO. Two times of hydrothermal reaction methods were conducted to fabricate the CFO-3DrGO nanoengineered as a pseudocapacitive/EDL electrode. The results have demonstrated that the SAC of CFO-3DrGO/CFO (64.5mgg-1) is greater than that of the CFO-graphene/CFO (55.16mgg-1) and CFO-CNTs/CFO (21.5mgg-1) due to the better surface area of the CFO-3DrGO nanocomposite (330 m2g-1). The higher surface area of the CFO-3DrGO is due to the porous and interconnected 3D structure of the 3DrGO, and it provides a larger surface area to form EDL capacitance. In addition, the added porous 3DrGO entangled with the spinel crystals (CoFe2O4) in the composite allowed for a quick ion diffusion across the interconnected open macroporous structures.

One step activation by ammonium chloride toward N-doped porous carbon from camellia oleifera for supercapacitor with high specific capacitance and rate capability

In recent years, various biomasses (such as coconut, cotton, wheat straw, basswood, bamboo, etc.) have been utilized to prepare porous carbon materials (PCMs) through carbonization and/or physical/chemical activation. Most of these carbon materials are limited by the electric double-layer capacitance, resulting in a limited specific capacitance. Moreover, the preparation processes are often complicated and the carbon yield is low. Therefore, from the perspective of green and sustainable preparation of PCMs with high carbon yield and high performance, in this study, N-doped porous carbon electrodes were prepared by one-step activation carbonization method using camellia oleifera branches as raw material and NH 4 Cl as the activator. The N-doped NCW-2 sample has a rational hierarchical porous structure and high N doping amount (3.35 at. %) and exhibited optimal rate performance with a specific capacitance of 250 F g −1 at 50 A g −1 . The symmetrical device also presented excellent performance with a capacitance retention of 93.7 % after cycling 30,000 times at 20 A g −1 and delivered superior rate performances of 22.3 W h kg −1 @100 W kg −1 to 11.8 W h kg −1 @4800 W kg −1 . This work may provide a certain reference for the preparation of N-doped biomass-derived PCMs and widen its practical application in supercapacitor devices. • The self-supporting N-doped porous carbon can be directly used without posttreatment. • The mechanism of doping and activation are preliminarily proposed. • The as-prepared material has a high nitrogen doping of 3.35 at. %. • Electrodes exhibited a high specific capacitance of 250 F g −1 even at 50 A g −1 . • The symmetrical device showed a capacitance retention of 93.7 % after 30,000 cycles.

Free-standing vanadium oxide hydration/reduced graphene oxide film for ammonium ion supercapacitors

Aqueous ammonium-ion energy storage systems have recently gained continuous attention owing to the advantages of sustainability and environmental-friendliness in the grid-scale application. However, ammonium-ion supercapacitors are still in their infancy, and it is of great challenge in developing suitable materials for application in wearable energy storage devices. Herein, we develop a vanadium oxide hydration (V2O5·nH2O)/reduced graphene oxide (rGO) composite film (denoted as VGF) as a free-standing paper-like electrode for ammonium-ion storage, where V2O5·nH2O shows an expanded interlayer spacing and is sandwiched by rGO through chemical bonds. As a result, the designed VGF exhibits a capacitance of 600F·g−1 at 0.2 A·g−1 and good cyclability of over 10,000 cycles with a retention of 93 % using PVA/NH4Cl gel electrolyte. Meanwhile, the ammonium-ion storage mechanism in VGF electrode is further verified to be dominated by the intercalation pseudocapacitance and electric double-layer capacitance. Furthermore, the quasi-solid-state symmetric supercapacitor (SSC) has been also assembled to assess the feasibility of practical applications in wearable devices. As expected, the SSC possesses an areal capacitance of 241 mF·cm−2 at 0.1 mA·cm−2 (0.82 Wh·m−2 at 0.09 W·m−2) and an excellent cyclability of 20,000 cycles with a retention of 92 %, which is comparable to that achieved in the vanadium oxides powder-made electrodes and the SSC made of. Together with the excellent flexibility and feasibility of parallel/series combination, the VGF SSC devices shows great possibility for the applications in wearable devices, which further proves the great potential of this designed VGF free-standing electrode for ammonium-ion storage.

Regulation of the electric double-layer capacitance of MoS2/ionic liquid by carbon modification

Regulation of the electric double-layer capacitance of MoS2/ionic liquid by carbon modification

Graphene-polymer nanocomposites electrode with ionic nanofibrous membrane for highly sensitive supercapacitive pressure sensor

Wearable pressure sensors have obtained significant interests owing to their diverse applications in electronic skins and smart health informatics. Ultrahigh sensitivity, wide linearity, and better pressure resolution are highly desirable attributes of the pressure sensors for versatile applications. Here, a flexible supercapacitive pressure sensor (SPS) based on a novel reversible ion pumping mechanism is reported that remarkably increases the pressure sensitivity over a broad linear range exceeding the limits of the existing iontronic pressure sensors. The SPS is composed of lower concentration ionic nanofibrous membrane between two graphene-polymer nanocomposite electrolyte films, which engages in ion pumping, triggering a high electrical double layer capacitance under external stimuli. The fabricated SPS exhibited an ultra-high sensitivity of 9029 kPa−1 over wide linear range (0–100 kPa) with outstanding pressure resolution of 0.446%. Additionally, a wireless fitness tracker system is successfully demonstrated by integrating the SPS, which can monitor the food consumption and posture of users to improve their lifestyle.

Compacting Electric Double Layer Enables Carbon Electrode with Ultrahigh Zn Ion Storage Capability.

Carbon-based cathodes for aqueous zinc ion hybrid supercapacitors (ZHSCs) typically undergo low Zn ion storage capability due to their electric double layer capacitance (EDLC) energy storage mechanism that is restricted by specific surface area and thickness of electric double layer (EDL). Here, we report a universal surface charge modulation strategy to effectively enhance the capacitance of carbon materials by decreasing the thickness of EDL. Amino groups with lone pair electrons were chosen to increase the surface charge density and enhanced the interaction between carbon electrode and Zn ions, thus effectively compacting the EDL. Consequently, amino functionalized porous carbon based ZHSCs can deliver an ultrahigh capacity of 255.2 mAh g-1 along with excellent cycling stability (95.5 % capacity retention after 50 000 cycles) in 1 M ZnCl2 electrolyte. This study demonstrates the feasibility of EDL modified carbon as Zn2+ storage cathode and great prospect for constructing high performance ZHSCs.

Compacting Electric Double Layer Enables Carbon Electrode with Ultrahigh Zn Ion Storage Capability

AbstractCarbon‐based cathodes for aqueous zinc ion hybrid supercapacitors (ZHSCs) typically undergo low Zn ion storage capability due to their electric double layer capacitance (EDLC) energy storage mechanism that is restricted by specific surface area and thickness of electric double layer (EDL). Here, we report a universal surface charge modulation strategy to effectively enhance the capacitance of carbon materials by decreasing the thickness of EDL. Amino groups with lone pair electrons were chosen to increase the surface charge density and enhanced the interaction between carbon electrode and Zn ions, thus effectively compacting the EDL. Consequently, amino functionalized porous carbon based ZHSCs can deliver an ultrahigh capacity of 255.2 mAh g−1 along with excellent cycling stability (95.5 % capacity retention after 50 000 cycles) in 1 M ZnCl2 electrolyte. This study demonstrates the feasibility of EDL modified carbon as Zn2+ storage cathode and great prospect for constructing high performance ZHSCs.

Co/Zn bimetallic organic framework nanoparticles on carbon fibers as cathode for a high-performance rechargeable aqueous Zn-ion hybrid supercapacitor

Zinc-ion hybrid supercapacitors (ZHCs) are attracting more attentions due to their high energy/power densities and safety. Pseudocapacitive materials can provide larger capacitances than carbon materials due to their specific faradaic processes. Metal-organic frameworks with good electronic conductivity and abundant redox functional groups are ideal cathodic materials. Herein, a bimetallic organic framework cathode (Co/Zn-ZIF(M24)@CC) is proposed as a high-performance cathode in Zn-ion hybrid supercapacitor. The Co/Zn-ZIF(M24)@CC cathode benefits from a dual-ion storage mechanism of the pseudocapacitive behavior of H+ and the electrical double-layer capacitance behavior of Zn2+, which is methodically explored by ex situ electroanalytic characterizations. The as-prepared Co/Zn-ZIF (M24)@CC electrode achieved the highest energy density of 124.6 Wh kg−1 at 49.2 W kg−1. This study lays the foundation for the rational design of metal-organic cathodes in ZHCs.

Perylene-Templated Hierarchically Porous Carbon Fibers as Efficient Supercapacitor Electrode Material

Abstract Nitrogen-doped nanoporous carbon fibers were prepared using chromonic perylene bisimide self-assemblies as templates. The method involves the formation of perylene-templated silica followed by carbonization and etching. This strategy does not require any additional carbon or nitrogen precursor and therefore omits the associated impregnation step. The obtained carbon fibers were tested as electrode materials for supercapacitor applications. Owing to the high surface area (695 m2 g−1) and well-developed porosity (pore volume ca. 0.67 cm3 g−1) with hierarchical micro- and mesopore structures, N-doping and high-wettability, amorphous carbon fibers show excellent electrical double-layer capacitance with faradaic pseudocapacitance performance in an aqueous electrolyte solution (1 M H2SO4). A working electrode prepared from the optimal sample achieved a high specific capacitance of 317 F g−1 at a current density of 1 A g−1 with excellent capacitance retention of 80% at a high current density of 50 A g−1 suggesting a fast electrolyte ion diffusion at the electrode surface. The electrode also showed outstanding cycle stability of 99% after 10,000 successive charge-discharge cycles. These results show the high potential of chromonic-derived hierarchically porous carbon fibers as electrode materials for high-performance supercapacitors with advantages over electrospinning and catalytic fabrication methods, such as the absence of heavy metals and organic solvents in the preparation procedure.

Self-Promoting Energy Storage in Balsa Wood-Converted Porous Carbon Coupled with Carbon Nanotubes.

For most electrodes fabricated with carbon, transition metal compounds, or conductive polymers, the capacitance may deteriorate with cyclic charging and discharging. Thus, an electrochemically stable supercapacitor has long been pursued by researchers. In this work, the hierarchical structure of balsa wood is preserved in the converted carbon which is used as a supporting framework to fabricate electrodes for supercapacitors. Well-grown carbon nanotubes (CNTs) on interior and exterior surfaces of balsa carbon channels provide two advantages including 1) offering more specific surface area to boost capacitance via electric double layer capacitance and 2) offering more active Fe and Ni sites to participate in the redox reaction to enhance capacitance of the balsa carbon/CNTs electrode. The balsa carbon/CNTs demonstrate an excellent area capacitance of 1940 mF cm-2 . As active sites on Ni and Fe catalysts and inner walls of CNTs are gradually released, the capacitance increases 66% after 4000 charge-discharge cycles. This work brings forward a strategy for the rational design of high-performance biomass carbon coupled with advanced nanostructures for energy storage.

Fabrication of high-performance supercapacitor using date leaves-derived submicron/nanocarbon

Offering a suitable and low-cost electrode material is one of the most important and challenging demands in supercapacitor research. In this aspect, carbon prepared from biomass by simply pyrolysis and ball milling could be one ideal electrode material for supercapacitor applications. Hence, a novel type of submicron/nanocarbon was prepared from date leaves by simple pyrolysis and ball milling. After morphological and chemical characterizations, the prepared carbon was used as the electrode material upon immobilizing on a steel substrate (current collector) to fabricate a high-performance symmetric supercapacitor. The fabricated supercapacitor took advantage of the carbon's electric double layer capacitance behaviour and pseudocapacitance behaviour of heteroatoms present in the carbon. The developed supercapacitor device provides significant charging/discharging using the optimum electrolyte (0.1 M sulfuric acid). That manifested with a high specific capacitance of (∼107 F/g) and maintained above 92% of its initial capacitance after 1000 charge/discharge cycles. Furthermore, the supercapacitor provides an energy density of ∼10 Wh/Kg at a power density of ∼200 W/Kg. This work provides an inexpensive, high-performance supercapacitor that depends on the biomass (date palm leaves) and nominates it as a capable candidate for mass-product in the future.

Synthesis of nitrogen-doped graphene driven from photothermal decomposition of ammonium bicarbonate and its application in supercapacitors

In this work, nitrogen-doped graphene is achieved in a short time at low temperature by UV light radiation which induces thermal decomposition of ammonium bicarbonate (NH4HCO3) to release NH3 as nitrogen source. XRD and XPS results confirm that the most of oxygen-containing functional groups are removed from graphene oxide after photoreduction and nitrogen doping, and thus graphene oxide was reduced to form N-doped graphene. The N content of the obtained graphene is 2.91 at.%. The SEM images show that the graphene film on Ni foam is composed of spherical graphene nanoparticles, making it easy to adsorb more ions to form electric double-layer capacitance effect and increase the specific capacitance. As expected, the specific capacitance of UV assisted N-doped graphene is as high as 328.85 F g−1 at 0.5 A g−1, which is larger than that of graphene without nitrogen doping (261.13 F g−1 at 0.5 A g−1). Meanwhile, N-doped graphene shows good rate performance and cycle stability (capacitance retention rate: 96.1 % after 10, 000 cycles). This work shows the excellent supercapacitive performance of N-doped graphene, and also provides a simple and environmentally friendly method for rapid reduction and nitrogen doping of graphene oxide to prepare high-performance graphene.

Anti-corrosion behavior of 2-(((4-((2-morpholinoethyl)(pyridin-2-ylmethyl)amino)butyl)imino)methyl)naphthalen-1-ol on mild steel in hydrochloric acid solution: Experimental and theoretical studies

A naphthalene derivative, namely 2-(((4-((2-morpholinoethyl)(pyridin-2-ylmethyl)amino) butyl) imino)methyl)naphthalen-1-ol (HL) was synthesized and its chemical structure characterized by spectroscopic techniques (1H, 13C Nuclear magnetic resonance, Fourier-transform infrared spectroscopy and Mass spectroscopy). Its action as a corrosion inhibitor against the corrosion of mild steel in 1.0 M HCl solution was fully investigated at ambient temperature using weight loss measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy techniques. The results indicated inhibition efficiency for HL at 100 ppm concentration of greater than 90%. It was determined that the adsorption of HL molecules on the metallic surfaces occurred through the heteroatoms, based on a combination of physical and chemical mechanisms (calculated value of ΔG0ads was -23.1 kJ/mol) and followed a Langmuir adsorption process leading to a reduction in electric double layer capacitance (20.40 µF.cm−2 at 100 ppm concentration). The highest occupied molecular orbital and lowest unoccupied molecular orbital calculations demonstrated that the existence of nitrogen and oxygen atoms in the morpholine and pyridine groups of the protonated form of the molecule assisted in the formation of stronger bonds with the surface of the metal, as an electrophilic agent.

Recent development of carbon electrode materials for electrochemical supercapacitors

Supercapacitors have gained much attention due to their remarkable merits such as stable cycle performance, high power density and excellent charge and discharge performance at high rate. From this perspective, carbon-based materials are widely explored as the active electrode materials for supercapacitors by taking advantages of hierarchical porous structure, excellent chemical stability, multistage pore structure, high surface area, and excellent conductivity. Various studies have explored many methods to utilize carbon-based electrodes. The large amount of defects inside carbon materials including functional groups, heteroatoms, name as foreign-doping, can provide pseudocapacitance. Meanwhile, self-doping (voids, vacancies, defects, etc.) may also enhance the electric double-layer capacitance. In this context, a brief overview of carbon materials for supercapacitor is expounded, including their characteristics, development process and the future challenges, providing a referential guide to those new to this field.

Polyaniline—Graphene Electrodes Prepared by Electropolymerization for High-Performance Capacitive Electrodes: A Brief Review

Both polyaniline (PANI) and graphene are widely studied for their application as capacitive electrodes in energy storage devices. However, although PANI can be easy synthesized, is of low cost and has a higher specific capacitance than graphene, pristine PANI electrodes do not present long-term stability due to their large volume changes during release/doping of the electrolyte ions and surface area reduction with charge-discharge cycling. That is why a combination of PANI with carbonaceous materials, especially conductive and high-surface-area graphene as well as more widely used reduced graphene oxide (rGO), provides an effective approach to solve these problems. At the same time, the electropolymerization process is one of the possible methods for synthesis of PANI composites with G or rGO as freestanding electrodes. Therefore, no binders or additives such as carbon black or active carbon need to be used to obtain PANI/rGO electrodes by electrochemical polymerization (EP), in contrast to similar electrodes prepared by the chemical oxidative polymerization method. Thus, in this paper, we review recent advances in EP synthesis of PANI/rGO nanocomposites as high-performance capacitive electrode materials, combining the advantages of both electrical double-layer capacitance of rGO and pseudocapacitance of PANI, which hence exhibit long cycle life and high specific energy.

An Incremental Double Layer Capacitance of a Novel Ring-Disk Electrodes Array for Avidin/Strepavidin Sensing

Electric double layer (EDL) is established by ion redistribution at a solid-liquid interface. This ion redistribution electrically screens solid-surface charges and renders the interface to neutral. As a result, EDL is highly related to the surface potential, and a capacitor or constant phase element (CPE) is always employed to model the relationship between EDL and surface potential. According to this mechanism, diverse applications have been developed by controlling EDL via modulate potential fields or surface modifications. However, most of previous methods are sophisticated and hard to implemented as an in-situ monitoring method. To address this demand, we proposed a ring-disk electrode array (RDA) architecture to detect the changes of EDL capacitance between ring and disk electrode.Based on the proposed architecture, the surface potential will change while the biomolecular is immobilized onto to the vertical nanogap. This effect is verified by immobilizing different charged functional groups and the correlation between the surface potential and incremental-capacitance variance is also demonstrated. Based on this effect, the application for Avidin detection is implemented. The detectable range for Avidin measurement is from 100 fg/ml to 1 ng/ml.Based on this work, the incremental double-layer capacitance of a planar nanogap structure can provide a simple and reliable method for surface potential monitoring and can be used for different chemical and clinical examinations. Figure 1

Unveiling the surface dominated capacitive properties in flexible ternary polyaniline/NiFe2O4/reduced graphene oxide nanocomposites hydrogel electrode for supercapacitor applications

The 3D ternary nanocomposites hydrogel have been effectively fabricated on carbon cloth using a two-step synthesis approach. Nickel ferrite nanoparticles (NiFe2O4) prepared by template method have been dispersed onto/within rGO nanosheets leading to the formation of NiFe2O4/rGO (NFG) nanocomposites. Afterward, polyaniline hydrogel has been polymerized on NFG nanosheets to prepare ternary polyaniline/NiFe2O4/rGO hydrogel (PNFG) nanocomposites on carbon cloth that can be further utilized as a binder-free supercapacitor electrode. The resulting 3D ternary nanocomposites hydrogel achieved maximum specific capacitance of 1134.28 F/g at a current density of 1 A/g and 76.46 % of capacitive retention at 10 A/g. The supercapacitor electrode exhibited outstanding rate capability and superior cyclic stability up to 5000 successive cycles. In addition, the symmetric supercapacitor cell delivered 0.61 kW/kg of specific power and 19.29 Wh/kg of specific energy. The excellent electrochemical characteristics of PNFG is ascribed to its well-designed 3D microstructure and the synergistic effect created by the capacitive mechanism due to electric double layer capacitance (EDLC) and pseudocapacitance (surface redox reactions) as well as diffusion-controlled mechanism (faradaic redox reactions). It has been revealed that the overall electrode reaction is dominated by surface-controlled processes, with a small contribution from diffusion-controlled faradaic processes.