Electric Double Layer Supercapacitors Research Articles

Bimetallic zeolitic imidazolate frameworks for symmetric electrical double-layer supercapacitors with aqueous electrolytes

We have investigated a facile synthesis of nanoporous carbon using a bimetallic (Co2+ and Zn2+) zeolitic imidazolate framework (ZIF) as a precursor. The properties of the as-prepared bimetallic ZIF-derived carbon, including the specific surface area, porosity, and degree of graphitization, are precisely controlled. This material has been directly applied in a symmetric electrical double-layer supercapacitor (EDLC). The specific capacitance of the symmetric EDLC is estimated to be 10.5F·g−1 at a high current density of 10A·g−1 in 0.5M sulfuric acid.

SURFACE–INTERFACE REACTION OF SUPERCAPACITOR ELECTRODE MATERIALS

Facing the challenge of low energy density of conventional electric double layer supercapacitors, researchers have long been focusing on the development of novel pseudocapacitive electrode materials with higher energy densities. Since capacitive charge storage reaction mostly occurs on the interface of electrode and electrolyte, the interface chemistry determines the achievable power and energy densities of a supercapacitor. Consequently, understanding of surface–interface reaction mechanism is a key towards efficient design of high-performance supercapacitor electrode materials. In this paper, we have reviewed the recent advances in the understanding of surfaces–interfaces in the system of pseudocapacitive supercapacitors. With significant research advancements in the understanding of surface–interface of supercapacitors, novel colloidal electrode materials with improved surface–interface structures have been developed in our previous work, which have the potential to deliver both high energy and power densities. This review aims to provide an in-depth analysis on the surface–interface control approaches to improve the energy and power densities of supercapacitors.

Nitrogen-doped worm-like graphitized hierarchical porous carbon designed for enhancing area-normalized capacitance of electrical double layer supercapacitors

Electrical double layer supercapacitors (EDLC) have an upper limit for their area-normalized capacitance (CA) and lead to a bottleneck that impede the commercialization of high-energy-density supercapacitor devices. Quantum capacitance (CQ) in series with electrical double layer capacitance (CEDL) has been demonstrated to be a tremendous obstacle for enhancing the CA of EDLC. Nitrogen doping can up-shift the Fermi-level and graphitization can improve the density of states (DOS), both of which can significantly mitigate the limiting influence of CQ. Here, a facile approach is developed for synthesizing an ideal carbon-based EDLC electrode material by simply adding ferrous sulfate heptahydrate (FSH) into the polymer when colloid aggregation. The morphology, porous structure, graphitization degree, doped N content and the types of the doped N of the samples can be easily tuned through changing the FSH ratio. The optimized nitrogen doped worm-like hierarchical porous carbon with graphitized porous carbon embossment (NWHC-GE) exhibits an exceptionally high CA (24.6 μF cm−2 at 1 A g−1 and 18.5 μF cm−2 at 100 A g−1). This demonstrates a way to enhance the CA and provides a potential strategy for breaking through the limiting specific capacitance of carbon-based materials.

Metal-free supercapacitor with aqueous electrolyte and low-cost carbon materials

Electric double-layer capacitors (EDLCs) or supercapacitors (SCs) are fast energy storage devices with high pulse efficiency and superior cyclability, which makes them useful in various applications including electronics, vehicles and grids. Aqueous SCs are considered to be more environmentally friendly than those based on organic electrolytes. Because of the corrosive nature of the aqueous environment, however, expensive electrochemically stable materials are needed for the current collectors and electrodes in aqueous SCs. This results in high costs for a given energy-storage capacity. To address this, we developed a novel low-cost aqueous SC using graphite foil as the current collector and a mix of graphene, nanographite, simple water-purification carbons and nanocellulose as electrodes. The electrodes were coated directly onto the graphite foil by using casting frames and the SCs were assembled in a pouch cell design. With this approach, we achieved a material cost reduction of greater than 90% while maintaining approximately one-half of the specific capacitance of a commercial unit, thus demonstrating that the proposed SC can be an environmentally friendly, low-cost alternative to conventional SCs.

Carbon nanospheres hanging on carbon nanotubes: a hierarchical three-dimensional carbon nanostructure for high-performance supercapacitors

We describe the single-step synthesis of carbon nanospheres hanging on carbon nanotubes (CNs/CNTs), using a simple chemical vapor deposition method.

The synergistic effect of nitrogen doping and para-phenylenediamine functionalization on the physicochemical properties of reduced graphene oxide for electric double layer supercapacitors in organic electrolytes

This work studied the synergistic effect of N-doping and p-PDA functionalization on the properties of RGO for supercapacitors.

Integrated Flexible Solid-State Supercapacitor Fabricated In A Single Fabric Layer

This paper presents the design, fabrication and characterization of a flexible solid- state electrical double layer supercapacitor fabricated in a single fabric layer. The proposed supercapacitors were based on fabric electrodes fabricated with low cost carbon materials via a spray coating technique. The single layer solid state supercapacitors achieved a specific capacitances of 40.5 F.g-1, area capacitance of 40.5 mF.cm-2.

Kinetically Controlled Assembly of Nitrogen-Doped Invaginated Carbon Nanospheres with Tunable Mesopores.

Mesoporous hollow carbon nanospheres (MHCS) have been extensively studied owning to their unique structural features and diverse potential applications. A surfactant-free self-assembly approach between resorcinol/formaldehyde and silicon alkoxide has emerged as an important strategy to prepare MHCS. Extending such a strategy to other substituted phenols to produce heterogeneous-atom-doped MHCS remains a challenge due to the very different polymerization kinetics of various resins. Herein, we report an ethylenediamine-assisted strategy to control the cooperative self-assembly between a 3-aminophenol/formaldehyde resin and silica templates. Nitrogen-doped mesoporous invaginated carbon nanospheres (N-MICS) with an N content of 6.18 at %, high specific surface areas (up to 1118 m2 g-1 ), large pore volumes (2.47 cm3 g-1 ), and tunable mesopores (3.7-11.1 nm) have been prepared. When used as electrical double-layer supercapacitors, N-MICS show a high capacitance of 261 F g-1 , an outstanding cycling stability (≈94 % capacitance retention after 10 000 cycles), and a good rate performance.

Development of Novel Hierarchically Microporous-Mesoporous Carbon and Carbon Nanospheres Based Materials and PEMFC Single Cells

Development and application of the proton exchange membrane fuel cell (PEMFC) based transport systems is one of the urgent problems for mega-cities and densely populated areas. However, low redox stability of the carbon supports in strongly oxidising/reducing fuel cells working conditions is the major unsolved problem in materials technology, hindering the wide scale application of PEMFC. Therefore the novel hierarchically microporous-mesoporous carbon supports for deposition of various catalytically active particles have been tested in order to establish the best materials with high cyclability. The carbon materials developed and used as PEMFC catalyst supports in this work have been tested for many years in electrical double layer supercapacitors under very high current density pulsation conditions. In the last years the synthesis methods for carbide derived carbon (C(VC), C(Mo2C), C(TiC), C(SiC) [1, 2] and carbon nanospheres [3, 4] have been developed and corresponding Pt, Ir, Ru-Ir, as well as d-metals nanoclusters activated catalysts have been synthesised [5-8]. All carbon as well as catalyst materials synthesised have hierarchically microporous-mesoporous structure verified by SEM-EDX, FIB-TOF-SIMS, high-resolution TEM and Brunauer-Emmett-Teller gas adsorption methods. The carbon materials have been tested by small angle neutron scattering methods and variable shape of pores has been verified [9]. The Ru, Pt and Ir nanoparticles were deposited onto a carbon support, using the well established liquid-phase reduction methods [5-8]. Thermogravimetric and thermodynamic analysis, X-ray diffraction and Raman spectroscopy methods were used in order to characterize the structure of the materials synthesised. The catalysts prepared were tested as electrodes in the three-electrode as well as in the single cell conditions. The polarization, rotating disk electrode, as well as chronoamperometric measurements were carried out in order to evaluate the activity and stability of the catalyst materials synthesised. The rotating disk electrode data show that the degradation of catalytic activity during 30 cycles was moderate. The electrochemically active surface area has been calculated from the hydrogen adsorption data. The electrochemical impedance method has been used to calculate the electrolyte resistance, polasization resistance and activation energy values. The assembled single cells demonstrated excellent cyclability (3000 cycles) and very high catalytic activity, thus noticeably better performance than those based on the traditional Vulcan electrode materials. Acknowledgements This work was supported by Estonian Target research project No. IUT20-13, Estonian Centre of Excellence projects (Nos. 3.20101.11-0030 and 2014-2020.4.01.15-0011), and Personal Research Grant PUT55. References A. Jänes, L. Permann, M. Arulepp, E. Lust, Electrochem. Commun. 6 (2004) 313−318.E. Tee, I. Tallo, H. Kurig, T. Thomberg, A. Jänes, E. Lust, Electrochim. Acta 161 (2015) 364−370.T. Thomberg, T. Tooming, T. Romann, R. Palm, A. Jänes, E. Lust, J. Electrochem. Soc. 160 (2013) A1834−A1841.I. Tallo, T. Thomberg, H. Kurig, K. Kontturi, A. Jänes, E. Lust, Carbon 67 (2014) 607−616.E. Lust, K. Vaarmets, J. Nerut, I. Tallo, P. Valk, S. Sepp, E. Härk, Electrochim. Acta 140 (2014) 294-303.S. Sepp, K. Vaarmets, J. Nerut, I. Tallo, E. Tee, H. Kurig, J. Aruväli, R. Kanarbik, E. Lust, Electrochim. Acta 2016, doi:10.1016/j.electacta.2016.03.158.S. Sepp, E. Härk, P. Valk, K. Vaarmets, J. Nerut, R. Jäger, E. Lust, J. Solid State Electrochem. 18 (2014) 1223-1229.R. Jäger, P. Ereth Kasatkin, E, Härk, E. Lust, Electrochem. Commun. 35 (2013) 97-99.H. Kurig, M. Russina, I. Tallo, : Siebenbürger, T. Romann, E. Lust, Carbon 100 (2016) 617-624.

Polymeric-Metal Oxide Nanostructures As Future Materials for Energy Applications

One of the most important directions of global research centers are studies on issues related to the acquisition, conversion and energy storage. Currently, more and more work is devoted to research on nanostructured materials as building blocks of batteries and electrochemical capacitors. Electrochemical capacitors (ECs) are energy storage devices which can find applications ranging from portable electronics to hybrid vehicles and large scale power generations. The ECs offer a number of desirable properties, such as fast charging (within seconds), reliability, long-term cycling (more than 500.000 cycles), and the ability to deliver 10 times more power than batteries. Moreover ECs can be used to recovery energy from repetitive processes (descending elevators, braking cars), due to their fast charging rate. Electrochemical capacitors may be divided into two main categories based on their energy storage mechanism: electric double-layer capacitors (EDLCs) and supercapacitors. EDLCs store electrical charge in a double layer at the interface between the electrode and electrolyte. On the other hand, supercapacitors are devices that yield two different capacitive behaviors: electric double-layer capacitance and super-capacitance related to a redox reaction at the interface between an electrolytic solution and electrode surface [1]. As super-capacitive materials metal oxides and conducting polymer have been extensively studied in the past decades [2]. Conducting polymers, such as polypyrrole (PPy), polyaniline (PANI) and poly(3,4-ethylenedioxythiophene) (PEDOT), combine advantages of organic polymers with electronic properties of semiconductors, and hence are attractive materials for the use in data storage media and photovoltaic cells. They also can be used as electrochromic devices, chemical sensors and biosensors, logic or switching elements and supercapacitors [3]. Furthermore, NiO-based nanostructures and thin films have been extensively used as electrode materials for lithium-ion batteries and fuel cells, electrochromic films, gas sensors, and electrochemical supercapacitors. Since NiO is cheaper than RuO2, environmentally benign, and easy to process using a variety of methods, it deserves considerable research activities toward high-performance electrochemical supercapacitor applications [3]. An important parameter characterizing supercapacitors is their active surface – a reaction that is a source of electric current and accumulation of the charge in a form of the electric double layer occurs at the electrolyte/electrode phase boundary. Excellent materials, suitable for fabrication of supercapacitors, seem to be polymeric and metal transition oxide nanowire arrays. It is reasonable to believe that one-dimensional nanostructures can reduce diffusion resistance of electrolytes in rapid charge/discharge processes. Furthermore, nanowires have high conductivity. In the search for new materials, composites play an important role. As a multicomponent system, composites combine the properties of their constituents, which make it possible to overcome the drawbacks of individual components. Therefore, the aim of this research was to synthesize and examine a material exhibiting a high capacitance. The first step of this work included the synthesis of nanostructured anodic aluminum oxide (AAO) by anodization aluminum foil in an oxalic acid solution. The second stage was devoted to the electrochemical reduction of the barrier layer at the bottom of pores. Then, DC electrodeposition of polymeric (e.g., PPy, PEDOT, PANI) nanowires directly in the pores of the AAO template was done. After the AAO template removal, the nanowire array was modified by NiO nanoparticles. The structural features of the hybrid polymeric-metal oxide nanowires were investigated by means of Field Emission Scanning Electron Microscopy (FE-SEM). The chemical composition of hybrid polymeric-NiO nanowires was evaluated by Energy-Dispersive X-ray Spectroscopy (EDAX). The surface states of the hybrid polymeric-NiO nanowire array was investigated by X-ray photoelectron spectroscopy (XPS). The hybrid polymeric-NiO nanowire arrays were examined by cyclic voltammetry, galvanostatic charge–discharge tests and electrochemical impedance spectroscopy in order to determine their capacitance values, optimal working potential range and charge propagation. The discussion will also include the cyclability tests and the capacitance retention during an accelerated ageing procedure.

Rational functionalization of reduced graphene oxide with imidazolium-based ionic liquid for supercapacitor application

Graphene-based materials are very promising for the development of energy storage devices like supercapacitor. Herein, we describe the rational covalent functionalization of reduced graphene oxide (rGO) with hydrophilic imidazolium-based ionic liquid (Im-IL) and the development of aqueous and all-solid supercapacitor devices. The rational functionalization of rGO significantly alters the wettability and increases the interlayer distance of the honeycomb carbon network. It effectively prevents the restacking of individual honeycomb carbon sheets. Im-IL functionalization on rGO surface significantly decreases the water contact angle (94°–37°). Aqueous symmetric electrical double layer supercapacitor based on functionalized rGO sheet (rGO-Im-IL) has been developed and it shows excellent performance with a wide potential window of 0–2 V. The device could provide an energy density of 36.67 Wh kg−1 at a power density of 2 kW kg−1. It has very good cycling stability and it retains 97% of its initial specific capacitance even after 5000 continuous charge–discharge cycles. The enhanced wettability, increased interlayer distance, large surface area and high electronic conductivity contributes to the excellent performance of the supercapacitor. The potential application of rGO-Im-IL is demonstrated by fabricating an all-solid-state supercapacitor device with gel electrolyte.

VO2 Nanoplatelets: A High Energy Electrode Material for Lithium Ion-Hybrid Electrochemical Capacitors

Lithium ion hybrid capacitors (LIC) is an energy storage solution that combines the best of both worlds in terms of high power and high energy density. One of the participating electrodes stores charge by a faradaic mechanism (battery) while the other electrode stores charge by the formation of an electrical double layer (supercapacitor). This configuration allows for the exploitation of the niche gap between batteries and supercapacitors, allowing for the development of a possible energy storage solution for Plug in hybrid vehicles with fast charging and long range capabilities. Vanadium dioxide has recently received much attention because of their high capacity when compared to other vanadium analogues. It consists of sheets of VO6 octahedras linked with each other at the corner, the layered structure allows for good lithium kinetics. The high capacity of Vanadium dioxide even at high power loads is postulated to mitigate one of the main issues faced by LIC’s, that the power density of the device is limited by the battery electrode and most battery electrodes tend to fail at high power loads. Vanadium Dioxide nano-platelets were synthesized using a mechanically assisted hydrothermal reaction. The material was characterized using X-ray diffraction to check for phase purity, scanning electron microscopy and high resolution tunneling electron microscopy were used to characterize the effects of agitation on the morphology of the sample. The morphology is then co-related to the electrochemical performance of the material to develop an understanding about the effect of mechanical agitation on cell performance. Comprehensive electrochemical studies were performed on both VO2 and commercial Activated carbon (acts as the supercapacitor electrode) to determine the mass loading in a full cell arrangement. Half cell studies on VO2 were conducted between 2-3 V vs. Li a high capacity of ~250 mAh g-1 was recorded with barely any capacity drop at high current rates. Because of the robustness of VO2 during high current operations it can be applied in applications that require to store a large amount of energy and at the same time be able to undergo fast charge discharge cycles.

One-step synthesis of hierarchically porous carbons for high-performance electric double layer supercapacitors

With plenty of unique porous structure at micro-/nano scale, hierarchically porous carbons (HPCs) are promising for usage in advanced electric double layer supercapacitors (EDLCs) as the electrode materials. However, wide-range adoption of HPC for practical application is largely shadowed by its extremely complex synthesis process with considerably low production efficiency. Herein we reported a simple template-free, one-step sintering method, to massively produce the HPCs for high-performance EDLCs. Resorting to the 3D structure modification of the wide pore size distribution, high surface area of HPCs (up to 3000 m2 g−1) was achieved. By using 1 M Na2SO4 as electrolyte, the as-fabricated HPCs based EDLCs can be operated reversibly over a wide voltage window of 1.6 V with superior specific capacitance of 240 F g−1 under a current density of 0.5 A g−1. In the meanwhile, the EDLCs exhibit excellent rate capability (high power density of 16 kW kg−1 at 10.2 Wh kg−1) and long-term cycling stability with 9% loss of its initial capacitance after 2000 cycles. This output performance distinguished itself among most of the carbon-based EDLCs with neutral aqueous electrolyte. Thus, the template-free one-step sintering method produced HPCs for EDLCs represents a new approach for high-performance energy storage.

Molecular dynamics simulation of amino acid ionic liquids near a graphene electrode: effects of alkyl side-chain length.

Electric double layer (EDL) supercapacitors, using ionic liquid electrolytes, have been receiving a great deal of attention in response to the growing demand for energy storage systems. In the present study, the nanoscopic structure of amino acid ionic liquids (AAILs) as biodegradable electrolytes near a neutral graphene surface was studied by molecular dynamics (MD) simulation. In order to explore the influence of the anion type and structure, the effect of the alkyl side-chain length of amino acids on the EDL was investigated. The results for the AAILs, composed of 1-ethyl-3-methylimidazolium ([EMIM]) cations near alanine ([ALA]) and isoleucine ([ILE]) anions, were compared to a conventional electrolyte, [EMIM][PF6]. A lower mobility of AAIL compared to [EMIM][PF6], with diffusions as low as 10-11 m2 s-1, was observed. The structural results demonstrated a layered structure near the surface and most of the adsorbed imidazolium cation rings lay flat on the graphene surface. Both MD and quantum computations were performed to shed light on the charge behavior of AAIL electrolytes. As the current results demonstrate, an increase in the anion side-chain length leads to a decrease in both the number of adsorbed ions on the surface and the thickness of the first adsorbed layer. More impressively, it was observed that a low charge concentration in the EDL of AAILs is due to more side-side interactions. This remarkable feature could introduce AAILs as more efficient electrolyte materials than conventional [EMIM][PF6].

High-energy density nanofiber-based solid-state supercapacitors

We have developed binder-free solid-state electric double layer supercapacitors using freestanding porous carbon nanofiber electrodes fabricated using electrospinning and silica-based ionic liquid gel electrolytes.

Electrochemical Performance of Graphene/Activated Carbon Based Electric Double Layer Supercapacitors

Electrochemical Performance of Graphene/Activated Carbon Based Electric Double Layer Supercapacitors

Nanoporous carbon materials with enhanced supercapacitance performance and non-aromatic chemical sensing with C1/C2 alcohol discrimination

We have investigated the textural properties, electrochemical supercapacitances and vapor sensing performances of bamboo-derived nanoporous carbon materials (NCM). Bamboo, an abundant natural biomaterial, was chemically activated with phosphoric acid at 400 °C and the effect of impregnation ratio of phosphoric acid on the textural properties and electrochemical performances was systematically investigated. Fourier transform-infrared (FTIR) spectroscopy confirmed the presence of various oxygen-containing surface functional groups (i.e. carboxyl, carboxylate, carbonyl and phenolic groups) in NCM. The prepared NCM are amorphous in nature and contain hierarchical micropores and mesopores. Surface areas and pore volumes were found in the range 218–1431 m2 g−1 and 0.26–1.26 cm3 g−1, respectively, and could be controlled by adjusting the impregnation ratio of phosphoric acid and bamboo cane powder. NCM exhibited electrical double-layer supercapacitor behavior giving a high specific capacitance of c.256 F g−1 at a scan rate of 5 mV s−1 together with high cyclic stability with capacitance retention of about 92.6% after 1000 cycles. Furthermore, NCM exhibited excellent vapor sensing performance with high sensitivity for non-aromatic chemicals such as acetic acid. The system would be useful to discriminate C1 and C2 alcohol (methanol and ethanol).

Phenolic carbon cloth-based electric double-layer capacitors with conductive interlayers and graphene coating

Phenolic resin-derived activated carbon (AC) cloths are used as electrodes for large-scale electric double-layer capacitors or supercapacitors. To increase the energy and power density of the supercapacitor, the contact resistance between the carbon cloth and the aluminium foil current collector is reduced by modifying the Al current collectors. Different modified Al current collectors, including Toyal-Carbo®(surface-modified Al), DAG® (deflocculated Acheson™ graphite) coating and poly(3,4-ethylenedioxythiophene) (PEDOT) coating, have been tested and compared. The use of modified Al current collectors are shown to greatly reduce the contact resistance between the AC cloth and the Al foil. Another solution investigated in this study is to coat AC cloth with graphene through electrophoretic deposition (EPD). The graphene coated AC cloth is shown increased the capacitance and greatly reduced internal resistance.

Combination of porous silica monolith and gold thin films for electrode material of supercapacitor

An all-solid electrical double layer supercapacitor was prepared, starting from a porous silica matrix coated with a gold thin-film. The metallization of the silica xerogel was performed by an original wet chemical process, based on the controlled growth of gold nanoparticles on two opposite faces of the silica monolith as a seed layer, followed by an electroless deposition of a continuous gold thin film. The thickness of the metallic thin film was assessed to be 700 nm. The silica plays two major roles: (1) it is used as a porous matrix for the gold electrode, creating a large specific surface area, and (2) it acts as a separator (non-metallized part of the silica). The silica monolith was soaked in a polyvinyl alcohol and phosphoric acid mixture which is used as polymer electrolyte. Capacitance effect was demonstrated by cyclic voltammetry experiments. The specific capacitance was found to be equal to 0.95 mF cm−2 (9.5 F g−1). No major degradation occurs within more than 3000 cycles.

Numerical Analysis of Electric Double Layer Capacitors with Mesoporous Electrodes: Effects of Electrode and Electrolyte Properties

A theoretical study is presented of the behavior of electric double layer (EDL) supercapacitors constructed from mesoporous activated carbon electrodes. A three-dimensional (3D) computational model is developed to predict the equilibrium charge distribution within the supercapacitor as a function of key electrode and electrolyte properties. The model is based on the modified Poisson–Boltzmann (MPB) equation and takes into account the impact of critical device parameters, including the size of the ions, the bulk ion concentration, the field-dependent permittivity of the electrolyte, the specific surface area of the electrodes, and the applied voltage. A key feature of the MPB model is that it limits the accumulation of ionic charge at the electrode–electrolyte interface by accounting for the finite size of the ions. This provides more accurate predictions of capacitance than models based on a point charge approximation. The model is used to perform a systematic parametric analysis of device performance and...