High Surface Area Carbon Materials Research Articles

Polysaccharide of agar based ultra-high specific surface area porous carbon for superior supercapacitor

Although extensive research has been focused on porous carbon in supercapacitor, the simple and non-template preparation of high specific surface area (SSA) carbon material with hierarchical porous structure is still a lingering issue. Herein, the cross-linked hierarchical porous carbon with ultra-high SSA of 3184 m2 g−1 is prepared via the sol-gel follows the freeze drying and followed activation process. Agar is used as carbon precursor, L-arginine is nitrogen sources, and the formed gel is activated by KHCO3. The obtained N-doped porous carbon shows a superior specific capacitance of 443.0 F g−1 at 0.5 A g−1 in 6 M KOH, and exhibits an excellent rate capability (255 F g−1 at 50 A g−1). Furthermore, due to the combined synergistic effect of high SSA, hierarchical porous structure and N doping, the symmetric supercapacitor that assembled with the prepared gel electrolyte of Agar-Na2SO4 achieves a superior energy density of 35.5 Wh kg−1 and a long cycle life with the capacitance retention of 99.7% after 20,000 cycles. This work provides an efficient and simple method to prepare ultra-high surface area, hierarchical porous structure carbon materials for high performance supercapacitor.

Pd(1 1 1)/SnO2(1 0 1) heterostructure on porous N-carbon material as enhanced catalyst for formic acid electrooxidation

High specific surface area carbon materials act as a critical factor of fuel cell catalyst carriers. In this study, the PtxPdy/SnO2/GC nanocatalysts were successfully synthesized at different molar ratios of Pt and Pd to conduct the formic acid oxidation. In addition, the N-doped porous carbon carrier (GC) was prepared with graphene oxide and gelatin through the solvated volatilization/nanometer SiO2 template/KOH activation, and the prepared carrier GC took up a large specific surface area (SBET = 1104.5 m2/g). The fine-tuning of the atomic ratio of Pt and Pd was demonstrated to further guide the growth of ultra-small nanocrystals that achieved an average size of 2.52 nm and displayed uniform distributions on the prepared GC carrier. Compared with PtPd/GC, PtSnO2/GC and Pt/GC catalysts, Pt1Pd1/SnO2/GC took up a larger electrochemical activity area of 528.93 cm2/mg, and the positive sweep peak current density reached 2258.45 mA/mgPt at 0.75 V. As confirmed by the DFT analysis, the heterojunction structure formed between the Pt-Pd (111) and SnO2 (101) surfaces would contribute to the electron transport. The optimal electrochemical performance was reasonably attributed to the synergistic effect exerted by PtPd alloy and SnO2, as well as N-doped porous carbon carrier.

High-Performance Supercapacitor Materials Based on Hierarchically Porous Carbons Derived from Artocarpus heterophyllus Seed

High-surface area and large porosity carbon materials with hierarchically porous structures are the preferred electrode materials for high-energy density supercapacitors. In this contribution, we report the preparation of ultrahigh surface area nanoporous carbon materials with hierarchically micro- and mesopore structures from Artocarpus heterophyllus (Jackfruit) seed. This involves a potassium hydroxide (KOH) activation method conducted at higher temperatures (600–1000 °C). The resulting amorphous carbon materials display outstanding performance as electrodes in electrical double-layer capacitors with an aqueous electrolyte (1 M H2SO4), which is due to their partially graphitic structures, ultrahigh surface areas of ca. 2104.3 m2 g–1, and large pore volumes of ca. 1.386 cm3 g–1. Electrodes prepared from the material with optimal textural parameters lead to a high specific capacitance of 323.8 F g–1 at 1 A g–1 and sustained 53.7% capacitance retention at a high current density of 50 A g–1, demonstrating the high rate performance of the electrode. The experimental results suggested fast diffusion of the electrolyte ions near the surface of the electrode, which was verified using molecular simulations. The simulations verified that the electrolyte enters the pores, thereby increasing the capacitance but reducing the charge rate compared to nonporous electrodes. Additionally, an exceptionally long cycle stability was observed with 97% of the capacitance retained after 10,000 charge–discharge cycles. The results show the considerable probability of Jackfruit-seed-derived hierarchically porous carbons as the electrode materials for high-performance supercapacitor applications.

Activation of Asphalt to Prepare High Surface Area Carbon Material

High surface area porous carbon material was prepared via a method of activating asphalt with pretreatment. The crystalline, textural structure, morphology, and surface functionalities of the samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), diffuse reflectance FTIR spectroscopy (DRIFTS), and Brunauer-Emmett-Teller (BET) techniques. When the asphalt was pretreated at 400 °C for 3 h under Ar flow, and then activated using KOH as activating agent at 800 °C for 3 h under Ar flow, the prepared porous carbon material has an amorphous nature and possesses a high surface area of 2460 m2/g, a narrow pore size distribution of 3 ∼ 5 nm, and a mean pore diameter of 3.8 nm.

Hydrogen Storage on Nanoporous Carbon Foam for Electrochemical Applications

To be able to mitigate the threat of climate change, we need an alternative to fossil fuels. The use of hydrogen in fuel cells is an ideal candidate because hydrogen can be produced in many different ways and has a high energy density. However, one challenge in using hydrogen as a fuel is its storage. Storing hydrogen as compressed gas typically requires large pressures to meet US Department of Energy (DOE) targets, which leads to large losses during compression. By using solid state storage, we can use lower pressures for storage. Of the different kinds of solid state storage, physisorption on carbon materials has great potential because of its fast kinetics, reversibility, and the cost effectiveness of carbon materials.In this research, we investigate the storage of hydrogen gas through physical adsorption on a sodium ethoxide-derived carbon foam. This carbon foam has all the necessary requirements of a good hydrogen sorbent: very large surface area and a large micropore volume. This material is also easy to synthesize: sodium ethoxide is pyrolyzed in N2 to make carbon, which is then washed in DI water and vacuum filtered. Unlike many other high surface area carbon materials, this carbon foam does not require a two-step carbonization-activation process, nor does it require a sacrificial template. This means it is more scalable and energy efficient compared to other synthetic carbon materials. [1,2]The hydrogen adsorption capability of this material is tested at both 77K and 298K at elevated pressures (up to 9.5 MPa). Both the excess hydrogen uptake and the total hydrogen uptake are discussed. The values obtained are comparable with benchmark materials such as MOF-5 and IRMOF-20, which have 8 wt% and 10 wt% total uptake at 10 MPa, respectively, [3] and could plausibly meet US DOE targets for light duty vehicle application (5.5 wt% total uptake) at a much lower pressure than conventional compressed gas storage (usually 70 MPa). This work shows the potential of nanoporous carbon materials such as ours to work as a new storage system or as a ‘range extender’ of sorts for existing fuel cell vehicles.[1] Lyth, S. M., Shao, H., Liu, J., Sasaki, K., and Akiba, E., 2014, “Hydrogen Adsorption on Graphene Foam Synthesized by Combustion of Sodium Ethoxide,” Int. J. Hydrogen Energy, 39(1), pp. 376–380.[2] Choucair, M., and Mauron, P., 2015, “Versatile Preparation of Graphene-Based Nanocomposites and Their Hydrogen Adsorption,” Int. J. Hydrogen Energy, 40(18), pp. 6158–6164.[3] Ahmed, A., Seth, S., Purewal, J., Wong-Foy, A. G., Veenstra, M., Matzger, A. J., and Siegel, D. J., 2019, “Exceptional Hydrogen Storage Achieved by Screening Nearly Half a Million Metal-Organic Frameworks,” Nat. Commun., 10(1), pp. 1–9.

Biomass-derived carbon hooks on Ni foam with free binder for high performance supercapacitor electrode

We use a carbonization method to synthesize a high-surface-area carbon (HSAC) material from a biomass source: peanut shells. Due to its high specific surface area of 1279 m2g−1 and porous structure, HSAC is a promising material for energy storage application. We employ a simple hydrothermal method to grow HSAC successfully on nickel (Ni) foam. The biomass-derived HSAC and HSAC growth on Ni foam (HSAC-Ni) is investigated by X-ray powder diffraction, Raman spectroscopy, Brunauer–Emmett–Teller-based analysis, scanning electron microscopy, and transmission electron microscopy. We study HSAC-Ni as a potential material for supercapacitor electrodes. A three-electrode system with HSAC-Ni as the working electrode in 1 M KOH and 1 M Li2SO4 aqueous electrolytes demonstrates maximum specific capacitances of 242.84 Fg−1 in KOH and 272 Fg−1 in Li2SO4 at a scan rate of 10 mVs−1. The HSAC-Ni shows stability after electrochemical measurement, which indicates that HSAC material is an excellent choice as an electrode material.

Nanoarchitectonics of Nanoporous Carbon Materials in Supercapacitors Applications.

High surface area and large pore volume carbon materials having hierarchical nanoporous structure are required in high performance supercapacitors. Such nanoporous carbon materials can be fabricated from organic precursors with high carbon content, such as synthetic biomass or agricultural wastes containing cellulose, hemicellulose, and lignin. Using recently developed unique concept of materials nanoarchitectonics, high performance porous carbons with controllable surface area, pore size distribution, and hierarchy in nanoporous structure can be fabricated. In this review, we will overview the recent trends and advancements on the synthetic methods for the production of hierarchical porous carbons with one- to three-dimensional network structure with superior performance in supercapacitors applications. We highlight the promising scope of accessing nanoporous graphitic carbon materials from: (i) direct conversion of single crystalline self-assembled fullerene nanomaterials and metal organic frameworks, (ii) hard- and soft-templating routes, and (iii) the direct carbonization and/or activation of biomass or agricultural wastes as non-templating routes. We discuss the appealing points of the different synthetic carbon sources and natural precursor raw−materials derived nanoporous carbon materials in supercapacitors applications.

On the Electrochemical Stability of PtRu Alloy Electrodes in Aqueous Acidic Baths: A Strategy for Recycling Pt and Ru

PtRu alloy nanoparticles supported on high surface area carbon material (PtRu/C) are common electrocatalysts used for the hydrogen oxidation reaction at polymer electrolyte membrane fuel cell (PEMFC) anodes. The recovery of these precious metals at the end of the lifetime of fuel cells is important for their further applications in a sustainable energy technology scenario. Here, new mechanisms for efficient recycling of the spent catalyst are proposed and examined based on the potentiodynamic dissolution of PtRu/C in chloride containing—and in chloride free dilute acidic baths, respectively, such as in 0.1 M HCl and 1 M H2SO4. During potential cycling, Ru exhibits a higher stability than Pt in 0.1 M HCl. This is in contrast to a relatively lower stability of Ru under potentiodynamic treatment in the absence of Cl−. For example, the % dissolutions of Pt and Ru are observed to be ∼72% and ∼33% during potential cycling between 0.2 and 1.6 V for 50 cycles at a scan rate of 100 mV s−1, in 0.1 M HCl. On the other hand, for similar initial Pt and Ru loadings, the corresponding dissolution values for Pt and Ru after potential cycling between 0.2 and 1.6 V for 10k cycles at a scan rate of 1 V s−1 in 1 M H2SO4 are observed to be ∼27% and ∼61%, respectively. This difference of behaviors is attributed to the formation and stability of soluble Pt and Ru species during potential cycling. The fast dissolution of Pt and higher stability of Ru found during potential cycling in dilute HCl may be explored towards separation of Pt and Ru and for separable recoveries from spent alloy catalysts. Finally, it is observed that the Pt and Ru dissolution rates during potential cycling may be enhanced through inhibition of redeposition of the dissolved species by using Cu as a surface switching species.

Surface area measurements of graphene and graphene oxide samples: Dopamine adsorption as a complement or alternative to methylene blue?

The possible use of dopamine, monitored spectroscopically, as a probe molecule for surface area measurements is investigated. Using high surface area carbon materials, including both graphene and graphene oxide (GO), the method is established as a complement or alternative to methylene blue or conventional N2 (BET) adsorption. The molecular reorientation (flat to vertical) of dopamine on the graphene and GO surface provides a direct indication of the monolayer coverage and the rapid adsorption (within 10 min to saturation) offers high convenience. The smaller dopamine molecule size and less self-repulsion compared to methylene blue can be considered to yield a more closely-packed surface coverage on the materials of interest. Especially for materials with complex morphologies and internal structures, the dopamine adsorption will therefore lead to a more ‘correct’ measurement.

Synthesis of a high-temperature stable electrochemically exfoliated graphene

A new and facile electrochemical exfoliation approach is proposed to produce better quality electrochemically exfoliated graphene with excellent high-temperature stability. The method is based on graphene exfoliation in inorganic electrolytes (e.g. (NH4)2HPO4 and (NH4)2SO4 and different combinations of these salts) where the electrolyte composition was found to have a significant impact on the yield, morphology, structure, and high-temperature stability of the graphene sheets. The graphene prepared using (NH4)2HPO4 electrolyte showed the lowest level of defects in comparison to the other electrochemically exfoliated graphene and an exceptional high-temperature stability in air, at temperatures of up to 750 °C; much higher than typical high surface area carbon materials which are unstable around 400 °C–500 °C in air. The addition of (NH4)2SO4 to the (NH4)2HPO4 electrolyte improved the exfoliation process and increased the production of single layer graphene sheets from 19% to ∼50%. These hybrid electrolytes also led to nitrogen, phosphorus, and sulphur tri-doped graphene sheets with a fewer defects and high-temperature stability in air. This simple process offers a promising approach for large scale preparation of doped graphene with fewer defects and exceptional properties for various applications.

Surface energetics of carbon nanotubes–based nanocomposites fabricated by microwave-assisted approach

Abstract

Structural Flexibility in Activated Carbon Materials Prepared under Harsh Activation Conditions.

Although traditionally high-surface area carbon materials have been considered as rigid structures with a disordered three dimensional (3D) network of graphite microdomains associated with a limited electrical conductivity (highly depending on the porous structure and surface chemistry), here we show for the first time that this is not the case for activated carbon materials prepared using harsh activation conditions (e.g., KOH activation). In these specific samples a clear structural re-orientation can be observed upon adsorption of different organic molecules, the structural changes giving rise to important changes in the electrical resistivity of the material. Whereas short chain hydrocarbons and their derivatives give rise to an increased resistivity, the contrary occurs for longer-chain hydrocarbons and/or alcohols. The high sensitivity of these high-surface area carbon materials towards these organic molecules opens the gate towards their application for sensing devices.

Preparation of Carbon Metal Oxide Composites for Hybrid Supercapacitor Applications

Hybrid supercapacitors made of carbon – metal oxide composites are devices which can combine the advantages of both electric double layer capacitors and pseudocapacitors e.g. high energy density, high power density and high cyclibilty. Although there are many ways to make carbon – metal oxide composites, carbon nanofibers (CNFs) as high surface area carbon materials were used as matrix to host the metal oxides. Covering the carbon with metal oxides will cause a decrease in conductivity of the carbon material, hence encapsulating the metal oxides with CNFs is a way for achieving high performance system. It has been shown that blending two immiscible polymers at certain ratios, electrospinning and carbonizing them will lead to formation of carbon, in which the metal oxides can be placed. Polyacrylonitrile (PAN) as the carbon source and polymethacrylic acid (PMAA) as both metal oxide precursor carrier and in-situ porogen were blended at 1:1 ratio and electrospun. Upon annealing PMAA degraded and left pores. Adding a metal precursor to the blend solution cause interaction of metal with PMAA, hence upon degradation of PMAA, metal oxides were left in the carbon fibers. The prepared carbon – metal oxide composites not only preserves the conductivity of carbon but also adds the pseudocapacitance of metal oxides to the system which leads to a material with enhanced performance. It is predicted to load higher amounts of metal oxides using PMAA compared to conventional metal oxide carriers such as polymethyl methacrylate (PMMA), due to carboxylic groups on PMAA backbone.

Design and Development of Advanced Air-Cathodes for Li-Air Battery

NASA’s future missions demand high energy density batteries. Current state-of-the-art lithium-ion batteries (LIBs) reach the specific energy capacity limits (<250 Wh/kg), thus new electrochemical storage technologies are needed to meet NASA’s future mission requirement of >400 Wh/kg. Battery chemistries with higher theoretical energy densities in particular, Li-metal based battery chemistries such as Li-air, are being actively pursued, but there remains a number of issues to be solved. Development of advanced and optimized air cathodes will be crucial for improving capacity retention and cycle life of Li-air battery. The microstructure of carbon substrates and the catalytic oxygen reduction of the air-cathode play critical roles in the electrochemical performance in Li-air batteries. With the development and proper design of air cathodes, the energy efficiency and energy density can be enhanced significantly. In this presentation, the results of advanced permeable air cathodes design with different substrates such as 2D carbon paper or carbon cloth, vs. 3D graphene or metal foam, different high surface area carbon materials and incorporation with catalysts on oxygen reduction reactions, different porosity controlling of air cathode as well the additives in electrolyte will be presented. The cycling and rate capability performance of these air-cathodes in the Li-air cells will be discussed as well.

High surface area carbon materials derived from corn stalk core as electrode for supercapacitor

The activated carbon materials from the corn stalk core raw materials were prepared through the carbonization and activation process and applied as electrode in supercapacitor. The biomass carbon materials activated under different temperatures were tested by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge-discharge cycling method. The corn stalk core-derived material activated at 700 °C with the highest specific surface area (2349.89 m2 g−1) has exhibited the maximum specific capacitance of 140 F g−1. Further detailed characterization and theoretical analysis have demonstrated that the corn stalk core derived activated carbon anode material can not only enhance the capacity of supercapacitor but also realize the comprehensive utilization of corn stalks.

Three-dimensional interconnected porous graphitic carbon derived from rice straw for high performance supercapacitors

Three-dimensional interconnected porous graphitic carbon materials are synthesized via a combination of graphitization and activation process with rice straw as the carbon source. The physicochemical properties of the three-dimensional interconnected porous graphitic carbon materials are characterized by Nitrogen adsorption/desorption, Fourier-transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, Scanning electron microscopy and Transmission electron microscopy. The results demonstrate that the as-prepared carbon is a high surface area carbon material (a specific surface area of 3333 m2 g−1 with abundant mesoporous and microporous structures). And it exhibits superb performance in symmetric double layer capacitors with a high specific capacitance of 400 F g−1 at a current density of 0.1 A g−1, good rate performance with 312 F g−1 under a current density of 5 A g−1 and favorable cycle stability with 6.4% loss after 10000 cycles at a current density of 5 A g−1 in the aqueous electrolyte of 6M KOH. Thus, rice straw is a promising carbon source for fabricating inexpensive, sustainable and high performance supercapacitors' electrode materials.

Ordered Mesoporous Carbons with High Micropore Content and Tunable Structure Prepared by Combined Hard and Salt Templating as Electrode Materials in Electric Double‐Layer Capacitors

AbstractSynthesis of high surface area carbon materials with hierarchical pore structure is reported. Combined salt templating with ZnCl2 and hard templating with SBA‐15 is used to produce ordered mesoporous and microporous hard–salt‐templated carbons (OM‐HSTCs) from simple sucrose as carbon precursor. OM‐HSTCs achieve specific surface areas of more than 2600 m2 g−1 and total pore volumes up to 2.2 cm3 g−1. In comparison to purely hard‐templated ordered mesoporous carbons, the additional salt template leads to high micropore volume and provides control over the size/distribution of micro‐ and mesopores and over the carbon microstructure. This method combines carbonization and the formation of well‐defined micropores in one step and is more versatile in terms of resulting pore structure than previously reported routes toward ordered mesoporous/microporous carbons. When applied as electrode materials in electric double‐layer capacitors with 1 m tetraethylammonium tetrafluoroborate in acetonitrile organic electrolyte, OM‐HSTCs combine high gravimetric capacitance (133 F g−1 at 0.1 A g−1) resulting from high micropore volume with high capacitance retention under high‐power conditions (126 F g−1 at 40 A g−1), exceeding the purely microporous or purely ordered mesoporous reference materials.

Durabilty of Pt-Based Alloy Nanoparticles Supported on Functionalized Carbon Materials for the ORR – Tuning the Interaction between Particles and Support Material

In the last decades, proton exchange membrane fuel cells (PEMFC) have attracted large attention as promising renewable and clean technology for energy conversion. Designing nanomaterials with the aim to improve their electrocatalytic performance and long-term durability is still a critical challenge. Today´s PEMFC research has focused on Pt-based alloy nanoparticles combined with high surface area carbon materials due to its improved activity and stability for the ORR compared to pure Pt/C.[1,2,3] Although many studies have focused on the relations between the structural and chemical properties of the catalytically active metal nanoparticles and their catalytic ORR performance, the interactions of these nanoparticles with the carbon substrate have been rarely investigated up to date. In particular, the immobilization and stabilization of the nanoparticles on the support material have a strong influence on the long-term durability of the ORR catalysts. Therefore, one crucial point is the functionalization of the carbon support with hydroxide and carboxylate groups which seems to improve nucleation and dispersion of the Pt alloy nanoparticles; on the other hand, these oxygen-containing surface groups can accelerate the carbon corrosion associated with particle detachment during the potential cycling. Therefore, another strategy is the introduction of hetero-atoms as N-C-, C-B, C-F and C-S-bonds into the carbon framework improving their electrochemical oxidation resistance.[4,5,6,7]One target of this work is the stabilization of the carbon support material by functionalization to prevent carbon corrosion under the operating fuel cell conditions. We modified the morphology, structure and chemical properties of the porous carbon materials by using different methods such as acid treatment or thermal treatment in a reactive gas atmosphere. On the other hand, we optimized the design of Pt-based alloy (Pt-Ni, Pt-Co) nanoparticles supported on these functionalized porous carbon support materials. The properties and behavior of these materials are monitored by using high resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX) and X-ray absorption spectroscopy (XAS). The electrochemical stability and durability of the catalysts were also investigated by applying various accelerated test protocols such as potential cycling between 0.5 - 1.0 (10.000 cycles), 0.5 - 1.5 (2000 cycles) and 1.0 - 1.5 V vs. RHE (2000 cycles). We monitored the electrochemically active surface area (ECSA) of the Pt and Pt alloy nanoparticles supported on these functionalized carbon materials during the runs to correlate its loss to the number of cycles, scan rate and potential range. Based on these results we evaluate the relationship between the carbon modification, size and chemical composition of the bimetallic nanoparticles, electrocatalytic properties and durability.Based on this study, we developed a model, describing the critical parameters to improve the interaction between the particles and the support material. This approach serves to enhance the catalytic properties and long-term durability of the ORR electrocatalysts for PEMFC applications.

Shaddock wadding created activated carbon as high sulfur content encapsulator for lithium-sulfur batteries

In this work, a microporous and high surface area carbon material with excellent electron conductivity is synthesized through carbonizing and activation processes using waste shaddock wadding. Because of the unique multi-hole, thin sheets cluster and irregular wrinkled surface coexisting structure, the shaddock wadding carbon-sulfur (SWD-S) composite can be used as a kind of cathode material for rechargeable lithium-sulfur batteries by loading element sulfur into the shaddock wadding activated carbon via simple heat treatments. Because of the high specific surface area of SWD (1637.3 m2 g−1), the SWD-S composite has a sulfur content about 73.7 wt%, and delivers a high initial discharge capacity of 1050 mAh g−1 at a rate of 0.2C. Moreover, SWD-S composite exhibits a good rate capacity and excellent cycle ability. Over 200 cycles it achieves with a high columbic efficiency around 95%. After 200 cycles at 0.2C, it still remains a capacity of 599 mAh g−1.

Natural Cellulose Materials for Supercapacitors

Supercapacitors are becoming important energy storage devices in efficient electrical systems and they are typically fabricated from high surface area carbon materials which are manufactured using complex, eco-destructive processes. An alternative approach is based on the conversion of biomass materials which we explore in this paper. Cellulose from cotton pulp is subject to a two-step carbonisation process at a range of elevated temperatures up 1900°C. The resultant materials are characterized using a range of physical methods, along with cyclic voltammetry and galvanostatic discharge techniques to measure the specific capacitance of the materials formed. It is shown that the optimum processing temperature is around 1000°C; at lower processing temperatures, the materials are insufficiently conductive whilst at high carbonization temperatures low capacitance is seen due to a loss of surface area. This arises from the inaccessibility of nanometre size pores which are present in abundance after the lower temperature carbonization steps. Cotton pulp carbonised at 1000°C showed the highest value of capacitance of 107Fg−1 with excellent stability for 2000 cycles. The electrochemical performance of this material is very competitive to other reported carbon materials and indicates the two-stage carbonisation method described is suitable for converting biomass into high quality carbon-based materials for supercapacitor applications.