双电层电容器用中孔活性炭电极的电化学性能

选用中孔活性炭作为双电层电容器的电极材料，实验发现，中孔活性炭电化学性能优异，比表面积利用率高达93．5％，用水蒸气活化可以增加活性炭的比表面积，随着活化时间的延长，活性炭收率降低，活化2h收率仅为26．5％,同时比表面积从原来的760m^2/g增加到1480m^2/g，且主要在2nm附近孔结构分布强度增强，比电容随活化时间的延长而增加，但增速低于比表面积的增加幅度。     

过渡金属/活性炭电极的电容性能研究

选用微孔和中孔活性炭采用浸渍法负载金属离子,考察在水性电解质中用于超级电容器的活性炭复合电极的电化学性能,探讨活性炭在负载前后的放电容量变化情况.采用低温氮吸附和直流恒流循环实验考察活性炭复合电极的孔结构及电容性能.研究表明:金属Cu、Mn具有比较明显的准电容效应,Co、Ni可提高中孔活性炭的放电容量,而金属Mo、Fe和Y的准电容效应不显著;中孔活性炭负载金属的作用明显强于微孔活性炭;中孔活性炭负载金属Cu时,放电容量随负载量的增加而上升.     

石油焦基活性炭电极电容特性研究

用石油焦作原料,KOH为活化剂,在不同活化条件下制备系列不同比表面积的活性炭。用直流恒流循环实验考察活性炭电极的电化学性能。实验发现,石油焦基活性炭随着活性炭比表面积的增加,活性炭比电容逐渐增大;活性炭孔结构分布相同,随比表面积的增加,比电容线性增加,比表面积利用率降低。活性炭孔结构对比电容有较大的影响,30％KOH电解液可以进入活性炭中大于0.6nm的微孔,孔径越大,其比表面积利用率越高。     

Development of 3D printing technology for the manufacture of flexible electric double-layer capacitors

This study presents a novel process and manufacturing system for the fabrication of Electric Double-Layer Capacitors (EDLCs) as energy storage devices. It shows an approach for printing multilayer EDLC components using 3D printing technology. This process allows layers of activated carbon (AC) slurry, gel electrolyte, and composite solid filaments to be printed with high precision. The study describes the detailed process of deposition of the AC and gel electrolyte using the dual nozzle system. The performance of the flexible EDLCs manufactured by 3D printing in a rectilinear infill pattern has been investigated. It describes the energy storage performance of the printed supercapacitors in relation to the differences in thickness of the AC printed layers and the differences in density of gel electrolyte. A supercapacitor based on printed AC and composite materials displays a specific capacitance of 38.5?mF?g^?1 when measured at a potential rate change of 20?mV?s^?1 and a current density of 0.136?A?g^?1. The highest energy density value for the flexible EDLC was 0.019?Wh?kg^?1 and power density of 165.0?W?kg^?1 in 1.6?M H₂SO₄/PVA gel electrolyte.     

Activated carbons derived from sugarcane bagasse for high-capacitance electrical double layer capacitors

Activated carbon (AC) from sugarcane bagasse was prepared using a simple two-step method of carbonization and chemical activation with four different activating agents (HNO₃, H₂SO₄, NaOH, and KOH). Amorphous carbon structure as identified by X-ray diffraction was observed in all samples. Scanning electron microscopy revealed that the AC had more porosity than the non-activated carbon (non-AC). Specific capacitance of the non-AC electrode was 32.58 F g^?1 at the current density of 0.5 A g^?1, whereas the AC supercapacitor provided superior specific capacitances of 50.25, 69.59, 109.99, and 138.61 F g^?1 for the HNO₃ (AC-HNO₃), H₂SO₄ (AC-H₂SO₄), NaOH (AC-NaOH), and KOH (AC-KOH) activated carbon electrodes, respectively. The AC-KOH electrode delivered the highest specific capacitance (about 4 times of the non-AC electrode) because of its good surface wettability, the largest specific surface area (1058.53 m² g^?1), and the highest total specific pore volume (0.474 cm³ g^?1). The AC-KOH electrode also had a great capacitance retention of almost 100% after 1000 GCD cycles. These results demonstrate that our AC developed from sugarcane bagasse has a strong potential to be used as high stability supercapacitor electrode material.

     

Preparation of activated carbon from sorghum pith and its structural and electrochemical properties

The cost effective activated carbon (AC) has been prepared from sorghum pith by NaOH activation at various temperatures, including 300 °C (AC1), 400 °C (AC2) and 500 °C (AC3) for the electrodes in electric double layer capacitor (EDLC) applications. The amorphous nature of the samples has been observed from X-ray diffraction and Raman spectral studies. Subsequently, the surface functional groups, surface morphology, pore diameter and specific surface area have been identified through FT-IR, SEM, histogram and N₂ adsorption/desorption isotherm methods. The electrochemical characterization of AC electrodes has been examined using cyclic voltammetry technique in the potential range of −0.1-1.2 V in 1.0 M H₂SO₄ electrolyte at different scan rates (10, 20, 30, 40, 50 and 100 mV/s). The maximum specific capacitances of 320.6 F/g at 10 mV/s and 222.1 F/g at 100 mV/s have been obtained for AC3 electrode when compared with AC1 and AC2 electrodes. Based on the characterization studies, it has been inferred that the activated carbon prepared from sorghum pith may be one of the innovative carbon electrode materials for EDLC applications.     

Capacitive behavior studies on electrical double layer capacitor using poly (vinyl alcohol)–lithium perchlorate based polymer electrolyte incorporated with TiO2

Electric double layer capacitors (EDLCs) based on activated carbon electrodes and poly (vinyl alcohol)–lithium perchlorate (PVA–LiClO₄)-nanosized titania (TiO₂) doped polymer electrolyte have been fabricated. Incorporation of TiO₂ into PVA–LiClO₄ system increases the ionic conductivity. The highest ionic conductivity of 1.3 × 10⁻⁴ S cm⁻¹ is achieved at ambient temperature upon inclusion of 8 wt.% of TiO₂. Differential scanning calorimetry (DSC) analyses reveal that addition of TiO₂ into polymer system increases the flexibility of polymer chain and favors the ion migration. Scanning electron microscopy (SEM) analyses display the surface morphology of the nanocomposite polymer electrolytes. The electrochemical stability window of composite polymer electrolyte is in the range of −2.3 V to 2.3 V as shown in cyclic voltammetry (CV) studies. The performance of EDLC is evaluated by electrochemical impedance spectroscopy (EIS), CV and galvanostatic charge–discharge technique. CV test discloses a nearly rectangular shape, which signifies the capacitive behavior of an ELDC. The EDLC containing composite polymer electrolyte gives higher specific capacitance value of 12.5 F g⁻¹ compared to non-composite polymer electrolyte with capacitance value of 3.0 F g⁻¹ in charge–discharge technique. The obtained specific capacitance of EDLC is in good agreement with each method used in this present work. Inclusion of filler into the polymer electrolyte enhances the electrochemical stability of EDLC.     

利用核桃壳制备高比表面积活性炭电极材料的研究

以核桃壳为原料,采用KOH活化法制备活性炭,并将其用作超级电容器电极材料。利用N2吸附和扫描电镜(SEM)表征活性炭的孔结构及表面形貌,系统研究碱炭比(KOH与核桃壳炭化料的质量比)对活性炭孔结构的影响,并采用恒流充放电及循环伏安等测定核桃壳活性炭电极材料在3mol/L KOH电解液中的电化学性能。结果表明,随着碱炭比的增大,活性炭的比表面积、总孔容及中孔比例先逐渐增大后稍有减小。当活化温度为800℃,活化时间为1h,碱炭比为4时,可制备出比表面积为2404m2/g,总孔容为1.344cm3/g,中孔比例为28.6%,孔径分布在0.7~3.0nm之间的高比表面积活性炭。该活性炭用作超级电容器电极材料具有良好的大电流放电特性和优异的循环性能,电流密度由50mA/g提高到5000mA/g时,其比电容由340F/g降低到288F/g,经1000次循环后,比电容保持率为93.4%。     

Efficient Supercapacitor Energy Storage Using Conjugated Microporous Polymer Networks Synthesized from Buchwald–Hartwig Coupling

Supercapacitors have received increasing interest as energy storage devices due to their rapid charge–discharge rates, high power densities, and high durability. In this work, novel conjugated microporous polymer (CMP) networks are presented for supercapacitor energy storage, namely 3D polyaminoanthraquinone (PAQ) networks synthesized via Buchwald–Hartwig coupling between 2,6‐diaminoanthraquinone and aryl bromides. PAQs exhibit surface areas up to 600 m² g^?1, good dispersibility in polar solvents, and can be processed to flexible electrodes. The PAQs exhibit a three‐electrode specific capacitance of 576 F g^?1 in 0.5 m H₂SO₄ at a current of 1 A g^?1 retaining 80–85% capacitances and nearly 100% Coulombic efficiencies (95–98%) upon 6000 cycles at a current density of 2 A g^?1. Asymmetric two‐electrode supercapacitors assembled by PAQs show a capacitance of 168 F g^?1 of total electrode materials, an energy density of 60 Wh kg^?1 at a power density of 1300 W kg^?1, and a wide working potential window (0–1.6 V). The asymmetric supercapacitors show Coulombic efficiencies up to 97% and can retain 95.5% of initial capacitance undergo 2000 cycles. This work thus presents novel promising CMP networks for charge energy storage.     

Active carbon/graphene hydrogel nanocomposites as a symmetric device for supercapacitors

Activated carbons (ACs) are successfully synthesized from Elaeagnus grain by a simple chemical synthesis methodology and demonstrated as novel, suitable supercapacitor electrode materials for graphene hydrogel (GH)/AC nanocomposites. GH/AC nanocomposites are synthesized via hydrothermal process at temperature of 180°C. The low-temperature thermal exfoliation approach is convenient for mass production of graphene hydrogel (GH) at low cost and it can be used as electrode material for energy storage applications. The GH/AC nanocomposites exhibit better electrochemical performances than the pure GH. Electrochemical performance of the electrodes is studied by cyclic voltammetry, and galvanostatic charge-discharge measurements in 1.0 M H₂SO₄ solution. A remarkable specific capacitance of 602.36 Fg^?1 (based on GH/AC nanocomposites for 0.4 g AC) is obtained at a scan rate of 1 mVs^?1 in 1 M H₂SO₄ solution and 155.78 Fg^?1 for GH. The specific capacitance was increased 3.87 times for GH/AC compared to GH electrodes. Moreover, the GH/AC nanocomposites for 0.2 g AC present excellent long cycle life with 99.8% specific capacitance retained after 1000 charge/discharge processes. Herein, ACs prepared from Elaeagnus grain are synthesized GH and AC supercapacitor device for high-performance electrical energy storage devices as a promising substitute to conventional electrode materials for EDLCs.     

Time and energy resolved ion mass spectroscopy studies of the ion flux during high power pulsed magnetron sputtering of Cr in Ar and Ar/N2 atmospheres

Mass spectroscopy was used to analyze the energy and composition of the ion flux during high power pulsed magnetron sputtering (HIPIMS/HPPMS) of a Cr target in an industrial deposition system. The ion energy distribution functions were recorded in the time-averaged and time-resolved mode for Ar⁺, Ar²⁺, Cr⁺, Cr²⁺, N₂⁺ and N⁺ ions. In the metallic mode the dependence on pulse energy (equivalent of peak target current) was studied. In the case of reactive sputtering in an Ar/N₂ atmosphere, variations in ion flux composition were investigated for varying N₂-to-Ar flow ratio at constant pressure and HIPIMS power settings. The number of doubly charged Cr ions is found to increase linearly with increasing pulse energy. An intense flux of energetic N⁺ ions was observed during deposition in the reactive mode. The time evolution of ion flux composition is analyzed in detail and related to the film growth process. The ionization of working gas mixture is hampered during the most energetic phase of discharge by a high flux of sputter-ejected species entering the plasma, causing both gas rarefaction and quenching of the electron energy distribution function. It is suggested that the properties (composition and energy) of the ion flux incident on the substrate can be intentionally adjusted not only by varying the pulse energy (discharge peak current), but also by taking advantage of the observed time variations in the composition of ion flux.     

Effects of activation agents and intrinsic minerals on pore development in activated carbons derived from a Canadian peat

Activated carbons (ACs) with very high specific surface areas up to approximately 900 m²/g and total pore volume up to 0.5 cm³/g were produced from a Canadian peat through chemical activation using either H₃PO₄ or ZnCl₂ as the activation agent, followed by activation/carbonization in air at 450 °C for 45 min. ZnCl₂ was found to be more effective for developing microporous structures in the ACs, while H₃PO₄ is more efficient in developing the mesopores. Demineralization of the AC precursor to remove intrinsic minerals greatly affected the development of pore structures during the activation process. The AC derived from the demineralized peat activated by ZnCl₂ attained the highest BET surface area with significantly increased micro-/mesopores.     

Longitudinal and lateral distributions of medium energy heavy ions in some semiconductor films

The depth distributions of Bi⁺ and Fe⁺ ions implanted into SiN_1.375H_0.603, α-Si, Si₃N₄ and SiO₂ films at different angles were measured by Rutherford backscattering technique. The results show that: (1) the experimental mean projected range R_p is in agreement with the calculated value by TRIM'98 within 9% for SiN_1.375H_0.603, Si₃N₄ α-Si cases; (2) the experimental range straggling ΔR_p is larger than the calculated value by TRIM'98, the reason is not known; and (3) the depth distributions of implanted ions at different angles in all cases exhibit nearly Gaussian behaviour; the agreement of the extracted lateral spread with the calculated value is best for the case of Bi⁺ ions implanted into SiO₂.     

Superior capacitive storage behavior of porous carbon electrode with high mass loading

Porous carbon (PC) derived from the petroleum pitch via the template-guidance coupled with activation methodology, possesses hierarchical pore structure in view of micropore and mesopore. As the electrode material for electrochemical double-layer capacitor, PC electrode not only possesses the good adaptability to aqueous and organic electrolytes, but also delivers the superior capacitive behavior with respect to capacitance and rate capability over those of counterparts (activation-derived carbon and commercial activated carbon). Furthermore, relatively high values of gravimetric and areal capacitances (247F g⁻¹ and 2470 mF cm⁻²) can be guaranteed simultaneously for PC electrode even at the commercial-level mass loading of 10 mg cm⁻², demonstrating the good compatibility to gravimetric and areal capacitances. The satisfactory capacitive storage behavior of PC is ascribed to the synergistic effect of hierarchical pore structure and extraordinary structural integrity. Besides, this work also presents a high value-added utilization strategy to prepare the high-performance porous carbon-based electrode material for capacitive energy storage.     

Synthesis and physical–chemical properties of N-containing nanoporous carbons

Meso- and microporous nitrogen-containing carbons, characterized by homogeneous meso- (V = 1.00 cm³/g, D = 3.5 nm) and microporous (V up to 0.26 cm³/g, D ≈ 0.5 nm) structure, and the presence of basic groups (up to 1.7 mmol/g) were obtained by matrix and bulk carbonization of sucrose in the presence of melamine or urea. It is shown that obtained N-containing microporous carbons possess good interfacial capacitance (0.21 F/m²) and they are characterized with stability during repeated charge–discharge cycles. Synthesized N-containing nanoporous carbons show higher adsorption of carbon dioxide (up to 6.3 mmol/g at ?20 °C) than the samples without nitrogen (up to 3.9 mmol/g at ?20 °C).     

Removal of lead (II) and nickel (II) ions from aqueous solution using activated carbon prepared from rapeseed oil cake by Na<Subscript>2</Subscript>CO<Subscript>3</Subscript> activation

In this study, rapeseed oil cake as a precursor was used to prepare activated carbons by chemical activation with sodium carbonate (Na₂CO₃) at 600 and 800 °C. The activated carbon with the highest surface area of 850 m² g^?1 was produced at 800 °C. The prepared activated carbons were mainly microporous. The activated carbon having the highest surface area was used as an adsorbent for the removal of lead (II) and nickel (II) ions from aqueous solutions. The effects of pH, contact time, and initial ion concentration on the adsorption capacity of the activated carbon were investigated. The kinetic data of adsorption process were studied using pseudo-first-order, pseudo-second-order kinetic models and intraparticle diffusion model. The experimental data were well adapted to the pseudo-second-order model for both tested ions. The adsorption data for both ions were well correlated with Langmuir isotherm. The maximum monolayer adsorption capacities of the activated carbon for the removal of lead (II) and nickel (II) ions were determined as 129.87 and 133.33 mg g^?1, respectively.     

Activated carbon from agave wastes (agave tequilana) for supercapacitors via potentiostatic floating test

To prepare an efficient supercapacitor, an activated carbon from agave wastes was prepared and their electrochemical performance was evaluated as a novel electrode for supercapacitor. The carbon was prepared by two thermal pyrolysis processes under nitrogen atmosphere. The first pyrolysis was achieved at 500 °C until the charring of the bagasse; in the second pyrolysis step, the char was impregnated with different mass ratios of KOH (1:2–1:4) and thermally treated at 800 or 900 °C, for 1 h under N₂ flow. The textural analysis showed that the activated carbon had a specific surface area of 1462 m² g^?1 and depicted a type I isotherm (IUPAC) characteristic of a microporous carbon. Raman spectroscopy and XRD measurements confirm that the activated carbon contains a small graphitization degree and a disordered structure. The electrochemical study of the symmetric carbon supercapacitor was carried out in 1 M Li₂SO₄ solution as the electrolyte. The electrochemical performance of the coin cell supercapacitor was evaluated under an accelerated aging floating test consisting of potentiostatic steps at different voltages (1.5, 1.6 and 1.8 V) for 10 h followed by galvanostatic charge/discharge sequences, and the overall procedure summarized a floating time up to 200 h. The highest capacitance was observed at a floating voltage of 1.5 V, with a large initial specific capacitance of 297 F g^?1.

     

Bimodal activated carbons derived from resorcinol-formaldehyde cryogels

Abstract

Resorcinol-formaldehyde cryogels prepared at different dilution ratios have been activated with phosphoric acid at 450 °C and compared with their carbonaceous counterparts obtained by pyrolysis at 900 °C. Whereas the latter were, as expected, highly mesoporous carbons, the former cryogels had very different pore textures. Highly diluted cryogels allowed preparation of microporous materials with high surface areas, but activation of initially dense cryogels led to almost non-porous carbons, with much lower surface areas than those obtained by pyrolysis. The optimal acid concentration for activation, corresponding to stoichiometry between molecules of acid and hydroxyl groups, was 2 M l^?1, and the acid–cryogel contact time also had an optimal value. Such optimization allowed us to achieve surface areas and micropore volumes among the highest ever obtained by activation with H₃PO₄, close to 2200 m² g^?1 and 0.7 cm³ g^?1, respectively. Activation of diluted cryogels with a lower acid concentration of 1.2 M l^?1 led to authentic bimodal activated carbons, having a surface area as high as 1780 m² g^?1 and 0.6 cm³ g^?1 of microporous volume easily accessible through a widely developed macroporosity.     

Binder-free polyaniline interconnected metal hexacyanoferrates nanocomposites (Metal = Ni,Co) on carbon fibers for flexible supercapacitors

Improvement of the electrical conductivity, specific capacitance and binder-free polyaniline (PANI) interconnected with metal(II) hexacyanoferrate(III) (MHCF) nanocomposites (M?=?Ni, Co) on flexible carbon fibers (CF) were designed in our present research goal. PANI/MHCF/CF nanocomposites were prepared by one-step co-polymerization method. Electrochemical studies like cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy were analyzed. Under the optimized conditions, the nanocomposites demonstrated remarkable electrochemical performances as supercapacitor electrode with outstanding specific capacitances of ~725 F g^?1 at a current density of 1 A g^?1, and retained ~325 F g^?1 even at a high current density of 20 A g^?1 in 0.5 M H₂SO₄?+?0.5 M Na₂SO₄ solution. The excellent cycling stability with capacitance retention of 80% after 1000 cycles may be a potential electrode material for future supercapacitor when its cycling stability and rate performance are addressed.     

Charge Transfer Salt and Graphene Heterostructure‐Based Micro‐Supercapacitors with Alternating Current Line‐Filtering Performance

The rapid development of lightweight and wearable devices requires electronic circuits possessing compact, high‐efficiency, and long lifetime in very limited space. Alternating current (AC) line filters are usually tools for manipulating the surplus AC ripples for the operation of most common electronic devices. So far, only aluminum electrolytic capacitors (AECs) can be utilized for this target. However, the bulky volume in the electronic circuits and limited capacitances have long hindered the development of miniaturized and flexible electronics. In this work, a facile laser‐assisted fabrication approach toward an in‐plane micro‐supercapacitor for AC line filtering based on graphene and conventional charge transfer salt heterostructure is reported. Specifically, the devices reach a phase angle of 73.2° at 120 Hz, a specific capacitance of 151 µF cm^?2, and relaxation time constant of 0.32 ms at the characteristic frequency of 3056 Hz. Furthermore, the scan rate can reach up to 1000 V s^?1. Moreover, the flexibility and stability of the micro‐supercapacitors are tested in gel electrolyte H₂SO₄/PVA, and the capacitance of micro‐supercapacitors retain a stability over 98% after 10 000 cycles. Thus, such micro‐supercapacitors with excellent electrochemical performance can be almost compared with the AECs and will be the next‐generation capacitors for AC line filters.