Electric double layer capacitor based on activated carbon electrode and biodegradable composite polymer electrolyte

A series of polymer electrolyte based on poly(vinyl alcohol), lithium perchlorate (LiClO₄), and antimony trioxide (Sb₂O₃) was prepared via solution casting technique with distilled water as solvent. The dielectric behavior study reveals the non-Debye properties of the polymer electrolytes. In frequency dependence conductivity measurement, dispersion at low frequency was due to the interfacial resistance and space charge polarization inside the polymer electrolytes. The linear sweep voltammetry has proven that the incorporation of Sb₂O₃ into polymer matrix increases the maximum operational potential region. Electric double-layer capacitors (EDLCs) based on activated carbon electrode assembled with solid polymer electrolyte and composite polymer electrolyte has been evaluated by cyclic voltammetry (CV) and galvanostatic charge–discharge technique. CV test disclosed rectangular shapes with slight distortion, and there is no evidence for any redox currents on both anodic and cathodic sweeps, which indicates the typical behavior of EDLC. Both EDLC cells demonstrate good cyclability throughout 200 cycles with specific capacitance retention more than 90 %.     

Potato starch-based activated carbon spheres as electrode material for electrochemical capacitor

Potato starch-based activated carbon spheres (PACS) were prepared from potato starch by stabilization, carbonization followed by activation with KOH. The obtained PACS are hollow and retain the original morphology of potato starch with decrease in size, as shown by scanning electron microscopy. Modification of textural properties of the PACS was achieved by varying the carbonization temperature and the ratio of KOH/PCS. The results of N₂ adsorption isotherms indicate that the samples prepared are mainly microporous. The electrochemical behaviors of the hollow PACS were studied by galvanostatic charge-discharge, cyclic voltammetry, and impedance spectroscopy. The results indicate that high specific capacitance of 335 F/g is obtained at current density 50 mA/g for PACS with specific surface area 2342 m²/g. Only a slight decrease in capacitance, to 314 F/g, was observed when the current density increases to 1000 mA/g, indicating a stable electrochemical property.     

Charge storage performance of lithiated iron phosphate/activated carbon composite as symmetrical electrode for electrochemical capacitor

In this study, a symmetric electrochemical capacitor was fabricated by adopting a lithium iron phosphate (LiFePO₄)-activated carbon (AC) composite as the core electrode material in 1.0 M Na₂SO₃ and 1.0 M Li₂SO₄ aqueous electrolyte solutions. The composite electrodes were prepared via a facile mechanical mixing process. The structural properties of the nanocomposite electrodes were characterised by scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) analysis. The electrochemical performances of the prepared composite electrode were studied using cyclic voltammetry (CV), galvanostatic charge–discharge (CD) and electrochemical impedance spectroscopy (EIS). The experimental results reveal that a maximum specific capacitance of 112.41 F/g was obtained a 40 wt% LiFePO₄ loading on an AC electrode compared with that of a pure AC electrode (76.24 F/g) in 1 M Na₂SO₃. The improvement in the capacitive performance of the 40 wt% LiFePO₄–AC composite electrode is believed to be attributed to the contribution of the synergistic effect of the electric double layer capacitance (EDLC) of the AC electrode and pseudocapacitance via the intercalation/extraction of H⁺, OH⁻, Na⁺ and SO₃²⁻ and Li⁺ ions in LiFePO₄ lattices. In contrast, it appears that the incorporation of LiFePO₄ into AC electrodes does not increase the charge storage capability when Li₂SO₄ is used as the electrolyte. This behaviour can be explained by the fact that the electrolyte system containing SO₄²⁻ only exhibits EDLC in the Fe-based electrodes. Additionally, Li⁺ ions that have lower conductivity and mobility may lead to poorer charge storage capability compared to Na⁺ ions. Overall, the results reveal that the AC composite electrodes with 40 wt% LiFePO₄ loading on a Na₂SO₃ neutral electrolyte exhibit high cycling stability and reversibility and thus display great potential for electrochemical capacitor applications.     

Influence of carbon structure on performance of electrode material for electric double-layer capacitor

An isotropic pitch and an anisotropic pitch with similar softening point were chosen to be precursors for activated carbons (ISO and ANISO, respectively). Chemical activations with same conditions were carried out and the effects of microstructure of precursors on characteristics of activated carbons were discussed. Isotropic pitch with more noncrystallite carbon atoms or edge carbon atoms on the microstructural defects had more reactive ability and more pores were manufactured through sufficient chemical activation. Electric double-layer capacitors (EDLC) were made with the two activated carbons as electrode materials and 1 M Et₄NBF₄/PC as the electrolyte. The performance of EDLC with the ISO has higher specific capacitance (43.5 F g⁻¹) than the ANISO (21.3 F g⁻¹) and has better power performance and lower resistance than the latter.     

Electrochemical synthesis and performance of PANI electrode material for electrochemical capacitor

Polyaniline (PANI) electrode materials doped with sulfuric acid (H₂SO₄) were prepared by cyclic voltammetry (CV) method in different reaction conditions. The structure and morphology of PANI samples were characterized by Fourier transform infrared spectroscopy and scanning electron microscope. The electrochemical properties of PANI samples were studied by CV, galvanostatic charge/discharge, and electrochemical impedance spectroscopy tests. Additionally, the effects of reaction conditions including aniline concentration, voltammetry scan rate, and deposition time on the morphology and properties of PANI samples were investigated in detail. The results showed that the PANI synthesized under the optimal conditions of 0.2 mol?L^?1 aniline, scan rate 20 mV?s^?1, and deposition time 50 min is in the form of nanorods with a cross-linked network structure. It exhibits an outstanding capacitive performance with good cycle stability and high rate performance. Besides, the specific capacitance of PANI is as high as 757 F?g^?1.     

碳气凝胶及活化碳气凝胶电极材料制备与性能

以间苯二酚(R)-甲醛(F)为原料,制备了有机气凝胶和碳气凝胶,并对其进行二氧化碳活化。X射线衍射(XRD)测试表明,二氧化碳渗入到碳气凝胶网络结构发生反应,造成(002)峰和(100)峰减弱;扫描电子显微镜(SEM)测试表明,活化没有破坏碳气凝胶的骨架结构,而是增加了大量的nm尺度微孔,从而大大提高了碳气凝胶的比表面积和微孔比例。在1 mol/L KOH电解液中进行了循环伏安和计时电位扫描测试,电极材料电化学性能稳定,具有较好的可逆性,在1 mA/s电流密度下进行充放电测试,得到活化前电极比电容为103 F/g,活化后由于比表面积的增加,比电容达到371 F/g,是一种理想的电化学电极材料。     

碳气凝胶及活化碳气凝胶电极材料制备与性能

 以间苯二酚(R)-甲醛(F)为原料,制备了有机气凝胶和碳气凝胶,并对其进行二氧化碳活化。X射线衍射(XRD)测试表明,二氧化碳渗入到碳气凝胶网络结构发生反应,造成(002)峰和(100)峰减弱;扫描电子显微镜(SEM)测试表明,活化没有破坏碳气凝胶的骨架结构,而是增加了大量的nm尺度微孔,从而大大提高了碳气凝胶的比表面积和微孔比例。在1 mol/L KOH电解液中进行了循环伏安和计时电位扫描测试,电极材料电化学性能稳定,具有较好的可逆性,在1 mA/s电流密度下进行充放电测试,得到活化前电极比电容为103 F/g,活化后由于比表面积的增加,比电容达到371 F/g,是一种理想的电化学电极材料。     

常压干燥法制备碳气凝胶及其电极性能研究北大核心CSCD

以间苯二酚-甲醛为前驱体,通过加入P123以增强有机气骨架的方法,采用常压干燥技术制备碳气凝胶电极材料,有机凝胶在干燥过程中收缩率极大降低。通过二氧化碳活化法对常压干燥获得的碳气凝胶孔结构进行了调控。研究了不同温度对其结构的影响,获得了最高比表面积达3544m2/g的碳气凝胶。6mol/L的KOH电解液中测试表明,常压干燥碳气凝胶具有稳定的充放电性能,随着活化温度的升高,比容量逐渐增加,最高比电容可达261F/g。常压干燥技术制备的碳气凝胶电极材料在降低生产成本的同时,仍具有理想的电化学性能。     

Influence of air-oxidation on electric double layer capacitances of multi-walled carbon nanotube electrodes

In this work, air-oxidized multi-walled carbon nanotube (MWCNT) electrodes have been prepared from catalytically grown MWCNTs of high purity and narrow diameter distribution. The experimental results show that air-oxidation modifies the intrinsic structure of individual MWCNTs and a little improves the dispersity of the MWCNTs. The specific capacitances of the electrodes in electric double layer capacitors (EDLCs) based on oxidized MWCNTs are obviously improved through air-oxidation. The specific capacitance of 50 F/g is obtained in the air-oxidized MWCNTs at 600 °C on a single cell device with 35 wt% H₂SO₄ as an electrolyte. This is probably increased BET specific surface area and mesopore volume of the oxidized MWCNT electrode materials of EDLCs. These properties are, therefore highly desirable for the development of electrochemical capacitors with high power and long cycle life.     

Preparation and electrochemical investigation of the cobalt hydroxide carbonate/activated carbon nanocomposite for supercapacitor applications

Cobalt hydroxide carbonate/activated carbon (AC) composite was successfully synthesized by hydrothermal method. Morphological characterizations of cobalt hydroxide carbonate/AC composite were carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the results show that the cobalt hydroxide carbonate nanorods are well dispersed on the AC. Due to the synergistic effects arising from cobalt hydroxide carbonate nanorods and AC, the electrochemical performances of pure cobalt hydroxide carbonate material is significantly improved by the addition of AC. The composite shows a specific capacitance of 301.44 F g⁻¹ at a current density of 1 A g⁻¹ in 6 M KOH electrolyte and exhibits good cycling stability. Based on the above results, the cobalt hydroxide carbonate/AC composite shows a considerable promise as electrode for electrochemical applications.     

Performance of C/C electric double layer capacitors with coal-based active carbon electrodes

Coal-based active carbon was prepared and used as electrodes of electric double-layer capacitors (EDLCs). The performance of EDLCs using active carbon electrodes with different pore structure was studied, including cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. With an increase of sodium hydrate/coal ratio, the pore structure of active carbon is greatly improved, resulting in larger double-layer capacitance. The capacitance of asymmetric EDLC is up to 65.98 F/g. Moreover, it is found that different pore structure of active carbon is necessary for positive and negative electrodes. Asymmetric EDLC not only exhibits high capacitance but also shows excellent charge-discharge performance, suggesting that it is very suitable and promising to design electrode materials for supercapacitors.     

氮/硫共掺杂多孔碳纳米片的制备及其电化学性能

二维多孔碳材料能够提供较短的电解质扩散通道和较快的电子传输过程,因此在能量转换和储存装置中表现出优异的电化学性能.近年来的理论和实验研究表明,两元素共掺杂可使二维多孔碳材料的电化学性能得到明显提高.因此,共掺杂二维多孔碳材料的制备成为目前的研究热点之一.本文以甲基橙-FeCl₃复合物为模板引发剂制备了甲基橙掺杂的聚吡咯纳米管,通过对聚吡咯纳米管与KOH混合物（重量比为1：2）在700 ℃进行热处理,制备了二维石墨烯状氮/硫共掺杂多孔碳纳米片.所制备的氮/硫共掺杂多孔碳纳米片相互连结,形成了多级孔结构.氮气吸附分析表明多级孔结构包含微孔、介孔和大孔,这使所制备的氮/硫共掺杂多孔碳纳米片具有较高的比表面积（1744.58 m²/g）和孔体积（1.01 cm³/g）.共掺杂多孔碳纳米片中的掺杂氮以吡啶氮、吡咯氮和季胺氮形式存在,掺杂硫以噻吩硫和氧化态硫形式存在,二者之间的协同效应能够明显改善碳纳米片表面的浸润性,增加表面电化学活性点.这些特征使所制备的氮/硫共掺杂多孔碳纳米片表现出优异的电化学性能.用氮/硫共掺杂多孔碳纳米片制备的量子点敏化太阳能电池对电极,对多硫电解质再生反应的电催化活性与传统PbS对电极相近,所组装电池的光电转换效率可达到4.30%（100 mW/cm²）.氮/硫共掺杂多孔碳纳米片作为超级电容器电极材料,以6 M（1 M=1 mol/L）KOH为电解质,电流密度为0.4 A/g,比电容达到312.8 F/g.即使电流密度增加到20 A/g,比电容仍达到200.6 F/g,表明其具有较好的倍率性能.     

Preparation of carbon aerogel in ambient conditions for electrical double-layer capacitor

Carbon aerogels were prepared by polycondensation of resorcinol with formaldehyde using sodium carbonate as a catalyst in ambient conditions, and they were used as an electrode of electrical double-layer capacitor. The effect of resorcinol to catalyst ratio (R/C ratio) on volume shrinkage, BET surface area, and electrochemical property of carbon aerogels was investigated by changing R/C ratio from 50 to 2000. In order to minimize volume shrinkage, solvent exchange was performed with acetone at 50 °C for 1 day. Volume shrinkage was <2% after 2-day gelation in the absence of CO₂ supercritical drying. BET surface area was strongly dependent on R/C ratio. Carbon aerogel prepared at R/C ratio of 500 showed the highest BET surface area (706 m²/g) with average pore diameter of 10.9 nm. Electrochemical property of carbon aerogels as an electrode of electrical double-layer capacitor was investigated by cyclic voltammetry measurement. Specific capacitance of carbon aerogel prepared at R/C ratio of 500 was found to be 81 F/g in 1 M H₂SO₄ electrolyte at the scan rate of 10 mV/s.     

Preparation and electrochemical performance of novel ruthenium-manganese oxide electrode materials for electrochemical capacitors

A series of novel ruthenium-manganese oxide (denoted as Ru_nMn_1−nO_x) has been formed by oxidative co-precipitating. The precursor was obtained by mixing Mn(VII) (potassium permanganate), Mn(II) (manganese acetate) and Ru(III) (ruthenium chloride) in neutral aqueous solution at room temperature. The powder of Ru_nMn_1−nO_x was obtained by calcinating the precursor at appropriate temperature. The crystalline structure and electrochemical performance of the powder have been studied as a function of the calcination temperature. At appropriate calcination temperature (e.g. 170 °C), the powder is in hydrous amorphous phase with a high specific capacitance. When the calcination temperature reaches up to 350 °C, the crystal form of α-MnO₂ is formed, but the ruthenium oxide still keeps amorphous structure, which will lead to the decrease of specific capacitance of the composite electrode materials. The X-ray photoelectron spectroscopy (XPS) analysis shows that the powder of Ru_nMn_1−nO_x prepared in this study belongs to the composite of RuO₂-MnO₂. The results from cyclic voltammetry (CV), chronopotentiometry and electrochemical impedance spectroscopy (EIS) indicate that the ruthenium weight density of 9 wt% in Ru_nMn_1−nO_x can improve the cost-performance of ruthenium-manganese composite electrode.     

Preparation of carbon supported Pt-P catalysts and its electrocatalytic performance for oxygen reduction

The carbon supported PtP (PtP/C) catalysts were synthesized from Pt(NO₃)₂ and phosphorus yellow at the room temperature. The content of P in the PtP/C catalysts prepared with this method is high and the average size of the PtP particles is decreased with increasing the content of P. The electrocatalytic performances of the PtP/C catalysts prepared with this method for the oxygen reduction reaction (ORR) are better than that of the commercial Pt/C catalyst. The promotion action of P for enhancing the electrocatalytic performance of the PtP/C catalyst for ORR is mainly due to that Pt and P form the alloy and then the electron density of Pt is decreased.     

Dynamic properties of the electric double layer in electrolytes

The aim of this paper is to numerically investigate the characteristics of the Electrical Double Layer in electrolytes. The surface adsorption is neglected, which means there is no electric current injected to the solution from the electrode. The analysis is done for a one-dimensional model as the Debye length for electrolytes is much smaller than other dimensions of the system. The discussion is focused on the behaviour of the electric current and the layer impedance at different frequencies of the supply voltage.     

Acrylamide based proton conducting polymer gel electrolyte for electric double layer capacitors

A new class of polymer gel electrolyte (PGE) was synthesized using acrylamide as host polymer and LiClO₄ as dopant. The polymer gel was subjected to electrochemical AC impedance analysis and thermal analysis. The polymer has conductivity in the order of 10⁻³ S cm⁻¹ at ambient temperature. Thermogravimetric analysis (TGA) revealed the effect of dopant on host polymer matrix. A supercapacitor was fabricated using acrylamide based polymer gel electrolyte with activated carbon as electrode material and it was subjected to various electrochemical techniques like cyclic voltammetry, electrochemical AC impedance analysis and galvanostatic charge–discharge tests at various current densities. From cyclic voltammetry a specific capacitance of 28 F/g was obtained at a scan rate of 10 mV/s. The capacitor had good self-discharge behavior and good cycle life of more than 10,000 cycles. The coulombic efficiency was more than 95%. These results indicate that this acrylamide-based polymer gel electrolyte doped with LiClO₄ is a potential electrolyte for electric double-layer capacitors (EDLCs).     

Electric double layer of anisotropic dielectric colloids under electric fields

Anisotropic colloidal particles constitute an important class of building blocks for self-assembly directed by electrical fields. The aggregation of these building blocks is driven by induced dipole moments, which arise from an interplay between dielectric effects and the electric double layer. For particles that are anisotropic in shape, charge distribution, and dielectric properties, calculation of the electric double layer requires coupling of the ionic dynamics to a Poisson solver. We apply recently proposed methods to solve this problem for experimentally employed colloids in static and time-dependent electric fields. This allows us to predict the effects of field strength and frequency on the colloidal properties.     

Preparation and electrochemical performances of nanoporous/cracked cobalt oxide layer for supercapacitors

Nanoporous/cracked structures of cobalt oxide (Co₃O₄) electrodes were successfully fabricated by electroplating of zinc–cobalt onto previously formed TiO₂ nanotubes by anodizing of titanium, leaching of zinc in a concentrated alkaline solution and followed by drying and annealing at 400 °C. The structure and morphology of the obtained Co₃O₄ electrodes were characterized by X-ray diffraction, EDX analysis and scanning electron microscopy. The results showed that the obtained Co₃O₄ electrodes were composed of the nanoporous/cracked structures with an average pore size of about 100 nm. The electrochemical capacitive behaviors of the nanoporous Co₃O₄ electrodes were investigated by cyclic voltammetry, galvanostatic charge–discharge studies and electrochemical impedance spectroscopy in 1 M NaOH solution. The electrochemical data demonstrated that the electrodes display good capacitive behavior with a specific capacitance of 430 F g^?1 at a current density of 1.0 A g^?1 and specific capacitance retention of ca. 80 % after 10 days of being used in electrochemical experiments, indicating to be promising electroactive materials for supercapacitors. Furthermore, in comparison with electrodes prepared by simple cathodic deposition of cobalt onto TiO₂ nanotubes(without dealloying procedure), the impedance studies showed improved performances likely due to nanoporous/cracked structures of electrodes fabricated by dealloying of zinc, which provide fast ion and electron transfer routes and large reaction surface area with the ensued fast reaction kinetics.     

Enhanced electrochemical performance of porous activated carbon by forming composite with graphene as high-performance supercapacitor electrode material

In this work, a novel activated carbon containing graphene composite was developed using a fast, simple, and green ultrasonic-assisted method. Graphene is more likely a framework which provides support for activated carbon (AC) particles to form hierarchical microstructure of carbon composite. Scanning electron microscope (SEM), transmission electron microscope (TEM), Brunauer–Emmett–Teller (BET) surface area measurement, thermogravimetric analysis (TGA), Raman spectra analysis, XRD, and XPS were used to analyze the morphology and surface structure of the composite. The electrochemical properties of the supercapacitor electrode based on the as-prepared carbon composite were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), charge/discharge, and cycling performance measurements. It exhibited better electrochemical performance including higher specific capacitance (284 F g^?1 at a current density of 0.5 A g^?1), better rate behavior (70.7% retention), and more stable cycling performance (no capacitance fading even after 2000 cycles). It is easier for us to find that the composite produced by our method was superior to pristine AC in terms of electrochemical performance due to the unique conductive network between graphene and AC.