Recent Advances in SiO2 Based Composite Electrodes for Supercapacitor Applications

Supercapacitors (SCs) have been widely exploited as a promising energy storage system due to their unique merits, including fast charge/discharge rates, long-term cycling stability and low maintenance cost. Therefore, researchers are focused on designing novel nanostructures with high surface area, optimum pore size and volume, and porous structure are highly desirable. Silicon dioxide (SiO₂) has recently attracted enormous research attention as the electrode materials for SCs due to ease fabrication and integration possibility. However, due to the intrinsically poor electrical conductivity of metal oxides and the short diffusion distance of electrolytes into pseudocapacitor electrodes, only the surface of electroactive materials can effectively contribute to the total capacitance, while the large portion of material underneath the surface could hardly participate in the electrochemical charge storage process, leading to areal specific capacitance (ASC) values lower than expected. The coating of SiO₂ has been recognized as a possible route to reduce the resistance and increase durability. Still, even for coated electrodes, the performance has always been several orders of magnitudes below that of carbon-based SCs. The morphology, structure, and particle size of SiO₂ are related to the synthesis conditions and electrochemical performances. The thin films of SiO₂ nanostructures deposited on conductive substrates and their composites both shows good performance (binder free electrodes). SiO₂ and its composites display a large potential window for asymmetric SCs, delivering high energy density. More importantly, the design and development of composite materials with novel nanostructures are also effective ways to enhance the electrochemical properties of SCs. In this review, the research progress of SiO₂ based composite electrodes for SCs are briefly reviewed. Consequently, the possible developmental direction, challenges, and opportunities for SiO₂ based composite are also discussed.

     

Unravelling the origin of the capacitance in nanostructured nitrogen-doped carbon - NiO hybrid electrodes deposited with laser

The full knowledge of the charge storage mechanisms occurring in complex composite electrodes is key for the straightforward development of advanced electrochemical capacitors. In this work, hybrid electrodes composed of reduced graphene oxide, multiwall carbon nanotubes and NiO nanostructures were fabricated through reactive inverse matrix assisted pulsed laser evaporation technique. Nitrogen doping of the carbon nanostructures was carried out by introducing ammonia, urea and melamine precursors in the target. The N-doped graphene electrodes exhibited a significant capacitance enhancement as compared to non-doped ones. This fact is commonly ascribed to faradaic mechanisms. However, our structural-compositional studies point to a significant change of the structural configuration of the composites at the nanoscale upon the nitrogen functionalization as the source of the electrodes’ capacitance enhancement. The composites fabricated with urea precursor exhibited the highest capacitance, and this fact was associated with the presence of pyridinic N groups that triggered the formation of a high amount of structural defects (vacancies – boundaries) and microporosity, not observed in the samples synthesized with other precursors that mainly contained pyrrolic-graphitic N.     

PVA基碱性聚合物电解质Ni(OH)2/AC超级电容器的电化学性能

Polyvinyl alcohol(PVA)-sodium polyacrylate(PAAS)-KOH-H₂O alkaline polymer electrolyte film with high ionic conductivity was prepared by a solution-casting method.Polymer Ni(OH)₂/activated carbon(AC) hybrid supercapacitors with different electrode active material mass ratios(positive to negative) were fabricated using this alkaline polymer electrolyte,nickel hydroxide positive electrodes,and AC negative electrodes.Galvanostatic charge/discharge and electrochemical impedance spectroscopy(EIS) methods were used to study the electrochemical performance of the capacitors,such as charge/discharge specific capacitance,rate charge/discharge ability,and charge/discharge cyclic stability.Experimental results showed that with the decreasing of active material mass ratio m(Ni(OH)₂)/m(AC),the charge/discharge specific capacitance increases,but the rate charge/discharge ability and the charge/discharge cyclic stability decrease.     

Polyaniline/Poly(acrylamide‐co‐sodium acrylate) Porous Conductive Hydrogels with High Stretchability by Freeze‐Thaw‐Shrink Treatment for Flexible Electrodes

With the development of alternatives to traditional fossil energy and the rise of wearable technology, flexible energy storage devices have attracted great attention. In this paper, a polyaniline/poly(acrylamide‐sodium acrylate copolymer) hydrogel (PASH) with high flexibility and excellent electrochemical properties for flexible electrodes is fabricated by freeze‐thaw‐shrink treatment of a highly water‐absorptive hydrogel, together with in‐situ polymerization of aniline at a low aniline concentration (0.1 mol L^?1). The PASH exhibits a conductivity of 4.05 S m^?1 and an elongation at break of 1245%. The freeze‐thaw‐shrink treatment greatly improves the electrochemical performance and stability of the conductive PASH. The area specific capacitance of PASH reaches 849 mF cm^?2 and the capacitance maintains 89% after 1000 galvanostatic charge–discharge cycles. All the raw materials are conventional industrialized materials and no additional templating agent is needed during the entire synthesis process. This study provides a cost‐efficient approach for the fabrication of conductive polymer hydrogels, which has a broad application prospect in flexible energy storage electronic devices.     

Chemical reduction-induced fabrication of graphene hybrid fibers for energy-dense wire-shaped supercapacitors

The emerging one-dimensional wire-shaped supercapacitors(SCs) with structural advantages of low mass/volume structural advantages hold great interests in wearable electronic engineering. Although graphene fiber(GF) has full of vigor and tremendous potentiality as promising linear electrode for wire-shaped SCs, simultaneously achieving its facile fabrication process and satisfactory electrochemical performance still remains challenging to date. Herein, two novel types of graphene hybrid fibers, n...     

Enhancing the performance of polypyrrole composites as electrode materials for supercapacitors by carbon nanotubes additives

In the framework of this study, a facile method to obtain polypyrrole (PPy)/carbon nanotubes composites is presented. Chemical polymerization of PPy directly on the carbon nanotubes allows to obtain a homogenous distribution of the polymer. A low amount of carbon additive, varying from 1.5 to 5.5 wt %, is applied in order to prevent the decrease of capacitance value due to the presence of a low-capacitance component and, at the same time, to protect the electrode material from mechanical changes during cycling electrical measurements. The electrochemical properties, such as capacitance, its retention at different current loads, cycling stability, or self-discharge, are discussed. Improvement of electrochemical performances of the synthesized materials is observed mostly during cyclic stability measurements and at high current regimes. The obtained results confirm that the addition of only 3% of carbon nanotubes provides the best electrochemical performances as electrode materials for supercapacitor application. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48867.     

聚苯胺/酚醛树脂基活性炭复合材料的制备及表征

采用KOH溶液活化后的酚醛树脂基活性炭作为复合材料前躯体,通过原位聚合法在活性炭表面沉积聚苯胺,制备得到聚苯胺/酚醛树脂基活性炭复合材料。采用透射电子显微镜(TEM)、X射线衍射(XRD)、循环伏安法以及恒电流充放电法对聚苯胺/酚醛树脂基活性炭复合材料的微观结构和电化学性能进行了研究表征。TEM照片表明聚苯胺薄膜整齐的沉积在活性炭表面上,形成了相互关联的多孔网状物,结合XRD图表明聚苯胺/酚醛树脂基活性炭复合材料处于纳米级无序形态,循环伏安法测试和恒电流充放电测试表明聚苯胺/活性炭复合材料电极有着良好的使用稳定性和电极可逆性,复合材料电极的比电容可达到187.5 F/g。     

A novel method for carbon modification with minute polyaniline deposition to enhance the capacitance of porous carbon electrodes

A novel method was developed for minute deposition of polyaniline onto microporous activated carbon fabric to enhance the capacitance of the carbon serving as electrodes for electrochemical capacitors. The deposition consisted of pre-adsorption of monomer into carbon micropores followed by electrochemical polymerization of the adsorbed monomer in a monomer-free H₂SO₄ solution at 0.85 V vs. Ag/AgCl. In comparison with the conventional polymerization in a monomer solution, the developed deposition resulted in a polymer framework distributed over the vast surface in carbon micropores, thus leading to a lower resistance for ion binding with the polymer in H₂SO₄ during charge-discharge. The lower resistance gave rise to a higher specific capacitance for the deposited polymer. In the assembled two-electrode capacitors, the usage of polyaniline redox reactions to store charges was more prominent for polymer-carbon composite electrodes from the developed method because of the higher electrode open circuit potentials. The present work has demonstrated that a capacitance enhancement of >50% in comparison with bare carbon can be achieved with minute polyaniline deposition (<5 wt.%) using the developed method, while only 22% was reached using the conventional method.     

High performance of a solid-state flexible asymmetric supercapacitor based on graphene films

Solid-state flexible energy storage devices hold the key to realizing portable and flexible electronic devices. Achieving fully flexible energy storage devices requires that all of the essential components (i.e., electrodes, separator, and electrolyte) with specific electrochemical and interfacial properties are integrated into a single solid-state and mechanically flexible unit. In this study, we describe the fabrication of solid-state flexible asymmetric supercapacitors based on an ionic liquid functionalized-chemically modified graphene (IL-CMG) film (as the negative electrode) and a hydrous RuO(2)-IL-CMG composite film (as the positive electrode), separated with polyvinyl alcohol-H(2)SO(4) electrolyte. The highly ordered macroscopic layer structures of these films arising through direct flow self-assembly make them simultaneously excellent electrical conductors and mechanical supports, allowing them to serve as flexible electrodes and current collectors in supercapacitor devices. Our asymmetric supercapacitors have been optimized with a maximum cell voltage up to 1.8 V and deliver a high energy density (19.7 W h kg(-1)) and power density (6.8 kW g(-1)), higher than those of symmetric supercapacitors based on IL-CMG films. They can operate even under an extremely high rate of 10 A g(-1) with 79.4% retention of specific capacitance. Their superior flexibility and cycling stability are evident in their good performance stability over 2000 cycles under harsh mechanical conditions including twisted and bent states. These solid-state flexible asymmetric supercapacitors with their simple cell configuration could offer new design and fabrication opportunities for flexible energy storage devices that can combine high energy and power densities, high rate capability, and long-term cycling stability.     

Determination of the specific capacitance of conducting polymer/nanotubes composite electrodes using different cell configurations

Composite materials containing 20 wt.% of multiwalled carbon nanotubes (MWNTs) and 80 wt.% of chemically formed conducting polymers (ECP) as polyaniline (PANI) and polypyrrole (PPy) have been prepared and used for supercapacitor electrodes. The well conducting properties of MWNTs and their available mesoporosity allow a good charge propagation in the composites. Moreover, due to the good resiliency of MWNTs, an excellent stability of the supercapacitor electrodes is observed. It has been shown that the capacitance values for the composites strongly depend on the cell construction. In the case of three electrode cells, extremely high values can be found from 250 to 1100 F/g, however in the two electrode cell much smaller specific capacitance values of 190 F/g for PPy/MWNTs and 360 F/g for PANI/MWNTs have been measured. It highlights the fact that only two-electrode cells allow a good estimation of materials performance in electrochemical capacitors. The applied voltage was found to be the key factor influencing the specific capacitance of nanocomposites. For operating each electrode in its optimal potential range, asymmetric capacitors have been built with PPy/MWNTs as negative and PANI/MWNTs as positive electrodes giving capacitance values of 320 F/g per electrode material.     

Fabrication of polypyrrole (PPy)/carbon nanotube (CNT) composite electrode on ceramic fabric for supercapacitor applications

Polypyrrole (PPy)/carbon nanotube (CNT) composite electrodes are fabricated on ceramic fabrics for electrochemical capacitor applications. The CNTs are grown on the ceramic fabrics by the chemical vapor deposition (CVD) method and PPy is subsequently coated on them by chemical polymerization. The large surface area and high conductivity of the CNTs on the porous ceramic fabrics enhance their energy storage capacity. PPy provides not only additional capacitance as an active material, but also enhances the adhesion between the CNTs and ceramic fabrics. Furthermore, PPy acts as a conducting binder for connecting every individual CNT to increase the capacitance. The morphology of the PPy–CNTs on the ceramic fabrics is confirmed by SEM and TEM, and the electrochemical characteristics are investigated by cyclic voltammetry and galvanostatic charge–discharge tests.     

Oxidation of hydrogen at platinum-polypyrrole electrodes

Polypyrrole, an electronic conducting polymer, is used as a matrix for the dispersion of Pt particles. These particles can be included by two methods, viz. (1) by electrochemical depositin of platinum particles on a polypyrrole covered glassy carbon disc and (2) by incorporation of Pt particles during the polymerization of pyrrole on a glassy carbon disc. As a model reaction the oxidation of hydrogen at these electrodes is studied. The polypyrrole electrodes prepared by method (1) exhibit a good catalytic behaviour. The other type of electrodes however show, despite the higher Pt loading, much less activity. Additionally, electrodes were prepared according to method (1) with poly(N-methylpyrrole) and polyaniline as the conducting polymer. These electrodes show a similar diffusion limited behaviour for the oxidation of hydrogen as polypyrrole-modified electrodes, however the oxidation starts at a much higher potential.     

Recent advances in electrochemistry of diamond

Conductive boron-doped chemically vapour-deposited diamond thin film and honeycomb electrodes were examined for various possible applications in electroanalysis and electric double layer capacitor applications, respectively. The possibility of voltammetric study of electrochemical reactions occurring at high oxidation and high reduction potentials was demonstrated at diamond electrodes, taking histamine and carbon tetrachloride as respective examples. High sensitivity and high stability of this electrode were demonstrated for the determination of histamine and sulfadiazine by flow injection analysis method. Nanostructured honeycomb diamond electrodes, prepared by oxygen plasma etching, exhibited a wide potential window similar to that of as-grown film but a capacitance 200 times higher than that of the as-grown film. These results indicate the usefulness of diamond electrode for electroanalysis and double layer capacitor applications.     

交联状聚苯胺包覆碳纤维复合纳米线 制备及电容特性

以交联状氮掺杂碳纳米纤维(CNF)为碳骨架,采用插层辅助原位氧化聚合法使聚苯胺(PANI)均匀地在CNF表面包覆生长,制备了交联状聚苯胺包覆碳纤维(PANI/CNF)复合纳米线。采用TEM、SEM、TG、FTIR、Raman、XRD、XPS和BET对PANI/CNF复合纳米线的形貌和结构进行了表征。通过CV、EIS和GCD测试了PANI/CNF复合纳米线的电容特性。结果表明:PANI/CNF复合纳米线相互连通,表面呈荆棘状,具有多级空间结构。CNF质量分数为40%的PANI/CNF40复合纳米线电极在电流密度为1.0 A/g时,比电容达到820.31 F/g。电流密度增加到20.0 A/g时,比电容保留率为74.8%。在10.0 A/g时,经过2000次充放电循环后电极的比电容保持率达到89.7%。     

Encapsulation of N-doped carbon layer via in situ dopamine polymerization endows nanostructured NaTi2(PO4)3 with superior lithium storage performance

NaTi₂(PO₄)₃ (NTP) anode with NASICON structure presents broad prospects for aqueous lithium ion battery. Nevertheless, its intrinsic poor conductivity and structure stability in aqueous solution restrict performance of materials. Herein, we used dopamine hydrochloride to fabricate N-doped carbon encapsulated NaTi₂(PO₄)₃ nanosphere via in situ dopamine polymerization under different solution environments. Composites show obvious improvement on electrochemical performance compared with NTP. Additionally, utilization of Tris-buffer solution endows N-doped carbon encapsulated NaTi₂(PO₄)₃ nanosphere with superior performance to those of composites acquired in other solution environments. Among all samples obtained in Tris-buffer, N-doped carbon encapsulated NaTi₂(PO₄)₃ nanosphere with proper carbon layer shows superb electrochemical performance with discharge capacities of 127.5, 113.8, and 90.9 mA h g⁻¹ at 0.2, 3.0, and 15C, respectively. Superb property may be due to the unique nanosphere structure. Nanospheres with better dispersion can shorten migration path of Li ions. Encapsulation of N-doped carbon layer improves stability in aqueous electrolyte and ameliorates electronic conductivity of materials. N doping enhances hydrophilicity and electronic conductivity, and also forms lots of defects on carbon layer, which contributes to Li ion intercalation/deintercalation. This work reveals that the combination of nanosphere and N-doped carbon layer offers a promising method to raise electrochemical performances of NaTi₂(PO₄)₃.     

Fabrication of bioanode by using electrically conducting polythiophene via entrapment technique

A glassy carbon electrode (GCE) was tailored with conducting polymer polythiophene and further immobilized by an enzyme glucose oxidase (GOx). A thin film of polymer was developed by electrochemical polymerization of thiophene monomer. During electrochemical polymerization of the monomer the enzyme GOx and the redox active mediator ferritin (Frt) were entrapped within this polymer matrix. In this novel approach, the entrapment of enzyme and mediators within a polymer matrix occurs without chemical reaction that could affect their activity. The entrapment of enzyme and mediator within the conducting polymer matrices increases the surface area of the electrode. The tailored GCE/Ptp/Frt/GOx electrode showed a high catalytic activity. The increased surface area causes a high rate of electron transfer between the electrode and Frt engaged as an electron transfer mediator. The electrochemical properties of the electrode were determined by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The fabricated bioanode showed a current density of 3.9mA cm^?2 at 1.0 V vs. Ag/AgCl in a 45 mM glucose solution and suggests proficient chances in biofuel cells (BFCs) applications.     

S-enriched porous polymer derived N-doped porous carbons for electrochemical energy storage and conversion

Porous polymers have been recently recognized as one of the most important precursors for fabrication of heteroatom-doped porous carbons due to the intrinsic porous structure, easy available heteroatom-containing monomers and versatile polymerization methods. However, the heteroatom elements in as-produced porous carbons are quite relied on monomers. So far, the manipulating of heteroatom in porous polymer derived porous carbons are still very rare and challenge. In this work, a sulfur-enriched porous polymer, which was prepared from a diacetylene-linked porous polymer, was used as precursor to prepare S-doped and/or N-doped porous carbons under nitrogen and/or ammonia atmospheres. Remarkably, S content can sharply decrease from 36.3% to 0.05% after ammonia treatment. The N content and specific surface area of as-fabricated porous carbons can reach up to 1.32% and 1508 m²·g⁻¹, respectively. As the electrode materials for electrical double-layer capacitors, as-fabricated porous carbons exhibit high specific capacitance of up to 431.6 F·g⁻¹ at 5 mV·s⁻¹ and excellent cycling stability of 99.74% capacitance retention after 3000 cycles at 100 mV·s⁻¹. Furthermore, as the electrochemical catalysts for oxygen reduction reaction, as-fabricated porous carbons presented ultralow half-wave-potential of 0.78 V versus RHE. This work not only offers a new strategy for manipulating S and N doping features for the porous carbons derived from S-containing porous polymers, but also paves the way for the structure-performance interrelationship study of heteroatoms co-doped porous carbon for energy applications.     

Densely-stacked N-doped mesoporous TiO2/carbon microsphere derived from outdated milk as high-performance electrode material for energy storages

Spherical N-doped mesoporous TiO₂/C (MTC) composite micro-particles are produced by spray drying (SD) and carbonization process. The particle size of MTC microsphere is between 2 and 3.4?µm, and the N-doped amorphous C around TiO₂ could provide a conductive matrix, and buffer the volume change. When evaluated as electrodes for Li-ion batteries (LIBs) and Li-S batteries (LSBs), the MTC microsphere exhibits relatively high discharge-voltage plateau, excellent capacity retention and rate capability. As anode for LIBs, after 200 cycles, a reversible capacity more than 230?mA?h?g^?1 can achieved at 1?C. And for LSBs, a specific capacity of 1317.7?mA?h?g^?1 at 1?C and the capacity retention of 73.8% after 500 cycles. The superior electrochemical performance is ascribed to robust scaffolding architecture and conductive N-doped carbon matrix. The excellent electrochemical performance and process ability of the MTC microspheres make them very attractive as electrode materials for use in high rate battery application.     

Corn Cob Lignin-based Porous Carbon Modified Reduced Graphene Oxide Film For Flexible Supercapacitor Electrode

Flexible supercapacitors (FSCs) have attracted widespread attention of many researchers as a type of portable energy storage devices. However, there are still challenges in preparing renewable and inexpensive electrode materials. Herein, we prepared the porous carbon (PC) by the two-step process involving hydrothermal method and low-temperature heat treatment using corn cob lignin as the carbon source, and different types for PC were obtained by changing the temperature of low temperature heat treatment (100?°C–300?°C). The flexible electrode film was prepared by combining the obtained corn cob lignin-based PC with reduced graphene oxide (RGO), in addition, we investigated the effect of PC obtained by different low-temperature heat treatment (100?°C, 150?°C, 200?°C, 250?°C, and 300?°C) on the electrochemical properties of the composite electrode. The optimal low-temperature heat treatment temperature (250?°C) was determined and the PC250/RGO film electrodes displayed a high area specific capacitance of 636 mF/cm² with a mass of 2.2?mg/cm² (specific capacitance of 289?F/g) at 0.2?mA/cm² and 82% of the capacitance was retained after 10,000 charge and discharge cycles at 5?mA/cm², at the same time on the electrode film flexibility test, the influence of different bending angle on the electrochemical properties can be ignored. The assembled supercapacitor had the advantages of flexible, lightweight, low price, and environment friendly, which can achieve area specific capacitance of 324.5 mF/cm² at 0.2?mA/cm² and 91.8% capacitance retention after 1000 charging/discharging cycles. These good electrochemical properties illustrate the application prospects of composite electrode materials in wearable and portable electronic devices.     

Conducting Polymer Nanostructures: Template Synthesis and Applications in Energy Storage

Conducting polymer nanostructures have received increasing attention in both fundamental research and various application fields in recent decades. Compared with bulk conducting polymers, conducting polymer nanostructures are expected to display improved performance in energy storage because of the unique properties arising from their nanoscaled size: high electrical conductivity, large surface area, short path lengths for the transport of ions, and high electrochemical activity. Template methods are emerging for a sort of facile, efficient, and highly controllable synthesis of conducting polymer nanostructures. This paper reviews template synthesis routes for conducting polymer nanostructures, including soft and hard template methods, as well as its mechanisms. The application of conducting polymer mesostructures in energy storage devices, such as supercapacitors and rechargeable batteries, are discussed.