Surface modification and dispersion of ceramic particles using liquid-liquid extraction method for application in supercapacitor electrodes

Particle extraction through liquid-liquid interface (PELLI) was used for the extraction of MnO₂, Mn₃O₄, FeOOH and ZnO particles from an aqueous synthesis medium to the n-butanol phase. The benefits of PELLI were demonstrated by the fabrication of supercapacitor electrodes, which showed good electrochemical performance at high active mass loadings. Octyl gallate (OG) was found to be an efficient and versatile extractor for the ceramic particles. The phase transfer of the particles resulted in reduced agglomeration, which allowed for improved electrolyte access to the particle surface and facilitated their mixing with conductive multiwalled carbon nanotube (MWCNT) additives. It was shown that OG is a promising extractor material for the fabrication of ceramic-ceramic, ceramic-metal and ceramic-MWCNT nanocomposites. The strong adsorption of OG on the particle surface involved bridging or chelating bidentate bonding of the catechol group to the metal atoms. The capacitive properties of FeOOH-MWCNT electrodes were tested in the negative potential window. MnO₂-MWCNT and Mn₃O₄-MWCNT electrodes were investigated for charge storage in the positive potential window. The highest capacitance of 5.7 F cm⁻² for positive electrodes was achieved using MnO₂-MWCNT composites with active mass loading of 36 mg cm⁻². The Mn₃O₄-MWCNT electrodes exhibited improved capacitance retention at high charge-discharge rates.     

Fabrication of Tiron‐doped polypyrrole/MWCNT composite electrodes with high mass loading and enhanced performance for supercapacitors

In this study, the aromatic sulfonate compound Tiron with high charge to mass ratio is used as an anionic dopant for synthesis of polypyrrole (PPy). The fabricated PPy is investigated for electrochemical supercapacitor (ES) application. Testing results show that Tiron allows reduced PPy agglomeration, smaller particle size and improved charge storage properties of PPy. High capacitance and improved capacitive retention at high scan rates are achieved by the fabrication of PPy/multiwalled carbon nanotube (MWCNT) composite electrode using safranin (SAF) as a co‐dispersant. The Tiron‐doped PPy electrode shows the highest capacitance of 7.8 F cm^?2 with a mass of 27 mg cm^?2. The Tiron‐doped PPy/MWCNT composite electrode shows good capacitance retention with a capacitance of 1.0 F cm^?2 at the scan rate of 100 mV s^?1. Symmetric supercapacitor cells are fabricated using PPy based active materials. An energy density of 0.36 mWh cm^?2 is achieved. The energy/power density and capacitance retention of the Tiron‐doped PPy/MWCNT ES is significantly improved in comparison with PPy‐based ES, prepared without Tiron or MWCNT. The Tiron‐doped PPy/MWCNT symmetric supercapacitor presents good cycling performance with 91.4% capacitance retention after 1000 charge–discharge cycles. The PPy/MWCNT composites, prepared using Tiron and SAF co‐dispersant, are promising electrodes for ES. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42376.     

Fe3O4 spinel-Mn3O4 spinel supercapacitor prepared using Celestine blue as a dispersant,capping agent and charge transfer mediator

An asymmetric spinel-spinel supercapacitor is fabricated with negative and positive electrodes respectively consisting of Fe₃O₄ and Mn₃O₄ nanoparticles, where carbon nanotubes (CNT) serve as conductive additives. High performance of the individual electrodes and devices is achieved at a high active mass (AM) loading of 40 mg cm⁻² of the individual electrodes. We implement a conceptually new strategy using multifunctional Celestine blue (CB) dye, which is strongly adsorbed on the spinel phases and CNT, facilitates dispersion, acts as a capping agent and allows for the fabrication of spinel decorated CNT. CB is an efficient charge transfer mediator, which allows for significant improvement of capacitive behavior. The use of CB as a charge transfer mediator allows for good utilization of capacitive properties of spinels at high AM. Mechanisms of spinel-CB-CNT interactions and charge transfer mediation are discussed. The capacitive properties of electrodes with different spinel/CNT mass ratios are tested by cyclic voltammetry, chronopotentiometry and impedance spectroscopy. The areal capacitances of 6.17 and 5.15 F cm⁻² are obtained for Fe₃O₄ and Mn₃O₄ based electrodes, respectively in 0.5 M Na₂SO₄ electrolyte. The high capacitances are achieved for the electrodes that have low resistance. Using these electrodes, an asymmetric device is fabricated that has a capacitance of 2.41 F cm⁻² in a voltage window of 1.6 V.     

Electrochemical performance of polymer-derived SiOC and SiTiOC ceramic electrodes for artificial cardiac pacemaker applications

In an implantable electrode, such as a pacemaker electrode, fibrotic tissue formation due to a foreign body reaction is an important challenge affecting the efficiency to transmit the electrical signal of the device. The chemical inertness, biocompatibility, and electrical conductivity of polymer-derived ceramics (PDCs) are promising features in terms of overcoming this challenge. Here, the electrochemical behavior of polymer-derived silicon oxycarbide (SiOC) and titanium-doped SiOC (SiTiOC) ceramic electrodes for use as pacemaker electrodes is investigated by measuring impedance spectroscopy and cyclic voltammetry. In addition, typical stimulation electrodes such as iridium oxide, titanium nitride, platinum, and glassy carbon were prepared and loaded simultaneously into a custom-made electrochemical testing platform for comparison with SiOC and SiTiOC electrodes under identical conditions. The SiOC and SiTiOC electrodes shows a wide electrochemical stability window in the range of ?0.9 to 1.2 V with a double layer capacitance as the charge injection mechanism at the electrode/phosphate-buffered saline interface. Also, analyzing the voltage transient shows that the maximum charge injection of the SiTiOC electrode was about 28 μC/cm². The results of the electrochemical evaluation and comparison of SiOC and SiTiOC stimulating electrodes will be helpful to understand fundamental characteristics for the potential of this material as candidate for next-generation pacemaker electrodes.     

Phase transfer of oxide particles for application in thin films and supercapacitors

This paper reports efficient liquid-liquid extraction strategies for concentrated suspensions of oxide particles and demonstrates the benefits of using such strategies for thin film applications and the fabrication of supercapacitor electrodes. We performed materials synthesis in an aqueous phase and achieved efficient materials transfer to an organic phase, avoiding agglomeration during the drying stage. The metal oxides, suspended in an organic solvent were used directly for the deposition of polymer-titania composite films and fabrication of Mn₃O₄-carbon nanotube composite electrodes for supercapacitors. Strategy E1 involved the modification of particles in-situ during synthesis and a Schiff base reaction with an extractor at the liquid-liquid interface. In the one-step E2 procedure the interface reactions were used for the extraction. We discuss advantages of the E1 and E2 strategies. Both strategies featured a biomimetic approach for the surface modification of the particles, which allowed for strong adsorption of the extractors. The ability to perform efficient extraction using concentrated suspensions allowed for the fabrication of Mn₃O₄–carbon nanotube electrodes with high active mass loading. The electrodes showed a capacitance of 2.63 F cm⁻², good capacitance retention at high charge-discharge rates and low impedance. The results of this investigation pave the way for the agglomerate free processing of various functional materials for applications in advanced films, coatings and devices     

Photovoltaic Properties and Negative Capacitance Spectroscopy of PCBM:P3HT/FTO Nanostructured Counter Electrode for TiO2-Based DSSC

Nano-clusters blind films of phenyl C61-butyric acid methyl ester (PCBM) and poly(3-hexylthiophene) (P3HT) were deposited on fluorine doped tin-oxide (FTO) substrate by spin coating and applied as counter electrodes instead of platinum for a new FTO/TiO₂?+?K30 dye-sensitized solar cell. The photovoltaic parameters of the fabricated solar cell; open circuit voltage, short circuit current, output power and fill factor, were studied under various light intensities in the range 20:110?mW?cm^?2. An impedance spectroscopy study was also performed in a wide frequency range (5?kHz–1?MHz) to study the electron transport properties of the solar cells. The capacitance–voltage of the prepared DSSC is characterized by two parts: positive values of capacitance at low frequency range, f?≤?100?kHz and negative capacitance i.e., an inductive behavior, in higher frequency range f?≥ 300 kHz Conducting polymer electrode based on PCBM:P3HT/FTO can be used as a counter electrode in a DSSC.     

Capacitive matching of pore size and ion size in the negative and positive electrodes for supercapacitors

The capacitive behavior of activated carbons with different pore structures in two kinds of electrolytes, Bu₄NBF₄ and Et₄NBF₄ in propylene carbonate (PC) was studied using three kinds of cell configuration. The correlations between adsorbed ion size and pore size on the positive and negative electrodes were investigated. The matching of pore size and cation size was more predominant in the capacitor unit, especially for the electrode materials with less developed porosity. The asymmetric capacitance distribution of 7 F g⁻¹ in the negative electrode and 113 F g⁻¹ in the positive electrode occurred for electrode materials with less developed porosity. This could be ascribed to the surface saturation of the negative electrode by electrolyte ions, limiting the overall capacitance and working voltage of device. However, very developed porosity could not profit from the sufficient unitization of surface area, due to a weakened interaction between ions and pores wall. The specific area capacitance experienced a significant decrease from 11.3 to 6.7 μF cm⁻² with the pore volume increasing. Since the different pore sizes were required for different electrolytes ion on the negative and positive electrodes, the optimal matching between pores size and ions dimension with respect to each electrode should be considered for the maximum capacitance value of the capacitor unit.     

Effect of unequal load of carbon xerogel in electrodes on the electrochemical performance of asymmetric supercapacitors

This paper investigates the electrochemical performance of asymmetric supercapacitors in an environmentally friendly aqueous electrolyte (1.0 mol L^?1 sodium sulfate solution). The asymmetric configuration is based on the use of a highly porous carbon xerogel as active material in both the positive and negative electrodes, but the carbon xerogel loading in each electrode has been substantially modified. This configuration leads to an increase in the operational voltage window up to values of 1.8 V and consequently to a higher specific capacitance (200 F g^?1) and energy density (~25 Wh kg^?1). Four different mass ratios were employed (1, 1.5, 2 and 3), and the electrochemical response of the cells was evaluated by means of cyclic voltammetry, galvanostatic charge–discharge and impedance spectroscopy. The results demonstrate that the optimal carbon mass ratio in the electrodes is about 2.0 because in these conditions the devices are able to operate with a maximum cell voltage of 1.8 V and with a high electrical efficiency.     

Preparation and electrochemistry of NiO/SiNW nanocomposite electrodes for electrochemical capacitors

This paper studies nickel oxide/silicon nanowires (NiO/SiNWs) as composite thin films in electrodes for electrochemical capacitors. The SiNWs as backbones were first prepared by chemical etching, and then the Ni/SiNW composite structure was obtained by electroless plating of nickel onto the surface of the SiNWs. Next, the NiO/SiNW nanocomposites were fabricated by annealing Ni/SiNW composites at different temperatures in an oxygen atmosphere. Once the electrodes were constructed, the electrochemical behavior of these electrodes was investigated with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). In 2 M KOH solution, the electrode material was found to have novel capacitive characteristics. Finally, when the NiO/SiNW composites were annealed at 400 °C, the maximum specific capacitance value was found to be as high as 681 F g⁻¹ (or 183 F cm⁻³), and the probing of the cycling life indicated that only about 3% of the capacity was lost after 1000 charge/discharge cycles. This study demonstrated that NiO/SiNW composites were the optimal electrode choice for electrochemical capacitors.     

Effects of electrolytic composition on the electric double-layer capacitance at smooth-surface carbon electrodes in organic media

As a fundamental research on the optimization of electrolyte composition in practical electrochemical capacitor device, double-layer capacitance at Glassy Carbon (GC) and Boron-doped Diamond (BDD), as typical smooth-surface carbon electrodes, has been studied as a function of the electrolyte composition in organic media. Specific capacitance (differential capacitance: F cm⁻²) determined by an AC impedance method, in which no contribution of mass-transport effects is included, corresponded well to integrated capacitance evaluated by conventional cyclic voltammetry. The specific capacitance at the GC electrode varied with polarized potential and showed clear PZC (potential of zero charge), while the potential dependence of the capacitance at BDD was very small. The effects of the solvent and the electrolytic salt on the capacitance behavior were common for both electrodes. That is, the sizes of the solvent molecule and the electrolytic ion (cation) strongly affected the capacitance at these smooth-surface carbon electrodes.     

Rational design of binder-free ZnCo2O4 and Fe2O3 decorated porous 3D Ni as high-performance electrodes for asymmetric supercapacitor

The development of hierarchical, porous film based current collector has created huge interest in the area of energy storage, sensor, and electrocatalysis due to its higher surface area, good electrical conductivity and increased electrode-electrolyte interface. Here, we report a novel method to prepare a hierarchically ramified nanostructured porous thin film as a current collector by dynamic hydrogen bubble template electro-deposition method. At a first time, we report a porous 3D-Ni decorated with ZnCo₂O₄ and Fe₂O₃ by simple, low-cost electrochemical deposition method. The fabricated porous 3D-Ni based electrodes showed an excellent electrochemical property such as high specific capacitance, excellent rate capability, and good cycle stability. The asymmetric solid-state supercapacitor device was fabricated using porous, 3D Ni decorated with ZnCo₂O₄ and Fe₂O₃ as the positive and negative electrodes. The fabricated ZnCo₂O₄//Fe₂O₃ asymmetric device delivered an areal capacitance of 92?mF?cm^?2 at a current density of 0.5?mA?cm^?2 with a maximum areal power density of 3?W?cm^?2 and areal energy density of 28.8?mWh?cm^?2. The higher performances of porous, 3D current collector have a huge potential in the development of high performance supercapacitor.     

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.     

Preparation and electrochemical properties of poly‐2,5‐dihydroxyaniline/activated carbon composite electrode in organic electrolyte

Poly‐2,5‐dimethoxyaniline coating has been fabricated on active carbon (AC) substrates by cyclic voltammetry (CV) in organic system. The resulted coating is hydrolyzed to produce poly‐2,5‐dihydroxyaniline (PDHA) to enhance the capacitance of the composite electrode. Scanning electron microscope, Fourier transform infrared spectroscopy, X‐ray diffraction, Raman spectra, CV, electrochemical impedance spectroscopy, and galvanostatic charge/discharge test are used to investigate the properties of these electrodes. In organic electrolyte, due to the introduced hydroquinone units, high value of capacitance up to 975 F g^?1 of the PDHA/AC has been obtained at a current density of 0.37 A g^?1 at a potential window of 0–1.5 V. An asymmetric capacitor has been assembled with the PDHA/AC positive and pure AC negative electrodes, which is able to obtain a specific energy as high as 178 Whkg^?1 in the potential range of 0–2.0 V at a current density of 0.93 A g^?1. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Electrochemical characterization of nanoporous honeycomb diamond electrodes in non-aqueous electrolytes

Oxygen plasma-etched nano-honeycomb diamond thin film electrodes were examined for electrochemical capacitor applications in non-aqueous electrolytes. As-deposited and nano-honeycomb diamond electrodes in 0.5 M TEABF₄/PC both exhibited a wide potential window (approx. 7.3 V), similar to that of glassy carbon electrodes. For as-deposited diamond, the impedance behavior was found to be similar for non-aqueous and aqueous electrolytes, and the double-layer capacitance was found to be 21.8 μF cm⁻², almost the same as that obtained in aqueous electrolytes. For the honeycomb diamond electrodes, however, the impedance behavior observed in non-aqueous electrolytes was significantly different from that in aqueous electrolyte and indicated that the ac signal cannot penetrate to the bottom of the honeycomb pores in the non-aqueous electrolytes due to low conductivity, and that not all the surface may contribute to the double-layer capacitance. This result was verified by mathematical simulation.     

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.     

氧化镍/碳纳米管构筑准固态不对称超级电容器及电化学性能

以Ni(NO₃)₂为原料、NaOH为沉淀剂和羟基化碳纳米管（CNT）为基质首先制备了Ni(OH)₂/CNT复合材料, 然后将其于一定温度下煅烧，使其转变为NiO/CNT复合材料。用X射线粉末衍射仪（XRD）、场发射电子显微镜（FESEM）和透射电子显微镜（TEM）表征了样品的晶相与形貌，结果表明NiO纳米粒子紧密锚附在碳纳米管表面。复合材料可能的形成机理被提出。采用循环伏安法（CV）、单电极充放电和电化学阻抗研究了反应条件对其电化学性能的影响，确定最佳制备条件。将复合材料正极、活性炭负极和PVA-KOH电解质膜组装成准固态不对称超级电容器，电化学性能测试结果表明，在充放电电流密度11.2mA/cm²下，其比电容达到868.0F/g并保持稳定循环3700圈。7500次循环后，其比电容值仍有564.2F/g，显示出高的比电容和长的循环稳定性。     

3D nanostructured CuxO modified copper foam as a binder-free electrode for all-solid-state supercapacitor

Copper oxides (Cu_xO) play an active role in the field of binder-free electrodes for supercapacitors due to their own advantages, including high theoretical capacity, non-toxicity, low cost, etc. Developing mild and cheap process to prepare Cu_xO nanomaterials would broad its application in supercapacitors. In this paper, copper oxide is used as an active material and copper foam (CF) is chosen as a substrate to synthesize metal oxide-based electrodes by an in-situ oxidation method. Ingeniously, the availability of copper foam has a dual nature encompassing as a collector as well as a copper source. The as-obtained Cu_xO/CF-60 electrode possesses an area capacitance of 354.6 mF cm⁻² under 2 mA cm⁻². It also has superior cycle stability with 93.8 % of initial capacitance undergo 5000 charge-discharge cycles. Moreover, the all-solid-state asymmetric supercapacitor, combining Cu_xO/CF-60 and activated carbon (AC) pasted on nickel foam (NF) as the respective positive and negative electrodes, exhibits an energy density of 25 μWh cm⁻² when power density reaches 3 mW cm⁻². The Cu_xO/CF-60//AC/NF device displays better cycling stability as 80.2 % of initial capacitance after 5000 cycles. This work provides a simple way for designing Cu_xO based electrodes and lays the foundation for subsequent improvements in electrochemical performance.     

Wood Pulp Fiber Wrapped by Fish-Scale Graphene as Flexible and Free-Standing Supercapacitor Electrode

Poplar wood pulp was adopted as both frame and precursor for the synthesis of pulp fiber (PF)/reduced graphene oxide composite via a simple and low-cost method. In this method, the PF based on graphene (PFG) composite film electrode was prepared by a simple vacuum filtration process with various ratios (PF: reduced graphene oxide (RGO)?=?5:1, PF:RGO?=?5:2, PF:RGO?=?5:3, PF:RGO?=?5:4, PF:RGO?=?5:5). In terms of special structures, the PFG can be used as electrodes without metal-collector, adhesives, and additives. The optimal ratio (PF:RGO?=?5:4) film electrode displayed a high areal-specific capacitance of 683 mF/cm² at 1?mA/cm² with a mass of 5.3?mg/cm² (specific capacitance of 129?F/g) and good cycling stability (87.5% capacitance retention after 10,000 cycles at 5?mA/cm²) as well as excellent rate capability and high flexibility (suitable for any angle, even 180°). Moreover, the device could possess a maximum energy density of 47.71?μWh/cm² and a maximum power density of 1251?μW/cm². These results suggest that the composite PGF film is a promising electrode material.     

Electropolymerization and energy storage of poly[Ni(salphen)]/MWCNT composite materials for supercapacitors

Ni(salphen), a Schiff base ligand compound, was synthesized and electropolymerized on multiwalled carbon nanotube (MWCNT) electrodes in an acetonitrile solution via the pulse potentiostatic method and then applied as a supercapacitor electrode material. The polymerization mode was investigated through methyl replacement in the para‐position of phenyl rings in the Ni(salphen) monomer, and it was found that the Ni(salphen) monomers would polymerize by the generation of C? C bonds between the phenyl rings in the para‐position of the phenol moieties. The optimum condition for polymerization was evaluated, and when the polymerization time was 8 min, poly[Ni(salphen)] exhibited a specific capacitance up to 200 F g^?1 at a current density of 0.1 mA cm^?2, and the capacitance remains at 164 F g^?1 at 20 mA cm^?2. The energy density of the poly[Ni(salphen)] electrode reached 40 Wh kg^?1 at 0.1 mA cm^?2, about eight times greater than for a pure MWCNT electrode. Electrochemical performances were investigated, and the composites showed good redox property and ion transfer capability. This work showed that Ni(salphen) may be an attractive material in supercapacitors© 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44464.     

Boosting the electrochemical properties of diamond electrodes using carbon nanotube scaffolds

Diamond is a very attractive electrode material for analytical measurements including for instance bio-sensing. However, it suffers from a relatively low double layer capacitance and high impedance when it comes to the development of supercapacitors or neural interfaces, applications for which it could also be extremely promising. One way to increase the double layer capacitance of the material is to increase its specific surface area. Here we propose here to use vertically aligned carbon nanotubes (VACNTs) with high surface areas as a template onto which boron doped diamond is grown. The resulting composite was found to exhibit a double layer capacitance as high as 0.58 mF cm⁻² and very low impedance when compared to planar diamond electrodes in phosphate buffer saline solution. The influence of the VACNT length as well as of the thickness of the diamond coatings on the electrode performances were also investigated and are discussed in this paper.