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Ti3C2Tx–Fe3O4–carbon nanotube composites were prepared for electrochemical energy storage in the negative electrodes of supercapacitors. The electrodes show a remarkably high areal capacitance of 6.59 F cm−2 in a neutral Na2SO4 electrolyte, which was obtained by the development of advanced nanofabrication strategies and due to the synergistic effect of the individual components. Enhanced capacitance was achieved using the in-situ synthesis method for the Fe3O4 nanoparticles. The superparamagnetic behavior of the Fe3O4 nanoparticles facilitated the fabrication of electrodes with a reduced binder content. Good mixing of the components was achieved using a celestine blue co-dispersant, which adsorbed on the inorganic components and carbon nanotubes and facilitated their co-dispersion and mixing. The capacitive behavior was optimized by the variation of the electrode composition and mass loading in a range of 30–45 mg cm−2. An asymmetric device was proposed and fabricated, which contained a Ti3C2Tx–Fe3O4–carbon nanotube negative electrode and a polypyrrole–carbon nanotube positive electrode for operation in an Na2SO4 electrolyte. The asymmetric supercapacitor device demonstrated high areal capacitance and excellent power-density characteristics in an enlarged voltage window of 1.6 V. This investigation opens a new avenue for the synthesis and design of MXene-based asymmetric supercapacitors for future energy storage devices. [ABSTRACT FROM AUTHOR]

This investigation is motivated by increasing interest in ferrimagnetic materials and composites, which exhibit electrical capacitance. It addresses the need for the development of magnetic materials with enhanced capacitive properties and low electrical resistance. γ-Fe2O3-multiwalled carbon nanotube (MWCNT) composites are developed by colloidal processing and studied for energy storage in negative electrodes of supercapacitors. High energy ball milling (HEBM) of ferrimagnetic γ-Fe2O3 nanoparticles results in enhanced capacitive properties. The effect of HEBM on particle morphology is analyzed. Gallocyanine is used as a co-dispersant for γ-Fe2O3 and MWCNTs. The polyaromatic structure and catechol ligand of gallocyanine facilitated its adsorption on γ-Fe2O3 and MWCNTs, respectively, and facilitated their electrostatic dispersion and mixing. The adsorption mechanisms are discussed. The highest capacitance of 1.53 F·cm−2 is achieved in 0.5 M Na2SO4 electrolyte for composites, containing γ-Fe2O3, which is high energy ball milled and co-dispersed with MWCNTs using gallocyanine. HEBM and colloidal processing strategies allow high capacitance at low electrical resistance, which facilitates efficient charge–discharge. Obtained composites are promising for fabrication of multifunctional devices based on mutual interaction of ferrimagnetic and capacitive properties. [ABSTRACT FROM AUTHOR]

Pseudocapacitive materials are used for supercapacitor applications due to their exceptionally high capacitance and low cost. Good capacitive performance of the pseudocapacitive materials at high active mass loadings is vital for the development of the next generation of supercapacitor devices. This review describes recent advances in materials and nanotechnologies, which allows the development of advanced pseudocapacitive devices with high active mass. An important breakthrough is the discovery of novel dispersing and capping agents for the colloidal processing of nanoparticles. Particularly important are novel co‐dispersants that exhibit enhanced adsorption on materials of different types, such as inorganic nanoparticles, carbon nanotubes, and graphene. Conceptually new strategies are designed to fabricate coated particles. Recent innovations pave the way for the development of multifunctional redox‐active dopants‐dispersants and dopants‐oxidants to manufacture conductive polymer composites. Among the most important advances in nanotechnology is the development of template methods and heterocoagulation techniques for composite manufacturing. The progress in the design of novel surface modification techniques and materials, discovery of advanced anchoring groups, and development of liquid–liquid extraction allows agglomerate‐free processing of nanomaterials and composites. This review describes fundamental aspects of novel technologies and their applications in the manufacturing of pseudocapacitive devices for energy storage. [ABSTRACT FROM AUTHOR]

Many material manufacturing techniques require the use of nonaqueous colloidal suspensions, containing well dispersed oxide particles and various water insoluble functional components. We report an efficient method for the direct transfer of MnO2 and titania particles, synthesized in water, to an organic solvent through the interface of two immiscible liquids. Particle agglomeration during the drying stage was avoided, and stable suspensions of nonagglomerated particles in the organic phase were obtained. The benefits of this method were demonstrated by the fabrication of advanced composite MnO2-multiwalled carbon nanotube electrodes, containing a polymer binder, for electrochemical supercapacitors with high active mass loading and high active material to current collector mass ratio. The electrodes showed a capacitance of 5.13 F/cm2 and low impedance. High extraction efficiency from concentrated suspensions was achieved by the use of an advanced extractor, which allowed strong adsorption on the particles by the polydentate bonding. The extraction mechanism is discussed. [ABSTRACT FROM AUTHOR]

Submicrometre particles of multiferroic BiMn 2 O 5 are prepared by a hydrothermal method. We demonstrate for the first time that BiMn 2 O 5 -multiwalled carbon nanotube (MWCNT) composite can be used as a new active material for positive electrodes of electrochemical supercapacitors (ES). The possibility of fabrication of BiMn 2 O 5 –MWCNT composites from colloidal suspensions using Celestine blue dye as a co-dispersant for BiMn 2 O 5 and MWCNT is demonstrated. The composite BiMn 2 O 5 –MWCNT electrodes with high mass loading and high active material to current collector mass ratio show a capacitance of 6.0 F cm −2 (540 F cm −3 ) at a scan rate of 2 mV s −1 and capacitance retention of 75 and 58% at scan rates of 100 and 200 mV s −1 , respectively. The new findings pave the way to the fabrication of efficient asymmetric devices, containing BiMn 2 O 5 –MWCNT positive electrodes and activated carbon–carbon black (AC–CB) negative electrodes. The asymmetric device shows good capacitive behavior and good cyclic stability in a voltage window of 1.8 V. The analysis of power-energy characteristics indicates that maximum energy density of 13.0 W h L −1 (9.0 W h kg −1 ) and maximum power density of 3.6 kW L −1 (2.5 kW kg −1 ) can be achieved. [ABSTRACT FROM AUTHOR]

Highlights: [•] Safranin was used as a dispersant for electrophoretic deposition of materials. [•] Carbon nanotubes, graphene and polypyrrole nanofibers were deposited cathodically. [•] Graphene–carbon nanotubes and graphene polypyrrole nanofiber composites were obtained. [•] Composite films were studied for electrodes of electrochemical supercapacitors. [•] The composite electrodes showed high capacitance and low resistance. [ABSTRACT FROM AUTHOR]

Abstract: Electrophoretic deposition (EPD) method has been developed for the fabrication of manganese dioxide (MD)–multiwalled carbon nanotubes (MWCNTs) nanocomposites. Cationic tyramine hydrochloride (TA) and anionic gallic acid (GA), chromotropic acid disodium salt (CA) and benzoic acid (BA) were investigated as charging additives. The results of deposition yield measurements, quartz crystal microbalance studies and Fourier transform infrared spectroscopy data showed that OH groups are involved in the adsorption of the phenolic compounds on the MD nanoparticles. The adsorption mechanism is based on the deprotonation of the OH groups and surface complexation of Mn ions. It was shown that the phenolic molecules, such as TA, GA and CA can be used as charging additives for the EPD of MD. Composite MD–MWCNTs films were prepared by cathodic and anodic EPD using TA and GA, respectively. In this approach, TA and GA were used as common charging additives for two different materials: MD and MWCNTs. Scanning electron microscopy studies showed the formation of composite films containing well-dispersed MWCNTs in the MD matrix. The results of the thermogravimetric analysis demonstrated that the amount of the MWCNTs in the composite materials can be varied. The composite films were studied for the application in electrochemical supercapacitors (ES). The ES electrodes showed good capacitive behavior in the 0.5M Na2SO4 electrolyte in a voltage window of 0–0.9V versus a standard calomel electrode (SCE). The films prepared by cathodic EPD showed higher specific capacitance (SC) compared to the films prepared by anodic EPD with the highest SC of 553Fg−1 at the scan rate of 2mVs−1. [Copyright &y& Elsevier]

This investigation addresses the challenges in the development of efficient nanostructured Mn3O4 cathodes for supercapacitors. A high areal capacitance and the ability to avoid a time-consuming activation procedure for electrodes with high active mass loading of 40 mg cm−2 are reported. This facilitates practical applications of Mn3O4 based electrodes. The highest capacitance of 6.11 F cm−2 (153 F g−1) is obtained from cyclic voltammetry at a scan rate of 2 mV s−1 and 6.07 F cm−2 (151.9 F g−1) from the chronopotentiometry at a current density of 3 mA cm−2 in a potential window of 0.9 V in a neutral Na2SO4 electrolyte. The new approach is based on the application of rhamnolipids (RL) as a capping agent for the synthesis of Mn3O4 particles and a co-dispersant for Mn3O4 and carbon nanotubes, which are used as conductive additives. The size and shape of the Mn3O4 particles are influenced by RL. The enhanced performance of the electrodes is linked to the chemical structure and properties of RL molecules, which exert influence on Mn3O4 particle size and shape during synthesis, reduce agglomeration, facilitate RL adsorption on Mn3O4 and carbon nanotubes, and influence their co-dispersion and mixing at the nanometric scale. [ABSTRACT FROM AUTHOR]

In this study, results from a conceptually new method for the preparation of Mn 3 O 4 -multiwalled carbon nanotube (MCNT) composites are presented. High active mass (HAM) Mn 3 O 4 -MCNT cathodes are prepared and tested for supercapacitors. The method is based on a salting-out aided dispersive extraction of Mn 3 O 4 particles precipitated in an aqueous phase to isopropanol and their co-dispersion with MCNT. The use of lauryl gallate as an extractor is a key factor for the phase transfer. Lauryl gallate is used as a co-dispersant for Mn 3 O 4 and MCNT. The mechanisms of lauryl gallate adsorption on Mn 3 O 4 and MCNT and the salting-out aided extraction mechanism are discussed. Enhanced electrochemical performance of the electrodes with HAM of 41 mg cm−2 is achieved due to enhanced mixing and co-dispersion of Mn 3 O 4 and MCNT. The electrodes show a high capacitance of 6 F cm−2 in aqueous Na 2 SO 4 and low electrical resistance. The obtained areal capacitance is substantially higher than that for Mn 3 O 4 -MCNT composites, prepared by other methods. The capacitance increase during initial cycling is linked to the microstructure changes. The salting-out aided extraction method overcomes the limitations of other extraction techniques and opens a new strategy for the manufacturing of nanocomposites with advanced functional properties. [Display omitted] [ABSTRACT FROM AUTHOR]

MXenes, such as Ti3C2Tx, are promising materials for electrodes of supercapacitors (SCs). Colloidal techniques have potential for the fabrication of advanced Ti3C2Tx composites with high areal capacitance (CS). This paper reports the fabrication of Ti3C2TX-Fe3O4-multiwalled carbon nanotube (CNT) electrodes, which show CS of 5.52 F cm−2 in the negative potential range in 0.5 M Na2SO4 electrolyte. Good capacitive performance is achieved at a mass loading of 35 mg cm−2 due to the use of Celestine blue (CB) as a co-dispersant for individual materials. The mechanisms of CB adsorption on Ti3C2TX, Fe3O4, and CNTs and their electrostatic co-dispersion are discussed. The comparison of the capacitive behavior of Ti3C2TX-Fe3O4-CNT electrodes with Ti3C2TX-CNT and Fe3O4-CNT electrodes for the same active mass, electrode thickness and CNT content reveals a synergistic effect of the individual capacitive materials, which is observed due to the use of CB. The high CS of Ti3C2TX-Fe3O4-CNT composites makes them promising materials for application in negative electrodes of asymmetric SC devices. [ABSTRACT FROM AUTHOR]

Cathodes for supercapacitors with enhanced capacitive performance are prepared using MnO2 as a charge storage material and carbon nanotubes (CNT) as conductive additives. The enhanced capacitive properties are linked to the beneficial effects of catecholate molecules, such as chlorogenic acid and 3,4,5-trihydroxybenzamide, which are used as co-dispersants for MnO2 and CNT. The dispersant interactions with MnO2 and CNT are discussed in relation to the chemical structures of the dispersant molecules and their biomimetic adsorption mechanisms. The dispersant adsorption is a key factor for efficient co-dispersion in ethanol, which facilitated enhanced mixing of the nanostructured components and allowed for improved utilization of charge storage properties of the electrode materials with high active mass of 40 mg cm−2. Structural peculiarities of the dispersant molecules are discussed, which facilitate dispersion and charging. Capacitive properties are analyzed using cyclic voltammetry, chronopotentiometry and impedance spectroscopy. A capacitance of 6.5 F cm−2 is achieved at a low electrical resistance. The advanced capacitive properties of the electrodes are linked to the microstructures of the electrodes prepared in the presence of the dispersants. [ABSTRACT FROM AUTHOR]

FeOOH-polypyrrole-multiwalled carbon nanotube (FeOOH-PPy-MWCNT) ternary nanocomposite for supercapacitor negative electrodes are prepared by liquid-liquid co-extraction (LLCE) technique using decylphosphonic acid (DPPA) as efficient co-extractor. LLCE offers advantages of reduced agglomeration and facilitates mixing of the individual components. This technique allows direct particle transfer from the reaction medium to the electrode fabrication slurry. The mechanism of LLCE extraction is analyzed. The synergetic effect of FeOOH, PPy and MWCNT significantly enhances charge storage properties of the FeOOH-PPy-MWCNT ternary nanocomposite electrodes. The FeOOH-PPy-MWCNT ternary nanocomposite electrode shows an integral capacitance of 5.1 F cm−2 (137.9 F g−1) in a negative potential window, which is significantly higher than capacitances of binary FeOOH-MWCNT and PPy-MWCNT nanocomposites. Moreover, the ternary composite offers advantages of a larger voltage window. Testing results for the ternary composites at different electrode potentials show reduced AC impedance. The asymmetric supercapacitor device composed of FeOOH-PPy-MWCNT anode and MnO 2 -MWCNT cathode exhibits a high areal capacitance of 2.5 F cm−2 at scanning rate of 2 m V s−1 in a voltage window of 1.6 V at an extremely small impedance. This facile LLCE fabrication technique opens a door for fabrication of advanced nanocomposite materials for supercapacitor applications. [Display omitted] • Liquid-liquid co-extraction technique was developed for composite fabrication. • FeOOH-polypyrrole-multiwalled carbon nanotube was used as for supercapacitor anode. • FeOOH-polypyrrole-multiwalled carbon nanotube exhibited a capacitance of 5.1F cm−2. • Asymmetric device was fabricated with FeOOH based anode and MnO 2 based cathode. • The asymmetric device exhibited a high areal capacitance of 2.5 F cm−2. [ABSTRACT FROM AUTHOR]

Manganese dioxide nanotubes and activated carbon coated multiwalled carbon nanotubes (AC-MWCNT) are prepared by hydrothermal methods. MnO 2 -graphene positive electrodes with good dispersion of individual components are fabricated using poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt] (PAZO) as a co-dispersant. The unique structure of PAZO, containing chelating aromatic monomers allows for efficient adsorption of this polyelectrolyte on MnO 2 and graphene, which is a prerequisite for their efficient electrosteric co-dispersion. The MnO 2 -graphene electrodes with active mass loading of 30 mg cm −2 show a capacitance of 3.3 F cm −2 at a scan rate of 2 mV s −1 and a capacitance retention of 64% is achieved with increase of scan rate from 2 to 100 mV s −1 . The use of AC-MWCNT with thick AC coating allows the fabrication of negative electrodes, which closely match the capacitive performance of the positive electrodes. The asymmetric supercapacitors containing MnO 2 -graphene positive electrodes and AC-MWCNT negative electrodes show capacitance of 1.42 F cm −2 at a scan rate of 2 mV s −1 , capacitance retention of 52% in the scan rate range of 2–100 mV s −1 in a voltage window of 1.8 V. [ABSTRACT FROM AUTHOR]

Polypyrrole (PPy) electrodes for electrochemical supercapacitors (ES) are prepared using amaranth as a new redox-active anionic dopant for chemical polymerization of PPy. The use of amaranth allows excellent electrochemical performance of electrodes with high mass loading and high PPy to current collector mass ratio. The specific capacitance of 4.2 F cm-2 is achieved at a scan rate of 2 mV s-1. The analysis of electrochemical testing results provides an insight into the influence of the chemical structure of amaranth on microstructure, electrochemical properties and cycling stability of PPy. New method is introduced for the fabrication of PPy coated multiwalled carbon nanotubes (MWCNT). The use of amaranth allows fine microstructure of PPy coatings formed on MWCNT, which are well dispersed in the presence of pyrocatechol violet dispersant. The use of PPy coated MWCNT allows significant improvement in capacitance retention at high charge-discharge rates, compared to pure PPy material, and good cycling stability of individual electrodes and ES cells. The ES cells, based on PPy show specific capacitance of 1.3-1.6 F cm-2 at discharge current densities of 1-33 mA cm-2. [ABSTRACT FROM AUTHOR]

Highlights: [•] New colloidal approach was proposed for the fabrication of composites. [•] Metal oxide particles were positively charged and dispersed using phosphate ester. [•] Carbon nanotubes were negatively charged and dispersed using organic dye. [•] MnO2–carbon nanotubes composites were obtained by heterocoagulation. [•] Composites are promising materials for electrochemical supercapacitors. [ABSTRACT FROM AUTHOR]

Abstract: Manganese dioxide nanofibers with length ranged from 0.1 to 1μm and a diameter of about 2–4nm were prepared by a chemical precipitation method. Composite electrodes for electrochemical supercapacitors were fabricated by impregnation of slurries of the manganese dioxide nanofibers and multiwalled carbon nanotubes (MWCNTs) into porous nickel foam current collectors. In the composite electrodes, MWCNT formed a secondary conductivity network within the nickel foam cells. Obtained composite electrodes, containing 0–20wt.% MWCNT with total mass loading of 40mgcm−2, showed a capacitive behavior in the 0.1–0.5M Na2SO4 solutions. The highest specific capacitance (SC) of 155Fg−1 was obtained at a scan rate of 2mVs−1 in the 0.5M Na2SO4 solutions. The SC increased with increasing MWCNT content in the composite materials and increasing Na2SO4 concentration in the solutions and decreased with increasing scan rate. [Copyright &y& Elsevier]

An asymmetric spinel-spinel supercapacitor is fabricated with negative and positive electrodes respectively consisting of Fe 3 O 4 and Mn 3 O 4 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 Fe 3 O 4 and Mn 3 O 4 based electrodes, respectively in 0.5 M Na 2 SO 4 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. [ABSTRACT FROM AUTHOR]

This review describes new strategies for the non-covalent functionalization and dispersion of CNT using small molecules, such as commercial bile acid salts (BAS) and organic dyes. Efficient CNT dispersion was achieved due to the small size, charge and unique adsorption properties of BAS and dyes, which facilitated the bundle “unzipping” mechanism. The discovery of interesting electrochemical and film-forming properties of BAS and organic dyes allowed electrophoretic deposition (EPD) of CNT films by cathodic or anodic methods. Of particular importance is the efficiency of BAS dispersants in the sorting of CNT by diameter, chirality and length. These studies allowed for the efficient separation of SWCNT by electronic type and size, which addressed the urgent needs for many advanced applications. New dispersants allowed the fabrication of functional polymer coated CNT and development of advanced techniques for the fabrication of composites. Chelating dyes were used as co-dispersants for CNT and inorganic nanoparticles. The use of BAS and organic dyes for CNT dispersion has driven the development of advanced composites, films, aerogels for electrochemical, electronic, energy generation and storage, biomedical, sensor and other applications. Colloidal and interface chemistry of new dispersing agents is emerging as a new area of technological and scientific interest. [ABSTRACT FROM AUTHOR]

Poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt] (PAZO) exhibits a number of unique physical properties. An electrophoretic deposition (EPD) method has been utilized for the deposition of PAZO films, which exhibited photoinduced birefringence. The advantages of EPD, deposition mechanism and kinetics of deposition are discussed. PAZO exhibits unique adsorption properties, which are related to its chemical structure. The salicylate ligands of PAZO monomers with strong chelating properties provide numerous adsorption sites for PAZO adsorption on inorganic materials. It was found that PAZO can function as a charging, dispersing and film forming agent for EPD of a wide array of materials, such as TiO 2 (anatase and rutile), micron size platelets and submicrometre particles of Al 2 O 3 , zirconia, MnO 2 , MgAl 2 O 4 , aluminium hydroxide, SiC, Pd metal, carbon nanotubes and polypyrrole nanofibers. The feasibility of incorporation of other polymers and organic dyes into the PAZO films has been demonstrated. PAZO showed superior performance compared to other dispersing agents for the EPD method, overcoming their limitations. Another major finding of this study was the possibility of EPD of composites, using PAZO as a co-dispersant for different materials. Testing results showed that composites can be used for optical, energy storage, corrosion protection and other applications. [ABSTRACT FROM AUTHOR]

Electrodes for electrochemical supercapacitors were fabricated by cathodic electrodeposition of MnO2 on carbon nanotubes (CNTs), which were grown by chemical vapour deposition on stainless steel meshes. The MnO2–CNT nanocomposites were characterized by scanning electron microscopy, transmission electron microscopy, cyclic voltammetry and impedance spectroscopy. The electrodes showed excellent capacitive behaviour in the 0.5M Na2SO4 electrolyte, with specific capacitance of 356Fg−1 at a scan rate of 2mVs−1. [Copyright &y& Elsevier]

MXene (Ti 3 C 2 T x) is an emerging material choice for advanced energy storage. However, the relatively low areal capacitance is a bottleneck in developing asymmetric supercapacitors with enhanced energy-power characteristics in large voltage windows. A simple and straightforward approach is proposed to design and fabricate Ti 3 C 2 T x -multiwalled carbon nanotube (Ti 3 C 2 T x -CNT) composite electrodes. Polymethylmethacrylate (PMMA) is used as a binder for electrodes with 40 mg cm−2 high active mass loadings (AML); meanwhile, both multilayered Ti 3 C 2 T x and CNT are efficiently dispersed in PMMA solution. The fabricated Ti 3 C 2 T x -CNT electrodes with different CNT contents are tested in a −1.1~-0.3 V negative potential window and analyzed by different electrochemical techniques. The optimization of Ti 3 C 2 T x -CNT-PMMA composition facilitates the design of anodes with capacitance of 2.26 F cm−2 in Na 2 SO 4 electrolyte, which is essentially higher than literature results for Ti 3 C 2 T x. The ability to obtain high capacitance in the Na 2 SO 4 electrolyte is a crucial result, which facilitates the fabrication of asymmetric aqueous devices operating at 1.6 V. The Ti 3 C 2 T x -CNT anode is combined with a MnO 2 -CNT cathode in an asymmetric cell, which shows a 1.24 F cm−2 capacitance at 3 mA cm−2. [Display omitted] • Ti 3 C 2 T x anodes for supercapacitors with high active mass loading were developed. • Carbon nanotubes were used as conductive additives. • A capacitance of 2.26 F cm−2 in Na 2 SO 4 electrolyte was achieved. • Asymmetric device based on Ti 3 C 2 T x anode and MnO 2 based cathode was developed. • The device showed a capacitance of 1.24 F cm−2 in Na 2 SO 4 electrolyte for 1.6 V. [ABSTRACT FROM AUTHOR]