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This investigation is motivated by the surge of interest in materials, combining high spontaneous magnetization and pseudocapacitance at room temperature. Ferrimagnetic MnFe 2 O 4 offers benefits of high magnetization. However, the non-pseudocapacitive behavior, low capacitance and high resistance of MnFe 2 O 4 are limiting factors for its applications in magnetic pseudocapacitive devices. This investigation demonstrates that nearly ideal pseudocapacitive behavior can be achieved for MnFe 2 O 4 electrodes in Na 2 SO 4 electrolyte. High pseudocapacitance is observed in positive and negative potential ranges and two different charging mechanisms are proposed. High capacitance is achieved at a low impedance. The ability to achieve comparable and high areal capacitances in the positive and negative potential ranges facilitates the fabrication of a symmetric pseudocapacitive device, containing ferrimagnetic MnFe 2 O 4 as cathode and anode material for operation in enlarged voltage window of 1.6 V. The symmetric device shows capacitance of 0.92 F cm−2 at a current density of 3 mA cm−2. The individual electrodes and device show good cycling stability. The approach is based on the use of murexide and gallocyanine as redox-active dispersants and charge transfer mediators. The analysis of testing results provides an insight into the influence of chemical structure, charge and redox properties of the dispersants on the capacitive behavior. The ability to fabricate a pseudocapacitive device, containing two ferrimagnetic electrodes is promising for energy storage, water purification and novel applications based on magnetocapacitive effects. [ABSTRACT FROM AUTHOR]

This investigation is motivated by the need in the development of manganese oxide cathodes for supercapacitors with high capacitance at high charge–discharge rates and enhanced capacitance retention in a wide range of charge–discharge rates. It also addresses the challenge of eliminating the time-consuming activation procedure, which limits the applications of Mn3O4 cathodes. The new approach is based on the use of environmentally friendly and biocompatible pH modifiers–dispersants, such as polyethylenimine (PEI) and meglumine (MG) for hydrothermal synthesis. In this approach, the use of inorganic alkalis is avoided. We demonstrate the benefits of this approach for the fabrication of manganese oxide nanoparticles, such as Mn-PEI and Mn-MG. Electrodes with a high active mass of 40 mg cm−2 are fabricated and electrochemically tested in 0.5 M Na2SO4 electrolyte. The method of electrode material fabrication offers benefits for the accelerated electrode activation procedure, which is practically eliminated for Mn-MG electrodes. The Mn-MG electrodes showed a remarkably high capacitance of 3.68 F cm−2 (93.19 F g−1) at a sweep rate of 100 mV s−1 and a high capacitance retention of 90.6% in the CV sweep range of 1–100 mV s−1. [ABSTRACT FROM AUTHOR]

Pseudocapacitive (PC) materials are under investigation for energy storage in supercapacitors, which exhibit exceptionally high capacitance, good cyclic stability, and high power density. The ability to combine high electrical capacitance with advanced ferrimagnetic or ferromagnetic properties in a single material at room temperature opens an avenue for the development of advanced magnetically ordered pseudocapacitive (MOPC) materials. This review covers materials science aspects, charge storage mechanisms, magnetocapacitance, and magnetoelectric (ME) phenomena in MOPC materials. Recent studies demonstrate high PC properties of advanced ferrimagnetic materials, such as spinel ferrites and hexagonal ferrites. Of particular importance is the discovery of PC properties of perovskite-type manganites, which exhibit room temperature ferromagnetism and giant negative magnetoresistance. The coupling of high capacitance and magnetization in MOPC provides a platform for strong ME interactions. Various strategies are used for manipulation of electrical capacitance/magnetization of MOPC by a magnetic field/electrode potential. Magnetocapacitance studies show significant increase in capacitance of MOPC under the influence of a magnetic field. Moreover, the application of a magnetic field results in enhanced energy density and power density, reduction of resistance, and improvement of cyclic stability. Such findings offer a potential of a breakthrough in the development of advanced supercapacitors. High magnetocapacitance and ME phenomena are linked to the influence of magnetic fields on electrolyte diffusion, structure of electrical double layer, charge transfer resistance, and variation of conductivity and magnetization of MOPC materials, which facilitate charge/discharge behavior. Various applications of ME effect in MOPC are discussed. Moreover, advantages of magnetocapacitive MOPC are described for applications in electronic and spintronic devices, supercapacitors, and devices for magnetically enhanced capacitive deionization of water. [ABSTRACT FROM AUTHOR]

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 interest in nanostructured FeOOH anodes for aqueous asymmetric supercapacitors operating in Na2SO4 electrolyte. The research goal is the fabrication of anodes with high active mass loading of 40 mg cm−2, high capacitance and low resistance. The influence of high-energy ball milling (HEBM), capping agents and alkalizer on the nanostructure and capacitive properties is investigated. HEBM promotes the crystallization of FeOOH, which results in capacitance reduction. Capping agents from the catechol family, such as tetrahydroxy-1,4-benzoquinone (THB) and gallocyanine (GC), facilitate the fabrication of FeOOH nanoparticles, eliminate the formation of micron size particles and allow the fabrication of anodes with enhanced capacitance. The analysis of testing results provided insight into the influence of the chemical structure of the capping agents on nanoparticle synthesis and dispersion. The feasibility of a conceptually new strategy for the synthesis of FeOOH nanoparticles is demonstrated, which is based on the use of polyethylenimine as an organic alkalizer-dispersant. The capacitances of materials prepared using different nanotechnology strategies are compared. The highest capacitance of 6.54 F cm−2 is obtained using GC as a capping agent. The obtained electrodes are promising for applications as anodes for asymmetric supercapacitors. [ABSTRACT FROM AUTHOR]

This investigation is motivated by increasing interest in the development of magnetically ordered pseudocapacitors (MOPC), which exhibit interesting magnetocapacitive effects. Here, advanced pseudocapacitive properties of magnetic CuFe2O4 nanoparticles in negative potential range are reported, suggesting that CuFe2O4 is a promising MOPC and advanced negative electrode material for supercapacitors. A high capacitance of 2.76 F cm−2 is achieved at a low electrode resistance in a relatively large potential window of 0.8 V. The cyclic voltammograms and galvanostatic charge–discharge data show nearly ideal pseudocapacitive behavior. Good electrochemical performance is achieved at a high active mass loading due to the use of chelating molecules of ammonium salt of purpuric acid (ASPA) as a co-dispersant for CuFe2O4 nanoparticles and conductive multiwalled carbon nanotube (MCNT) additives. The adsorption of ASPA on different materials is linked to structural features of ASPA, which allows for different interaction and adsorption mechanisms. The combination of advanced magnetic and pseudocapacitive properties in a negative potential range in a single MOPC material provides a platform for various effects related to the influence of pseudocapacitive/magnetic properties on magnetic/pseudocapacitive behavior. [ABSTRACT FROM AUTHOR]

• Pseudocapacitive polypyrrole – ferromagnetic La 0.8 Sr 0.2 MnO 3 composites were prepared. • Polyaromatic and bile salt type dopants were used for polypyrrole polymerization. • Polypyrrole electrodes showed capacitance of 4.89F cm−2 in neutral electrolyte. • Composite electrodes showed ideal capacitive behavior with capacitance of 2.82 F cm−2. • Composites combine advanced pseudocapacitive properties with high magnetization. 1-Diazo-2-naphthol-4-sulfonic acid (DNS), and sodium taurocholate (ST) are used as new anionic dopants-dispersants for the fabrication of polypyrrole (PPy) supercapacitor electrodes. The electrodes show ideal pseudocapacitive behavior with capacitances of 4.89 and 4.77 F cm−2 for DNS and ST, respectively. Composites with high active mass of 40 mg cm−2 containing ferromagnetic La 0.8 Sr 0.2 MnO 3 (LSM) and conductive PPy are obtained. The approach of this investigation eliminates the problems of previous works on PPy-LSM composites related to the use of negative potential window and alkaline electrolyte. In contrast to previous works, the electrodes showed nearly ideal pseudocapacitive behavior in a neutral Na 2 SO 4 electrolyte. Moreover, the composite electrodes showed significantly higher capacitances of 2.82 and 2.60 F cm−2 for DNS and ST, respectively, and enhanced capacitance retention at high charging rates. The composites combine advanced pseudocapacitive properties of PPy with high magnetization of ferromagnetic LSM. [ABSTRACT FROM AUTHOR]

Manganese oxides are prepared by a hydrothermal method from MnCl 2 solutions. The feasibility of tetrahydroxy-1,4-quinone (THQ) and 2-hydroxy-1,4-naphthoquinone (HNQ) application as capping agents (CAs) at hydrothermal conditions is demonstrated. The analysis of synthesis results provides an insight into the effect of chemical structure of THQ and HNQ on their adsorption on nanoparticles, phase content and dispersion of the nanoparticles. The use of CAs facilitates size reduction of the nanoparticles and offers multiple benefits for MnO x applications in cathodes of supercapacitors. An important finding is the ability to form MOF-like particle-based structures, which opens a door for the development of novel materials with advanced functionality. This finding expands the range of building blocks that can be used for producing MOF-like structures. Electrochemical testing of electrodes with mass of 39.8 ± 0.3 mg cm−2 is performed in 0.5 M Na 2 SO 4 electrolyte. Testing of electrodes prepared using HNQ (Mn-HNQ) and THQ (Mn-THQ) shows highly accelerated electrode activation rate and the ability to avoid the long activation procedure, which are critically important for practical applications. Cyclic voltammetry shows high capacitances of 5.29 F and of 5.58 F cm−2 for Mn-HNQ and Mn-THQ, respectively at a sweep rate of 1 mV s−1, which are achieved at low electrode resistances (<1 Ohm for 1 cm2 electrode area). Another key advantage of the developed electrodes is their high cyclic stability and enhanced capacitance retention of 67.5 % and 68.6 % for Mn-HNQ and Mn-THQ, respectively at a sweep range of 1–100 mV s−1. As a result, the electrodes exhibit remarkably high capacitances at a sweep rate of 100 mV s−1. The approach of this investigation successfully addresses key challenges in the development of manganese oxide supercapacitors and opens an avenue for further advances in the fabrication of cathodes for supercapacitors. [Display omitted] • MnOx nanoparticles were prepared by hydrothermal synthesis using capping agents. • Composite MnOx - carbon nanotube electrodes for supercapacitors were prepared. • MOF-like particle-based structures were formed in the presence of capping agent. • The activation procedure for high active mass electrodes can be avoided. • High capacitance and capacitance retention at high charge rates were obtained. [ABSTRACT FROM AUTHOR]

MnO2-carbon nanotube electrodes with high active mass loadings for supercapacitors have been fabricated with the goal of achieving a high area normalized capacitance, low impedance and enhanced capacitance retention at high charge-discharge rates. Interface synthesis and liquid-liquid extraction of MnO2 particles produced non-agglomerated MnO2 particles which allowed the fabrication of electrodes with good dispersion of carbon nanotubes in the MnO2 matrix. This strategy was used to fabricate electrodes with active mass loadings in the range of 21-50 mg cm-2 and mass ratios of active material to the nickel foam current collector of 0.33-0.78. The comparison of the experimental data for different extractor molecules provided an insight into the influence of the molecular structure, adsorption mechanism and interface phenomena on particle size and electrode performance. The analysis of capacitance data at different charge-discharge rates and different mass loadings was utilized to optimize electrode performance. The highest capacitance of 7.52 F cm-2 was achieved at a scan rate of 2 mV s-1 and active mass loading of 47 mg cm-2. Electrodes with mass loading of 35 mg cm-2 showed improved capacitance retention at high scan rates and the highest capacitance of 2.63 F cm-2 at a scan rate of 100 mV s-1. [ABSTRACT FROM AUTHOR]

ABSTRACT Experimental results on cathodic electrosynthesis of MnO2 electrodes for electrochemical supercapacitors are presented. The deposition yield data at different pulse durations and electrosynthesis mechanism are discussed. Electron microscopy investigations show porous structure of the electrodes, which is beneficial for good electrolyte access to the active material. The capacitance of 2.6 F cm-2 (199 F g-1), energy density of 20 Wh kg-1 and power density of 28 kW kg-1 are achieved for 13 mg cm-2 electrodes. The electrodes show improved capacitance retention at high scan rates. The Ni plaque-based MnO2 electrodes are promising for energy storage applications in electrochemical supercapacitors. [ABSTRACT FROM AUTHOR]

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]

The purpose of this investigation was the development of a new colloidal route for the fabrication of Mn3O4 electrodes for supercapacitors with enhanced charge storage performance. Mn3O4-carbon nanotube electrodes were fabricated with record-high capacitances of 6.67 F cm−2 obtained from cyclic voltammetry tests at a scan rate of 2 mV s−1 and 7.55 F cm−2 obtained from the galvanostatic charge–discharge tests at a current density of 3 mA cm−2 in 0.5 M Na2SO4 electrolyte in a potential window of 0.9 V. The approach involves the use of murexide as a capping agent for the synthesis of Mn3O4 and a co-dispersant for Mn3O4 and carbon nanotubes. Good electrochemical performance of the electrode material was achieved at a high active mass loading of 40 mg cm−2 and was linked to a reduced agglomeration of Mn3O4 nanoparticles and efficient co-dispersion of Mn3O4 with carbon nanotubes. The mechanisms of murexide adsorption on Mn3O4 and carbon nanotube are discussed. With the proposed method, the time-consuming electrode activation procedure for Mn3O4 electrodes can be avoided. The approach developed in this investigation paves the way for the fabrication of advanced cathodes for asymmetric supercapacitors and multifunctional devices, combining capacitive, magnetic, and other functional properties. [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]

The ability to achieve high areal capacitance for oxide-based supercapacitor electrodes with high active mass loadings is critical for practical applications. This paper reports the feasibility of the fabrication of Mn3O4-multiwalled carbon nanotube (MWCNT) composites by the new salting-out method, which allows direct particle transfer from an aqueous synthesis medium to a 2-propanol suspension for the fabrication of advanced Mn3O4-MWCNT electrodes for supercapacitors. The electrodes show enhanced capacitive performance at high active mass loading due to reduced particle agglomeration and enhanced mixing of the Mn3O4 particles and conductive MWCNT additives. The strategy is based on the multifunctional properties of octanohydroxamic acid, which is used as a capping and dispersing agent for Mn3O4 synthesis and an extractor for particle transfer to the electrode processing medium. Electrochemical studies show that high areal capacitance is achieved at low electrode resistance. The electrodes with an active mass of 40.1 mg cm−2 show a capacitance of 4.3 F cm−2 at a scan rate of 2 mV s−1. Electron microscopy studies reveal changes in electrode microstructure during charge-discharge cycling, which can explain the increase in capacitance. The salting-out method is promising for the development of advanced nanocomposites for energy storage in supercapacitors. [ABSTRACT FROM AUTHOR]

Particle extraction through liquid-liquid interface (PELLI) was used for the extraction of MnO 2 , Mn 3 O 4 , 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. MnO 2 -MWCNT and Mn 3 O 4 -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 MnO 2 -MWCNT composites with active mass loading of 36 mg cm−2. The Mn 3 O 4 -MWCNT electrodes exhibited improved capacitance retention at high charge-discharge rates. [ABSTRACT FROM AUTHOR]

Rare earth doped Cobalt Chromates are exhibits a significant interest among other materials for supercapacitors Applications. In the present work we reported Dysprosium(Dy3+) doped Cobalt Chromate(CoCr 2 O 4) for possible application in supercapacitors. Samples were prepared by solution combustion method with the general formula CoCr 2-x Dy x O 4 (where x = 0, 0.01, 0.03, and 0.05) using glucose and urea as fuels. As prepared samples were characterized by using "X-ray diffractometer"(XRD), "Transmission electron microscopy"(TEM), and "field emission scanning electron microscopy(FESEM) techniques to study the analytical and morphological structure of the CoCr 2-x Dy x O 4. For the first time, the electrochemical fabrication of CoCr 2-x Dy x O 4 were reported. Using "cyclic voltammetry"(CV), "galvanostatic charge–discharge'(GCD), electrochemical impedance spectroscopy (EIS), and cyclic stability testing, the electrochemical capabilities of CoCr 2-x Dy x O 4 were explored in great detail. The behavior of capacitance was evaluated utilizing CV at a variety of scan speeds, GCD at a selection of constant current densities, and EIS at a selection of frequencies. CV and GCD data for tested electrodes showed their capacitive behavior. The calculated capacitance was 0.29–0.38 F cm−2. It is found increasing with Dy3+ concentration. Based on CV testing results at a scan rate of 1 mV s−1. At a current density of 3 mA cm2, the obtained capacitance was 0.21, 0.22 and 0.23 F cm−2 respectively. The analysis of the compared Nyquist plots of complex impedance revealed that the actual part of the impedance dropped as the Dy3+ content increased. This pointed to an increase in conductivity, which was advantageous for the storage of charge, as also supported by density of states calculations, which demonstrated the remarkable distribution of density of states across the fermi level after Dy3+ doping in CoCr 2 O4, indicating improved electronic features of CoCr 2-x Dy x O 4. [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]

The development of 3D ceramic pseudocapacitive micro-supercapacitors (pMSCs) with patterned design was greatly hindered by the existing fabrication techniques that requires expensive equipment, harsh manufacturing environments, expensive materials and complicated fabrication processes. Herein, for the first time, one step electric discharge direct writing (EDDW) technique has been developed to fabricate 3D pMSCs, which are composed of Mo-MoO x integrated electrodes with designable patterns. The developed 3D pMSCs exhibited a high capacitance of 49.1 mF cm−2 (Scanning Rate: 5 mV s−1) and achieved a good capacitance retention of 96% after 5000 cycles. Additionally, the 3D pMSCs without adding any conductive additives could be operated up to an extremely high scanning rate of 20 V s−1 and retained a high areal capacitance of 6.3 mF cm−2. This simple, safe, low-cost, binder-free, conductive additive free and environmentally friendly fabrication technique of EDDW opens a new strategy for efficient fabricating different kinds of energy storage devices with designable 3D patterns and improved electrochemical performance. [Display omitted] [ABSTRACT FROM AUTHOR]

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]