MnO2 Multiwalled Carbon Nanotube Research Articles

Polypyrrole-Coated Manganese Dioxide Nanowires and Multi-Walled Carbon Nanotubes as High-Performance Electrodes for Zinc-Ion Batteries

Free-standing films based on MnO2@multi-walled carbon nanotubes (MWCNTs)@Polypyrrole (PPy) have been fabricated for aqueous zinc-ion batteries. A simple hydrothermal method was adopted to synthesize ß-MnO2 nanowires. PPy coated the ß-MnO2 nanowires@MWCNTs composite by an in-situ polymerization process. Free-standing films of ß-MnO2@MWCNTs@PPy composite were prepared by a convenient vacuum-assisted filtration. A zinc-ion battery is fabricated with a zinc foil anode and a ß-MnO2@MWCNTs@PPy composite cathode. The Zn//ß-MnO2@ MWCNTs@PPy system in ZnSO4@MnSO4 aqueous electrolyte exhibits high electrochemical performances, such as an initial capacity of 258.5 mAh g-1 at 0.2 A g-1, and about 74.6% retention after 100 cycles with near 100% Coulombic efficiency. The strategy of conductive polymer coating makes the technology of rechargeable zinc-ion batteries (ZIBs) very promising and provides opportunities of organic-inorganic composite materials for energy storage applications.

MnO2/multi-walled carbon nanotubes based nanocomposite with enhanced electrocatalytic activity for sensitive amperometric glucose biosensing

Abstract Functional nanostructured transition metal oxides hold great promise in catalysis based sensors due to their superb catalytic activity, good stability, ease of preparation and cost-effectiveness. In this work, MnO2 nanowires and MnO2/multi-walled carbon nanotubes (MWCNTs) nanocomposite were prepared via a simple hydrothermal method. The MnO2/MWCNTs nanocomposite was developed by deposition of MnO2 on MWCNTs surface, which have abundant hydrophilic groups facilitating ion-adsorption and nucleation process. The MWCNTs/MnO2 exhibited higher catalytic activity upon hydrogen peroxide (H2O2) electrooxidation, with reduced overpotential by 100 mV and 220 mV in contrast to those values of MWCNTs and MnO2 nanowires, respectively. Thus the MnO2/MWCNTs nanocomposite modified glass carbon electrode (GCE) enabled to detect H2O2 sensitively. Moreover, by incorporation of glucose oxidase (GOx), a glucose biosensor GOx/MnO2/MWCNTs/GCE was prepared. The as-proposed biosensor had wide linear range (5–200 μM and 0.2–1 mM) and a low detection limit of 2 μM (S/N = 3), which could be applicable to detect real sample with satisfying accuracy and reproducibility. Due to the superb electrochemical properties, the as-developed MnO2/MWCNTs nanocomposite is prospected in electrochemical sensor, electrocatalysis and supercapacitor.

PANOA/MnO2/MWCNT nanocomposite: Synthesis, characterization, and electrochemical performance as efficient electrode materials for supercapacitors

The MnO2/multi-walled carbon nanotube (MWCNT)/poly (aniline-co-o-aminophenol) (PANOA) nanocomposite electrode were prepared by electrochemical polymerization on graphite electrode. Cyclic voltammetry and galvanostatic charge/discharge used the electrochemical properties of the composite. The doping of MnO2/MWCNT enhances the electrochemical activity and reversibility of the copolymer. Scanning electron micrographs (SEM), UV–vis spectra, and X-ray diffraction diagram clearly revealed the formation of nanocomposites on the surface of the working electrode and demonstrated that the doping process is effective. The test results in acidic solutions show that the composites have similar and enhanced cyclic voltammetry performance compared with pure PANOA based electrode material. The PANOA/MnO2/MWCNT nanocomposite synthesized possessed excellent capacitive behavior with a high specific capacitance. The specific capacitance of the PANOA/MnO2/MWCNT nanocomposite film is 560 F/g at scan rate of 25 mV s−1. These results demonstrate exciting potentials of the composite for high performance supercapacitors or other power source system.

Extractor-free phase transfer of inorganic particles and application for supercapacitors

Conceptually novel strategies have been developed for extraction of inorganic particles from a synthesis medium to a device processing medium using undecanal as a particle receiving liquid and a phase transfer vehicle. Another major finding was the feasibility of liquid-solid extraction and formation of new organic-inorganic gels using inorganic particles as gelators. Building on the advantages offered by liquid-liquid extraction we fabricated advanced MnO2-multiwalled carbon nanotubes (MWCNT) electrodes for supercapacitors, which showed a capacitance of 6.3 F cm−2. The key to achieving enhanced capacitance was agglomerate-free processing of MnO2 and improved mixing of MnO2 and MWCNT. The extraction and gel formation mechanisms were analyzed using MnO2, Al(OH)3, ZnO, CeO2 particles and MWCNT.

Manganese dioxide–carbon nanotube composite electrodes with high active mass loading for electrochemical supercapacitors

MnO2–multiwalled carbon nanotube (MWCNT) composites were prepared for application in supercapacitor electrodes and devices. Good dispersion and mixing of the individual components were achieved using conceptually new strategies, allowing for significant improvement in the electrochemical charge storage properties. Composite C1 was prepared using chelating polyaromatic sulfasalazine molecules, which adsorbed on the individual components, allowed for their good dispersion and improved mixing by creating links between the components. Composite C2 utilized a Schiff base linkage mechanism for improved mixing between MnO2 and MWCNT. New electrochemical strategies allowed for high capacitance and good capacitance retention at high charge–discharge rates at high active mass loading, which was 30 mg cm−2. Composites C1 and C2 showed capacitances of 4.5 and 4.4 F cm−2, respectively, at a scan rate of 2 mV s−1. However, composite C2 showed a higher capacitance retention at high scan rates, which was found to be 66% at a scan rate of 100 mV s−1. The asymmetric devices, prepared using composite C2 as positive electrodes and activated carbon–carbon black negative electrodes, showed promising performance in a voltage window of 1.6 V.

Enhanced capacitive performance of MnO2- multiwalled carbon nanotube electrodes, prepared using lauryl gallate dispersant

Composite MnO2-multiwalled carbon nanotube (MWCNT) electrodes for electrochemical supercapacitors (ES) have been prepared by the colloidal methods based on the use of lauryl gallate (LG). In this investigation LG was used for efficient dispersion of MnO2 and MWCNT and for their improved mixing in the heterocoagulation method. Moreover, LG was utilized as a vehicle for the particle transfer in the liquid-liquid extraction method. The analysis of the experimental data provided an insight into the mechanisms of LG adsorption on MnO2 and MWCNT. It was found that the heterocoagulation method is not limited to the fabrication of MnO2-MWCNT composites. The improved mixing of the individual components allowed for improved capacitive performance of the MnO2-MWCNT electrodes. The liquid-liquid extraction method offers the additional benefit of reduced agglomeration, which resulted in improved mixing at the nanometric scale. Good capacitance performance and low impedance were achieved at high active mass loadings, which allowed for high integral and differential capacitances, especially at high charge-discharge rates. Graphene coated Ni foam current collectors allowed for significant improvement in capacitance performance of MnO2-MWCNT electrodes, compared to the electrodes prepared using uncoated Ni foam current collectors. It was found that the increase in capacitance is not related to capacitive properties of graphene. The high capacitance of 4.8Fcm−2 and excellent capacitance retention of 67% achieved in the scan rate range from 2 to 100mVs−1 are promising for practical ES applications.

Electrophoretic deposition of materials using humic acid as a dispersant and film forming agent

Abstract Electrophoretic deposition (EPD) method has been developed for the deposition of humic acid (HA) from solutions in water or mixed water–ethanol solvent. The deposition mechanism was based on the electrophoresis of anionic HA species, local pH decrease at the anode, charge neutralization and HA precipitation. The deposition yield can be varied by the variation of HA concentration and deposition voltage. HA showed remarkable adsorption on various materials, which involved different adsorption mechanisms. HA was used as a dispersing, charging and film forming agent for the EPD of materials of different types, such as oxide nanoparticles of TiO2 and MnO2, mineral particles of halloysite nanotubes and huntite platelets, metal nanoparticles of Ni and Pd, and other materials, such as SiC and multiwalled carbon nanotubes (MWCNT). The use of HA as a co-dispersant allowed for the fabrication of MnO2–MWCNT composites with various MWCNT content. The obtained films can be used for different applications based on the functional properties of the deposited materials, such as catalytic, flame retardant, molecular storage and electronic properties. Testing results showed promising performance of MnO2–MWCNT composites for applications in the electrodes of electrochemical supercapacitors.

Colloidal methods for the fabrication of carbon nanotube–manganese dioxide and carbon nanotube–polypyrrole composites using bile acids

Nature inspired strategies have been developed for the colloidal processing of advanced composites for supercapacitor applications. New approach was based on the use of commercially available bile acid salts, such as sodium cholate (ChNa) and taurocholic acid sodium salt (TChNa). It was demonstrated that cholic acid (ChH) films can be obtained by electrophoretic deposition (EPD) from ChNa solutions. The analysis of deposition yield, quartz crystal microbalance and cyclic voltammetry data provided an insight into the anodic deposition mechanism. The outstanding suspension stability of multiwalled carbon nanotubes (MWCNT), achieved using bile acids as anionic dispersants, allowed the fabrication of MWCNT films by EPD. The use of ChNa for EPD offered advantages of binding and film forming properties of this material. Composite MnO2–MWCNT films, prepared using ChNa as a dispersant and film forming agent for EPD, showed promising capacitive behavior. In another colloidal strategy, TChNa was used as a dispersant for MWCNT for the fabrication of polypyrrole (PPy) coated MWCNT. The use of PPy coated MWCNT allowed the fabrication of electrodes with high active mass loading, high capacitance and excellent capacitance retention at high charge–discharge rates.

Aqueous electrostatic dispersion and heterocoagulation of multiwalled carbon nanotubes and manganese dioxide for the fabrication of supercapacitor electrodes and devices

A conceptually new approach has been developed for the fabrication of MnO2-multiwalled carbon nanotube (MWCNT) composites for electrodes of electrochemical supercapacitors (ES). Benzyldimethylhexadecylammonium chloride (BAC) surfactant and caffeic acid (CA) selectively adsorbed on MWCNT and MnO2, respectively, and allowed the formation of stable aqueous suspensions of positively charged MWCNT and negatively charged MnO2. The comparison of the electrophoretic deposition yield data for BAC, CA and other molecules provided an insight into the influence of the molecular structure on adsorption of the molecules and dispersion of MWCNT and MnO2. Advanced composite materials with good mixing of the individual components were obtained by heterocoagulation, based on an ion-pairing assembly of BAC and CA. The composite electrodes, prepared by the new method showed superior electrochemical performance. It was found that high capacitance and good capacitance retention at high charge–discharge rates can be achieved at high active mass loadings. A practical outcome of this study was the fabrication of an asymmetric SC device, containing a positive MnO2–MWCNT electrode and negative activated carbon–carbon black composite electrode with a voltage window of 1.8 V in an aqueous electrolyte. The asymmetric device showed high capacitance, high power-energy characteristics, good capacitance retention at high charge–discharge rates and cyclic stability.

New colloidal route for electrostatic assembly of oxide nanoparticle – carbon nanotube composites

A conceptually new colloidal method for the fabrication of metal oxide–multiwalled carbon nanotube (MWCNT) composites is proposed. The approach is based on the use of phosphate ester (PE) for the dispersion of oxide nanoparticles and m-cresolsulfonphthalein (CS) dye for the dispersion of MWCNT. PE imparts a positive charge to the particles in ethanol. The adsorption of anionic CS on MWCNT allows the formation of stable suspensions of negatively charged MWCNT in ethanol. The adsorption of CS on MWCNT is confirmed by Fourier transform infrared and UV–vis spectroscopy. The heterocoagulation of positively charged oxide nanoparticles and negatively charged MWCNT allows the fabrication of advanced nanocomposites with improved dispersion of individual components. The proof of principle is demonstrated by the fabrication of MnO2–MWCNT composite electrodes for electrochemical supercapacitors, which exhibited significant improvement in capacitance at high charge–discharge rates, reduced electrical resistance and good cycling stability. The hybrid cells, containing composite MnO2–MWCNT electrodes, show promising electrochemical performance.

Preparation of MnO2 and Composites for Ultracapacitors

New dispersants were investigated for the preparation of MnO2 and composites by electrophoretic deposition (ED). The investigation of molecules from salicylate, phenolate, catecholate, and phthalate families allowed the comparison of different mechanisms, which provided dispersant bonding to the MnO2. The deposition yield was studied at various experimental conditions. Catecholate bonding resulted in significantly higher colloidal stability and deposition rate, compared to salicylate bonding. It was shown that agglomeration of MnO2 nanoparticles can be avoided when MnO2 synthesis is performed in the presence of dispersants. MnO2-multiwalled carbon nanotubes (MWCNT) composites for ultracapacitors were obtained by ED. The use of Ni plaque current collectors allowed high capacitance and low electrochemical impedance at higher material loadings, compared to stainless steel foil current collectors. The electrodes showed a capacitance of 185 Fg−1. The MnO2–MWCNT electrodes can be used for applications in ultracapacitors.

High-performance LiMn2O4 with enwrapped segmented carbon nanotubes as cathode material for energy storage

This paper reports a spinel-type LiMn2O4/carbon nanotube (CNT) composite cathode material with high electrochemical performance for energy storage applications. The composite material is prepared by hydrothermal reaction between birnessite MnO2/multiwalled carbon nanotube (MWCNT) composite and LiOH solution, followed by heat treatment at 700 °C in air atmosphere, where the MnO2/MWCNT precursor is obtained by in situ redox reaction between KMnO4 solution and MWCNTs. The heat treated LiMn2O4/CNT composite material consists of well-crystallized spinel LiMn2O4 with small amount of enwrapped segmented carbon nanotubes, which is confirmed by X-ray diffraction and transmission electron microscopy. Electrochemical experimental results demonstrate that the LiMn2O4/CNT composite material heat treated for 8 h exhibits high specific capacity and excellent high-rate capability in 5 M LiNO3 aqueous electrolyte. The (LiMn2O4/CNT)/5 M LiNO3/activated carbon hybrid supercapacitor with this LiMn2O4-based composite material as the cathode presents excellent high-power capability and good charge/discharge cyclability.

Surface modification of MnO2 and carbon nanotubes using organic dyes for nanotechnology of electrochemical supercapacitors

Efficient dispersion and electrophoretic deposition (EPD) of multiwalled carbon nanotubes (MWCNTs) was achieved using organic dyes, such as pyrocatechol violet (PV) and m-cresol purple (CP). The problem of MnO2 nanoparticle dispersion in concentrated suspensions was addressed by the use of PV as a dispersant. The analysis and comparison of experimental data for PV and CP provided insight into the influence of chemical structures of the dyes on their adsorption on MWCNTs and MnO2. The adsorption of PV on MWCNTs and MnO2 was attributed to π–π interactions and catecholate type bonding, respectively. The EPD yield can be varied by the variation of the PV concentration in the suspensions, deposition voltage and time. It was found that PV can be used as a co-dispersant for EPD of MWCNTs and MnO2 and the fabrication of MnO2–MWCNT composites. The proposed approach offers advantages of uniform distribution of individual components and low binder content in the composite. MnO2–MWCNT films were prepared by EPD for thin film electrodes of electrochemical supercapacitors (ES). Bulk MnO2–MWCNT electrodes with a material loading of 40 mg cm−2 were obtained by the impregnation of Ni foam current collectors. The highest specific capacitance of 5.9 F cm−2 (148 F g−1) was achieved. The composite materials are promising for ES applications.

Electrophoretic assembly of organic molecules and composites for electrochemical supercapacitors

Electrophoretic deposition (EPD) method has been developed for the fabrication of 1-pyrenebutyric acid (PBH) films from aqueous solutions. The films can be deposited at constant voltage or potentiodynamic conditions. The method allowed the formation of 0.1–2μm thick films, containing needle-shape PBH particles. The deposition mechanism involved the electrophoresis, pH decrease at the anode surface, charge neutralization and formation of insoluble PBH films. The film morphology and shape of the PBH particles are controlled by the π–π stacking mechanism of the polyaromatic PBH molecules. The important finding was the possibility of controlled EPD of multiwalled carbon nanotubes (MWCNTs) using PBH as a charging, dispersing and film forming agent. It was found that at low voltages or low PBH concentrations the deposits contained mainly MWCNT. The increase in the deposition voltage or/and PBH concentration resulted in co-deposition of MWCNT and needle-shape PBH particles. The new approach to the deposition of MWCNT was used for the fabrication of composite MnO2–MWCNT films for electrodes of electrochemical supercapacitors, which showed a specific capacitance of 250Fg−1. The EPD method developed in this investigation paves the way for the deposition of other small organic molecules and composites and their applications in new materials and devices, utilizing functional properties of the organic molecules, CNT, and other advanced materials.

Silver decorated γ-manganese dioxide nanorods for alkaline battery cathode

γ-Manganese dioxide nanorods were prepared using a simple hydrothermal method based on redox reactions between S 2O 8 2− and Mn 2+ and decoration of silver nanoparticles was performed by a wet impregnation method. The as-prepared materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Electrochemical discharging capacity of Ag/MnO 2, MnO 2/multi-walled carbon nanotubes (MWNTs), and Ag/MnO 2/MWNTs electrodes were determined at 0.1 C discharging rate. The results showed that utility efficiency of MnO 2 was greatly enhanced when silver particles were introduced and there was strong interaction between silver nanoparticles and bulk MnO 2 materials. Electrochemical impedance spectroscopy (EIS) measurements were performed to investigate the discharging mechanism of the Ag/MnO 2/MWNTs electrodes. Silver nanoparticles not only enhanced electronic conductivity of the network, but also improved proton diffusion process.