Carbon-supported,nano-structured,manganese oxide composite electrode for electrochemical supercapacitor

Carbon-supported MnO₂ nanorods are synthesized using a microemulsion process and a manganese oxide/carbon (MnO₂/C) composite is investigated for use in a supercapacitor. As shown by high-resolution transmission electron microscopy the 2 nm × 10 nm MnO₂ nanorods are uniformly dispersed on the carbon surface. Cyclic voltammograms recorded for the MnO₂/C composite electrode display ideal capacitive behaviour between −0.1 and 0.8 V (vs. saturated calomel electrode) with high reversibility. The specific capacitance of the MnO₂/C composite electrode found to be 165 F g⁻¹ and is estimated to be as high as 458 F g⁻¹ for the MnO₂. Based on cyclic voltammetric life-cycle tests, the MnO₂/C composite electrode gives a highly stable and reversible performance for up to 10,000 cycles.     

Sulphur-reduced graphene oxide composite with improved electrochemical performance for supercapacitor applications

In this research, carbon nanorods/fibers materials were successfully synthesized from sulphur-reduced graphene oxide (RGO-S) composite by using an improved Hummers' method. Morphological, structural, compositional and textural characterization of the composite material were obtained via scanning electron microscope (SEM), energy dispersive x-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), respectively. The electrochemical performance of the composite sample as a promising supercapacitor electrode revealed a peak specific capacity of 113.8 mAh g⁻¹ at 0.5 A g⁻¹ estimated via GCD curves in 6 M KOH aqueous electrolyte. The half-cell could retain a columbic efficiency of about 98.7% with a corresponding energy efficiency of about 98.5% over 2000 constant charge/discharge cycle at a specific current of 5 A g⁻¹. Remarkably, an assembled hybrid device with carbonized iron cations (C-FP) and the RGO-S composite delivered high energy and power densities of 35.2 Wh kg⁻¹ and 375 W kg⁻¹ at 0.5 A g⁻¹ within a 1.5 V operating potential, respectively. A good cycling stability performance with an energy efficiency of 99% was observed for the device for up to 10,000 cycling at a specific current of 3 A g⁻¹.     

High electrochemical performance of PANI/CdO nanocomposite based on graphene oxide as a hybrid electrode materials for supercapacitor application

In the last decade, the production of clean and sustainable energy sources for energy storage purposes have grown dramatically due to the population growth and increasing demand for energy in the world. In this regard, supercapacitors have proved to be promising candidates in energy storage applications. Therefore, in this study, polyaniline/cadmium oxide/graphene oxide (PANI/CdO/GO) nanocomposite was prepared by co-precipitation method to evaluate the electrochemical performance. The structural and surface properties, morphology and particle size distribution were analyzed by XRD diffraction spectroscopy (XRD), field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), N₂ adsorption-desorption, and Fourier transform infrared spectroscopy (FT-IR). Furthermore, the synthesized nanocomposite was applied as an active electrode material and its performance was investigated by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) in terms of energy storage. The results of these tests confirmed that PANI/CdO/GO nanocomposite provides great electrochemical behavior, including specific capacity of 647 F g^?1, energy density of 116.6 W h kg^?1, power density of 388 W kg^?1 compared to the other electrode. According to the stability test, the initial capacity maintenance was about 82% after 500 charge-discharge cycles, which indicated relatively good electrochemical stability. Moreover, the impedance spectroscopy studies showed that the nanocomposite possessed much lower internal strength and charge transfer reaction resistance in comparison to the other synthesized materials. Based on these results, it was found that the prepared nanocomposite has a good performance in the field of energy storage.     

Reduced graphene oxide decorated with thionine,excellent nanocomposite material for a powerful electrochemical supercapacitor

In this paper, reduced graphene was decorated with thionine to synthesize Th/rGO nanocomposite via diazonium reaction. The nanocomposite was identified using several techniques including SEM, EDX, XRD, XPS, and IR techniques. The behavior of the nanocomposite, as a supercapacitor electrode, was examined using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. The results obtained demonstrated that the nanocomposite has an excellent specific capacitance of 1255 F/g at a current density of 0.5 A/g. Furthermore, the stability of the electrode was examined after 5000 cycles. The results showed that 93% of the initial capacity appears after 5000 cycles.     

Enhanced manganese dioxide supercapacitor electrodes produced by electrodeposition

Electrodeposited thin films of manganese dioxide, prepared using chronoamperometry on a platinum substrate in an electrolyte of MnSO₄ in H₂SO₄, possess a significantly higher capacitance compared to the literature materials (>2000 F g⁻¹ which is at least a 250% increase in performance) when cycled over a 0.8 V potential window in an aqueous electrolyte of 0.5 M Na₂SO₄. This excellent performance is discussed in terms of the manganese dioxide electrodeposition mechanism, in particular the growth mechanism under the preferred slow mass transport of electro-active species, and its effects on morphology. Furthermore, the origin of the enhanced capacitance is discussed, in which case we have proposed arises from contributions made by hydroxyl groups on the manganese dioxide nano-particulate surface, in addition to the fast redox reactions that are necessary for pseudo-capacitance.     

Synthesis and electrochemical performance of multi-walled carbon nanotube/polyaniline/MnO2 ternary coaxial nanostructures for supercapacitors

Multi-walled carbon nanotube (MWCNT)/polyaniline (PANI)/MnO₂ (MPM) ternary coaxial structures are fabricated as supercapacitor electrodes via a simple wet chemical method. The electrostatic interaction between negative poly(4-styrenesulfonic acid) (PSS) molecules and positive Mn²⁺ ions causes the generation of MnO₂ nanostructures on MWCNT surfaces while the introduction of PANI layers with appropriate thickness on MWCNT surfaces facilitates the formation of MWCNT/PANI/MnO₂ ternary coaxial structures. The thickness of PANI coatings is controlled by tuning the aniline/MWCNT ratio. The effect of PANI thickness on the subsequent MnO₂ nanoflakes attachment onto MWCNTs, and the MPM structures is investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and field-emission scanning electron microscopy (FESEM). The results suggest that appropriate thickness of PANI layers is important for building MPM ternary coaxial structures without the agglomeration of MnO₂ nanoflakes. The MPM ternary coaxial structures provide large interaction area between the MnO₂ nanoflakes and electrolyte, and improve the electrochemical utilization of the hydrous MnO₂, and decrease the contact resistance between MnO₂ and PANI layer coated MWCNTs, leading to intriguing electrochemical properties for the applications in supercapacitors such as a specific capacitance of 330 Fg⁻¹ and good cycle stability.     

Layered NiFe-LDH/MXene nanocomposite electrode for high-performance supercapacitor

Layered double hydroxide (LDH) is potentially excellent supercapacitor (SC) materials, but the low conductivity and easy agglomeration limit the further improvement of their electrochemical properties. Therefore, LDHs are requisite to grow on some conductive substrates to produce high-performance SC. In this paper, the conductive two-dimensional (2D) transition metal carbides, nitrides and carbonitrides (called MXene) were explored as the substrate to directly deposit NiFe-LDH nanosheets by a one-step hydrothermal method, then a three-dimensional (3D) porous NiFe-LDH/MXene electrode was obtained. The morphology and electrochemical performance of the composite electrodes were analyzed and investigated. The results show that the NiFe-LDH/MXene electrode has larger specific capacitance (720.2 F/g) than NiFe-LDH (465 F/g), and the capacitance of the composite electrode retained 86% after 1000 cycles (only 24% for NiFe-LDH), showing excellent cycle stability. The improved electrochemical performance of the composites is caused by the stable sheet-like structure of NiFe-LDH during charge-discharge time and the conductive network formed by the MXene, which can accelerates electron transport. In addition, the asymmetric SC based on NiFe-LDH/MXene positive electrode display a power density of 758.27 W/kg at an energy density of 42.4 Wh/Kg. These results indicate the NiFe-LDH/MXene composites can be applied as the novel candidate of high-performance SC electrodes.     

Electrochemical properties of nanosized hydrous manganese dioxide synthesized by a self-reacting microemulsion method

Manganese dioxide has been synthesized by a new simple self-reacting microemulsion method. The synthesized MnO₂ has been found to be amorphous structure containing a moderate amount of water by X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetric analysis. Particles in a spherical shape with about 4 nm in diameter have been observed by transmission electron microscopy. Cyclic voltammetic tests have been performed between −0.5 and 0.5 V versus Hg/Hg₂SO₄ in 1 mol L⁻¹ Na₂SO₄ solution at sweep rates up to 50 mV s⁻¹. A specific capacitance value as high as 246.2 F g⁻¹ was obtained, which was much higher than 146.5 F g⁻¹ of MnO₂ prepared by chemical co-precipitation. After 600 cycles, only 6% decrease of specific capacitance was measured which indicated that such a material possesses good cycling property.     

Polyaniline/fullerene derivative nanocomposite for highly efficient supercapacitor electrode

The effect of intercalation of fullerene derivative Phenyl-C60-butyric acid methyl ester (PCBM) into polyaniline (PANI) matrix with different ratio is reported. The PANI/PCBMx (where x = 0, 2.5, 5 and 10) nanocomposites are characterized by UV-VIS spectroscopy, Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy and X-ray diffraction spectroscopy (XRD). The results confirm that the PANI/PCBM nanocomposites are synthesized successfully. The prepared nanocomposites are cast onto Nickel foam as a current collector and tested as a supercapacitor electrode in 2 M KOH electrolyte using cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD). The effect of different current collector substrates including stainless steel, nickel metal and graphite sheet on the supercapacitor performance is compared. The electrochemical measurements show an improvement by more than two times in the specific capacitance of PANI/PCBM5 electrode compared to pure PANI electrode. It is found that, the specific capacitance is 2201 F/g at a current density of 2 A/g with a good rate capability of about 73% at 10 A/g. The energy and power densities of PANI/PCBM5 electrode are 61.9 W h/Kg and 2250 W/Kg, respectively. Furthermore, the PANI/PCBM5 electrode shows an excellent cycling stability with 96% of the capacity retention after 1000 cycles.     

MnO2 nanotube and nanowire arrays by electrochemical deposition for supercapacitors

Highly ordered MnO₂ nanotube and nanowire arrays are successfully synthesized via a electrochemical deposition technique using porous alumina templates. The morphologies and microstructures of the MnO₂ nanotube and nanowire arrays are investigated by field emission scanning electron microscopy and transmission electron microscopy. Electrochemical characterization demonstrates that the MnO₂ nanotube array electrode has superior capacitive behaviour to that of the MnO₂ nanowire array electrode. In addition to high specific capacitance, the MnO₂ nanotube array electrode also exhibits good rate capability and good cycling stability, which makes it promising candidate for supercapacitors.     

Electrodeposition of mesoporous manganese dioxide supercapacitor electrodes through self-assembled triblock copolymer templates

Mesoporous manganese dioxide supercapcitor electrode materials were electrochemically deposited onto silicon substrates coated with Pt using triblock copolymer species (Pluronic P123 and F127) as the structure-directing agents. Deposited electrodes of manganese dioxide film were physically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and were electrochemically characterized by cyclic voltammetry (CV) in 0.5 M Na₂SO₄ electrolyte. Maximum specific capacitance (SC) values of 449 F g⁻¹ was obtained at a scan rate of 10 mV s⁻¹ from F127 templated mesoporous MnO₂.     

Study and optimisation of manganese oxide-based electrodes for electrochemical supercapacitors

A manganese oxide material was synthesised by an easy precipitation method based on reduction of potassium permanganate(VII) with a manganese(II) salt. The material was treated at different temperatures to study the effect of thermal treatment on capacitive property. The best capacitive performance was obtained with the material treated at 200 °C. This material was used to prepare electrodes with different amounts of polymer binder, carbon black and graphite fibres to individuate the optimal composition that gave the best electrochemical performances. It was found that graphite fibres improve the electrochemical performance of electrodes. The highest specific capacitance (267 F g⁻¹ MnO_x) was obtained with an electrode containing 70% of MnO_x, 15% of carbon black, 10% of graphite fibres and 5% of PVDF. This electrode, with CB/GF ratio of 1.5, showed a higher utilization of manganese oxide. The results reported in the present paper further confirmed that manganese oxide is a very interesting material for supercapacitor application.     

Optimization of MnO2/vertically aligned carbon nanotube composite for supercapacitor application

The optimization strategy for producing manganese oxide supercapacitors based on vertically aligned carbon nanotubes (VACNTs) deposited on large area electrodes is presented. A single sequential process of sputtering, annealing and plasma enhanced chemical vapour deposition (PECVD) is applied to produce dense and uniform VACNTs electrodes. As dielectric layer of the supercapacitor, manganese oxide is electrodeposited lining the surface of the VACNTs electrodes. The control of the growing parameters such as catalyst thickness layer, temperature and deposition time for tuning the density, length and diameter of the VACNTs and their structure are found to be key points for the optimization of the MnO₂ electrodeposition process in view to improve the efficiency of the supercapacitor devices.The electrochemical properties of the obtained electrodes are characterized using cyclic voltammetry and galvanostatic charge-discharge techniques. A specific capacitance of 642 Fg⁻¹ is obtained for MnO₂/VACNTs nanocomposite electrode at a scan rate of 10 mV s⁻¹.     

Core-shell structured ZIF-7@ZIF-67 with high electrochemical performance for all-solid-state asymmetric supercapacitor

Zeolitic imidazolate frameworks (ZIFs) are considered as a promising material for energy storage in recent years. Here, core-shell structured ZIF-7@ZIF-67 is synthesized in this work. The core-shell structured material can promote electron transfer of inner-outer metals ions of ZIF-7@ZIF-67, quicken diffusion of electrolyte ions and improve the capacitance performance compared to the ZIF-7 and ZIF-67. ZIF-7@ZIF-67 delivers good energy storage ability with a specific capacitance of 518.9 F g⁻¹ at a current density of 1 A g⁻¹ and remarkable stability with a retention of 99.6% after 4000 cycles in the three-electrode system. Furthermore, an all-solid-state asymmetric supercapacitor (ASC) device is assembled based on core-shell structured ZIF-7@ZIF-67 as positive electrode. Impressively, the ASC device displays an energy density of 31 Wh kg⁻¹ at a power density of 400 W kg⁻¹ and an excellent cyclic stability with 99.5% retention after 10,000 cycles at a current density of 10 A g⁻¹. Finally, two all-solid-state ASCs are contacted to power various lighting-emitting diodes (LED). The red LED can be kept glowing for over 10 min. These electrochemical characteristics suggest that core-shell structured ZIF-7@ZIF-67 is a potential material for energy storage device with long-life cyclic stability.     

Polypyrrole/carbon aerogel composite materials for supercapacitor

Polypyrrole (PPy)/carbon aerogel (CA) composite materials with different PPy contents are prepared by chemical oxidation polymerization through ultrasound irradiation and are used as active electrode material for supercapacitor. The morphology of PPy/CA composite is examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that PPy is deposited onto the surface of CA. As evidenced by cyclic voltammetry, galvanostatic charge/discharge test and EIS measurements, PPy/CA composites show superior capacitive performances to CA, moreover, the results based on cyclic voltammograms show that the composite material has a high specific capacitance of 433 F g⁻¹, while the capacitance of CA electrode is only 174 F g⁻¹. Although the supercapacitor used PPy/CA as active electrode material has an initial capacitance loss due to the instability of PPy, the specific capacitance after 500 cycles stabilizes nearly at a fixed value.     

Construction of composite electrodes comprising manganese dioxide nanoparticles distributed in polyaniline-poly(4-styrene sulfonic acid-co-maleic acid) for electrochemical supercapacitor

This work demonstrated a novel and simple route for preparing a composite comprising of manganese oxide (MnO₂) nanoparticles and polyaniline (PANI) doped poly(4-styrene sulfonic acid-co-maleic acid) (PSSMA) by “electrochemical doping-deposition”. The PANI-PSSMA-MnO₂ composite was characterized by scanning electron microscopy (SEM)), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). SEM images revealed a uniform dispersion of MnO₂ nanoparticles in the porous structure of PANI-PSSMA structure. XRD measurements showed the distortion of the crystal structure of β-MnO₂ after deposition of MnO₂ in PANI-PSSMA structure. Thus, the XRD pattern of PANI was predominating. Cyclic voltammetry and chronopotentiometry were employed in 0.5 M Na₂SO₄ to evaluate the capacitor properties. The results showed a significant improvement in the specific capacitance of the composite electrode. The specific capacitance of PANI-PSSMA-MnO₂ (50.4 F g⁻¹) had improvement values of 172% compared to that of PANI (18.5 F g⁻¹). When only the MnO₂ mass was considered, the composite had a specific capacitance of 556 F g⁻¹.     

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 S₂O₈²⁻ and Mn²⁺ 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/MnO₂, MnO₂/multi-walled carbon nanotubes (MWNTs), and Ag/MnO₂/MWNTs electrodes were determined at 0.1 C discharging rate. The results showed that utility efficiency of MnO₂ was greatly enhanced when silver particles were introduced and there was strong interaction between silver nanoparticles and bulk MnO₂ materials. Electrochemical impedance spectroscopy (EIS) measurements were performed to investigate the discharging mechanism of the Ag/MnO₂/MWNTs electrodes. Silver nanoparticles not only enhanced electronic conductivity of the network, but also improved proton diffusion process.     

On-chip growth of patterned ZnO nanorod sensors with PdO decoration for enhancement of hydrogen-sensing performance

In this study, we used a low-temperature hydrothermal technique to fabricate arrays of sensors with ZnO nanorods grown on-chip. The sensors on the glass substrate then were sputter decorated with Pd at thicknesses of 2, 4, and 8 nm and annealed at 650 °C in air for an hour. Scanning electron microscopy, high resolution transmission microscopy, X-ray diffraction, and surface analysis by X-ray photoelectron spectroscopy characterization demonstrated that decoration of homogenous PdO nanoparticles on the surface of ZnO nanorods had been achieved. The sensors were tested against three reducing gases, namely hydrogen, ethanol, and ammonia, at 350, 400, and 450 °C. The ZnO nanorods decorated with PdO particles from the 2 and 4 nm layers showed the highest responses to H₂ at 450 and 350 °C, respectively. These samples also generally exhibited better selectivity for hydrogen than for ethanol and ammonia at the same concentrations and at all tested temperatures. However, the ZnO nanorods decorated with PdO particles from the 8 nm layer showed a reverse sensing behaviour compared with the first two. The sensing mechanism behind these phenomena is discussed in the light of the spillover effect of hydrogen in contact with the PdO particles as well as the negative competition of the PdO thin film formed between the sensor electrodes during sputter decoration, Pd–Zn heterojunction that forms at high temperature and thus influences the conductivity of the ZnO nanorods.     

Structure, morphology and electrochemical behaviour of manganese oxides prepared by controlled decomposition of permanganate

Hydrothermal decomposition of permanganate, conducted in a range of pH-controlled solutions (from strongly acidic to strongly basic), is used to prepare manganese dioxides that are well-suited for use as supercapacitor electrode materials. While permanganate is thermodynamically unstable, the kinetics of its decomposition in an aqueous environment are very slow, until the temperature is raised to 200 °C. Although the resultant materials are relatively crystalline and have low total pore volume, their prominent meso-porosity leads to good electrochemical performance. Best behaviour is obtained for material from permanganate decomposition in 0.01 M H₂SO₄ solution, for which composite electrodes (150 μm thick) yield 150 F g⁻¹ at 5 mV s⁻¹ in a 9 M KOH electrolyte.     

Controlled synthesis of MnO2/CNT nanocomposites for supercapacitor applications

Abstract

In this work, manganese oxide (MnO₂)/carbon nanotube (CNT) nanocomposites have been prepared as electrode materials for supercapacitor applications. The materials were synthesised using a traditional and facile chemical deposition method. Effects from CNT amounts, synthesis time, pH value and CNT treatment using nitric acid have been thoroughly investigated. It was found that the sample synthesised for 3 h at pH 5 had achieved the best performance with a specific capacitance of 115 F g^?1 at a discharge rate of 0·5 A g^?1. A capacitance retention of 95% after 1000 cycles has been observed for the sample synthesised in the neutral environment. We believe that findings from this work will pave a road for nanostructured MnO₂/CNT composites with better performance in energy storage applications.