MnO2 Nanoflowers Research Articles

Facile Synthesis of Nanostructured MnO2 as Anode Materials for Sodium‐Ion Batteries

AbstractNanostructured MnO2 (including nanorods and nanoflowers) has been synthesized by a simple two‐step hydrothermal method and thermal treatment. When employed as anode materials for sodium‐ion batteries, MnO2 nanorods and nanoflowers demonstrate high initial sodium ion storage capacities of 427.4 and 487.8 mA h g−1, respectively, at a current density of 50 mA g−1. Compared with MnO2 nanorods, MnO2 nanoflowers achieved a much better electrochemical performance including good rate capability (103.3 mA h g−1 at 800 mA g−1 after 100 cycles) and superior cyclability (133.6 mA h g−1 at 400 mA g−1 after 1000 cycles). The good performance can be ascribed to the nanocrystalline nature and the three‐dimensional hierarchical architecture of MnO2 nanoflowers, which promotes the contact between MnO2 and electrolyte and shortens the electronic sodium ion pathway in the charge and discharge processes.

SUPERCONDENSADORES SIMÉTRICOS DE ALTO RENDIMIENTO BASADOS EN ELECTRODOS HÍBRIDOS DE NANO-FLORES CONDUCTORAS DE GRAFITO/MnO2

This paper develops a facile and inexpensive approach of boiling water-bath with simultaneous magnetic stirring to synthesize MnO2 nanomaterials. In this paper, we report a novel structure of conducting graphite (G)/MnO2 nanoflower (NF) hybrid electrodes, in which conducting graphite and MnO2 nanomaterials hybrid solution were conformally naturally deposited onto carbon paper. Such NF structures effectively decrease the charge transport resistance and facilitate ion or electron transmission in the electrode. G/MnO2 NF hybrid electrodes exhibit a high specific capacitance (Cs) of 506 F/g, high energy/power densities, and excellent cycling stability with 94% capacitance retained over 2000 cycles. Furthermore, symmetric supercapacitors (SSCs) with G/MnO2 NF hybrid materials as electrodes were successfully fabricated, which achieved promising characteristics with a maximum energy density of 11.72 Wh/kg and a power density of 16.88 kW/kg. Such low-cost, high-performance carbon paper-based G/MnO2 NF hybrid electrodes may hold promise for superior performance supercapacitors. Keywords: Graphite, MnO2 nanoflower, Natural deposition, Supercapacitor

Fabrication of Functionalized Graphene-Based MnO2 Nanoflower through Electrodeposition for High-Performance Supercapacitor Electrodes

Graphene is a potential energy storage material for supercapacitor electrodes because of its unique electronic and physical properties. In this study, graphene was functionalized chemically. The functionalized graphene (G) is an ideal substrate for anchoring MnO2 nanoflower (NF) through controlled electrodeposition to improve the performance of supercapacitors. The controlled weight ratio of functionalized graphene and MnO2 NF is 1:8. The G/MnO2 NF electrodes exhibit excellent electrochemical performance with a high specific capacitance of 320.59 F g−1 at a current density of 0.5 A g−1 and excellent cycling stability with 95.5% capacitance retention over 3000 cycles. Symmetric supercapacitors with G/MnO2 NF hybrid materials were also assembled as electrodes. The cells exert promising characteristics with a specific capacitance of 55.37 F g−1 at a scan rate of 5 mV s−1, maximum energy density of 5.67 Wh kg−1, and power density of 5.11 kW kg−1. The facile and low-cost preparation technique of functionalized graphene and high-performance G/MnO2 NF nanocomposites may provide a new paradigm for fabricating supercapacitors with superior performance.

Enhanced simultaneous detection of ractopamine and salbutamol – Via electrochemical-facial deposition of MnO2 nanoflowers onto 3D RGO/Ni foam templates

In this paper, we report a facile method to successfully fabricate MnO2 nanoflowers loaded onto 3D RGO@nickel foam, showing enhanced biosensing activity due to the improved structural integration of different electrode materials components. When the as-prepared 3D hybrid electrodes were investigated as a binder-free biosensor, two well-defined and separate differential pulse voltammetric peaks for ractopamine (RAC) and salbutamol (SAL) were observed, indicating the simultaneous selective detection of both β-agonists possible. The MnO2/RGO@NF sensor also demonstrated a linear relationship over a wide concentration range of 17nM to 962nM (R=0.9997) for RAC and 42nM to 1463nM (R=0.9996) for SAL, with the detection limits of 11.6nM for RAC and 23.0nM for SAL. In addition, the developed MnO2/RGO@NF sensor was further investigated to detect RAC and SAL in pork samples, showing satisfied comparable results in comparison with analytic results from HPLC.

Controlled synthesis of hierarchical birnessite-type MnO2 nanoflowers for supercapacitor applications

Birnessite-type MnO2 nanoflowers assembled by hierarchical nanosheets were successfully synthesized via a facile and simple hydrothermal process. The ration of reactants is a critical factor affects formation process of MnO2 nanoflowers. The electrochemical test of the as-synthesized birnessite-type MnO2 exhibits excellent electrochemical property with ideal voltammetry behavior, high specific capacitance (197.3Fg−1 at 1Ag−1) and superior cycling stability (only 5.4% capacitance loss after 1000 cycling test). The distinct hierarchical nanostructure and impressive electrochemical performances suggest the birnessite-type MnO2 is a promising material for supercapacitor applications.

Preparation of a manganese dioxide/carbon fiber electrode for electrosorptive removal of copper ions from water

MnO2 is an effective adsorbent for many metal ions and a promising electrode material for electrochemical supercapacitors. In this paper, we successfully combined the two functions through preparing a MnO2/carbon fiber (CF) composite as an electrosorptive electrode. The thin MnO2 film was deposited onto CF by an anodic eletrodeposition method. The MnO2/CF electrodes had ideal pseudocapacitive behavior and high capacitive reversibility. The specific capacitance of the MnO2/CF electrode reached a maximum value of 387F/g, which is quite competitive compared with literature values. At 0.8V applied potential, the maximum Cu2+ adsorption capacity of the MnO2/CF electrode was 172.88mg/g, which is more than 2 times higher than common MnO2 adsorbents without an electric field imposed. SEM images showed that MnO2 nanoflowers with several “petals” were uniformly distributed on the CF surface. Enhancement of adsorption by the polarization potential and the unique microstructure of the deposited MnO2 may be the source of the outstanding adsorption ability of the MnO2/CF electrode. The MnO2/CF electrode could be regenerated quickly by reversing the voltage. The deposition time of 1000s was optimum for achieving maximum capacitance and Cu2+ removal performance. The MnO2/CF composite electrosorptive electrode is a promising candidate for Cu2+ removal from aqueous solution.

A three dimensional Pt nanodendrite/graphene/MnO2 nanoflower modified electrode for the sensitive and selective detection of dopamine.

An electrochemical sensor using a novel three dimensional (3D) ternary Pt nanodendrite/reduced graphene oxide/MnO2 nanoflower (Pt/RGO/MnO2) modified glassy carbon electrode was proposed for the selective and sensitive determination of dopamine (DA) in the presence of ascorbic acid (AA) and uric acid (UA). Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used to evaluate electrochemical behaviors of DA on the as-prepared electrode. The oxidation peak current of DA is linearly proportional to its concentration in the range from 1.5-215.56 μM, with a detection limit of 0.1 μM (at S/N = 3). Compared to bare RGO, Pt nanodendrite/RGO and MnO2 nanoflower modified electrodes, the 3D hierarchical ternary Pt/RGO/MnO2 composites displayed the highest electrocatalytic activity for the selective detection of DA. Moreover, the 3D Pt/RGO/MnO2 modified electrode can be reused with no obvious deterioration in the electrocatalytic performance. This work paves the way for developing a novel 3D nanostructure and offers new opportunities for improving the performance of electrochemical sensors with excellent sensitivity, repeatability and anti-interference.

Electrochemical performance studies of MnO2 nanoflowers recovered from spent battery

The electrochemical performance of MnO2 nanoflowers recovered from spent household zinc–carbon battery is studied by cyclic voltammetry, galvanostatic charge/discharge cycling and electrochemical impedance spectroscopy. MnO2 nanoflowers are recovered from spent zinc–carbon battery by combination of solution leaching and electrowinning techniques. In an effort to utilize recovered MnO2 nanoflowers as energy storage supercapacitor, it is crucial to understand their structure and electrochemical performance. X-ray diffraction analysis confirms the recovery of MnO2 in birnessite phase, while electron microscopy analysis shows the MnO2 is recovered as 3D nanostructure with nanoflower morphology. The recovered MnO2 nanoflowers exhibit high specific capacitance (294Fg−1 at 10mVs−1; 208.5Fg−1 at 0.1Ag−1) in 1M Na2SO4 electrolyte, with stable electrochemical cycling. Electrochemical data analysis reveal the great potential of MnO2 nanoflowers recovered from spent zinc–carbon battery in the development of high performance energy storage supercapacitor system.

High performance MnO2 nanoflower electrode and the relationship between solvated ion size and specific capacitance in highly conductive electrolytes

Flower shaped birnessite type manganese oxide (δ-MnO2) nanostructures are synthesized using a simple hydrothermal process with an aim to fabricate high performance supercapacitors for energy storage electrode. The studies reveal that layered δ-MnO2 had a basal plane spacing of ∼0.73nm and are composed of thin nanosheets of thickness ∼23nm. A detailed investigation is undertaken to draw a relationship between the solvated ion size of alkaline electrolytes (LiOH, NaOH and KOH) and pore size in the electrode material favoring high specific capacitance and faster electrode kinetics. The present work not only develops a high performance supercapacitive material but also identifies that by suitably tuning the sizes of solvated ion and the pores, supercapacitive behavior of a single material system can be tailored.

Formation of ultrafine three-dimensional hierarchical birnessite-type MnO2 nanoflowers for supercapacitor

Ultrafine (50–100nm in diameter) birnessite-type MnO2 nanoflowers assembled by numerous ultrathin nanosheets (3–6nm in thickness and 30–50nm in width) have been synthesized via a simple and scalable solution route under ambient conditions. The ratio of reactants plays a significant role in the formation of MnO2 nanoflowers and the as-prepared MnO2 hierarchical nanostructure exhibits excellent electrochemical performance with high specific capacitance (251.3Fg−1 at 0.5Ag−1) and superior cycling stability (only 7.5% SC loss after 10,000 cycling test) and good rate capability. The unique microstructures of MnO2 nanoflowers are responsible for their superior electrochemical properties, and thus it may be a promising for supercapacitor application.

Hierarchical nanostructures of polypyrrole@MnO2 composite electrodes for high performance solid-state asymmetric supercapacitors

A solid-state high performance flexible asymmetric supercapacitor (ASC) was fabricated. Its anode is based on organic-inorganic materials, where polypyrrole (PPy) is uniformly wrapped on MnO2 nanoflowers grown on carbon cloth (CC), and its cathode is made of activated carbon (AC) on CC. The ASC has an areal capacitance of 1.41 F cm(-2) and an energy density of 0.63 mW h cm(-2) at a power density of 0.9 mW cm(-2). An energy storage unit fabricated using multiple ASCs can drive a light-emitting diode (LED) segment display, a mini motor and even a toy car after full charging. The high-performance ASCs have significant potential applications in flexible electronics and electrical vehicles.

MnO2-modified hierarchical graphene fiber electrochemical supercapacitor

A novel hybrid fiber that MnO2 modified graphene sheets on graphene fiber has been fabricated by direct deposition of MnO2 onto graphene network surrounding graphene fiber (MnO2/G/GF). In this hierarchical structure, the graphene fiber with a sheath of 3D graphene network is coated with MnO2 nanoflowers. The 3D graphene on graphene fibers (G/GF) serves as highly conductive backbones with high surface area for deposition of nanostructured MnO2, which provide the high accessibility of electrolytic ions for shorten diffusion paths. An all-solid-state flexible supercapacitor based on a MnO2/G/GF hybrid fiber structure has been developed on the basis of the intrinsic mechanical flexibility of GF and the unique hierarchical structure. By combination of electric double layer capacitance of graphene network with the pseudocapacitance of MnO2 nanostructures, the all-solid-state fiber supercapacitor shows the much enhanced electrochemical capacitive behaviors with robust tolerance to mechanical deformation, promising for being woven into a textile for wearable electronics.

Hydrothermal preparation and the capacitance of hierarchical MnO2 nanoflower

Hierarchical MnO2 nanoflower has been simply prepared via a hydrothermal treatment technology in a mixed solution of KMnO4 and cetyltrimethylammonium hydroxide at 90°C for 12h. The morphology and structure of the obtained material are examined by XRD, SEM, TEM, HRTEM, SAED, and N2 adsorption–desorption. The electrochemical properties are characterized by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy in 1.0M Na2SO4 aqueous solution. The obtained material has layered birnessite-type structure and shows flower-like hierarchical morphology. The hierarchical nanostructure is assembled by manganese oxide nanosheets with a diameter of about 30nm and a thickness of 3–5nm. The hierarchical MnO2 nanoflower exhibits not only high specific capacitance of 347Fg−1, but also excellent cycle stability (97.5% capacitance retention after 10,000 cycles at a scan rate of 20mVs−1). An asymmetric electrochemical capacitor based on the obtained hierarchical MnO2 nanostructures as a positive electrode and graphene as a negative electrode is assembled. The assembled asymmetrical electrochemical capacitor can cycle reversibly in a voltage of 0–1.6V and gives a high energy density of 20.9Whkg−1 at a power density of 400Wkg−1.

Asymmetric supercapacitors with dominant pseudocapacitance based on manganese oxide nanoflowers in a neutral aqueous electrolyte

Unique MnO2 nanoflowers (∼25 nm) composed of ultrathin K0.26MnO2 nanoflake assemblies were synthesized by a facile and green procedure. Prototype MnO2-NFs//KCl//CNTs asymmetric supercapacitors in a neutral aqueous electrolyte demonstrated pseudocapacitive dominance for the first time in addition to outstanding energy and power densities and superior cycling performance.

Thermal transformation of δ-MnO2 nanoflowers studied by in-situ TEM

In-situ transmission electron microscopy in combination with a heating stage has been employed to real-time monitor variations of δ-phase MnO2 nanoflowers in terms of their morphology and crystalline structures upon thermal annealing at elevated temperatures up to ∼665 °C. High-temperature annealing drives the diffusion of the small δ-MnO2 nanocrystallites within short distances less than 15 nm and the fusion of the adjacent δ-MnO2 nanocrystallites, leading to the formation of larger crystalline domains including highly crystalline nanorods. The annealed nanoflowers remain their overall flower-like morphology while they are converted to α-MnO2. The preferred transformation of the δ-MnO2 to the α-MnO2 can be ascribed to the close lattice spacing of most crystalline lattices between δ-MnO2 and α-MnO2, that might lead to a possible epitaxial growth of α-MnO2 lattices on the δ-MnO2 lattices during the thermal annealing process.

High-performance electrochemical capacitors using electrodeposited MnO2 on carbon nanotube array grown on carbon fabric

Carbon fabric (CF)-carbon nanotube array (CNTA)/MnO2 composites with a 3D porous structure are prepared by the electrochemical deposition for high-performance electrochemical capacitors. MnO2 nanoflowers assembled with the petal-like nanosheets uniformly attach on the surface of CNTs. Electrochemical characterization indicates that the maximum specific capacitance of CF-CNTA/MnO2 reach to 740Fg−1 (based on MnO2 alone) with a mass loading of 0.34mgcm−2 at the scan rate of 2mVs−1, which is much better than that of MnO2 electrodeposited on the stainless steel and the CF. And the specific capacitance can remain 326Fg−1 even with a mass loading of 4.09mgcm−2. While a reasonable area-normalized capacitance of 2081mFcm−2 is achieved with this high mass loading at 0.1mVs−1. The rate capability measurement shows the CF-CNTA/MnO2 achieved a high retention of 70% with a scan rate range of 2–200mVs−1, which outperform others 3D porous MnO2-based electrodes reported previously. These excellent electrochemical performances are attributed to large surface area, 3D porous structure and aligned ion diffusion channels of the CF-CNTA/MnO2 composite electrodes.

Symmetrical MnO2–Carbon Nanotube–Textile Nanostructures for Wearable Pseudocapacitors with High Mass Loading

While MnO(2) is a promising material for pseudocapacitor applications due to its high specific capacity and low cost, MnO(2) electrodes suffer from their low electrical and ionic conductivities. In this article, we report a structure where MnO(2) nanoflowers were conformally electrodeposited onto carbon nanotube (CNT)-enabled conductive textile fibers. Such nanostructures effectively decrease the ion diffusion and charge transport resistance in the electrode. For a given areal mass loading, the thickness of MnO(2) on conductive textile fibers is much smaller than that on a flat metal substrate. Such a porous structure also allows a large mass loading, up to 8.3 mg/cm(2), which leads to a high areal capacitance of 2.8 F/cm(2) at a scan rate of 0.05 mV/s. Full cells were demonstrated, where the MnO(2)-CNT-textile was used as a positive electrode, reduced MnO(2)-CNT-textile as a negative electrode, and 0.5 M Na(2)SO(4) in water as the electrolyte. The resulting pseudocapacitor shows promising results as a low-cost energy storage solution and an attractive wearable power.

Nano-Flower MnO2 Coated Graphene Composite Electrodes for Energy Storage Devices

ABSTRACTGraphene, two-dimensional layers of sp2-bonded carbon, has many unique properties. In this paper, graphene is decorated with flower-like MnO2 nanostructures for the application in energy storage devices. The as-prepared graphene and MnO2 nano-flowers, which were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), were assembled into an asymmetric supercapacitor. The specific capacitance of the graphene electrode reached 245 F/g at a charging current of 1 mA. The MnO2 nano-flowers which consisted of tiny rods with a diameter of less than 10 nm were coated onto the graphene electrodes by electrodeposition. The specific capacitance after the MnO2 deposition is 328 F/g at the charging current of 1 mA with an energy density of 11.4Wh/kg and power density of 25.8 kW/kg. This work suggests that our graphene-based electrodes can be a promising candidate for high-performance energy storage devices.