MnO2 Nanowires Research Articles

MnO2-nanowire@NiO-nanosheet core-shell hybrid nanostructure derived interfacial Effect for promoting catalytic oxidation activity

Nanostructure-derived interfacial effect plays a great role in enhancing catalytic activities. Herein, a MnO2 nanowires@NiO nanosheets core-shell hybrid nanostructure was successfully prepared by uniformly decorating NiO nanosheets on the one-dimensional MnO2 nanowires. The physi-chemical properties of the MnO2 and MnO2@NiO were characterized by using XRD, BET, SEM, H2-TPR and XPS techniques. Compared to the single MnO2 nanowires, the MnO2@NiO nanocomposite with better low-temperature reducibility and more active surface oxygen species exhibited much better performance in complete oxidation of benzene, giving the temperatures for 100% benzene conversion of 320°C under the conditions of 1000ppm benzene in air and space velocity of 120,000mLg−1h−1 while the value over pure MnO2 was 380°C. The novel hetero-interface constructed between MnO2 and NiO core-shell nanostructures might make a great contribution on this significantly promoting effect.

Fabrication of MnO nanowires implanted in graphene as an advanced anode material for sodium-ion batteries

MnO nanowires/graphene (MnO/GR) composite is prepared through a simple two-step route, which including a hydrothermal and a subsequent calcination process. Morphology and structure characterizations indicate the successful incorporation of MnO nanowires with GR sheets. The electrochemical performance of the composite as an anode material for sodium-ion batteries (SIBs) was investigated. The results show that the composite could deliver good cycling performance of 191mAhg−1 at the current density of 50mAg−1 after 100 cycles together with excellent rate performance by taking the advantages of GR. This work offers promise for the potential application of MnO/GR as an anode for SIBs.

Efficient Production of Coaxial Core–Shell MnO@Carbon Nanopipes for Sustainable Electrochemical Energy Storage Applications

Adverse structural changes and poor intrinsic electrical conductivity as well as the lack of an environmentally benign synthesis for MnO species are major factors to limit their further progress on electrochemical energy storage applications. To overcome the above constraints, the development of reliable and scalable techniques to confine MnO within a conductive matrix is highly desired. We herein propose an efficient and reliable way to fabricate coaxial core–shell hybrids of MnO@carbon nanopipes merely via simple ultrasonication and calcination treatments. The evolved MnO nanowires disconnected/confined in pipe-like carbon nanoreactors show great promise in sustainable supercapacitors (SCs) and Li-ion battery (LIB) applications. When used in SCs, such core–shell MnO@carbon configurations exhibit outstanding positive and negative capacitive behaviors in distinct aqueous electrolyte systems. This hybrid can also function as a prominent LIB electrode, demonstrating a high reversible capacity, excellent rat...

Novel biotemplated MnO2 1D nanozyme with controllable peroxidase-like activity and unique catalytic mechanism and its application for glucose sensing

To get recyclable and highly active peroxidase mimetics, MnO2 nanowires (NWs) were prepared by using genetically engineered filamentous phages as biotemplates. The morphology of NWs was tailored by controlling the synthesis temperature. The synthesis conditions could influence the peroxidase-like activity of MnO2 NWs. The catalytic mechanism of the prepared MnO2 NWs was investigated, which is Ping-pong BiBi electron transfer mechanism, different from Fenton reaction and some other mechanisms of nanozymes reported so far. Based on the excellent catalytic activity and stability, MnO2 NWs coupled with glucose oxidase were applied to the colorimetric sensing glucose, which showed the good re-utilization performance and reproducibility. The MnO2 NWs are promising to be applied to the bioanalysis and industrial catalyst.

Fiber electrode by one-pot wet-spinning of graphene and manganese oxide nanowires for wearable lithium-ion batteries

Flexible and mechanically robust fiber electrodes, for their application in wearable lithium-ion batteries, are prepared by one‐pot wet‐spinning of a liquid crystal dispersion of graphene oxide and manganese oxide (MnO2) nanowires. MnO2 nanowires, which are synthesized by a microwave-assisted hydrothermal reaction, are mixed with the graphene oxide aqueous dispersion and then assembled into the continuous fibers by the wet-spinning. The nanowire morphology and the high-aspect ratio of MnO2 contribute to maintain structural integrity of the fiber shape during the wet‐spinning process, as well as to achieve a high loading density of the active materials in the fiber. Furthermore, our simple one‐pot fiber electrode fabrication process allows for a more uniform distribution of the active materials throughout the fiber electrode, and a lower contact resistance between the MnO2 and graphene. The resulting fiber electrode delivers a high reversible capacity, excellent cycling performance, and good rate capability. Flexible and mechanically robust fiber electrodes, for their application in wearable lithium ion batteries, were prepared by one-pot wet-spinning of a liquid crystal dispersion of graphene oxide and MnO2 nanowires. The wire-shape with high aspect ratio of MnO2 allows excellent fiber formability as well as high battery capacity and good cycle performance.

MnO2 Nanowire/Biomass-Derived Carbon from Hemp Stem for High-Performance Supercapacitors.

Hierarchical 3D nanostructures based on waste biomass are being offered as promising materials for energy storage due to their processabilities, multifunctionalities, environmental benignities, and low cost. Here we report a facile, inexpensive, and scalable strategy for the fabrication of hierarchical porous 3D structure as electrode materials for supercapacitors based on MnO2 nanowires and hemp-derived activated carbon (HC). Vertical MnO2 wires are uniformly deposited onto the surface of HC using a one-step hydrothermal method to produce hierarchical porous structures with conductive interconnected 3D networks. HC acts as a near-ideal 3D current collector and anchors electroactive materials, and this confers a specific capacitance of 340 F g-1 at 1 A g-1 with a high rate capability (88% retention) of the 3D MnO2/HC composite because of its open-pore system, which facilitates ion and electron transports and synergistic contribution of two energy-storage materials. Moreover, asymmetric supercapacitors fabricated using 3D HC as the anode and 3D MnO2/HC as the cathode are able to store 33.3 Wh kg-1 of energy and have a power delivery of 14.8 kW kg-1.

Three-Dimensional Cobalt Phosphide Nanowire Arrays as Negative Electrode Material for Flexible Solid-State Asymmetric Supercapacitors.

Despite the great progress that has been accomplished in supercapacitors, the imbalance of the development of positive and negative electrode materials still remains a critical issue to achieve high energy density; therefore, exploring high-performance negative electrode materials is highly desirable. In this article, three-dimensional cobalt phosphide (CoP) nanowire arrays were synthesized on a carbon cloth and were utilized as a binder-free supercapacitor negative electrode. The as-synthesized CoP nanowire arrays presented a high capacitance of 571.3 mF/cm2 at a current density of 1 mA/cm2. By using CoP nanowire arrays as the negative electrode and MnO2 nanowire arrays as the positive electrode, a flexible solid-state asymmetric supercapacitor has been fabricated and has exhibited excellent electrochemical performance, such as a high energy density of 0.69 mWh/cm3 and a high power density of 114.2 mW/cm3. In addition, the solid-state asymmetric supercapacitor shows high cycle stability with 82% capacitance retention after 5000 charge/discharge cycles. This work demonstrates that CoP is a promising negative electrode material for high-performance supercapacitor applications.

Supercharging a MnO2 Nanowire: An Amine-Altered Morphology Retains Capacity at High Rates and Mass Loadings.

The influence of hexamethylenetetraamine (HMTA) on the morphology of δ-MnO2 and its properties for electrical energy storage are investigated-specifically for ultrathick δ-MnO2 layers in the micron scale. Planar arrays of gold@δ-MnO2, core@shell nanowires, were prepared by electrodeposition with and without the HMTA and their electrochemical properties were evaluated. HMTA alters the MnO2 in three ways: First, it creates a more open morphology for the MnO2 coating, characterized by "petals" with a thickness of 6 to 9 nm, rather than much thinner δ-MnO2 sheets seen in the absence of HMTA. Second, the electronic conductivity of the δ-MnO2 is increased by an order of magnitude. Third, δ-MnO2 prepared in HMTA shows a (001) interlayer spacing that is expanded by ≈30% possibly accelerating Li transport. The net effect of "HTMA doping" is to dramatically improve high rate performance, culminating in an increase in the specific capacity for the thickest MnO2 shells examined here by a factor of 15 at 100 mV/s.

Different morphologies of MnO2 grown on the graphene@nickel foam electrode for supercapacitor application

A binder-free 3D electrode of MnO2 arrays on graphene@nickel foam was successfully prepared via a two-step method. The nickel foam was first coated with a graphene sheet by chemical vapor deposition (CVD) and then decorated with MnO2 of different morphologies, ultrathin MnO2 nanosheets and ultralong MnO2 nanowires, by facile hydrothermal method. Due to the large specific surface area, high electronic conductivity and good capacitance of electrode materials, the obtained electrode exhibited rapid electron and ion transport, large electroactive surface area, and excellent structural stability. The electrode showed a high specific capacitance of 723Fcm−2 at a high current density of 30mAcm−2 and a good cycling stability (with a negligible 2.4% decay in specific capacitances after 2300 cycles), promising its applications to high-performance supercapacitors.

Enhanced Dielectric Performance of Polymer Nanocomposites Based on CNT/MnO2 Nanowire Hybrid Nanostructure

We report a new highly efficient polymer nanocomposite for charge storage applications based on carbon nanotube (CNT) and MnO2 nanowire (MnO2NW). Our study suggested that combination of conductive filler (CNT) and ferroelectric filler (MnO2NW) is an effective method to fabricate nanocomposite with outstanding dielectric permittivity and low dielectric loss if two fillers share similar length and geometry. This strategy leads us to fabricate a hybrid nanocomposite (CNT:MnO2NW (3.0:4.5 wt %)) with a high dielectric permittivity (50.6) and low dielectric loss (0.7), which are among the best-reported values in the literature in the X-band frequency range (8.2–12.4 GHz). We postulated that superior dielectric properties of the new hybrid nanocomposites were attributed to (i) better dispersion state of CNT in the presence of MnO2NW, which increases the effective surface area of CNTs, as nanoelectrodes, (ii) dimensionality match between the nanofillers, which increases their synergy, and (iii) barrier role of Mn...

Decoupling atomic-layer-deposition ultrafine RuO2 for high-efficiency and ultralong-life Li-O2 batteries

Li-O2 batteries with ultrahigh theoretical energy density have triggered worldwide research interests and hold the prospect for powering electric vehicles. However, the poor cycling stability and low energy efficiency of Li-O2 batteries still remain and hamper their practical application. Configuring desirable porous cathodes with uniformly dispersed and highly active catalysts is a noteworthy and feasible approach to overcoming these critical obstacles. Herein, we report on a novel strategy for the fabrication of Mn3O4 nanowires and carbon nanotubes composite film (Mn3O4/CNTs film) with ultrafine RuO2 nanoparticles (Mn3O4/CNTs-RuO2 film), in which the Mn3O4/CNTs film was employed as a conductive and porous matrix and extremely low amount of RuO2 (just 2.84wt%) are uniformly dispersed onto this matrix by using atomic layer deposition method, and reveal its electrochemical behaviors as a free-standing air electrode for Li-O2 batteries. The Mn3O4/CNTs-RuO2 film delivers a high specific capacity, improved round-trip energy efficiency and ultra-long cycle life (251 cycles). The superior electrochemical performance can be attributed to the enhanced catalytic activity of the grafted RuO2 with modulated electronic structure as the result of the interaction with substrate, which is evidenced by the corresponding X-ray absorption spectroscopy results and the unique nanosheet-shaped discharge product which can be smoothly decomposed.

Electrophoretic Deposition of MnOx@Carbon Nanotubes Film with Nest‐Like Structure as High‐Performance Anode for Lithium‐Ion Batteries

AbstractA binder‐free nest‐like structured MnOx@carbon nanotubes anode for lithium‐ion batteries (LIBs) was prepared through a facile electrophoretic deposition (EPD) method. Through the EPD process, both MnO2 nanowires and carbon nanotubes (CNTs), as starting materials, were interwoven tightly to form a uniform co‐deposited film, possessing a nest‐like architecture. After annealing the film under an inert atmosphere, the MnO2 nanowires transformed into Mn3O4 and MnO, as confirmed by the X‐ray diffraction patterns. The nest‐like electrode formed a porous and integrated conductive framework and provided the buffer space for the volume change of manganese oxides during cycling processes. As a result, this MnOx@CNTs electrode exhibited excellent cycling performance with a reversible capacity of 1152.1 mAh g−1 at 0.2 A g−1 and a superior cycling stability with 88.0 % capacity retention at 1 A g−1 after 200 cycles.

Recovery of uranium(vi) from aqueous solutions using a modified honeycomb-like porous carbon material.

Researchers have focused their attention on environment-friendly adsorption materials to solve the energy shortage problem and guarantee the sustainable development of human society. For that matter, pomelo peel, which is a low-cost and universal biomass waste, can be used as an effective carbon source with a large specific surface area. In this paper, a novel composite adsorbent, consisting of a three-dimensional honeycomb-like porous carbon material and MnO2 nanowires (HLPC/MnO2), has been successfully synthesized using alkaline activation followed by a carbonization procedure at high temperatures and in situ growth of MnO2 nanowires. The as-prepared composite was characterized using XRD, FT-IR, XPS, SEM, TEM and BET. The surface area of the HLPC reached 1147.41 m2 g-1. The results of the adsorption experiments show that the highest adsorption value of the HLPC/MnO2 composite was 238.09 mg-U per g-adsorbent at pH 5. The thermodynamic and kinetic parameters demonstrate that the removal process correlates well with a Langmuir adsorption isotherm model and pseudo-second-order kinetic model. Thus, the HLPC/MnO2 composite is an excellent adsorbent for removing uranium(vi) ions from aqueous solutions.

High rate Li-ion storage properties of MOF-carbonized derivatives coated on MnO nanowires

Carbonized derivatives of ZIF-67 MOFs on MnO2 NWs are fabricated as high rate Li-ion storage anode materials.

Synthesis of CuO<sub>x</sub>/MnO<sub>2</sub> Heterostructures with Enhanced Visible Light-Driven Photocatalytic Activity

Organic pollutants coming from various industry processes are harmful to the environment, and semiconductor heterostructure is a promising candidate catalyst for poisonous wastewater treatment in the future. In this study, CuOx/MnO2 heterostructures were successfully constructed, using a facile and effective hydrothermal method and chemical both/calcination route, which exhibited higher photocatalytic activity towards the photodegradation of organic contaminants under visible-light driven irradiation. The resulting CuOx/MnO2 heterostructures were systematically characterized using various microscopic and spectroscopic techniques. Morphological characterizations show that the CuOx nanoparticles are well anchored on the surface of the MnO2 nanowires (NMs). The photocatalytic activity enhancement of the CuOx/MnO2 heterostructures (M-4) could be ascribed to the introduction of CuOx on the surface of MnO2 NWs and the efficient separation of the electron-hole pairs compared to other CuOx/MnO2 heterostructures and pure MnO2 NMs. These results show that CuOx/MnO2 heterostructures can be a suitable candidate for efficient visible light photocatalysts.

Efficient Synthesis of Graphene Nanoscrolls for Fabricating Sulfur-Loaded Cathode and Flexible Hybrid Interlayer toward High-Performance Li-S Batteries.

A modified lyophilization approach is developed and used for highly efficient transformation of 2D graphene oxide sheet into 1D graphene nanoscroll (GNS) with high topological transforming efficiency (∼94%). Because of the unique open tubular structure and large specific surface area (545 m2 g-1), GNS is utilized for the first time as a porous cathode scaffold for encapsulating sulfur with a high loading (81 wt %), and also as a conductive skeleton for assembling MnO2 nanowires into a flexible free-standing hybrid interlayer, both enabling high-rate and long-life Li-S battery.

Gold nanoparticles decorated MnO2 nanowires for high performance supercapacitor

We have synthesized highly crystalline MnO2 nanowires by wet chemical biphasic method. Further, the gold nanoparticles were decorated on MnO2 nanowires. The MnO2 nanowire and gold nanoparticle decorated MnO2 nanowire samples were well characterized using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence (PL) spectroscopy etc. The supercapacitor performance for both the samples was tested under the identical conditions. The gold nanoparticles decorated on MnO2 nanowire exhibits cyclic stability cycles with only 3% capacity loss and maximum energy density of 37.08Wh/kg. It has been observed that the gold decorated MnO2 nanowire shows superior performance towards supercapacitor application due to the increased defects, surface area and increase in the capacity towards charge storage. Our results can open up new avenue towards utilization of MnO2 nanowires and other metal oxide nanomaterials with controlled functionalization/decoration of metal nanoparticles for superior charge storage devices.

Facile preparation of ultrafine manganese dioxide nanowires on activated carbon paper with enhanced capacitance for supercapacitors

In this paper, a structure with growing MnO2 nanowires (NWs) on activated carbon paper was designed and prepared using a simple hydrothermal method. Electrochemical measurements show that the specific capacitance of these MnO2 nanowires/ACP reached 390 F g−1 at a scan rate of 10 mV s−1 and 529 F g−1 at a current density of 2.0 A g−1. The long-term cycle life stability for MnO2 nanowires/ACP was examined and the results show that the capacitance decay was ~12% over 5000 cycles, indicating its long cycle life. Furthermore, they could also be used to assemble simple solid-state supercapacitors with high capacitance. These results show that the MnO2 nanowires/ACP could be a promising electrode material for energy storage.

Ultrafine MnO2 Nanowire Arrays Grown on Carbon Fibers for High-Performance Supercapacitors

Large-area ultrafine MnO2 nanowire arrays (NWA) directly grew on a carbon fiber (CF, used as a substrate) by a simple electrochemical method, forming three-dimensional (3D) hierarchical heterostructures of a CF@MnO2 NWA composite. As an electrode for supercapacitors, the CF@MnO2 NWA composite exhibits excellent electrochemical performances including high specific capacitance (321.3 F g−1 at 1000 mA g−1) and good rate capability. Further, the overall capacitance retention is ~99.7 % capacitance after 3000 cycles. These outstanding electrochemical performances attribute to a large number of transport channels for the penetration of electrolyte and the transportation of ions and electrons of electrodes. The as-prepared CF@MnO2 NWA composite may be a promising electrode material for high-performance supercapacitors.

In Situ Reactive Synthesis of Polypyrrole-MnO2 Coaxial Nanotubes as Sulfur Hosts for High-Performance Lithium-Sulfur Battery.

Lithium-sulfur batteries are considered as a promising candidate for high energy density storage applications. However, their specific capacity and cyclic stability are hindered by poor conductivity of sulfur and the dissolution of redox intermediates. Here, we design polypyrrole-MnO2 coaxial nanotubes to encapsulate sulfur, in which MnO2 restrains the shuttle effect of polysulfides greatly through chemisorption and polypyrrole serves as conductive frameworks. The polypyrrole-MnO2 nanotubes are synthesized through in situ polymerization of pyrrole using MnO2 nanowires as both template and oxidization initiator. A stable Coulombic efficiency of ∼98.6% and a decay rate of 0.07% per cycle along with 500 cycles at 1C-rate are achieved for S/PPy-MnO2 ternary electrodes with 70 wt % of S and 5 wt % of MnO2. The excellent trapping ability of MnO2 to polysulfides and tubular structure of polypyrrole with good flexibility and conductivity are responsible for the significantly improved cyclic stability and rate capability.