MnO2 Nanorods Research Articles

Morphology-controlled syntheses of α-MnO2 for electrochemical energy storage.

Manganese dioxide (MnO2) nanoarchitectures including microspheres assembled by nanosheets and hollow urchins assembled by nanorods have been successfully synthesized using a facile and efficient hydrothermal method at 150 °C. The effects of concentrations of the reactants and reaction time on the structures and morphologies of MnO2 were systematically investigated. The experimental results showed that the morphologies of MnO2 transformed into nanosheet-assembled microspheres (10 min) from nanorod-assembled hollow urchins (5 min) by tuning the suitable reaction time. The nanorod-assembled hollow urchins experienced the morphology transformation cycle from urchin to a disordered structure to urchin with the extension of the reaction time. Furthermore, the nanorods with different diameters and lengths were formed with different concentrations of reactants at the same reaction time (8 h). The MnO2 nanorods fabricated with 0.59 g KMnO4 showed a maximum specific capacitance (198 F g(-1)) with a good rate capability and excellent cycling stability (maintained 94% after 2000 cycles). Furthermore, the nanosheet-assembled microspheres exhibited the higher specific capacitance of 131 F g(-1) at 1 A g(-1) with a long-term cycling stability for the samples at different reaction times. These results indicated their promising applications as high-performance supercapacitor electrodes and provided a generic guideline in developing different nanostructured electrode materials for electrochemical energy storage.

Fabrication of Ag nanoparticles supported on one-dimensional (1D) Mn3O4 spinel nanorods for selective oxidation of cyclohexane at room temperature

Silver nanoparticles supported on spinel Mn3O4 nanorods efficiently catalyze cyclohexane to cyclohexanone with high yield at room-temperature.

Fabrication of Ag/Mn3O4 nano-architectures for the one-step selective oxidation of 3-picoline to niacin: a key to vitamin B3 production

Silver nanoparticles supported on spinel Mn3O4 nanorods efficiently transformed 3-methylpyridine to niacin using hydrogen peroxide as an oxidant.

Hierarchical three-dimensional MnO nanorods/carbon anodes for ultralong-life lithium-ion batteries

N-Doped carbon network encapsulated MnO nanorods demonstrate 95% capacity retention at a current density of 4000 mA g−1for 3000 cycles. In this case, almost no pulverization or size variation of the nanorods can be observed.

Facile preparation of MnO2 nanorods and evaluation of their supercapacitive characteristics

The first time pulsed base (OH−) electrogeneration to the cathodic electrodeposition of MnO2 in nitrate bath was applied and MnO2 nanorods were obtained. The deposition experiments were performed under a pulse current mode with typical on-times and off-times (ton=10ms and toff=50ms) and a peak current density of 2mA cm−2 (Ia=2mA cm−2). The structural characterization with XRD and FTIR revealed that the prepared MnO2 is composed of both α and γ phases. Morphological evaluations through SEM and TEM revealed that the prepared MnO2 contains nanorods of relative uniform structures (with an average diameter of 50nm). The electrochemical measurements through cyclic voltammetry and charge–discharge techniques revealed that the prepared MnO2 nanostructures reveal an excellent capacitive behavior with specific capacitance values of 242, 167 and 98 F g−1 under the applied current densities of 2, 5 and 10 A g−1, respectively. Also, excellent long-term cycling stabilities of 94.8%, 89.1%, and 76.5% were observed after 1000 charge–discharge cycles at the current densities of 2, 5 and 10 A g−1.

Decontamination of 2-chloro ethyl ethyl sulphide and dimethyl methyl phosphonate from aqueous solutions using manganese oxide nanostructures

Current study investigates the efficiency of reactive adsorbent composed of MnO2 nanoparticles and nanorods for the detoxification of 2-chloro ethyl ethyl sulphide (CEES) and dimethyl methyl phosphonate (DMMP), well-known simulants of sulphur mustard and sarin, respectively. The MnO2 nanoparticles and nanorods were synthesised using novel reactive magnetron sputtering technique and then characterised by powder XRD, Raman spectroscopy, FE-SEM, TEM, BET, FT-IR and Thermogravimetry (TG) analysis. Powder XRD and Raman results confirm the formation of pure tetragonal phase of MnO2 nanostructure material. The FE-SEM and TEM analysis exhibited the formation of aggregate MnO2 nanoparticles and nanorods. The surface area of the synthesised aggregate MnO2 nanoparticles and nanorods (164.28m2/g) was found to be enhanced significantly in comparison with what was reported in the literature. Decontamination reactions of synthesised nanostructure material were examined by GC equipped with FID and the products obtained after reaction were analysed by GC–MS and FT-IR techniques. It was observed that the currently synthesised MnO2 nanoparticles and nanorods exhibit much better decontamination results towards CEES as well as DMMP in comparison to or as per existing solid decontaminants. The reactions exhibited pseudo first order kinetic behaviour with rate constant and half life value 0.267h−1 and 2.58h for CEES and 0.068h−1 and 10.10h for DMMP, respectively. The data exhibits the formation of non-toxic hydrolysis products in the detoxification of CEES as well as DMMP.

One-pot synthesized ultrathin MnO2 nanorods as advanced electrodes for high-performance supercapacitors

Novel ultrathin MnO2 nanorods are successfully prepared by a one-pot hydrothermal process, which endows with porous one-dimensional (1 D) nanostructures. As a result, the MnO2 nanorods show good electrochemical performance as electrode materials for supercapacitors, including high specific capacitance of 820.8F/g, long life over 5000 cycles, and good rate capability (562.5F/g at 10A/g). The fabrication strategy present here is facile, cost-effective, and can offer a way for energy storage device applications.

The (2 × 2) tunnels structured manganese dioxide nanorods with α phase for lithium air batteries

The (2 × 2) tunnels structured manganese dioxide nanorods with α phase (α-MnO2) are synthesized via simplistic hydrothermal method at low temperature. The obtained tunnels structured α–MnO2 nanorods are characterized by, Transmission electron microscopy, Scanning electron microscopy, and X-ray diffraction techniques. The oxygen reduction reaction (ORR) activity was studied by cyclic voltammetry and rotating ring-disc electrode voltammetry techniques in alkaline media. Moreover; the highly electrocatalytic tunnels structured α–MnO2 nanorods were then also applied as cathode in rechargeable Li–O2 cells. The Li–O2 cells exhibited initial discharge capacity as high as ∼4000 mAh/g with the tunnels structured α–MnO2 nanorods which was double the original capacity of the cells without any catalyst. Also we obtained 100% round trip efficiency upon cycling with limited capacity for more than 50 cycles.

Crystallographic Structure and Morphology Transformation of MnO2 Nanorods as Efficient Electrocatalysts for Oxygen Evolution Reaction

MnO2 nanostructures with different crystallographic structure and morphologies have been synthesized through a facile template-free hydrothermal method. The growth mechanisms of these MnO2 nanostructures have been discussed. At 140°C, slim solid α-MnO2 nanorods are obtained. At 160°C, the crystal phase begins to transform from α-MnO2 to β-MnO2. And at 180°C, uniformly hollow β-MnO2 nanorods are formed. The electrocatalytic properties for oxygen evolution reaction (OER) of these as-prepared MnO2 samples have been systematically studied in alkaline media. It is obvious that the structure-function relationship of MnO2 samples for OER activity is dependent on the crystallographic structure and morphology, following the order α-MnO2 > α-MnO2/β-MnO2 > broken β-MnO2 > β-MnO2. The best OER electrocatalyst is α-MnO2, with an overpotential of 0.45 V (at j = 10 mA cm−2). The enhanced OER activity is owing to not only the highest BET surface area (45.6 m2 g−1), but also the largest electrochemical active surface area (Cdl = 3225.0 μF cm−2). In addition, the intrinsic activity of each Mn atom in α-MnO2 (TOF = 0.0056 s−1 at η = 0.45 V) is larger than that of β-MnO2 (TOF = 0.0003 s−1 at η = 0.45 V).

Parametric study of hydrothermal soft chemical synthesis and application of Na0.44MnO2 nanorods for Li-ion battery cathode materials: Synthesis conditions and electrochemical performance

In this paper, synthesis parameters were thoroughly investigated to understand and optimize the hydrothermal soft chemical synthesis of Na0.44MnO2 nanorods. Structural characterization reveals that a layered Na-birnessite precursor, a high NaOH concentration (15.0 mol/L) and a high hydrothermal reaction temperature (180 °C) are required for rapid formation of the tunnel Na0.44MnO2 phase. Additionally, the hydrothermal reaction time is greatly reduced to 8 h. More significantly, from electrochemical testing it is observed that the cycling stability and rate capability of Na0.44MnO2 electrode materials are enhanced after the addition of carbon nanotubes. The capacity retention increases from 70% to 82% at 0.1 A/g after 50 cycles, and the Li storage capacity at a high rate of 2.0 A/g increases from 45 mAh/g to 99 mAh/g. The parameters are optimized for fast, high-yield and large-scale production of high performance Na0.44MnO2 nanorod cathode materials used in lithium-ion batteries.

Hierarchical porous MnO2/CeO2 with high performance for supercapacitor electrodes

Hierarchical porous manganese dioxide/cerium dioxide (MnO2/CeO2) nanocomposite material as supercapacitor electrode was synthesized by hydrothermal method. Through synergistic effects from good reversible redox reaction characteristics of CeO2 and well cycling performance of MnO2, we obtained binary composite metal oxide with preferable capacitance, rate capability and cycling stability. XANES, FT-TR and XRD results indicate that MnO2/CeO2 composite (α-MnO2 and fluorite CeO2 respectively) has been prepared successfully with good crystallinity. SEM, TEM, HRTEM and Mapping reveal that CeO2 particles with loose distribution uniformly grow along MnO2 nanorods surface. The particle size largely reduces, and the agglomeration relieves evidently with loose structure and even arrangement. N2 adsorption tests show that BET specific surface areas (SBET) of MnO2/CeO2 are larger than that of original single component. MnO2/CeO2 is typical hierarchical mesoporous material with more widespread pore structure and distribution, much different from MnO2 and CeO2 being rich microporous materials. SBET and specific capacitance (Csp) of the optimal composite in this work (MnO2/CeO2-1) are up to 73.4m2g−1 and 274.3Fg−1 respectively, much higher than that of pure MnO2 (20.6m2g−1 and 190.2Fg−1) and CeO2 (63.6m2g−1 and 66.2Fg−1). After 1000 charge–discharge cycles, the Csp no longer decreases and remains 93.9%. In addition, MnO2/CeO2-1 obtains a low Rs, Rct and Zw. It is a good supercapacitor electrode material generally.

Hydrogen Generation of Cu2O Nanoparticles/MnO–MnO2 Nanorods Heterojunction Supported on Sonochemical-Assisted Synthesized Few-Layer Graphene in Water-Splitting Photocathode

In this study, we investigated the production of hydrogen by photochemical water splitting. A multi-shaped Cu2O nanoparticles/MnO–MnO2 nanorods heterojunction on a few-layer graphene-based electrode serves as the photocathode. Multi-shaped Cu2O nanoparticles, including truncated cubic shape, cuboctahedral shape, truncated octahedral shape, and octahedral shape, were then coated on square manganese nanorods on a few-layer graphene-based electrode as the photosensitizer. Finally, the efficiency of hydrogen production was measured and recorded. The Cu2O nanoparticles/MnO–MnO2 nanorods heterojunction generates photoelectrons to reduce hydrogen ions into hydrogen gas. The manganese dioxide nanorods were combined with cuprous oxide multi-shaped nanoparticles to be simultaneously utilized in hydrogen production as a photochemical water-splitting solar cell. The highest rate of hydrogen generation is 33.0 mL/min m2 under solar simulation radiation. This study highlights the significance of a back electron–hole re...

Hierarchical architecture of nanographene-coated rice-like manganese dioxide nanorods/graphene for enhanced electrocatalytic activity toward hydrogen peroxide reduction

Rice-like MnOx nanorods covered by nanographene (MxNRS@NG) are prepared via a simple one-step hydrothermal route. After combination with graphene (GS) and calcination, MxNRS are converted into MnO2 nanorods (MNRS) and the hierarchical architecture of MNRS@NG/graphene (MNRS@NG/GS) is obtained. In this ternary architecture, GS is an excellent supporting substrate for the electrocatalysis of MNRS, and NG can provide abundant active carbon atoms of edge phase and accelerate the electron transfer between MnO2 and GS. Electrochemical results demonstrate that the electroreduction of MNRS toward H2O2 is significantly enhanced by the assembly of GS and NG. The MNRS@NG/GS modified electrode exhibits excellent performance in H2O2 detection over the concentration range of 0.002–4.44mM, with a high sensitivity (707.9μAmM−1cm−2) and a low detection limit (0.2μM).

Porous Mn2O3 nanorods synthesized from thermal decomposition of coordination polymer and used in hydrazine electrochemical sensing

Porous Mn2O3 nanorods were prepared via the decomposition of a coordination polymer precursor, as evidenced by XRD and TEM results. Electrochemistry results showed obvious electrocatalytic activity of Mn2O3 nanorods toward the oxidation of hydrazine. When Au nanoparticles were loaded onto Mn2O3 nanorods, the performance in hydrazine determination was improved obviously. The sensitivity of 500mAmol-1Lcm−2 was obtained in linear range of 2×10−6−1.3×10−3molL−1, and the detection limit was 1.1×10−6molL−1.

Facile synthesis of 3-D composites of MnO2 nanorods and holey graphene oxide for supercapacitors

A facile method was developed to prepare MnO2/holey graphene oxide (MnO2/HGO) materials based on graphene oxide (GO) flakes for supercapacitor applications. FESEM images show that MnO2 nanorods were formed on the surface of HGO flakes, serving as spacers and preventing the HGO layers from stacking. This provides pathways between the layers for the electrolyte to access the bulk active materials. By introducing the high intrinsic capacitance MnO2 nanorods together with the modified 3-D structure, capacitance increases to 71.0 F/g compared with 30.0 F/g of GO. More pathways were created by nitric acid etching holes on the surface of the GO. This 3-D holey MnO2/HGO structure achieves a capacitance of 117.45 F/g, which is 1.65 times higher than that of MnO2/GO composite and 3.9 times higher than that of GO only. BET surface area, XRD, and AC impedance were also used to analyze the possible reasons for the enhanced electrochemical performance.

Hydrothermal synthesis of γ-MnOOH nanorods and their conversion to MnO2, Mn2O3, and Mn3O4 nanorods

Single crystal γ-MnOOH nanorods were successfully prepared by employing a hydrothermal process based on the direct reaction between potassium permanganate (KMnO4) and ethylene glycol (EG). It was found that the reaction time and temperature play important roles in the structural and morphological modifications. Our results show that the γ-MnOOH nanorods are formed through a lamellar growth, assembly and ripening process. Moreover, MnO2, Mn2O3, and Mn3O4 nanorods were obtained by the subsequent calcination of γ-MnOOH precursors under different temperatures and atmospheres. These one-dimensional manganese oxide and oxyhydroxide nanorods are expected to have possible novel properties and wide applications.

Hydrogenated TiO2 Branches Coated Mn3O4 Nanorods as an Advanced Anode Material for Lithium Ion Batteries

Rational design and delicate control on the component, structure, and surface of electrodes in lithium ion batteries are highly important to their performances in practical applications. Compared with various components and structures for electrodes, the choices for their surface are quite limited. The most widespread surface for numerous electrodes, a carbon shell, has its own issues, which stimulates the desire to find another alternative surface. Here, hydrogenated TiO2 is exemplified as an appealing surface for advanced anodes by the growth of ultrathin hydrogenated TiO2 branches on Mn3O4 nanorods. High theoretical capacity of Mn3O4 is well matched with low volume variation (∼4%), enhanced electrical conductivity, good cycling stability, and rate capability of hydrogenated TiO2, as demonstrated in their electrochemical performances. The proof-of-concept reveals the promising potential of hydrogenated TiO2 as a next-generation material for the surface in high-performance hybrid electrodes.

Growth mechanism and magnetic and electrochemical properties of Na0.44MnO2 nanorods as cathode material for Na-ion batteries

Nanorods of Na0.44MnO2 are a promising cathode material for Na-ion batteries due to their large surface area and single crystalline structure. We report the growth mechanism of Na0.44MnO2 nanorods via solid state synthesis and their physical properties. The structure and the morphology of the Na0.44MnO2 nanorods are investigated by X-ray diffraction (XRD), scanning and tunneling electron microscopy (SEM and TEM), and energy-dispersive X-ray (EDX) techniques. The growth mechanism of the rods is investigated and the effects of vapor pressure and partial melting of Na-rich regions are discussed. The magnetic measurements show an antiferromagnetic phase transition at 25K and the μeff is determined as 3.41 and 3.24μB from the χ–T curve and theoretical calculation, respectively. The electronic configuration and spin state of Mn3+ and Mn4+ are discussed in detail. The electrochemical properties of the cell fabricated using the nanorods are investigated and the peaks in the voltammogram are attributed to the diffusion of Na ions from different sites. Na intercalation process is explained by one and two Margules and van Laar models.

Preparation of LiMn<sub>2</sub>O<sub>4</sub> Microstructure by Low Temperature Solid-State Reaction for Cathode Material

This study aims at investigating a better condition of calcination at different temperature to produce LiMn2O4 microstructure. In this study, cubic LiMn2O4 was synthesized using a low temperature solid-state reaction. We report, here, MnO2 nanorods synthesis by reflux and their chemical conversion to LiMn2O4. The compound was characterized by XRD and TEM. Further, the analysis of LiMn2O4 microstructure was carried out by Direct Method using winPLOTR package program and Diamond using XRD data. At low calcination temperature, Mn2O3 is present as an impurity, but it disappears along with the increase in calcination temperature. It is also found that solid state reaction at is 750oC give nanoLiMn2O4. The lattice parameters and cell volumes of LiMn2O4 increases with the increase in heating temperature.

MnO2 nanorod catalysts for magnesium–air fuel cells: Influence of different supports

MnO2 nanorods adsorbed with different supports (non-support, carbon black, and MWCNTs) were prepared through hydrothermal method for magnesium–air fuel cells (MAFCs). The morphological characteristics of the catalysts indicate that the combination modes of nanorods and MWCNTs are parallel, cross, and bend intersect, which provide a large surface areas and enhance electron transfer process. X-ray diffraction pattern illustrates the crystal form of MnO2, and X-ray photoelectron spectroscopy reveals that the existing form of manganese is Mn4+. The ORR performance investigated using a rotating disk electrode shows that the initial reduction potential of MnO2/C and MnO2/MWCNTs in the LSV curves are −0.02 and 0.03 V vs. Hg/HgO (+0.098 V vs. NHE), respectively. The electron transfer number of MnO2/MWCNTs is 3.86, which corresponds to four electrons. In the I–t curves, the oxygen reduction current density of MnO2/MWCNTs decreases by 18.1% and MnO2/C decays by 27.9% after 60 h. The CVs reveal that the current density losses of MnO2/MWCNTs and MnO2/C are 0.4 and 0.8 mA cm−2 after scanning for 5000 cycles. The potential values of the air electrode loaded with MnO2/C and MnO2/MWCNTs catalysts are −0.78 and −0.62 V vs. SCE, respectively, at 150 mA cm−2, respectively. The discharge performance of a single-chamber MAFC shows that the peak power densities of MnO2/C and MnO2/MWCNTs are 60.95 and 70.47 mW cm−2, respectively, 20 °C in 10 wt% NaCl solutions. The single cells of MnO2/MWCNTs can continuously discharge for more than 24 h at a current density of 20 mA cm−2. The EIS proves that the conductivity of MnO2/MWCNTs is higher than MnO2/C.