MnO2 Nanowires Research Articles

MnO2 nanowires electrodeposited on freestanding graphenated carbon nanotubes as binder-free electrodes with enhanced supercapacitor performance

MnO2 nanowires/graphenated carbon nanotubes (CNTs) have been fabricated on stainless steel (SS) substrate through chemical vaporous deposition (CVD) and electrodeposition method as binder-free supercapacitor electrodes. The MnO2 nanowires/graphenated CNTs nanocomposites have high areal capacitance of 492.5 mF/cm2 (615.6 F/g) at the current density of 0.5 mA/cm2 and outstanding energy density of 985 Wh/m2 with power density of 2.98 kW/m2. After 5000 cycles at 0.5 mA/cm2, the capacity retention of the MnO2/graphenated CNTs is still maintained 95% of the initial capacitance, suggesting exceptional capacitance retention and superior stability. The predominant electrochemical performance of the MnO2/graphenated CNTs is contributed to the synergistic effects of high conductivity of graphenated CNTs and high pseudocapacitance of MnO2 nanowires.

Transition of hexagonal to square sheets of Co3O4 in a triple heterostructure of Co3O4/MnO2/GO for high performance supercapacitor electrode

Cobalt oxide and manganese oxides are promising electrode materials amongst the transition metal oxides (TMOs) for pseudocapacitors. The lack of reversibility and deterioration of capacitance at higher current densities is major flaw in Co3O4 as an electrode for supercapacitor while MnO2 suffers from low electrical conductivity and poor cycling stability. It is inevitable to bridge the performance gap between these two TMOs to obtain a high performance supercapacitor based on environmental benign and earth abundant materials. Herein, we fabricated a hybrid triple heterostructure high-performing supercapacitor based on hexagonal sheets of Co3O4, MnO2 nanowires and graphene oxide (GO) to form a composite structure of Co3O4/MnO2/GO by all hydrothermal synthesis route. The Co3O4 square sheets serves as an excellent backbone with good mechanical adhesion with the current collector providing a rapid electronic transfer channel while the integrated nanostructure of MnO2 NW/GO permits more electrolyte ions to penetrate capably into the hybrid structure and allows effective utilization of more active surface areas. A triple heterostructured device exhibits a high areal capacitance of 3087 mF cm−2 at 10 mV s−1 scan rate along with the exceptional rate capability and cycling stability having capacitance retention of ∼170% after 5000 charge/discharge cycles. The TMOs based pseudocapacitor with the conducting scaffolds anchoring based on graphene derivatives like this will pave an encouraging alternatives for next generation energy storage devices.

MnO2-decorated hierarchical porous carbon composites for high-performance asymmetric supercapacitors

In this study, the growth of 1-dimensional manganese oxide (δ-MnO2) nanowire on hierarchical ordered mesoporous carbons/graphene composites (C) was synthesized by a relatively low-cost, simple, effective and eco-friendly redox process. It is found in both experimental results and theoretical simulations that the carbon surface, especially the mesoporous channels of ordered mesoporous carbons (amorphous carbons), would be favorable to serve as the nucleated sites for the growth of MnO2 nanowires. Likewise, the strong adsorptive interactions between MnO2 and amorphous carbons result in the high deposition efficiency of MnO2 on C (98%) and the outstanding stability of MnO2-decorated hierarchical porous carbon composites (MnO2@C) together with the relatively low equivalent series resistance. This electrode material exhibits excellent electrochemical behavior with a specific capacitance high up to 756.2 F g−1 in KOH electrolytes. In addition, an asymmetric supercapacitor (ASCs) assembled by using MnO2@C and C as the positive and negative electrodes in 1.0 M Na2SO4 solution achieves a maximum energy density of 34.56 Wh kg−1 at a power density of 450 Wkg-1 and excellent cycling stability. The results demonstrate the MnO2-decorated hierarchical porous carbon composites are promising candidates for the future high-performance supercapacitors.

Synthesis of lithium rich layered oxides with controllable structures through a MnO2 template strategy as advanced cathode materials for lithium ion batteries

The electrochemical performance of lithium ion batteries depend largely on the structural properties of electrode materials. In this work, we propose an approach to synthesize lithium-rich layered oxides (LLOs) materials using a manganese dioxide (MnO2) template strategy, which could control the structure and particle size of final products via choosing different MnO2 templates. Through precisely optimizing, we successfully prepare cross-linked nanorods (CLNs) and agglomerate microrods (AMs) Li1.2Ni0.15Co0.1Mn0.55O2 cathode materials by using carbon-decorated MnO2 nanowires and MnO2 nanorods as templates, respectively. The lithium ion battery based on the CLNs exhibits excellent performance, delivering a high capacity of 286.2 mAh g−1 at 0.1 C and 237.5 mAh g−1 at 1 C. In addition, the device remains 98% and 89% of its initial capacity after 50 cycles at 0.1 C and 100 cycles at 1 C, respectively. The remarkable electrochemical performance can be mainly attributed to the cross-linked nanorods structure which can provide relatively shorter lithium ion diffusion length, larger reaction surface and more internal cavity. This universal structure engineering strategy may shed light on new material structures for high performance lithium-rich layered oxide cathode materials.

Shape control and selective decoration of Zn2SnO4 nanostructures on 1D nanowires: Boosting chemical–sensing performances

One–dimensional (1D) heterostructures are promising for the fascinating physical/chemical properties. However, the selective deposition of innovative materials as efficient active sites on the backbone material is still challenging and meaningful. Herein, a universal strategy is presented to synthesize the novel 1D heterostructure, which is constituted of Mn3O4 nanowires (Mn3O4 NWs) and nano–sized Zn2SnO4 subunits with controllable morphologies including Zn2SnO4 nanorods (Zn2SnO4 NRs), Zn2SnO4 nanocubes (Zn2SnO4 NCs) and Zn2SnO4 nanooctahedrons (Zn2SnO4 NOs). The 1D Mn3O4/Zn2SnO4 heterostructure is proved to generate abundant surface adsorbed oxygen molecules to modulate the sensing activity in chemical sensors (CSs) for application in the acetone vapor detection. The developed gas sensor shows enhanced responses, ultrafast response time and great stability. The selective deposition method and interface engineering will open up an avenue to design the heterostructured nanomaterials for high–performance CSs and other potential applications.

Silver-Quantum-Dot-Modified MoO3 and MnO2 Paper-Like Freestanding Films for Flexible Solid-State Asymmetric Supercapacitors.

Free-standing paper-like thin-film electrodes have great potential to boost next-generation power sources with highly flexible, ultrathin, and lightweight requirements. In this work, silver-quantum-dot- (2-5 nm) modified transition metal oxide (including MoO3 and MnO2 ) paper-like electrodes are developed for energy storage applications. Benefitting from the ohmic contact at the interfaces between silver quantum dots and MoO3 nanobelts (or MnO2 nanowires) and the binder-free nature and 0D/1D/2D nanostructured 3D network of the fabricated electrodes, substantial improvements on the electrical conductivity, efficient ionic diffusion, and areal capacitances of the hybrid nanostructure electrodes are observed. With this proposed strategy, the constructed asymmetric supercapacitors, with Ag quantum dots/MoO3 "paper" as anode, Ag quantum dots/MnO2 "paper" as cathode, and neutral Na2 SO4 /polyvinyl alcohol hydrogel as electrolyte, exhibit significantly enhanced energy and power densities in comparison with those of the supercapacitors without modification of Ag quantum dots on electrodes; present excellent cycling stability at different current densities and good flexibility under various bending states; offer possibilities as high-performance power sources with low cost, high safety, and environmental friendly properties.

One Step Synthesis of One Dimensional Nano MnO2 and Their Application as Oxidizing Agent for Polysulfide Polymers

In this work, MnO2 nanowires and nanorods have been prepared via a simple hydrothermal reaction. The morphology of MnO2 can be easily controlled by the change of the mole ratio of Mn7+ to Mn2+. And the obtained products are well characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), the high-resolution TEM (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectrometer (XPS), etc. The obtained MnO2 samples are employed as the curing agent for polysulfide sealant. The maximum torque of the polysulfide polymer cured by MnO2 nanowires is the highest. The performances are verified by rheological tests of the curing profile, mechanical analysis, and tensile strength tests. The results demonstrate that both of the nanowires and nanorods have excellent vulcanization effects and reinforcing effects in comparison with commercial MnO2. The surface area, structure, and morphology of MnO2 are used to analyze the possible reasons for their promising application in vulcanizing agents for polysulfide rubber.

Single atomic Ag enhances the bifunctional activity and cycling stability of MnO2

Heterogeneous electrocatalyst with single atom feature has attracted great interests. Although significant progress has been made on constructing and understanding carbon supported single atom electrocatalysts (SAECs), few attentions has been paid to metal oxide supported SAECs. The effect of single atom in enhancing electrocatalytic activity and stability of metal oxides has been poorly understood. Here, we reported MnO2 nanowires loaded with single atomic Ag (Ag-MnO2) that can simultaneously catalyze oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). The incorporation of Ag into the crystal framework of α-MnO2 provided multiple benefits including an improved conductivity and a substantial increase in both lattice distortion and oxygen vacancies. As a result, Ag-MnO2 outperformed α-MnO2 in oxygen electrocatalysis and showed ∼3-fold enhancement in kinetic current density. The Zinc air battery containing the Ag-MnO2 displayed a high discharge peak power of 273.2 mW cm−2, an energy density of 915.4 Wh kgZn−1 and an outstanding rate performance. The Zinc air battery (ZAB) stably operated up to 3200 cycles of charge-discharge. Such excellent rechargeability can be ascribed to the promoted crystal phase transformation from α-MnO2 to δ-MnO2 that is beneficial for OER due to the presence of atomic Ag.

MnO2 nanowires/CNTs composites as efficient non-precious metal catalyst for oxygen reduction reaction

The non-precious metal catalyst for oxygen reduction reaction (ORR) is highly demanding due to the increasing global energy challenge. A 3-D network composed of MnO2 nanowires and carbon nanotube (CNT) was synthesized via crystal growth of MnO2 under hydrothermal and annealing process. The composite was characterized by PXRD, SEM and TEM. Due to its unique structure, the MnO2/CNT composite exhibits superior electrocatalytic performance towards ORR in alkaline medium compared to the commercial Pt/C in terms of the current density, methanol tolerance and long-term durability. These prominent electrochemical performances along with low cost and high abundance of the synthesized MnO2/CNT make it a promising cathode material in fuel cells.

MnO2 nanowires tuning of photoluminescence of alloy Cu/Ag NCs and thiamine enables a ratiometric fluorescent sensing of glutathione

By tuning the photoluminescence of alloy Cu/Ag nanoclusters (NCs) and thiamine (VB1) simultaneously through MnO2 nanowires, we report a simple and label-free ratiometric fluorescent platform for sensitively and selectively sensing of glutathione (GSH). Ag doping of Cu NCs significantly enhances the quantum yield (QY, about 2-fold enhancement), oxidation resistance to air, storage stability (60 days versus 1 day), photostability and salt stability of the resultant Cu/Ag NCs. Impressively, MnO2 nanowires quench the fluorescence of Cu/Ag NCs, while they enhance the fluorescence of nonfluorescent VB1 via oxidation reaction between VB1 and dissolved oxygen to produce oxVB1 as a nanozyme catalyst. Upon introduction of GSH as a target, the MnO2 nanowires are reduced to Mn2+ and lose their quenching capacity and oxidase-like activity, resulting in FL recovery of Cu/Ag NCs and fluorescent decrease of oxVB1. Hence, a ratiometric luminescence signal is obtained, providing a novel ratiometric fluorescent strategy for detecting GSH through target induced regulation of the catalytic activities and quenching ability of MnO2 nanowires. The sensor exhibited a wide linear concentration range (10 nM to 70 μM) for GSH with a detection limit of 6.5 nM. The ratiometric sensor was successfully used for GSH detection in biological samples.

Bionics-Inspired Strong Coupling of Streptococcus-Like NiCo2O4 to Needle-Like MnO2 for Enhanced Electrocatalytic Determination of Glucose

Bionics-inspired streptococcus-like NiCo2O4 coated needle-like MnO2 architecture has been synthesized successfully, denoted as NiCo2O4-MnO2, and the nonenzymatic electrochemical sensor based on NiCo2O4-MnO2 exhibits highly sensitive determination toward glucose. MnO2 nanowires are regarded as effective nucleation sites, which allows uniformly growing of NiCo2O4 as electrocatalytic centers on its surface by a hydrothermal method. The rational combination of streptococcus-like NiCo2O4 and needle-like MnO2 can effectively prevent the aggregation of nanomaterials due to the formation of 3D network, promote the electron transportation, and provide more electrocatalytic sites. The attractive nanostructure and composition were better confirmed by scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy, etc. The strong coupling of NiCo2O4-MnO2 inspires the synergistic effect, showing a low detection limit of 0.036 μM (S/N = 3) for glucose in 0.1 M NaOH, a high sensitivity of 2887.57 μAmM−1cm−2 and a wide response range (from 1 to 7100 μM). Moreover, the novel sensor exhibited high stability and good reproducibility. The sensor was highly selective to glucose in the presence of commonly interfering species like dopamine, uric acid, ascorbic acid, sodium chloride, fructose, galactose and mannose, and successfully applied to sensing glucose concentration in human serum samples.

A technology of preparing MnO2 nanowire from the low grade manganese ore

Manganese dioxide nanowire was synthesized from the low grade manganese dioxide ore by hydrothermal method Low grade manganese ore was firstly reduced to be dissolvable MnO by mixing reductant of the sawdust in ceramic crucible at deg C the reduced ore was leached with diluted sulfuric acid to be MnSO solution at deg C in min The obtained MnSO solution was mixed with KMnO solid particle in homogeneous reactor to prepare MnO nanowire the optimized experimental conditions are that the mole ratio of MnSO KMnO is pH value of the solution is the reaction temperature is deg C the reaction time is h and the stirring speed is Hz The MnO nanowire with alpha MnO crystal structure was characterized by X ray diffraction XRD and scanning electron microscope SEM

Capture and elimination of Staphylococcus aureus based on Langmuir–Blodgett MnO2 nanowire monolayer promotes infected wound healing

An antibacterial membrane, consisting of PDMS and TBBPA coated with a human immunoglobulin G modified MnO2 nanowire monolayer, was applied to capture and eliminate Staphylococcus aureus and promote infected wound healing.

Surface Gradient Ti-Doped MnO2 Nanowires for High-Rate and Long-Life Lithium Battery.

Cryptomelane-type α-MnO2 has been demonstrated as a promising anode material for high-energy Li-ion batteries because of its high capacity and intriguing [2 × 2] tunnel structure. However, applications of MnO2 electrode, especially at high current rates and mass active material loading, are limited by the poor mechanical stability, unstable solid electrolyte interphase layer, and low reversibility of conversion reactions. Here, we report a design of homogeneous core-shell MnO2 nanowires (NWs) created by near-surface gradient Ti doping (Ti-MnO2 NWs). Such a structurally coherent core-shell configuration endowed gradient volume expansion from the inner core to the outer shell, which could effectively release the stress of the NW lattice during cycling and avoid pulverization of the electrode. Moreover, the gradiently doped Ti is able to avoid the Mn metal coarsening, reducing the metal particle size and improving the reversibility of the conversion reaction. In this way, the Ti-MnO2 NWs achieved both high reversible areal and volumetrical capacities (2.3 mA h cm-2 and 991.3 mA h cm-3 at 200 mA g-1, respectively), a superior round-trip efficiency (Coulombic efficiency achieved above 99.5% after only 30 cycles), and a long lifetime (a high capacity of 742 mA h g-1 retained after 3000 cycle at 10 A g-1) at a high mass loading level of 3 mg cm-2. In addition, the detailed conversion reaction mechanism was investigated through in situ transmission electron microscopy, which further evidenced that the unique homogeneous core-shell structure could largely suppress the separation of core and shell upon charging and discharging. This new NW configuration could benefit the design of other large-volume-change lithium battery anode materials.

Biological cell template synthesis of nitrogen-doped porous hollow carbon spheres/MnO2 composites for high-performance asymmetric supercapacitors

Nitrogen-doped porous hollow carbon spheres were fabricated via hydrothermal pre-carbonization and pyrolysis carbonization using yeast cell templates. After that, the MnO2 nanowires were deposited by the in-situ hydrothermal reaction. By controlling the reaction concentration, various MnO2 nanostructures with different morphologies and electrochemical properties were obtained. The as-prepared sample exhibited an ultrahigh specific capacitance of 255 F g-1 at a current density 1 A g-1 in 1 M Na2SO4 electrolyte. The MnO2/HCS-30 material was used as the positive electrode, and the HCS was used as the negative electrode to assemble the asymmetric supercapacitor. The maximum energy density operating at the 2.0 V voltage window is 41.4 Wh kg−1 at a power density of 500 W kg−1 and still maintains 23.0 Wh kg−1 at a power density of 7901 W kg−1. Moreover, it displayed excellent cycle stability, retained approximately 93.9% of the capacitance after 5000 cycles. This work innovatively combines biomass and energy, provides an environmentally benign strategy and new insights for the preparation of electrode materials.

Conversion of electrolytic MnO2 to Mn3O4 nanowires for high-performance anode materials for lithium-ion batteries

A simple and versatile approach has been implemented for the preparation of some manganese oxide (MnxOy)-based lithium-ion battery anode materials from low-cost electrolytic manganese dioxide (EMD). Depending on the additive, calcination temperature and time used in the preparation, the raw EMD exhibits different nano−/micro-structure morphologies, confirmed from X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). The specific capacity (obtained at 100mAg−1) of the MnO2 nano-rods/wires, Mn2O3 nano-particles and Mn3O4 of mixed morphology (i.e., nano-rods/wires and nanoparticles) were approximately 710, 830 and 850mAhg−1, respectively. Of the various MnxOy investigated, the Mn3O4 nanowires obtained at 600°C within 2h showed enhanced rate capability properties, long-term cycling stability and the best Li-ion and electronic transportation, suggesting that the formation of the solid-electrolyte interphase (SEI) film during the first cycle protected these anode materials against possible electrolyte decomposition. The high-performance of this Mn3O4 anode material is ascribed to its 1-D nanostructures (nano-rods/wires) which confers on it high aspect ratios, large pore size as well as the ability to serve as efficient electron transport channels or interconnects. This study provides the first insight into the viability of Mn3O4 as an anode material for lithium-ion battery, and opens doors of opportunity for the development of energy storage materials from the low-cost EMD precursor.

A Conductive and Highly Deformable All‐Pseudocapacitive Composite Paper as Supercapacitor Electrode with Improved Areal and Volumetric Capacitance

Flexible energy storage electronics have gained increasing attention in recent years, but the simultaneous acquiring of high volumetric and high areal capacities as well as excellent flexibility in order to truly implement wearable and portable electronics in practice remains challenging. Here, a conductive and highly deformable freestanding all-pseudocapacitive paper electrode (Ti3 C2 Tx /MnO2 NWs) is fabricated by solution processing of hybrid inks based on Ti3 C2 Tx MXene and ultralong MnO2 nanowires. The resulting Ti3 C2 Tx /MnO2 NWs hybrid paper manifests a remarkable areal capacitance of up to 205 mF cm-2 and outstanding volumetric capacitance of 1025 F cm-3 . Both the values are highly comparable with, or in most cases much higher than those of previously reported MXene-based flexible electrodes. The excellent energy storage performance is well maintained with a capacitance retention of 98.38% during 10 000 charge-discharge cycles. In addition, the flexible supercapacitor demonstrates excellent flexibility and electrochemical stability during repeated mechanical bendings of up to 120°, suggesting great potentials for the applications in future flexible and portable electronics.

Dual Responsive Enzyme Mimicking of Ternary Polyaniline–MnO2–Pd Nanowires and Its Application in Colorimetric Biosensing

In recent years, a significant challenge in material science has been to fabricate novel functional nanomaterials to mimic the function of natural enzymatic systems. Herein, ternary polyaniline (PANi)–MnO2–Pd nanowires (NWs) are synthesized through a two-step redox reaction process. The prepared PANi–MnO2–Pd NWs were explored to exhibit dual responsive enzyme-like efficiencies, e.g., peroxidase and oxidase-like activities. With the assistance of H2O2, the obtained ternary PANi–MnO2–Pd NWs were able to oxidize the typical peroxidase substrate of 3,3′,5,5′-tetramethylbenzidine (TMB) to yield the oxidized TMB with a blue color, exhibiting a much better peroxidase-like activity than the synthesized PANi–MnO2 NWs alone and Pd nanoparticles owing to the interfacial electron transfer effect among the components. In addition, in the absence of H2O2, the prepared PANi–MnO2–Pd NWs could also oxidize TMB to display an excellent oxidase-like activity. Based on the dual responsive enzyme-like characteristic of the obt...

Hydrothermal assembly of MnO-graphene core-shell nanowires with superior anode performance

Wide application of high capacity anode materials for Li ion batteries (LIBs) is hindered by their structural instability. Assembling graphene and high capacity nanostructures with tight interaction is highly desirable for obtaining high performance anode materials. Here, we report a novel hydrothermal synthesis of homogeneous graphene-wrapped MnO nanowires. MnCO3 anchors formed by the redox reaction between graphene oxide (GO) and MnOOH have helped to assemble the core-shell structured nanowires. With an optimized graphene amount, the graphene-wrapped MnO nanowires exhibit high reversible capacities at a low voltage platform ∼1 V (1185 mAh g−1 at 50 mA g−1), excellent rate performance (884 mAh g−1 at 500 mA g−1 and 508 mAh g−1 at 3 A g−1), high initial coulombic efficiency (86.3%), and long-term cyclic stability (undiminished after 500 cycles at 1 A g−1). These remarkable electrochemical performances in LIBs are significantly associated with the special core-shell conductive framework. Our results show that the highly reactive groups in GO can be used to in-situ assemble graphene-coated nanostructures, and that the MnO-graphene core-shell nanowires are promising anode candidate for LIBs.

Crosslinked MnO 2 Nanowires Anchored in Sulfur Self‐Doped Porous Carbon Skeleton with Superior Lithium Storage Performance

A facile process for the in-situ anchoring of crosslinked MnO2 nanowires (MNs) in a preformed sulfur self-doped porous carbon material (SPC) derived from antibiotic bacterial residues (ABRs) was developed, only involving impregnation of potassium permanganate aqueous solution into SPC and consequently occurring in-situ redox reaction at room-temperature. In the obtained [email protected] composite, SPC serves as a conductive collector for accelerating lithium-ion transfer and a buffer carrier for reliving the volume-expansion of MNs, and the in-situ formed MNs homogeneously anchored in SPC can fully imply potential electrochemical properties and enable the whole skeleton more stable to guarantee good cycling stability. The proposed approach can not only solve the environmental problems associated with the accumulation of ABRs, but also achieve the maximization of dual energy storage and conversion of the [email protected] composite by elaborately utilizing the combinative merits of SPC and MNs. As a result, the [email protected] composite shows a reversible capacity of 953.4 mAh/g at 0.2 A/g after 80 cycles, and 745.9 mAh/g at 1 A/g after 450 cycles when used as anode for lithium-ion batteries.