Growth Of MnO2 Research Articles

Highly Nanoporous Nickel Foam as Current Collectors in 3D All-Solid-State Microsupercapacitors.

This study reports a streamlined method for producing a highly nanoporous current collector with a substantial specific surface area, serving as an electrode for microsupercapacitors (MSCs). Initially, commercial Ni foams are patterned into an interdigitated structure by laser cutting. Subsequently, the Ni foams are infused with NiO nanopowders through dip coating, sintering, and reduction in an H2 atmosphere, followed by the growth of MnO2 through a redox reaction. The incorporation of NiO within this three-dimensional Ni current collector results in notable porosity within the range of approximately 200-600 nm. Such a 3D, highly nanoporous electrode dramatically increases the specific surface area by 30 times and substantially boosts the amount of active material deposition, surpassing those of commercially available Ni foams. Performance evaluations of this highly nanoporous electrode in a 1 M KOH solution demonstrate an areal capacity of 19.3 F/cm2, retaining more than 95% capacitance at 5 mA/cm2, and exhibiting an energy density of 671 μW h/cm2, 25 times greater than commercial Ni foams. Moreover, in the realm of solid-state applications for MSCs, the remarkably high porous electrode achieves a commendable areal capacity of 7.22 F/cm2 and an energy density of 263.9 μW h/cm2, rendering it exceptionally suitable for use in MSC applications.

The function of phenylphosphonic acid on diversifying the property of manganese dioxide applied in the aqueous zinc-ion battery

The manganese-based rechargeable aqueous zinc-ion batteries have garnered significant attention due to their advantageous properties including high theoretical specific capacity, low cost, simple preparation, and environmental friendliness. The properties of the manganese-based cathode material depend strongly on its crystalline structure, the particle size, the morphology, and the functional elements, which plays a crucial role in further determining the electrochemical performance of the battery system. In this study, we disclose a distinctive function of phenylphosphonic acid (H2PP) in diversifying the intrinsic properties and electrochemical performance of manganese dioxide (MnO2) as the cathode material in the aqueous zinc-ion battery. By adding H2PP during preparation, the growth of MnO2 can be induced to form γ-MnO2 and α-MnO2, depending on the amount of H2PP used, in contrast to β-MnO2 prepared without the addition of H2PP. Moreover, the morphology of the cathode material can also be differentiated. Additionally, MnO2 can be functionalized by P-based groups from H2PP. By incorporating 0.5 % H2PP, a porous γ-MnO2 with a large specific surface area and high ionic conductivity is formed, which results in the battery exhibiting a high specific capacity of 225 mAh/g at the current density of 1 A/g, along with decent cycling performance.

Adjusting Competitive Reaction to Control Nucleation and Growth of MnO2 for a High-Stress Output Electrochemical Actuator

Adjusting Competitive Reaction to Control Nucleation and Growth of MnO₂ for a High-Stress Output Electrochemical Actuator

Boosting the Areal Capacity of Titanium-Manganese Single Flow Battery by Fe2+ /Fe3+ Redox Mediator.

Aqueous manganese-based flow batteries (AMFBs) have attracted great attention due to the advantages of low cost and environmental friendliness. Extending the cycle life of AMFBs has long been a challenging theme. The titanium-manganese single-flow batteries (TMSFB) are promising due to their special structure and electrolyte composition. However, TMSFB with high areal capacity faces capacity decay for unknown reasons. In this work, the capacity decay mechanism (accumulation and growth of MnO2 ) is clarified by a homemade in situ microscope system. Given that, a redox mediator of Fe2+ /Fe3+ is specially designed to boost the areal capacity of TMSFB without side reaction. The directional promoting principle of the Fe2+ /Fe3+ is elaborated in detail. Fe2+ chemically reacts with the residual MnO2 to form Fe3+ , which is reduced to Fe2+ by the electrochemical reaction. And then Fe2+ continues reacting with MnO2 until MnO2 is consumed completely. As a result, the TMSFB with the areal capacity of ≈55mA h cm-2 can stably operate at a current density of 40mA cm-2 , which is the highest areal capacity reported in aqueous manganese-based batteries. This work provides a new strategy for boosting the capacity of manganese-based batteries, shedding light on the improvement of other deposition-type batteries.

Oxygen‐Generated Hierarchical‐Structured AuNRs@MnO2@SiO2 Nanocarrier for Enhanced NIR‐ and H2O2‐Responsive Mild‐Hyperthermia Photodynamic/Photothermal Combined Tumor Therapy

AbstractTumor hypoxia greatly restricts photodynamic therapy (PDT) efficiency. Photothermal therapy (PTT) implemented at high temperatures induces local skin burning and surrounding tissue damage. Herein, an near‐infrared (NIR)‐ and H2O2‐double responsive heat‐ and O2‐generating core–shell–shell AuNRs@MnO2@SiO2 nanocarrier with Au nanorods (AuNRs) as core and MnO2 as sandwiched nanolayer is developed to realize enhanced photodynamic/photothermal combined tumor therapy at mild‐hyperthermia temperatures. Coating poly‐l‐lysine on AuNRs is capable of preventing AuNRs from aggregation and facilitating the on‐site growth of MnO2. The mesoporous SiO2 nanoshell provides large loading sites for payload indocyanine green (ICG). The MnO2 nanolayer greatly enhances the singlet oxygen (1O2) generation efficiency of ICG both in testing tubes and in cancer cells. Consequently, the O2‐enhanced PDT endows the AuNRs@MnO2@SiO2‐ICG nanoparticles (NPs) dramatically stronger antitumor effect both in vitro and in vivo. Their tumor growth inhibition ratio (67.6%) is significantly higher than that of AuNRs@SiO2‐ICG (28.5%) after one dose intratumor injection and NIR irradiation. Together with their good biosafety, the AuNRs@MnO2@SiO2‐ICG is promisingly translational. The multifunctionality should provide the AuNRs@MnO2@SiO2 NPs a nanocarrier platform for various therapeutic agents to modulate the tumor microenvironment and enhance tumor therapy efficiency.

Effects of CTAB and SDS on the nucleation and growth of MnO2 and Ag-doped MnO2 nanoparticles formation

Permanganate (MnO4−) redox reaction with cysteine and sodium borohydride (NaBH4) were studied spectrophotometrically in absence and presence of cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium dodecyl sulphate (SDS) surfactants. Water soluble dark brown color MnO2 was formed as the stable product with CTAB and SDS. Absorbance of MnO4− at 526 nm increases with CTAB concentrations. The order of mixing of CTAB and reducing agents (cysteine and NaBH4) have significant effect on the redox reactions of MnO4−. The MnO4− purple color was not decolorized in a reaction system containing CTAB + MnO4− + NaBH4. These observations can be rationalized due to the strong MnO4− and BH4− electrostatic interactions with the ionized CTAB. Such type of observations were not noticed with SDS. Cationic and anionic head groups of CTAB and SDS were responsible to the incorporation as well as exclusion of MnO4−, cysteine, and BH4− from the Stern-layer of both micelles. Ag-Doped MnO2 was prepared using seedless and seed growth methods with SDS and CTAB. Morphology of MnO2 and Ag-Doped MnO2 were determined with SEM, EDX, XRD, and FTIR.

Remove elemental mercury from simulated flue gas by flower-like MoS2 modified with nanoparticles MnO2

In this work, MoS2/MnO2 synthesized by hydrothermal methods was employed to remove Hg0 in flue gas. Benefited from the growth of MnO2 on the surface of MoS2, the specific surface area of the Mm adsorbent has increased. Compared with pure MoS2, specific surface area of Mm-30 has increased by 26.0287 m2/g. The MoS2 modified with 30 w.t. % MnO2 revealed higher mercury removal performance at 120 °C, which reached 93%. The oxidation of mercury over Mm-30 is proposed to follow Mars-van Krevelen mechanism, whereby the lattice oxygen in the adsorbent is consumed. In presence of NO, HCl, O2 and SO2, the effect of different concentrations on mercury oxidation is observed. Mm-30 adsorbent reveals stable mercury removal performance in the presence of NO and HCl, while it also exhibited good sulfur resistance under the condition of 400 ppm SO2 + N2. This phenomenon indicates that the adsorbent can be applied in power plants with medium concentrations of SO2, which facilitated the application of Mm-30 as a potential mercury removal adsorbent for power plants.

An Advanced Dual‐Function MnO2‐Fabric Air Filter Combining Catalytic Oxidation of Formaldehyde and High‐Efficiency Fine Particulate Matter Removal

AbstractComprehensive treatment of indoor contaminants such as volatile organic compounds (VOCs) and fine particulate matter (PM2.5) using transition metal oxide catalysts or functional fibrous filters has gained substantial attention recently. However, coupling VOC oxidation catalysts into high‐performance filter systems remains a challenge. Herein, an overall solution to strongly bind manganese dioxide (MnO2) nanocrystals onto polypropylene (PP) nonwoven fabrics is provided. For the first time, uniform heterogeneous nucleation and growth of MnO2 onto PP nonwoven fabrics using intermediate inorganic nucleation films, including Al2O3, TiO2, and ZnO, formed conformally on the fabrics via atomic layer deposition (ALD) are demonstrated. How different ALD thin films influence the crystallinity, morphology, surface area, and surface oxygen species of the MnO2 grown ALD‐coated PP fibers is further investigated. In addition to uniformity and integrity, ZnO thin films give rise to MnO2 crystals with the largest fraction of available surface oxygen, enabling 99.5% catalytic oxidation of formaldehyde within 60 min. Moreover, the metal oxide filters provide excellent PM removal efficiencies (ePM), achieving ePM2.5 90% and ePM10 98%, respectively, making the approach an outstanding method to produce fully dual‐functional filtration media.

In Situ MOF-Templating of Rh Nanocatalysts under Reducing Conditions

Manganese-based metal–organic frameworks (MOFs) metalated with Rh were used as pre-catalysts for CO2 hydrogenation. Activated insitu (80% H2, 20% CO2, 350°C), the resulting templated catalysts displayed CO2 conversion of up to 20%, with CH4 as the main product. Used catalysts were compared with samples templated in 5% H2/Ar at 350°C using powder X-ray diffraction, electron microscopy, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy. It was found that under reducing atmosphere Rh0 nanoparticles formed and organic MOF components decomposed, which allowed growth of MnO or MnCO3 and the formation of a mesh of catalytic Rh0 nanoparticles.

Spontaneous reductive decomposition behavior of hydrogen permanganate in water for chemical decontamination of nuclear power plants

The spontaneous reductive decomposition behavior of HMnO4 in water as a function of the initial HMnO4 concentration and reaction temperature was investigated. The decomposition of HMnO4 was fast in the early stage of the reaction and thereafter slowed down significantly, regardless of the initial HMnO4 concentration. The loss of HMnO4 by spontaneous reductive decomposition increased with increasing reaction temperature. Based on the experimental results and the classical nucleation theory, a mathematical model was developed using a combination of two first-order reactions representing the nucleation and crystal growth of MnO2 to predict the spontaneous reductive decomposition behavior of HMnO4.

Tuning the property of Mn-Ce composite oxides by titanate nanotubes to improve the activity, selectivity and SO2/H2O tolerance in middle temperature NH3-SCR reaction

Mn-Ce composite oxides were regarded as a promising alternative to substitute V-based catalysts for the abatement of NOx. However, the obstacles in activity, selectivity and SO2/H2O tolerance still remained. In this paper, titanate nanotubes (TNTs) were used to tune the property of Mn-Ce composite oxides and led to an outstanding catalytic performance in selective catalytic reduction of NO by NH3 within middle temperature region. Compared with conventional MnCe/TiO2 and V2O5/TiO2 nanoparticle catalysts, a higher NO conversion with good SO2/H2O tolerance could be observed at 200–300°C over the prepared MnCe/TNTs catalyst. More interestingly, much lower N2O concentration was detected in the SCR reaction over this catalyst. Characterization results revealed that MnCe/TNTs had larger BET surface area and greatly enhanced NH3 adsorption, which were beneficial to SCR activity. Moreover, the growth of MnO2 was improved and the redox property of the catalyst was tuned in the nano-confined space of TNTs. Thus the oxidative abstraction of hydrogen from ammonia was suppressed, resulting in less N2O production.

A facile one-step approach to hierarchically assembled core–shell-like MnO2@MnO2 nanoarchitectures on carbon fibers: An efficient and flexible electrode material to enhance energy storage

Hierarchical core–shell-like MnO2 nanostructures (NSs) were used to anchor MnO2 hexagonal nanoplate arrays (HNPAs) on carbon cloth (CC) fibers. The NSs were prepared by a novel one-step electrochemical deposition method. Under an external cathodic voltage of -2.0 V for 30 min, hierarchical core–shell-like MnO2-NS-decorated MnO2 HNPAs (MnO2 NSs@MnO2 HNPAs) were uniformly grown on CC with reliable adhesion. The phase purity and morphological properties of the samples were characterized by various physicochemical techniques. At a constant external cathodic voltage, growth of MnO2 NSs@MnO2 HNPAs on CC was carried for different time periods. When utilized as a flexible, robust, and binder-free electrode for pseudocapacitors, the hierarchical core–shell-like MnO2 NSs@MnO2 HNPAs on CC showed clearly enhanced electrochemical properties in 1 M Na2SO4 electrolyte solution. The results indicate that the MnO2 NSs@MnO2 HNPAs on CC have a maximum specific capacitance of 244.54 F/g at a current density of 0.5 A/g with excellent cycling stability compared to that of bare MnO2 HNPAs on CC (112.1 F/g at 0.5 A/g current density). We believe that the superior charge storage performance of the pseudocapacitive electrode can be mainly attributed to the hierarchical MnO2 NSs@MnO2 HNPAs building blocks that have a large specific surface area, offering additional electroactive sites for efficient electrochemical reactions. The facile and single-step approach to growth of hierarchical pseudocapacitive materials on textile based electrodes opens up the possibility for the fabrication of high-performance flexible energy storage devices.

Preparing MnO 2/PSS/CNTs composite electrodes by layer-by-layer deposition of MnO 2 in the membrane capacitive deionisation

It is of great interest to control the pore structure, conductivity and electrochemical activity properties of electrode materials, as their capacitance in the electrosorption process is determined by these properties. These properties can be modified effectively during the synthesis process. The layer-by-layer deposition approach was employed to prepare a manganese oxide (MnO 2)/carbon nanotubes (CNTs) composite. In this study, Polystyrene Sodium Sulfonate (PSS) facilitated the dispersion of CNTs and even growth of MnO 2. The resulting composite material was used for electrodes in the membrane capacitive deionisation (MCDI) process and a high salt removal efficiency of 96.8% was achieved, with an ion adsorption capacity of 80.4 μmol/g of MnO 2/PSS/CNTs electrode material. Conversely, a MnO 2/CNTs composite that was prepared using a hydrothermal synthesis process did not show such excellent advantages.

Magnetic-Field-Assisted Hydrothermal Growth of Manganese Dioxide Nanostructures and their Phase Transformation

MnO2 nanostructures were successfully synthesized by a magnetic-field-assisted hydrothermal approach. By applying a pulsed magnetic field to the reaction system, the crystal phase transformation progress of MnO2 at different temperature has been changed comparing to those synthesized without magnetic field. The effect of pulsed magnetic field on the growth of MnO2 was investigated by tracking the phase of the sample by using X-ray diffraction. It is found the pulsed magnetic field has an obvious effect on the nucleation and growth of MnO2 nanostructures and therefore influences the phase transformation.

HYDROTHERMAL SYNTHESIS OF NANOCRYSTAL MNO2 UNDER PULSED MAGNETIC FIELD

Nanocrystal MnO 2 was successful synthesized by hydrothermal method under pulsed magnetic field. The effect of pulsed magnetic field on the nucleation and growth of MnO 2 was studied by XRD and SEM analysis. It was found that the morphology of MnO 2 has been changed comparing without magnetic field. However, there were no different phases presented when pulsed magnetic field was applied.

Epitaxial stabilization of MnO(111) overlayers on a Pd(100) surface

The growth of epitaxial MnO(100) and MnO(111) layers on Pd(100) surface has been investigated by spot-profile analysis low-energy electron diffraction, dynamic atomic force microscopy, photoemission and high-resolution electron energy loss spectroscopy, and density functional theory. We have found that despite the large lattice mismatch to the Pd(100) substrate, the MnO(100) layers are kinetically stabilized at low temperatures $(\ensuremath{\leqslant}350\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C})$ and at oxygen pressures between $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ and $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}\phantom{\rule{0.3em}{0ex}}\mathrm{mbar}$. Annealing in ultrahigh vacuum at $650\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ or, alternatively, deposition of manganese metal in oxygen pressure $l1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}\phantom{\rule{0.3em}{0ex}}\mathrm{mbar}$ causes the transformation of the MnO(100) to a polar MnO(111) surface, which is decorated by triangular pyramids with (100) side facets. It is suggested that the growth of MnO(111) layers is energetically preferred over MnO(100) due to the epitaxial stabilization at the metal-oxide interface.