MnO2 Nanowires Research Articles

MnO2 Nanowires as an Electrode Material for Gel Polymer Electrolyte‐Based Zn‐Air Battery

AbstractZn‐air batteries (ZABs) have drawn an attention due to their high energy density, less complicated chemistry, and relatively low cost. Electrocatalyst plays a significant role in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) that occurs during the operation. Various valance states of manganese make MnO2 as an attractive electrocatalyst. In the present work, MnO2 nanowires with diameter of 80–90 nm are synthesized via hydrothermal route and tested for electrocatalytic performance in a comparative study of ZABs fabricated using liquid and gel polymer electrolytes (GPEs). The open circuit voltage (OCV) of device lies in the range of 1.35–1.4 V. GPEs based devices show higher stability and exhibited 45 cycles (20 min per cycle) having discharge plateau above 1.06 V at a discharge current density of 1.59 mA cm−2 while liquid electrolyte‐based devices show 20 cycles (4 min per cycle at discharge current rate of 3 mA cm−2).

Hydrothermal synthesis of NiO nanoparticles decorated hierarchical MnO2 nanowire for supercapacitor electrode with improved electrochemical performance

In this work, MnO2/NiO nanocomposite electrode materials have been synthesized by a cost-effective hydrothermal method. The effect of the concentrations (0, 1, 3, 5, and 7 wt%) of NiO nanoparticles on the surface morphology, structural properties, and electrochemical performance of the nanocomposites was characterized by different characterization techniques. The scanning electron micrographs (SEM) reveal that the as-prepared NiO nanoparticles are well connected and stuck with the MnO2 nanowires. The transmission electron microscopy (TEM) analysis showed an increase in the interplanar spacing due to the incorporation of NiO nanoparticles. The different structural parameters of MnO2/NiO nanocomposites were also found to vary with the concentration of NiO. The MnO2/NiO nanocomposites provide an improved electrochemical performance together with a specific capacitance as high as 343 F/g at 1.25 A/g current density. The electrochemical spectroscopic analysis revealed a reduction in charge transfer resistance due to the introduction of NiO, indicating a rapid carrier transportation between the materials interface. The improved electrochemical performance of MnO2/NiO can be attributed to good interfacial interaction, a large interlayer distance, and low charge transfer resistance. The unique features of MnO2/NiO and the cost-effective hydrothermal method will open up a new route for the fabrication of a promising supercapacitor electrode.

Single-atom Zn on MnO2 for selective nitrite electrolysis to ammonia

Electrochemical nitrite-to-ammonia reduction (NO2RR) represents an attractive method to simultaneously attain hazardous NO2− removal and renewable NH3 synthesis. In this study, we first design single-atom Zn anchored on MnO2 nanowires (Zn1/MnO2) as a highly active and durable NO2RR catalyst. Atomic-scale characterizations reveal that Zn single atoms are coordinated with three surface-O atoms of MnO2 to form Zn1-O3 units. A combination of in situ electrochemical measurements and theoretical computations unravel that Zn1-O3 units enhance the NO2− activation, stabilize the key intermediate of *NHO and lower the energy barrier of NO2−-to-NH3 hydrogenation process. Consequently, Zn1/MnO2 assembled in a special flow cell reactor achieves the highest NH3 yield rate of 1559.1 μmol h−1cm−2 and NH3-Faradaic efficiency of 95.3 % at −288.5 mA cm−2, superior to nearly all previously reported NO2RR electrocatalysts.

Controllable synthesis of NiCo2O4 nanoparticles supported on MnO2 nanowires with excellent oxidase-mimicking performance

In this work, we developed a facile approach to decorate NiCo2O4 nanoparticles on MnO2 nanowires, leading to the formation of 1D hierarchical heterostructures as efficient oxidase mimics for the detection of glutathione.

Ag-doped MnO2 nanowires integrated with graphitic carbon nitride for enhanced photocatalytic applications for waste water treatment

For the synthesis of Ag-doped MnO2 nano-wires-like morphology, the hydrothermal method was used. The composite of Ag-doped MnO2 nano-wires nanocomposite with g-C3N4 (Ag–MnO2/g-C3N4 (10 %) was made using an ultra-sonication approach. The formation of doped and un-doped MnO2 nano-wires (NWRs) was confirmed by XRD, and for the detection of functional groups, FTIR analysis was done. Surface morphology and optical analysis were done by SEM and UV–visible spectro-photometry. The Ag–MnO2/g-C3N4 (10 %) showed tremendous photo-catalytic efficiency towards MB and BA. Ag–MnO2/g-C3N4 (10 %) exhibited 51.38 % degradation of BA and 83.67 % of MB under visible light irradiation. Ag-doped MnO2 nano-wires (NWRs) exhibited better photo-catalytic efficiency as compared to bare MnO2. This work represents that the photo-catalyst Ag–MnO2/g-C3N4 (10 %) is capable of photodegradation of dyes and organic compounds as it has a greater potential for establishing a better green environment.

Nanowires-based MnO2-Ru/rGO: An efficient oxygen reduction reaction electrocatalyst

Oxygen Reduction Reaction (ORR) for clean energy is hindered by expensive Pt-based electrocatalysts, prompting efforts to replace it with alternative electrocatalysts. Thus, we started by synthesizing MnO2 nanowires through a hydrothermal approach, followed by the growth of ruthenium nanoparticles (Ru NPs) without surface modification, using just 2.0 wt% of the noble metal (MnO2-Ru). However, to further enhance the electrocatalyst's performance and reduce costs, we combined different ratios of reduced graphene oxide (rGO) with the electrocatalyst. X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy were employed to characterize the chemical composition and morphological properties of MnO2-Ru. These analyses identified the presence of the compounds during synthesis and confirmed the deposition of Ru NPs on the surface of MnO2 nanowires. The optimized MnO2-Ru/rGO demonstrated superior ORR activity than rGO, MnO2, and MnO2-Ru individually, with more positive onset potential (−0.054 V) and half-wave potential of −0.173 V. Notably, MnO2-Ru/rGO reduced oxygen via the four-electron transfer pathway. Furthermore, the higher stability and excellent methanol tolerance of MnO2-Ru/rGO compared to the commercial 20 wt% Pt/C indicates its suitability for fuel cells, maintaining approximately 70 % of its initial current after 8000 s.

Influence of phase structure of MnO2 for enhancing the electrochemical sensitivity of environmental pollutant chlortetracycline

Electrochemical sensing of chlortetracycline (CTC) using α and β- MnO2 nanowires has been studied. The influence of different phase structures (α and β) of MnO2 nanowires on the determination of chlortetracycline (CTC) was studied systematically. To enhance the sensitivity of MnO2, a high conductivity microporous carbon (MC) was employed as a support matrix for MnO2. The electrochemical sensing results illustrate that the α-MnO2 exhibited better electrochemical performance than β-MnO2. This better activity was correlated with its excellent properties like more exposed MnO6 edges, higher conductivity, and lowest average oxidation state . The kinetics study illustrated that the MnO2 modified electrodes perform much better than the bare electrodes. The number of electron transfer, electron transfer coefficient, and diffusion coefficient of CTC were calculated from the scan rate effect; the values are 1, 0.50, and 1.581 × 10−6 cm2 s−1 respectively. Amperometry was used to calculate the lowest detection limit (LOD) at a potential of 0.82 V. The α-MnO2/MC electrode exhibits a better linear range (1–55 µM) with a LOD value of 103 nM towards CTC. Furthermore, the proposed sensor exhibited better anti-interference ability towards KCl, kanamycin sulfate, zinc acetate, magnesium chloride, tetracycline, streptomycin sulfate, and oxytetracycline. The sensor's ability to accurately determine the level of CTC in samples of drinking water, tap water, poultry farm soil, and milk highlights its suitability for industrial applications. The developed sensor showed better reproducibility (RSD=0.45%) and repeatability (RSD=2.06%) towards CTC. Therefore, the proposed sensor can be used as a more practical platform for monitoring environmental contaminants.

Fabrication of multiple core-shell structures MnO@HsGDY@NC@HsGDY hybrid nanofibers for enhanced microwave absorption

Optimizing the structure and composition of emerging materials to produce efficient absorbers are one strategy for addressing electromagnetic pollution and radar stealth. For the first time, hydrogen-substituted graphdiyne (HsGDY) is used as a functional component for the preparation of microwave-absorbing materials in this paper. By using MnO2 nanowires as template and sequentially coating HsGDY, polydopamine (PDA) and HsGDY shell layers, MnO2@HsGDY@PDA@HsGDY nanowire precursors are obtained. The one-dimensional (1D) nanowires combine the advantages of multicomponent composite, multiple core-shell structures. After calcination, 1D microwave absorption absorber MnO@HsGDY@NC@HsGDY with multi-layer and core-shell structures is produced. The high conductivity of HsGDY enhances the material's dielectric loss, and the multiple heterogeneous interfaces in the material structure cause interface polarization, resulting in the excellent microwave absorption properties. MnO@HsGDY@NC@HsGDY exhibits the advantages of low filler content, thin matching thickness, strong microwave absorption capacity and wide effective absorption band (EAB). The minimum reflection loss (RLmin) can reach −68.57 dB@13.8 GHz@2.4 mm, and the EAB is 6.7 GHz as the filler content is 11 %. This work enriches the types of 1D materials and absorbers, expands the application fields of HsGDY, and provides a reference for the design and preparation of absorbers.

Enhanced separation properties of polyvinylidene membranes with MnO2 nanowire addition

In this study, novel MnO2-PVDF ultrafiltration membranes were prepared by incorporating MnO2 nanowires through the immersion-precipitation phase inversion process. Scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FT-IR) and X-ray powder diffraction (XRD) were employed to investigate the microstructure of the prepared membranes. The characterization results indicated that the hydrophilicity and smoothness of the membranes increased with increasing MnO2 nanowire content. When the MnO2 nanowires is 1.5 wt%, the MnO2-PVDF nanowire membrane has the best performance, the water flux of the membrane increased from 491.98 L·(m2h)−1 to 657.75 L·(m2h)−1 compared with the pure PVDF membrane. At the same time, the BSA rejection of the membrane reached to 100% and the FRR% increased to 85.37%. Furthermore, the PVDF membrane with 1.5 wt% MnO2 nanowire content exhibited outstanding BSA and oil rejection. This method has potential for the preparation of high flux and good antifouling ultrafiltration membranes.

Reticulation of 1D/2D Mo2TiC2 MXene for excellent supercapacitor performance

Heterostructures of MXene are promising for electrochemical energy storage devices (EESDs) because of their synergistic effect and interfacial-driven properties. However, the fabrication process of MXene heterostructures based on transition metal oxides (TMOs) is very challenging due to the poor compatibility of selected materials with MXene. Herein, we fabricate a novel reticulate heterostructure (MnO2 NWs@Mo2TiC2) composed of one-dimensional (1D) ultrathin manganese oxide (MnO2) nanowires (NWs) and two-dimensional (2D) double transition metal (DTM) carbides-based MXene (Mo2TiC2) via a facile liquid-phase pre-pillaring and pillaring method. This unique heterostructure was designed by mixing pre-pillared Mo2TiC2 MXene (cetyltrimethylammonium bromide (CTAB)) and MnO2 NWs in equal mass ratios under specific experimental conditions. The MnO2 NWs not only enhance the performance but also prevent the restacking of nanosheets, while 2D Mo2TiC2 facilitates ion diffusion and ultrafast electron transport. Due to the pillaring effect of MnO2 NWs between the layers of Mo2TiC2 and the synergistic effect between MnO2 NWs and Mo2TiC2 matrix, the heterostructure exhibits a superior gravimetric capacitance for both cyclic voltammetry (CV) 918.6 F/g at 2 mV/s (459.3 C/g) and galvanostatic charge-discharge (GCD) 399.2 F/g at 1 A/g (159.7 C/g) measurements, which is significantly higher than that of pristine MXene, and also show excellent cycling stability (83.3% capacitance retention after 10000 cycles at 10 A/g). These results may open the ways to extend the research more extensively to explore the properties of double transition metal based MXenes and their composites.

Polypyrrole Film Decorated Manganese Oxide Electrode Materials for High-Efficient Aqueous Zinc Ion Battery

Aqueous zinc-ion batteries (AZIBs) have raised wide concern as a new generation energy storage device due to their high capacity, low cost, and environmental friendliness. It is a crucial step to develop the ideal cathode materials that match well with the Zn anode. In this work, we report polypyrrole-(PPy)-encapsulated MnO2 nanowires as cathode materials for AZIBs. The assembled Zn//MnO2@PPy batteries deliver a reversible capacity of 385.7 mAh g−1 at a current density of 0.1 A g−1. Also, they possess an energy density of 192 Wh kg−1 at a power density of 50 W kg−1. The cells show long-term cycling stability, with a retention rate of 96% after 1000 cycles. The outstanding electrochemical performance indicates their potential applications in large-scale energy storage.

Electrocatalytic nitrite-to-ammonia reduction on isolated Cu sites

We report that isolated Cu atoms anchored on MnO2 nanowires (Cu1/MnO2) can be an effective catalyst towards the electrocatalytic NO2–-to-NH3 reduction (NO2RR). A combination of experiments and theoretical calculations reveals that isolated Cu sites can effectively activate NO2–, lower the energy barrier of *NO→*NOH rate-determining step and suppress the competitive hydrogen evolution, thus facilitating both activity and selectivity towards the NO2RR. As a result, Cu1/MnO2 shows the maximum NH3-Faradaic efficiency of 93.3% with a corresponding NH3 yield rate of 439.8 μmol h−1 cm−2 at −0.7 V vs. RHE, together with an excellent electrocatalytic durability.

Polyphosphazene-derived carbon modified nanowires for high-performance electrochemical energy storage

Two one-dimensional nanowires, Fe3O4 and MnO2 nanowires, were modified with polyphosphazene-derived carbon (PZSC) using in situ polymerization and high-temperature calcination methods. PZSC coated with MnO2 nanowire (MnO2/PZSCNW) was designed as the positive electrode, while PZSC coated with Fe3O4 nanowire (Fe3O4/PZSCNW) was designed as the negative electrode. Both MnO2/PZSCNW (+) and Fe3O4/PZSCNW (−) exhibit much larger specific capacities than the corresponding MnO2 and Fe3O4 nanowires, reaching 75.5 mAh g−1 and 75.9 mAh g−1, respectively. The maximum specific capacity, power and energy density of MnO2/PZSCNW (+)//Fe3O4/PZSCNW (−) in alkaline electrolyte are up to 63.2 mAh g−1, 429.6 W kg−1 and 53.7 Wh kg−1, respectively. After 10 000 cycles, the cell maintains 100% capacity. The experimental results indicate that the polyphosphazene-derived carbon coating can significantly improve the electrochemical performance, providing a feasible solution for constructing high-performance supercapacitors.

Novel Electrochemical Sensor Based on MnO2 Nanowire Modified Carbon Paper Electrode for Sensitive Determination of Tetrabromobisphenol A

In this paper, a MnO2 nanowire (MnO2-NW) modified carbon paper electrode (CP) was developed as a novel electrochemical sensor for the sensitive determination of tetrabromobisphenol A (TBBPA). The MnO2 nanowire was prepared by a hydrothermal synthesis method, and the morphology and structure of MnO2 were characterized using scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The electrochemical performance of TBBPA on MnO2-NW/CP was investigated by cyclic voltammetry, and the result confirmed that MnO2-NW/CP exhibited excellent sensitivity for the determination of TBBPA due to the high specific surface area and good electrical conductivity of the nanowire-like MnO2. Moreover, the important electrochemical factors such as pH value, incubation time and modified material proportion were systematically studied to improve the determination sensitivity. The interferences from similar structure compounds on TBBPA have also been investigated. Under the optimal conditions, MnO2-NW/CP displayed a linear range of 70~500 nM for TBBPA with a detection limit of 3.1 nM. This was superior to some electrochemical methods in reference. The work presents a novel and simple method for the determination of TBBPA.

Dual-modification of oxygen vacancies and PEDOT coating on MnO2 nanowires for high-performance zinc ion battery

MnO2 has outstanding potential for application in cathode materials of zinc ion batteries (ZIBs). However, the poor electrical conductivity, poor ion diffusion kinetics, and structural instability greatly limit its rate performance, specific capacity, and cycling stability. Herein, we prepared PEDOT-coated MnO2 cathode material with oxygen vacancy defects, namely Vö-MnO2@PEDOT, by Dual-modification of MnO2 nanowires. The PEDOT coating optimizes the electron transfer capability of the material while inhibiting the dissolution of MnO2. The oxygen vacancies accelerate ion diffusion. Vö-MnO2@PEDOT possesses a joint energy storage mechanism, containing the insertion/extraction of H+/Zn2+ and dissolution/precipitation of MnO2. This joint energy storage mechanism explains the high specific capacity and the increase in capacity. The Vö-MnO2@PEDOT displays a high specific capacity of 400 mAh/g at 0.2 A/g. Besides, at 2 A/g, Vö-MnO2@PEDOT outputs a high capacity of 213 mAh/g after 2000 cycles. This research provides a feasible research idea for the performance optimization of manganese oxide cathode materials.

A mesh network of MnO nanowires and CNTs reinforced by molecularly imprinted structures for the selective detection of para-nitrophenol

A mesh network of MnO nanowires and CNTs reinforced by molecularly imprinted structures for the selective detection of para-nitrophenol

Nitrogen and iron co-doped carbon quantum dots/MnO2 nanowire composites for flexible solid-state supercapacitors with high areal capacitance

Herein, the synthesis of MnO2 nanowires decorated with transition metal-doped carbon quantum dots (MCQDs) is described for use as binder-free flexible solid-state supercapacitors. In particular, the water-soluble Fe and N co-doped MCQDs prepared by amidation reaction with ferric ammonium citrate and urea had ultrafine particle morphologies and showed super-hydrophilicity in aqueous solution, which greatly improved the contact probability between the electrode and the electrolyte. In addition, the co-doped MCQDs increased both the electrical conductivity and specific capacitance of the MnO2/carbon-based nanocomposites and limited the collapse and exfoliation of the MnO2 structure during extended cycling. Compared with pristine MnO2 electrode, the MCQDs/MnO2 composite electrode exhibited faster charge-discharge rate and improved cycle stability with increased specific capacitance. The flexible symmetric supercapacitor constructed from the MCQDs/MnO2 composite had a capacitance retention of 85.6 % after 10,000 charge/discharge cycles at a current density of 2 mA cm−2. In addition, the device showed a maximum power density of 4.8 W cm−2 at an energy density of 2.3 mW h cm−2, and a maximum energy density of 11.16 mW h cm−2 at a power density of 311.6 mW cm−2. Data Availability StatementThe data that support the findings of this study are available from the corresponding author upon reasonable request.

Thick‐Network Electrode: Enabling Dual Working Voltage Plateaus of Zn‐ion Micro‐Battery with Ultrahigh Areal Capacity

AbstractAqueous Zn‐ion micro‐batteries (AZMBs) have been recently shown to be promising integrated and safe micropower sources for portable electronics but with wide commercial adoption greatly constrained by their relatively low areal capacity. Although increasing the electrode thickness is proposed, the performance is compromised due to sluggish reaction kinetics, slow ion diffusion rate, and underutilization of active materials. Herein, the technique of utilizing a 3D thick‐network electrode, consisting of closely interweaved MnO2 nanowires (MnO2 NWs), silver nanowires (AgNWs), and carbon nanotubes (CNTs) is presented. The technique readily enables electrode realization up to a thickness of 351 µm, where the porous structure, high hydrophilicity, and fast electrolyte infiltration jointly contribute to fast kinetics. Matching with a Zn metal anode, the prototyped AZMBs acquire an ultra‐high areal capacity/power density of 809 µAh cm−2/1951 µW cm−2. Additionally, as MnO2 NWs and AgNWs collectively participate in the reaction as active substances, the AZMBs deliver dual voltage plateaus to further improve the areal energy density, realizing a maximum value of 896 µWh cm−2. The 3D thick‐network electrode supporting dual working voltage plateaus can provide a path forward for developing AZMBs with simultaneously ultra‐high areal capacity and energy density.

Hydrophilic MnO2 nanowires coating with o-fluoroaniline for electrocatalytic water oxidation

In the active Mn4CaO5 cluster of the natural water oxidation system, one of the dangling Mn atoms is surrounded by water molecules through coordination and hydrogen bonding. It means that the enrichment of water molecules around the Mn catalysts has a positive effect on the water oxidation catalysis. Inspired by nature photosynthesis, the hydrophilic surfaces are believed to be able to capture water molecules to assist water oxidation. Herein, we report MnO2@PFANI nanowires with improved mass transfer efficiency and conductivity for electrocatalytic water oxidation. The as-prepared nanowires are synthesized by coating hydrophilic polymers on MnO2 nanowires. The hydrophilic surface captures water molecule and promotes mass transfer processes, and the conductivity of the polymer can also increase charge transfer processes. To reach a current density of 10 mA cm−2, a low overpotential of 440 mV is required in a 1.0 M KOH solution for the MnO2@PFANI nanowires. The hydrophilicity and conductivity are systematically investigated by both physical and electrochemical measurements. This study provides a surface engineering idea for the fabrication of efficient electrocatalysts.

Rational engineering NiMoO4 nanosheets or Mn3O4 nanowires on Fe2O3 microdiscs as novel hierarchical anodes for high-performance lithium-ion batteries

Since current graphite-based lithium-ion battery anode has a low theoretical capacity, the development of high-performance lithium-ion battery is severely restricted. Here, novel hierarchical composites composing of microdisc and the secondarily grown nanosheets and nanowires are developed, taking NiMoO4 nanosheets and Mn3O4 nanowires growing on Fe2O3 microdiscs as demonstrating examples. The growth processes of the hierarchical structures have been investigated by adjusting a series of preparation conditions. The morphologies and structures have been characterized by using scanning electron microscopy, transmission electron microscope and x-ray diffraction. Fe2O3@Mn3O4 composite-based anode displays a capacity of 713 mAh g−1 after 100 cycles at 0.5 A g−1 with a high Coulombic efficiency. A good rate-performance is also achieved. Fe2O3@NiMoO4 anode delivers 539 mAh g−1 after 100 cycles at 0.5 A g−1, which is obviously higher than that of pure Fe2O3. The hierarchical structure is conducive to improve the transport of electrons and ions, and provide numerous active sites, thus significantly enhancing the electrochemical performance. Moreover, the electron transfer performance is investigated by using density functional theory calculations. It is expected the findings presented here and the rational engineering of nanosheets/nanowires on microdiscs would be applicable for developing many other high-performance energy-storage composites.