Structure Of MnO Research Articles

Synthesis, Structure, and Electrochemical Performance of Bi-induced Stabilization of MnO2 Cathodes for Use in Highly Acidic Aqueous Electrolytes (pH

MnO2 cathode materials are widely studied in alkaline and neutral aqueous electrolytes. In these mediums, the MnO2 cathode shows suboptimal performance limited by dissolution and electrochemically inactive compound formation, leading to capacity fading. This study explores the enhancement of MnO2 cathode performance through Bi3+ ion doping (0, 1, 2.5, 5, and 10mol%) in a highly acidic electrolyte (pH < 2). By incorporating up to 10mol% Bi ions into the MnO2 structure, we significantly improved specific capacity and capacity retention stability. Energy-dispersive X-ray spectroscopy (EDX) analysis revealed a uniform dispersion of Bi3+ ions throughout the MnO2 cathode after electrochemical cycling, contributing to performance enhancements. X-ray photoelectron spectroscopy (XPS) results indicated that Bi3+ ion concentration from 1 to 10mol% stabilises Mn3+ within the MnO2 lattice. Also, Bi3+ ion doping promotes the formation of a 2×2 tunnel structured α-MnO2 phase. Electrochemical impedance spectroscopy results demonstrated a reduction in double-layer and overall bulk capacitance. These findings suggest that Bi3+ ion doping effectively enhances MnO2 electrochemical performance and could enhance its use in aqueous metal-ion batteries.

Structural disorder Triggered by small organic molecules Boosting δ-MnO2 cathode for Ultra‐Stable aqueous zinc ion batteries

The inferior cycling stability of MnO2-based cathodes, resulting from Mn dissolution and crystal structure transition during Zn-ion insertion/extraction, poses a significant challenge hindering their widespread adoption in aqueous zinc-ion batteries (AZIBs). To mitigate these issues, we propose an approach involving the incorporation of small organic molecules (methylformamide, dimethylformamide, and formamide) to modify the crystalline structure of MnO2. These molecules, characterized by their low orbital energy levels, facilitate the creation of energetically equivalent electron transfer pathways with the unoccupied eg orbitals in Mn4+, as evidenced by the DFT calculations. Furthermore, they modulate the electron cloud density of Mn-O and introduce structural disorder in the MnO2 crystalline lattice, thereby greatly enhancing the structural stability of the Mn-based cathode. In AZIBs tests, the MnO2/methylformamide (MO/NMF) cathode demonstrates a remarkable reversible specific capacity exceeding 270 mAh g−1 at 1 A g−1 and exceptional durability, exhibiting negligible capacity degradation after 2000 cycles at 3 A g−1. In-situ X-ray diffraction, neutron powder diffraction and high-angle annular dark-field scanning transmission electron microscopy analyses confirm the structure stability of MO/NMF during Zn-ion insertion/extraction, attributed to the NMF modification. Additionally, the electrochemical data indicate that modifications with dimethyl formamide and formamide also positively impact the electrochemical performance of the MnO2 cathode. This study offers valuable insights for the development of high-performance Mn-based cathodes.

Tailoring MnO2 nanowire defects with K-doping for enhanced electrochemical energy storage in aqueous supercapacitors

The fabrication of supercapacitors with outstanding performance is presented with a distinct defect-rich nanostructures. A one-pot, energy-efficient method for synthesizing defective manganese dioxide nanowires doped with potassium (K0.35MnO2) was developed. The introduction of potassium ions at 35 % birnessite resulted in a significant increase in lattice defects and an improvement in conductivity. Addition of KOH induces a phase transition from α-MnO2 to δ-MnO2. These imperfections result in a greater quantity of active sites, which are crucial for the process of energy storage. The K0.35MnO2 structure demonstrates a 405F/g increased capacity at a current density of 1 A/g. The asymmetric supercapacitor (K0.35MnO2/AC) that was manufactured exhibits a capacitance of 106.4F/g when operating at 1 A/g, while maintaining a maximum energy density of 71.5 Wh kg−1 and a power density of 672 W kg−1. Furthermore, 92.7 % of the initial capacitance of the device is retained even after 8,000 cycles at 20 A/g. This study presents novel insights into the production of defective materials for energy storage applications through the utilization of a one-pot process as opposed to the multi-step method. In order to produce high-performance supercapacitors for practical applications, the results indicate that defect engineering is a crucial factor.

Breaking the Passivation Effect for MnO2 Catalysts in Li-S Batteries by Anion-Cation Doping.

Transition metal oxides (TMOs) are recognized as high-efficiency electrocatalyst systems for restraining the shuttle effect in lithium-sulfur (Li-S) batteries, owing to their robust adsorption capabilities for polysulfides. However, the sluggish catalytic conversion of Li2S redox and severe passivation effect of TMOs exacerbate polysulfide shuttling and reduce the cyclability of Li-S batteries, which significantly hinders the development of TMOs electrocatalysts. Here, through the anion-cation doping approach, dual incorporation of phosphorus and molybdenum into MnO2 (P,Mo-MnO2) was engineered, demonstrating effective mitigation of the passivation effect and allowing for the simultaneous immobilization of polysulfides and rapid redox kinetics of Li2S. Both experimental and theoretical investigations reveal the pivotal role of dopants in fine-tuning the d-band center and optimizing the electronic structure of MnO2. Furthermore, this well-designed configuration processes catalytic selectivity. Specifically, P-doping expedites rapid Li2S nucleation kinetics by minimizing reaction-free energy, while Mo-doping facilitates robust Li2S dissolution kinetics by mitigating decomposition barriers. This dual-doping approach equips P,Mo-MnO2 with robust bi-directional catalytic activity, effectively overcoming passivation effect and suppressing the notorious shuttle effect. Consequently, Li-S batteries incorporating P,Mo-MnO2-based separators demonstrate favorable performance than pristine TMOs. This design offers rational viewpoint for the development of catalytic materials with superior bi-directional sulfur electrocatalytic in Li-S batteries.

Porous CrO[formula omitted]: A ferromagnetic half-metallic member in sparse hollandite oxide family

A stable polymorph of CrO2 is predicted using PBE+U method. The porous material is isostructural with α−MnO2 making it the second transition metal oxide in sparse hollandite group of materials. However, unlike the anti-ferromagnetic semiconducting character of the α−MnO2, it is found to be a ferromagnetic half-metal. At Fermi level, the hole pocket has ample contribution from O−2p orbital, though, the electron pocket is mostly contributed by Cr−3dxy and Cr−3dx2−y2. A combination of negative charge transfer through orbital mixing and extended anti-bonding state near Fermi level is responsible for the half-metallic ferromagnetic character of the structure. A comparative study of rutile and hollandite CrO2 and hollandite MnO2 structures delineate the interplay between structural, electronic and magnetic properties. The material shows a robust magnetic character under hydrothermal pressure, as well as, the band topology is conserved under uniaxial strain. Moderate magneto-crystalline anisotropy is observed and it shows a correspondence with the anisotropy of elastic constants. Occurrence of type−II Weyl nodes and their evolution under pressure is explored.

Self‐healable Mn‐doped PVA‐borax hydrogel electrodes for supercapacitor applications

AbstractThis study aims to investigate the effect of Mn doping on the performance of polyvinyl alcohol/borax‐structured (PMB) supercapacitor electrodes for high‐capacity, flexible, and self‐healing supercapacitor electrodes. The PMB electrodes were characterized by x‐ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM). Electrochemical characterization was conducted using cyclic voltammetry (CV), which revealed that redox reactions, which are evident at low scan rates, enhance capacitive performance. However, high scan rates introduce limitations owing to the increased vibrations of the PVA chains and incomplete electrolyte polarization. The PMB electrodes exhibited remarkable electrochemical properties and capacitive performances, which were significantly affected by the MnO₂ structure. The electrodes exhibited self‐healing properties and demonstrated flexibility to stretch by up to 40%. In addition, the results indicate that the electrode capacity of the PVA/borax system increased by 2.03 times after 1000 cycles with manganese doping. The solid electrolyte interface (SEI) layer formed on the electrode surface plays a critical role in stabilizing the capacity loss during prolonged charge–discharge cycles. The study concluded that PMB supercapacitors offer higher capacitance in 0‐2 V applications compared to other PVA/borax combination hydrogels. Moreover, the incorporation of metal‐based additives, particularly manganese, enhanced the capacitive performance, and operating voltage levels.

Polymorphic Engineering of MnO2 Structure as a Diffusion Blocking Layer for Selective Seawater Electrolysis

The water splitting via renewable energy is one of the sustainable process to generate the future clean energy in form of hydrogen. One of the key challenge for the large-scale water electrolysis is the availability of pure water. The sweater can be consider as an alternate feedstock for the large-scale water electrolysis. However, the presence of undesirable components like chlorides, bromides etc. are the potential challenge to make the use of seawater as a facile feedstock. As per the electrochemical potentials, chlorine evolution reaction (CER) along with the oxygen evolution reaction (OER) at the anode is one of the primary existing challenge in seawater electrolysis. Where thermodynamics favour OER and kinetic benefits, the CER process with two-electron transfers reaction. As of now, precious noble metal catalysts such as ruthenium and iridium-based oxides have been explored as a catalyst for seawater electrolysis. However, their high cost does not recommend the use of these catalysts for the large-scale production and limits its commercialization. Here, we are exploring the non-precious Mn based catalyst for OER vs. CER and make make seawater electrolysis as a commercial favourable process. We have explored various polymorphs of MnO2, such as α, β, γ, and δ-MnO2, considering the MnO2 as diffusion blocking layer for the selective OER process during the seawater electrolysis. The polymorphic engineering provide the window to tune the catalytic properties to make it selective towards the OER. Further, the results suggest that α- and β-MnO2 are OER selective however, the γ-, and δ- MnO2 are CER selective. We have identified the reaction mechanism using various electrochemical tools and shown the structure-activity-selectivity trends for the polymorphic structure of MnO2.

Enhanced water oxidation stability and activity in MnO2 nanosheet arrays through Ti doping

Efficient and sustainable hydrogen production via water electrolysis relies on the utilization of highly active electrocatalysts for the oxygen evolution reaction (OER). Birnessite (δ-MnO2), a type of manganese oxide with a local atomic structure similar to the oxygen-evolving complex in photosystem II, has emerged as a highly promising OER catalyst. Despite considerable efforts have been dedicated to enhancing its activity, the crucial aspect of stability has been often overlooked. Herein, Ti ions have been selectively incorporated into the in-layered lattice of δ-MnO2 nanosheet arrays using a hydrothermal method, aiming to enhance the stability without reducing its activity. The resulting optimal Ti-MnO2 catalyst demonstrates enhanced OER activity in alkaline electrolyte, exhibiting an impressive 85 mV reduction in overpotential at 10 mA cm−2, surpassing the initial MnO2 (495 mV reduced to 410 mV). Remarkably, it shows exceptional durability, with negligible performance decrease observed over the entire 50-hour testing period. It has been demonstrated that the incorporation of Ti serves a dual purpose: it adjusts the electronic structure around Mn, enhancing activity, and simultaneously stabilizes the Mn3+ active sites, resulting in exceptional durability. Furthermore, density functional theory (DFT) calculations provide additional confirmation of the optimized electronic structure of MnO2 achieved through Ti doping, leading to a reduction in the free energy of adsorbed intermediates and expediting the kinetics of the OER process. Our findings open a pathway for enhancing OER stability and activity by doping electrocatalytic inert ions into the lattice of MnO2, applicable not only to Mn-based oxides but also other non-precious metal-based electrocatalysts.

Electronic Structure Modification of MnO2 Nanosheet Arrays with Enhanced Water Oxidation Activity and Stability by Nitrogen Plasma.

The strategic design of catalysts for the oxygen evolution reaction (OER) is crucial in tackling the substantial energy demands associated with hydrogen production in electrolytic water splitting. Despite extensive research on birnessite (δ-MnO2) manganese oxides to enhance catalytic activity by modulating Mn3+ species, the ongoing challenge is to simultaneously stabilize Mn3+ while improving overall activity. Herein, oxygen (O) vacancies and nitrogen (N) doping have been simultaneously introduced into the MnO2 through a simple nitrogen plasma approach, resulting in efficient OER performance. The optimized N-MnO2v electrocatalyst exhibits outstanding OER activity in alkaline electrolyte, reducing the overpotential by nearly 160 mV compared to pure pristine MnO2 (from 476 to 312 mV) at 10 mA cm-2, and a small Tafel slope of 89 mV dec-1. Moreover, it demonstrates excellent durability over a 122 h stability test. The introduction of O vacancies and incorporation of N not only fine-tune the electronic structure of MnO2, increasing the Mn3+ content to enhance overall activity, but also play a crucial role in stabilizing Mn3+, thereby leading to exceptional stability over time. Subsequently, density functional theory calculations validate the optimized electronic structure of MnO2 achieved through the two engineering methods, effectively lowering the intermediate adsorption free energy barrier. Our synergistic approach, utilizing nitrogen plasma treatment, opens a pathway to concurrently enhance the activity and stability of OER electrocatalysts, applicable not only to Mn-based but also to other transition metal oxides.

Effect of Cu doping on structure, morphology, and microwave absorption performance of MnO2

Effect of Cu doping on structure, morphology, and microwave absorption performance of MnO2

Defect engineering of copper-doped mesoporous manganese dioxide nanoflowers for enhancing electrocatalytic detection of hydrogen peroxide

Birnessite-type δ-MnO2 nanoflowers doped with copper ions (Cu-MnO2) can enhance the catalytic performance of MnO2-based catalysts for efficient electrochemical sensing of H2O2. There are no significant changes in the surface morphology and lattice structure of bulk MnO2 after Cu doping via engineered cation exchange. The catalytic Cu species are effectively incorporated into the tunnel entrance of δ-MnO2, the Mn site in the MnO6 octahedron, and surface defects. The Cu doping enhances the electrical and ionic conductivities, and generates numerous Mn3+ defects, oxygen vacancies, and Cu+/Cu2+ redox sites. Thus, the Cu doping facilitates the transport and adsorption of more H2O2 molecules to the catalytic sites, significantly increasing the catalytic rate. In contrast, pristine MnO2 exhibits negligible catalytic performance for H2O2 reduction because of its slow catalytic kinetics and low electrical conductivity. The Cu-MnO2 catalyst exhibits higher sensitivity (105.7 μA·mM−1·cm−2), a lower detection limit (0.6 μM), and a broader linear range (0.005 ∼ 4.2 mM) compared to pristine δ-MnO2.

Enhanced pseudocapacitive properties of cobalt-doped manganese oxide electrode utilizing magnesium sulfate electrolyte for supercapacitors

This paper investigates the enhanced pseudocapacitive properties of cobalt-doped manganese oxide (Co-doped MnO2) electrode in magnesium sulfate (MgSO4) electrolyte for supercapacitor applications. Co-doped MnO2 was synthesized on nickel foam through a controlled hydrothermal process and specific heat treatment parameters. This resulted in the transformation into α-MnO2 with a 2 × 2 tunnel structure. Morphological investigation illustrates the presence of a hierarchical micro-flower structure with a substantial surface area and mesoporous distribution. The specific surface area of the Co-doped MnO2 electrode significantly increased to 158 m2 g−1, compared to the pristine (bare MnO2) electrode (80 m2 g−1). Electrochemical analyses revealed a specific capacitance of 527 F g−1 at 1 A g−1 in MgSO4 (1 M), showcasing a 1.6 times improvement over Na2SO4 (1 M). The unique structure of the Co-doped MnO2, combined with magnesium ions as efficient electron donors, contributes to superior charge-storage, making it a promising candidate for high-performance supercapacitors. Comprehensive characterizations, such as XRD, XPS, BET, SEM, GCD, and EIS, confirm the advantageous electrochemical performance and durability of the Co-doped MnO2 electrode in MgSO4 electrolyte.

Enhancing zinc-ion batteries: PEDOT-MnO2 cathodes for superior stability and capacity

Of late, zinc-ion batteries (ZIBs) are emerging as a vital component in sustainable energy storage, ensuring an environmentally friendly alternative to traditional battery systems. Herein, this study provides a novel approach to ZIB research, undertaking to encapsulate PEDOT in a layered MnO2 structure. Through the use of comprehensive analytical techniques, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray absorption spectroscopy (XAS), a detailed analysis of the enhanced PEDOT-MnO2 heterostructure is presented. Our research demonstrates that the encapsulation of PEDOT results in a substantial increase in initial discharge capacity (∼40%) compared to traditional MnO2 alongside improvements in structural stability. These findings, facilitated by in-situ X-ray absorption near-edge structure (XANES) and ex-situ extended X-ray absorption fine structure (EXAFS) techniques, underscore the potential of PEDOT-MnO2 in advancing the development of manganese-based cathode materials for non-aqueous electrolyte ZIBs. The work represents a crucial advancement in the field of sustainable energy storage solutions, highlighting the role of innovative material design in improving the efficiency and stability of rechargeable battery systems.

Synthesis of Nano-electrolytic Manganese Dioxide for Alkaline Batteries Mediated by Organic Additives

This article discusses the impact of adding organic additives like glycine (GLY), sucrose (SUC), and saccharine (SACCH) on the electrical characteristics and microstructure of electrolytic manganese dioxide (EMD), which is made from an acidic aqueous sulphate solution. The structure and chemistry of EMD were ascertained by means of Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD). To assess the material's potential for use in alkaline batteries, its charge-discharge properties were ascertained. It was found that the majority of MnO2 in all the EMD samples was in the γ-phase, which is electrochemically active and useful for energy storage applications. When glycine, sucrose, and saccharine were added to the solution as organic additives, the electrochemical deposition of manganese dioxide (MnO2) resulted in an increase in current efficiency and a decrease in energy consumption. The SEM images demonstrated that when EMD was deposited with an additive, small grain sizes and discrete particles free of agglomeration were formed, but large grain sizes were obtained in the absence of additives. Charge-discharge characteristics suggested that the additions improve the ability of MnO2 structure to store energy. This suggested that the additions may have an impact on the morphology and size of the particles, and consequently, the electrochemical activities of the material that was electrodeposited. In the case of the additives examined in this paper, the outcome was the creation of a material with possible use in battery technology.

Advanced three-dimensional hierarchical porous α-MnO2 nanowires network toward enhanced supercapacitive performance

Hierarchical α-MnO2 nanowires with oxygen vacancies grown on carbon fiber have been synthesized by a simple hydrothermal method with the assistance of Ti4+ ions. Ti4+ ions play an important role in controlling the morphology and crystalline structure of MnO2. The morphology and structure of the as-synthesized MnO2 could be tuned from δ-MnO2 nanosheets to hierarchical α-MnO2 nanowires with the help of Ti4+ ions. Based on its fascinating properties, such as many oxygen vacancies, high specific surface area and the interconnected porous structure, the α-MnO2 electrode delivers a high specific capacitance of 472 F g−1 at a current density of 1 A g−1 and the rate capability of 57.6% (from 1 to 16 A g−1). The assembled symmetric supercapacitor based on α-MnO2 electrode exhibits remarkable performance with a high energy density of 44.5 Wh kg−1 at a power density of 2.0 kW kg−1 and good cyclic stability (92.6% after 10 000 cycles). This work will provide a reference for exploring and designing high-performance MnO2 materials.

In situ nitrogen-doped into MnO2/carbon derived from manganese (II) – triazole framework to achieve superior zinc ions storage

The widespread application of MnO2 as cathodes for aqueous zinc ions batteries (AZIBs) suffers from challenging issues of inferior ion storage capability, poor intrinsic electronic conduction and undesirable Mn dissolution. Herein, we demonstrate that the nitrogen can be successfully in situ doped into both the MnO2 and carbon lattice to form N-doped MnO2/C (NMC) by pyrolyzing the Mn based metal-triazole (Mn-MET) framework. The generation of oxygen vacancies in MnO2 and the presence of N-doped carbon in the composite not only increase the electronic conductivity to accelerate charges transfer in MnO2, but also relieve the Mn dissolution to stabilize the MnO2 structure. As a result, the NMC cathode based AZIB is able to display high discharge capacity of 339.3 mAh g−1, much higher than the bare Mn2O3 cathode (147.8 mAh g−1). The excellent long-term cycling life with a capacity retention of 82.8 % can be also achieved after 1000 cycles under 3 A g−1. The energy storage mechanism of the NMC cathode related to the reversible H+ and Zn2+ interaction/extraction are systematically investigated through multiple ex situ characterizations. Thus, these inspiring results in our work are expected to stimulate the exploitation of MOFs derived cathode materials for high-performance AZIBs.

MnO2/AgNPs Composite as Flexible Electrode Material for Solid-State Hybrid Supercapacitor

A MnO2/AgNP nanocomposite was synthesized using a sonochemical method and investigated as an electrode material in a solid-state hybrid supercapacitor. Aquivion’s sodium and lithium electrolyte membrane serves as an electrolyte and separator. For comparison, MnO2 was used as the active material. The developed supercapacitor containing a carbon xerogel as a negative electrode, the MnO2/AgNP composite as a positive electrode and a Na+-exchange membrane demonstrated the highest performance characteristics. These results indicate that the incorporation of silver nanoparticles into the MnO2 structure is a prospect for obtaining an active composite electrode material for solid-state supercapacitors.

Three‐Dimensional Conductive Interface and Tip Structure of MnO2 Electrode Facilitate Superior Zinc Ion Batteries

Manganese dioxide has been significantly utilized in zinc ion batteries (ZIBs). However, in the rechargeable battery system, the manganese dioxide cathode suffers from poor conductivity, volume expansion, and substance dissolution, resulting in low capacity and poor stability. Herein, a 3D frame structure MnO2@CNTs cathode is proposed. In this system, the electrodeposited spherical MnO2 is anchored and interlinked via the in‐situ growth carbon nanotubes (CNTs) onto the carbon cloth. Benefiting the unique 3D frame structure, the MnO2 structure crush problem and the pathway of the electrons and ions are dramatically improved. The optimized MnO2@CNTs cathode demonstrate a high capacity of 256.35 mAh g−1 at 0.1 A g−1 and exceptional cycling stability. Furthermore, in‐situ Raman spectroscopy elucidates the energy storage mechanism of aqueous ZIBs (AZIBs). Moreover, COMSOL finite elements analysis demonstrates that the petal edge‐rich nanostructures of MnO2@CNTs generate a localized high electric field under constant current, accelerating ion/electron transfer. This work explains the rationale for CNTs to improve the properties of MnO2 cathodes, providing a new perspective for the design of high‐performance batteries.

Highly Effective Non-Noble MnO2 Catalysts for 5-Hydroxymethylfurfural Oxidation to 2,5-Furandicarboxylic Acid.

Noble metal-free catalyst or catalytic oxidation of 5-hydroxymethylfurfural into 2,5-furandicarboxylic acid are proposed in this study as a proposal to solve one of the great disadvantages of this reaction of using preferably noble metal-based catalysts. The catalytic activity of six MnO2 crystal structures is studied as alternative. The obtained results showed a strong connection between catalytic activity the type of MnO2 structure organization and redox behavior. Among all tested catalysts, ϵ-MnO2 showed the best performance with an excellent yield of 74 % of 2,5-furandicarboxylic acid at full -hydroxymethylfurfural conversion.

One-step hydrothermal synthesis of Fe3+-doped sheet-like δ-MnO2 for high-performance hybrid supercapacitors

KMnO4 was the Mn source, FeCl3·6H2O was the Fe source, and Fe3+-doped δ-MnO2 was prepared by a one-step hydrothermal method. The effects of different addition amounts of FeCl3·6H2O on the morphology, crystal structure and electrochemical properties of MnO2 were studied. The results show that pure phase MnO2 has a sheet morphology. The doping of Fe3+ decreases the size of sheet MnO2 and increases the specific surface area of MnO2, but XRD shows that MnO2 still retains the δ-type. At the same time, the doping of Fe3+ causes MnO2 to expose high-energy crystal faces, which enhances the electrochemical activity of MnO2. Further studies found that Fe3+ of FeCl3·6H2O plays an important role, while Cl− has nothing to do with it. The electrochemical test results show that when 3 mmol Fe3+ is added, the specific capacitance of MnO2–0.3 reaches the maximum value (196 F g−1), which is much higher than that of pure MnO2 (123.4 F g−1). Finally, the hybrid supercapacitor assembled from MnO2–0.3 and activated carbon has an energy density of 19.9 Wh kg−1, which can maintain 83.3 % of the initial value after 20,000 cycles. This work provides us with a new way to control the structure of electrode materials.