Amorphous Manganese Dioxide Research Articles

Comparative study of the performance of α-MnO2 and amorphous manganese dioxide air electrodes for zinc-air batteries

Comparative study of the performance of α-MnO2 and amorphous manganese dioxide air electrodes for zinc-air batteries

Crystallization Behavior of Co‐Doped Amorphous Manganese Dioxide and Its Cathode Performance for Aqueous Zinc Ion Batteries

AbstractIn order to explore the crystallization behavior of Co‐doped amorphous manganese dioxide(Co‐doped AMO) and to investigate the electrochemical properties of its different crystallization products as cathodes for aqueous zinc ion batteries. In this work, the effects of heat treatment temperature on the microstructure and phase composition of Co‐doped AMO and their electrochemical properties of Zn‐MnO2 battery cathode materials are systematically investigated. The results show that Co‐doping increases the crystallization temperature of pure AMO. When the heat treatment temperature is 400 °C, Co‐doped AMO is amorphous. At 500 and 550 °C, part of the Co‐doped AMO crystallizes into tetragonal spinel structured (Co, Mn)(Co, Mn)2O4 material between MnCo2O4 and Mn3O4. At 650 °C, the crystallized product is completely nano‐α‐Mn(Co)O2 crystal. The maximum discharge specific capacities and the retention rate after 100 cycles of the samples at 100 mA g−1 are 325.40 mAh g−1, 86.88%; 217.00 mAh g−1, 13.94%; 186.68 mAh g−1, 41.01%; and 149.03 mAh g−1, 31.27% for the unheated and 400, 550, 650 °C heat‐treated samples, respectively. It is proved that the Co‐doped AMO without heat treatment is superior to the partially or fully crystallized materials in terms of comprehensive performance and cost as cathode materials for AZIB.

In situ architecting amorphous manganese oxide/MXene heterostructure electrode with fast ion transport and structural stability in aqueous Zn–Mn batteries

An in situ constructed a-MnO2/Ti3C2F heterojunction combines the advantages of 2D layered and amorphous structures, providing abundant ion diffusion channels that facilitate rapid Zn ion diffusion and the reversible formation of ZSH.

Effect of Heat Treatment on the Crystallization Behavior of Amorphous Manganese Dioxide and its Electrochemical Properties in Zinc‐Ion Battery Cathodes

Herein, amorphous manganese dioxide (AMO) is prepared by the liquid‐phase coprecipitation method, the effect of heat treatment temperature on the microstructure, and phase composition of AMO and the electrochemical properties as cathode materials for aqueous Zn–MnO2 batteries are investigated. The results show that the AMO didn't crystallize at 250 °C, but its structure stability increases. When the temperature is 350 and 400 °C, part of the AMO crystallizes into rod‐shaped nano‐α‐MnO2 crystals. At 540 °C, the products crystallize into nano‐α‐MnO2 crystals. Continuing to increase the temperature to 650 °C, the structural stability of the products is further improved. Heat treatment leads to reduced specific surface area and porosity of the material, which in turn leads to reduced specific capacity and cycling stability. In addition, the heat‐treated products show a sharp drop in capacity during the discharge process; this was because the volume change caused by the irreversible phase change of the electrode material is difficult to release in the anisotropic crystal, resulting in the collapse of the structure. This study shows that unheated AMO is better than heat‐treated AMO as a cathode material for aqueous Zn–MnO2 battery cathode material in terms of overall performance and cost.

Amorphous Heterostructure Derived from Divalent Manganese Borate for Ultrastable and Ultrafast Aqueous Zinc Ion Storage.

Aqueous zinc-manganese (Zn-Mn) batteries have promising potential in large-scale energy storage applications since they are highly safe, environment-friendly, and low-cost. However, the practicality of Mn-based materials is plagued by their structural collapse and uncertain energy storage mechanism upon cycling. Herein, this work designs an amorphous manganese borate (a-MnBOx ) material via disordered coordination to alleviate the above issues and improve the electrochemical performance of Zn-Mn batteries. The unique physicochemical characteristic of a-MnBOx enables the inner a-MnBOx to serve as a robust framework in the initial energy storage process. Additionally, the amorphous manganese dioxide, amorphous Znx MnO(OH)2 , and Zn4 SO4 (OH)6 ·4H2 O active components form on the surface of a-MnBOx during the charge/discharge process. The detailed in situ/ex situ characterization demonstrates that the heterostructure of the inner a-MnBOx and surface multicomponent phases endows two energy storage modes (Zn2+ /H+ intercalation/deintercalation process and reversible conversion mechanism between the Znx MnO(OH)2 and Zn4 SO4 (OH)6 ·4H2 O) phases). Therefore, the obtained Zn//a-MnBOx battery exhibits a high specific capacity of 360.4 mAh g-1 , a high energy density of 484.2Wh kg-1 , and impressive cycling stability (97.0% capacity retention after 10000 cycles). This finding on a-MnBOx with a dual-energy storage mechanism provides new opportunities for developing high-performance aqueous Zn-Mn batteries.

In situ micro-current collector of amorphous manganese dioxide as cathode material for sodium-ion batteries

In situ micro-current collector of amorphous manganese dioxide as cathode material for sodium-ion batteries

Influence of Co on the Microstructure, Electrochemical and Pseudocapacitive Properties of Amorphous Manganese Dioxide

Manganese dioxide is a cathode material for zinc-ion batteries which is low in cost and high in performance, whereas, traditional manganese dioxide materials have poor cycle stability and poor conductivity. In response to this problem, many researchers have carried out related research, such as the preparation of various crystal forms of manganese dioxide, element doping (Co, Sn, V, etc.) and so on. However, the research on doping amorphous materials to solve the above problems is in scarcity. In this paper, amorphous manganese oxide and Co doping were combined for the first time, and Co-doped amorphous manganese dioxide was prepared by in-situ liquid phase dispersion coprecipitation method. The influence of Co doping on the microstructure and electrochemical properties of amorphous manganese dioxide were also investigated for the first time. As can be observed from the results, despite that Co doping preserves the abundant structural defects in amorphous manganese dioxide, it transforms the amorphous manganese dioxide particles from spherical to nano-sheet shape, significantly increases the particular area of surface and pore size of amorphous manganese dioxide, and stabilizes its crystal structure. Furthermore, Co doping can not only reduce the impedance of the amorphous manganese dioxide cathode, but also extremely boost the pseudocapacitive performance of amorphous manganese dioxide, thereby greatly improving its discharge specific capacity, the rate performance and the cycle stability. The prepared Co-doped amorphous manganese dioxide cathode has a maximum discharge specific capacity of 325 mAh g−1, and a capacity retention rate of 64% at 600 cycles under a current density of 1 A g−1.

A Binder-Free Amorphous Manganese Dioxide for Aqueous Zinc-Ion Battery

Aqueous zinc-ion battery has attracted much attention due to its low price, high safety, and high theoretical specific capacity. However, most of their performances are limited by the unsatisfied architecture of cathodes. Herein, we fabricated amorphous manganese dioxide by an in situ deposition method. The amorphous manganese dioxide can directly serve as the cathode of an aqueous zinc-ion battery without a binder. The resultant cathode exhibits a high specific capacity of 133.9 mAh/g at 200 mA/g and a capacity retention of 82% over 50 cycles at 1 A/g.

K+-stabilized nanostructured amorphous manganese dioxide: excellent electrochemical properties as cathode material for sodium-ion batteries

Various transition metal oxide materials like MnO2 have been reported as cathode for sodium-ion batteries. However, the large sodium-ion radius and migration barrier cause its poor structural stability and low electrochemical performance. Herein, we present a simple pre-potassiation way to stabilize the nanostructure of amorphous manganese dioxide (a-MnO2). The pre-potassiation amorphous manganese dioxide (K-a-MnO2) heating treatment at 400 °C manifests outstanding electrochemical properties in the aspect of specific capacity and cyclic stabilization, the reversible specific capacity maintains at 180.8 mAh g−1 after 200th cycles under a current density of 0.1 C, and it shows a rate capability of 178.2 mAh g−1, 157.5 mAh g−1, 120.8 mAh g−1, 95.5 mAh g−1, 71.4 mAh g−1, and 47.1 mAh g−1 at 0.1 C, 0.2 C, 0.5 C, 1 C, 2 C and 5 C, respectively. The findings exhibit that the pre-potassiation way can stabilize the structural of a-MnO2 and effectively improve its electrochemical performance.

Sustainable redox processes induced by peroxymonosulfate and metal doping on amorphous manganese dioxide for nonradical degradation of water contaminants

Manganese oxides have been applied in advanced oxidation processes (AOPs), however, underlying oxidation regimes are still debatable. In this work, we synthesized various crystalline manganese oxides and single or dual metal-doped amorphous MnO2 (M-AMO, M = Fe, Co, Ni, and Cu) for organic oxidation with peroxymonosulfate (PMS). M-AMO at 1 mol% exhibited much higher activities than crystalline manganese oxides and Cu-AMO displayed the rate constant at 3.5 times as high as that of AMO. Different from conventional radical oxidation, nonradical degradation occurred via two pathways. Cu-doping resulted in relatively higher-crystallized structure, more oxygen vacancies, and a higher ratio of Mn4+/Mn3+ for a faster redox cycle between MnⅣ(s) and MnⅢ(s) to boost PMS activation and direct/indirect (Cu-AMO–PMS complex-based) phenol oxidation. This study contributes to a new insight to the structure-catalysis relationship in manganese-catalyzed PMS oxidation. The outcomes will direct the rational synthesis of reaction-oriented catalysts for nonradical AOPs and novel remediation technologies.

Amorphous manganese dioxide with the enhanced pseudocapacitive performance for aqueous rechargeable zinc-ion battery

Aqueous rechargeable zinc-manganese dioxide batteries have attracted extensive attention due to their high energy density, low cost, and environmental friendliness. However, the crystalline MnO2 polymorphs suffer from substantial phase changes upon cycling, leading to structural collapse and poor long-term cycling performance. Here, a highly reversible amorphous manganese dioxide with structural defects is reported as the cathode for aqueous rechargeable zinc-ion batteries (ARZIBs). Because of the existence of the abundant structural defects and intrinsic isotropic nature, the A-MnO2-δ exhibits significant pseudocapacitive contribution and facilitated reaction kinetics. As expected, the A-MnO2-δ delivers a high specific capacity of 301 mAh g−1 at 100 mA g−1 and long cycle-life with a capacity retention of 78% over 1000 cycles at 1 A g−1, which is better than its crystalline counterparts. In addition, a reversible H+ and Zn2+ two-step insertion storage mechanism of the A-MnO2-δ electrode is demonstrated. This study not only suggests that amorphous manganese dioxide can serve as a stable cathode for ARZIBs but also provides significant guidance to realize other high-capacity and long-lifespan aqueous batteries by using the amorphous materials.

Amorphous Manganese Dioxide Coated Polydopamine Nanoparticles for Acid-Sensitive Magnetic Resonance Imaging-Guided Tumor Photothermal Therapy.

Photothermal therapy (PTT) is a powerful technique for tumor ablation. However, there is a problem that PTT cannot accurately locate the tumor site, so it is easy to cause heat damage to the surrounding normal tissues. In this study, PEGylated amorphous manganese dioxide (MnO₂) coated polydopamine (PDA) core-shell nanoparticles (PDA@MnO₂-PEG) with regular morphology and uniform dimensions were prepared for acid-sensitive magnetic resonance imaging-guided tumor photothermal therapy. The results showed that amorphous MnO₂ shell provided markedly acid-sensitive T1-weighted magnetic resonance imaging (MRI). The relaxation rate (r1 value) of PDA@MnO₂-PEG in pH=7.4 was measured to be 0.310 mM-1·S-1, while that in pH=6 became 4.364 mM-1·S-1. In mice tumor models, MRI of tumors exhibited dramatically whitening effects compared with the signal before injection. Besides, the in vivo experiments revealed that the tumors in PTT group with PDA@MnO₂-PEG injection and NIR laser irradiation were almost eliminated within 14 days, indicating the effective photothermal therapy of tumor generated by the PDA core. In conclusion, we successfully synthesized amorphous MnO₂ coated PDA core-shell nanoparticles with the function of acid-sensitive magnetic resonance imaging guided photothermal therapy, which provide a new approach for improving the effect of photothermal therapy of tumors.

Further insights into the combination of permanganate and peroxymonosulfate as an advanced oxidation process for destruction of aqueous organic contaminants

Recent studies have reported a novel advanced oxidation process (AOP) by combining permanganate (KMnO4) and peroxymonosulfate (PMS) for destruction of organic contaminants (i.e., acid orange 7, trichloroethylene, and benzene), where hydroxyl (•OH) and sulfate radicals (SO4•−) are proposed to be generated from PMS activation by amorphous manganese dioxide (MnO2) formed in situ from KMnO4 reduction. In this work, appreciable degradation of p-chlorobenzoic acid (p-CBA) was confirmed in KMnO4/PMS system, while KMnO4 or PMS alone showed inert reactivity toward p-CBA. Moreover, it was found that pre-synthesized amorphous MnO2 showed invalid PMS activation for p-CBA degradation, and pre-addition of inorganic or organic reducing agents to promote the formation of amorphous MnO2 showed negligible influence on p-CBA degradation as well. In these regards, a tentative mechanism for PMS activation by KMnO4 rather than its product MnO2 was proposed, involving the substitution of oxo atoms of KMnO4 by peroxo groups, subsequent reductive generation of peroxomanganese (VI) complexes, and intramolecular disproportionation of these complexes to generate radicals. Efficient degradation of p-CBA was achieved at acid or basic conditions with a maximum rate occurring at pH 3. The coexisting chloride anions showed suppressive effect on p-CBA degradation for scavenging SO4•− and •OH, while metal ions accelerated the degradation of p-CBA, possibly due to the cation bridging function between negatively-charged MnO4− and HSO5−. Hydroxylated intermediates of p-CBA were identified in KMnO4/PMS system. This work improved the fundamental understanding of a new class of AOPs by combining KMnO4 and PMS for environmental decontamination.

Amorphous hierarchical porous manganese oxides for supercapacitors with excellent cycle performance and rate capability

Manganese oxides are considered as great pseudo-capacitance materials due to their high theoretical capacitance, but they usually suffer from unstable cycle performance and poor rate capability. To explore whether above problems are associated with crystallinity, electrochemical performances of amorphous and crystalline manganese dioxide are thoroughly investigated. Especially, ex-situ XPS and ICP-OES measurements are carried out to examine whether the amount of intercalated Na+ ions is determined by crystallinity and has influence on cycle performance and rate capability. Meanwhile, relationship between pore size distribution and electrochemical performance of manganese dioxides is discussed. We find that the amorphous manganese dioxide with hierarchical pores presents the best performance in this work, which exhibits a specific capacitance of 405.2 F g−1 at a scan rate of 1 mV s−1 and 391.9 F g−1 at a current density of 0.1 A g−1 in a three-electrode system. Moreover, the amorphous-phase nanoparticle electrode possesses an excellent cycle life with 95.1% retention of its initial capacitance after 5200 cycles and a good rate capability of 75.3% retention at 10 mV s−1, which are superior to that of the crystalline one in this work and lots of reported crystalline MnO2 nano-materials.

Oxidation of bisphenol A by nonradical activation of peroxymonosulfate in the presence of amorphous manganese dioxide

This work demonstrated that bisphenol A (BPA) was rapidly degraded by peroxymonosulfate (PMS) in the presence of amorphous manganese dioxide (MnO2). Chemical quenching experiments and electron paramagnetic resonance spectroscopy (EPR) suggested that hydroxyl radical (OH), sulfate radical (SO4−), and singlet oxygen (1O2) were unlikely responsible for BPA oxidation. As such, a nonradical mechanism involving the formation of reactive complexes between amorphous MnO2 and PMS was tentatively proposed based on the PMS decomposition and Raman spectra. The presence of phosphate ions (H2PO4−) remarkably suppressed the degradation of BPA, while the addition of divalent metal ions (Ca2+, Mg2+, and Zn2+) appreciably enhanced BPA degradation. The discrepancy was likely resulted from their contrasting influences on the formation of reactive PMS-MnO2 complexes. Based on identified oxidation products (i.e., dimers, 4-hydroxycumyl alcohol, mono-hydroxylated BPA and its quinone derivative) by liquid chromatography tandem mass spectrometry, the transformation pathways of BPA in amorphous MnO2/PMS system involving one-electron oxidation, radical coupling, bond cleavage, and hydroxylation were proposed. In addition to BPA, thirteen other selected phenolic compounds were also efficiently degraded by amorphous MnO2/PMS system, and good correlations between apparent pseudo-first-order reaction rate constants (kobs) and descriptor variables (i.e., Hammett constants σ+ and half-wave potentials E1/2) were obtained.

Characterizing the Impacts of Deposition Techniques on the Performance of MnO2 Cathodes for Sodium Electrosorption in Hybrid Capacitive Deionization.

Capacitive deionization (CDI) is currently limited by poor ion-selectivity and low salt adsorption capacity of porous carbon electrodes. To enhance selectivity and capacity via sodium insertion reactions, carbon aerogel electrodes were modified by depositing amorphous manganese dioxide layers via cyclic voltammetry (CV) and electroless deposition (ED). MnO2-coated electrodes were evaluated in a hybrid capacitive deionization system to understand the relationship between oxide coating morphology, electrode capacitance, and sodium removal efficacy. Both deposition techniques increased electrode capacitance, but only ED electrodes improved desalination performance over bare aerogels. SEM imaging revealed ED deposition distributed MnO2 throughout the aerogel, while CV deposition created a discrete crust, indicating that CV electrodes were limited by diffusion. Sodium adsorption capacity of ED electrodes increased with MnO2 mass deposition, reaching a maximum of 0.77 mmol-Na+ per gram of cathode (2.29 mmol-Na+ g-MnO2-1), and peak charge efficiency of 0.95. The presence of MnO2 also positively shifted the electrode potential window of sodium removal, reducing parasitic oxygen reduction and inverting the desalination cycle so that energy discharge coincides with salt removal (1.96 kg-NaCl kWh-1). These results highlight the importance of deposition technique in improving desalination with MnO2-coated electrodes.

Asymmetric supercapacitors based on functional electrospun carbon nanofiber/manganese oxide electrodes with high power density and energy density

Carbon nanofibers modified with carboxyl groups (CNF-COOH) possessing good wettability and high porosity are homogeneously deposited with amorphous manganese dioxide (amorphous MnO2) by potentiodynamic deposition for asymmetric super-capacitors (ASCs). The potential-cycling in 1 M H2SO4 successfully enhances the hydrophilicity of carbonized polymer nanofibers and facilitates the access of electrolytes within the CNF-COOH matrix. This modification favors the deposition of amorphous MnO2 and improves its electrochemical utilization. In this composite, MnO2 homogeneously dispersed onto CNF-COOH provides desirable pseudocapacitance and the CNF-COOH network works as the electron conductor. The composite of CNF-COOH@MnO2-20 shows a high specific capacitance of 415 F g−1 at 5 mV s−1. The capacitance retention of this composite is 94% in a 10,000-cycle test. An ASC cell consisting of this composite and activated carbon as positive and negative electrodes can be reversibly charged/discharged to a cell voltage of 2.0 V in 1 M Na2SO4 and 4 mM NaHCO3 with specific energy and power of 36.7 Wh kg−1 and 354.9 W kg−1, respectively. This ASC also shows excellent cell capacitance retention (8% decay) in the 2V, 10,000-cycle stability test, revealing superior performance.

Influence of synthesis parameters on amorphous manganese dioxide catalyst electrocatalytic performance

Oxygen reduction reaction (ORR) catalysts with applications in fuel cells and metal-air batteries can be tailored to overcome the slow kinetics and to reduce overpotentials of the reaction. In this work, a series of amorphous manganese dioxides are synthesised via a chemical redox synthesis method. Synthesis parameters including molar ratio, the order of adding sequence of reactants, pH, and temperature are found to affect the catalyst’s physical and chemical properties such as morphology, lattice hydration, active surface area, and surface properties. The samples are characterised by SEM, BET, XPS and XRD as well as cyclic voltammetry, rotating disc electrode, and gas diffusion electrode measurements. The results indicated that an optimal catalyst sample can be synthesized by reduction of KMnO4 with Mn(CH3COO)2 in MnO4−/Mn2+ molar ratio of 2.67 by addition of KMnO4 into Mn(CH3COO)2 at pH 12, 295K. The gas diffusion electrode coated with amorphous manganese dioxide catalyst ink in 10:10:2wt% of MnO2:XC-72R:PTFE with a loading of 2mgcm−2, was shown to support current densities up to 100mAcm−2 with improved performance.

Electrochemical accessibility of porous submicron MnO2 spheres as active electrode materials for electrochemical capacitors

The electrochemical utilization of various submicron amorphous manganese dioxide spheres (SMnO2) with highly controlled shape and size was investigated by cyclic voltammetry and electrochemical impedance spectroscopy. MnO2 spheres were synthesized by reaction between KMnO4 and 1–butanol in aqueous butyric acid solution at room temperature. Particle size was tuned by adjusting the concentration of KMnO4. The materials were characterized by X-ray diffraction, scanning electron microscopy, dynamic light scattering and nitrogen gas adsorption measurements. SEM results reveal that spheres with average diameter of 451±9, 218±12 and 195±85nm were produced by using a 20, 8 and 2mM of KMnO4 solution, respectively. DLS measurements showed similar mean particle diameter with a relatively high polydispersity-index that indicates the presence of larger agglomerated particles. The BET surface area of the three SMnO2 is ranging between 216 and 259m2g−1. Since very similar specific capacitance values of about 200Fg−1 (per active material mass) at 2mVs−1 were found for all three samples, MnO2 electrochemical utilization is more related to the pore size distribution rather than the particle size.

Bismuth oxide coated amorphous manganese dioxide for electrochemical capacitors

With MnSO4, NaOH and K2S2O8 as the raw materials, the amorphous and δ-type manganese dioxide (MnO2) is separately prepared by using different chemical precipitation-oxidation methods. The results of charge–discharge and electrochemical impedance spectroscopy (EIS) tests show that (i) the specific capacitance of the amorphous MnO2 reaches to 301.2 F g−1 at a current density of 200 mA g−1 and its capacitance retention rate after 2000 cycles is 97%, which is obviously higher than 250.8 F g−1 and 71% of the δ-type one, respectively; (ii) good electrochemical capacitance properties of the amorphous MnO2 should be contributed to easy insertion/extraction of ions within the material; (iii) when 5 wt% Bi2O3 is coated on the amorphous MnO2, its specific capacitance increases to 352.8 F g−1 and the capacitance retention rate is 90% after 2000 cycles.