Recent Advances on Challenges and Strategies of Manganese Dioxide Cathodes for Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries(AZIBs)are regarded as promising electrochemical energy storage devices owing to its low cost,intrinsic safety,abundant zinc reserves,and ideal specific capacity.Compared with other cathode materials,manganese dioxide with high voltage,environmental protection,and high theoretical specific capacity receives considerable attention.However,the problems of structural instability,manganese dissolution,and poor electrical conductivity make the exploration of high-performance manganese dioxide still a great challenge and impede its practical applications.Besides,zinc storage mechanisms involved are complex and somewhat controversial.To address these issues,tremendous efforts,such as surface engineering,heteroatoms doping,defect engineering,electrolyte modification,and some advanced characterization technologies,have been devoted to improving its electrochemical performance and illustrating zinc storage mechanism.In this review,we particularly focus on the classification of manganese dioxide based on crystal structures,zinc ions storage mechanisms,the existing challenges,and corresponding optimization strategies as well as structure-performance relationship.In the final section,the application perspectives of manganese oxide cathode materials in AZIBs are prospected.

Red mud and fly ash-based ceramic foams using starch and manganese dioxide as foaming agent

Ceramic foams were prepared using red mud and fly ash as raw materials with sodium borate as sintering aid agent,starchand MnO2as foaming agent,respectively.The influence of the amount of starch or MnO2on the crystalline phase,pore morphologyand physical–chemical porosities was studied.The results showed that the main crystal phases of samples with starch addition andMnO2addition were sodalite phase Na6(AlSiO4)6and Na8(SiAlO4)6MnO4,respectively.The SEM images showed that the variation ofporous structure was mainly dominated by the addition of foaming agent.With the increase of foaming agent,the samples exhibitedbetter comprehensive properties:bulk density of0.59?0.96g/cm3,porosity of41.82%?63.51%,water absorption of3.16%?9.17%,compressive strength of4.22?8.38MPa,flexural strength of2.44?5.82MPa,acid resistance of95.59%?99.60%,alkali resistance of99.82%?99.99%.Based on these properties,the ceramic foams can be used in building field.

Carbon-coated manganese dioxide nanoparticles and their enhanced electrochemical properties for zinc-ion battery applications

In this study, we report the cost-effective and simple synthesis of carbon-coated α-MnOnanoparticles(α-MnO@C) for use as cathodes of aqueous zinc-ion batteries(ZIBs) for the first time. α-MnO@C was prepared via a gel formation, using maleic acid(CHO) as the carbon source, followed by annealing at low temperature of 270 °C. A uniform carbon network among the α-MnOnanoparticles was observed by transmission electron microscopy. When tested in a zinc cell, the α-MnO@C exhibited a high initial discharge capacity of 272 m Ah/g under 66 m A/g current density compared to 213 m Ah/g, at the same current density, displayed by the pristine sample. Further, α-MnO@C demonstrated superior cycleability compared to the pristine samples. This study may pave the way for the utilizing carbon-coated MnOelectrodes for aqueous ZIB applications and thereby contribute to realizing high performance eco-friendly batteries.

Preparation of chemical manganese dioxide from manganese sulfate

Chemical Manganese Dioxide （CMD） was prepared by an alkali-oxidation method. There are several virtues to this environmental friendly and clean process, including the nontoxic and harmless reagents and products, easy operations, no pollutants, easily obtained raw materials and moderate reaction conditions. The synthesized manganese dioxide was characterized by XRD and SEM. The particles were small, consisting primarily of α-MnO2 and γ-MnO2. Experimental results showed that the optimum conditions were： MnSOa.H20 to NaOH ratio, 1.0：2.4; catalyst concentration （catalyst TF-2）, 6% of the MnSO4; initial solution pH, 11; reaction time and temperature, 20 min and 80 ℃; air flow, 0.20 m3/h; and, agitation rate, 700 r/rain. The conversion of MnSO4 can exceed 80% under these optimum conditions.

A Facile and Efficient Oxidation of α,β-Unsaturated Alcohols with Manganese Dioxide in Ionic Liquids under Mild Conditions

The oxidation of a,b-unsaturated primary and secondary alcohols to corresponding aldehydes and ketones by manganese dioxide in ionic liquids as a safe recyclable and accelerative reaction medium under mild conditions are described. The rate of the oxidation reaction is faster and the yield is higher than that with conventional procedures.

Manganese Dioxide with High Specific Surface Area for Alkaline Battery

The authors reported a facile method for the synthesis of manganese dioxide without any template and catalyst at a low-temperature. The prepared sample was characterized with X-ray diffraction（XRD）, scanning electron microscopy（SEM）, Brunauer-Emmett-Teller（BET） surface analysis, Fourier transform infrared（FTIR） spectrometry, cyclic voltammetry, alternative current（AC） impedance test and battery discharge test. It is found that the prepared sample belongs to α-MnO2 and has a microsphere morphology and a large BET surface area. The electrochemical characterization indicates that the prepared sample displays a larger electrochemical capacitance than the commercial electrolytic manganese dioxides（EMD） in Na2SO4 solution, and exhibits larger discharge capacity than EMD, especially at a high rate discharge condition when it is used as cathode of alkaline Zn/MnO2 battery.

Anticlastogenic Effect of Redistilled Cow's Urine Distillate in Human Peripheral Lymphocytes Challenged With Manganese Dioxide and Hexavalent Chromium

Objective To study the anticlastogenic effect of redistilled cow＇s urine distillate （RCUD） in human peripheral lymphocytes （HLC） challenged with manganese dioxide and hexavalent chromium. Methods The anticlastogenic activity of redistilled cow＇s urine distillate was studied in human polymorphonuclear leukocytes （HPNLs） and human peripheral lymphocytes in vitro challenged with manganese dioxide and hexavalent chromium as established genotoxicants and clastogens which could cause induction of DNA strand break, chromosomal aberration and micronucleus. Three different levels of RCUD： 1 μL/mL, 50 μL/mL and 100 μL/mL, were used in the study. Results Manganese dioxide and hexavalent chromium caused statistically significant DNA strand break, chromosomal aberration and micronucleus formation, which could be protected by redisfilled cow＇s urine distillate. Conclusion The redistilled cow＇s urine distillate posseses strong anfigenotoxic and antielastogenic properties against HPNLs and HLC treated with Cr^＋6 and MnO2. This property is mainly due to the antioxidants present in RCUD.

Effects of current density on preparation of grainy electrolytic manganese dioxide

Grainy electrolytic manganese dioxide was prepared by electrodeposition in a 0.9 mol/L MnSO4 and 2.5 mol/LH2SO4 solution. The structure, particle size and appearance of the grainy electrolytic manganese dioxide were determined by powder X-ray diffraction, laser particle size analysis and scanning electron micrographs measurements. Current density has important effects on cell voltage, anodic current efficiency and particle size of the grainy electrolytic manganese dioxide, and the optimum current density is 30 A/dm2. The grainy electrolytic manganese dioxide electrodeposited under the optimum conditions consists of γ-MnO2 with an orthorhombic lattice structure; the grainy electrolytic manganese dioxide has a spherical or sphere-like appearance and a narrow particle size distribution with an average particle diameter of 7.237 μm.

Facile Preparation of Novel Manganese Dioxide Modified Nanofiber and Its Uranium Adsorption Performance

In this study a novel manganese dioxide modified nanofiber was facile prepared using the electrospinning technique. The as-prepared manganese dioxide/poly(vinyl alcohol)/poly (acrylic acid) (briefly as MnO2-PVA/PAA) was firstly characterized by SEM, FT-IR, XRD, stress-strain test and secondly tested as an adsorbent to remove uranium from aqueous solution. Effect of pH, ionic strength, initial uranium concentration, mixing time, temperature on the adsorption, reusability and adsorption mechanism were illustrated. The theoretical adsorption amount of MnO2-PVA/PAA calculated as 398.85 mg/g was competitive compared with the reported values. The study proved MnO2-PVA/PAA is promising in the uranium removal from aqueous medium.

Effects of temperature and concentration of sulfuric acid on the electrodeposition of grainy electrolytic manganese dioxide

The effects of temperature and the concentration of sulfuric acid on the cell voltage, the anode current efficiency of electrodeposition and the particle size of grainy electrolytic manganese dioxide （EMD） were investigated. The structure, particle size and appearance of grainy EMD were determined by powder X-ray diffraction, laser particle size analysis and scanning electron micrograph measurements. As the concentration of sulfuric acid increases, both the cell voltage and the average anode current efficiency decrease. With the increase of electrolysis temperature in the range of 30-60℃, the cell voltage, average anode current efficiency and particle size decrease. The optimum temperature of 30℃ and concentration of sulfuric acid of 2.5 mol/L for electrodeposition of the grainy EMD were obtained. XRD patterns show that the grainy EMD electrodeposited under the optimum conditions consists of γ-MnO2 and has an orthorhombic lattice structure. According to the results of SEM, the grainy EMD has a spherical or sphere-like appearance and a narrow particle size distribution with an average size of about 7μm. The grainy EMD is a promising cathode of rechargeable alkaline batteries for high energy density and a prospective precursor for production of the LiMn2O4 cathode of lithium ion batteries.

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.

Manganese Dioxide (MnO2) Gaining by Calcination of Manganese Carbonate (MnCO3) Precipitated from Cobalt Removal Solutions

Precipitation was carried out to obtain manganese carbonate by adding a precipitating agent, sodium carbonate (NaCO3). This was followed by calcination of the manganese carbonate (MnCO3) to obtain manganese dioxide (MnO2). For precipitation tests, a pH ranging from 8 to 10, a time of one to two hours, and a temperature of 25°C and 50°C are the parameters that are considered. The calcination of MnCO3 is carried out under the following conditions: time (1, 2, 3, and 4 hours) and temperature (370°C, 420°C, and 470°C). It should be noted that the temperature range selected for the calcination tests is based on thermodynamic data obtained using the HSC CHEMISTRY software. The results obtained show an effective recovery of manganese at 25°C, in one hour, with a pH of 8.5 with a precipitation yield and manganese content in the precipitate around 98.43% and 24.21%, respectively. During calcination tests, results show an increase in mass loss, for a constant calcination time, as temperature increases. On the other hand, increasing the calcination time at a given temperature causes an increase in mass loss. However, a significant decrease in mass loss is noted at 3 hours of calcination. The highest mass loss is obtained at a temperature of 470°C after 4 hours of calcination.

Effects of manganese dioxide additives on the electrical characteristics of Al-doped ZnO varistors

The effects of manganese dioxide (MnO 2 ) additives on the electrical characteristics of the Al-doped ZnO varistors are investigated. The leakage current densities of the samples decrease first and then increase again with the increase of the amount of MnO 2 additives. Correspondingly, the nonlinear coefficients of the samples keep on increasing and then decrease. In addition, the donor densities increase monotonously with the amount of the doped MnO 2 increasing. The effects of MnO 2 additives on the electrical characteristics of the samples are different from the conclusion of previous literatures. The reasons of the distinct effects are supposed to be related with the donor and interface state densities of the samples.

Recyclable polymer-based nano-hydrous manganese dioxide for highly efficient Tl(I) removal from water

TI（I） in water even at a trace level is fatal to human beings and the ecosystem. Here we fabricated a new polymer-supported nanocomposite （HMO-001） for efficient TI（I） removal by encapsulating nanosized hydrous manganese dioxide （HMO） within a polystyrene cation exchanger （D-001）. The resultant HMO-001 exhibited more preferable removal of TI（I） than D-001 and IRC-748, an iminodiacetic chelating polymer, particularly in the presence of competing Ca（II） ions at greater levels in solution. Such preference was ascribed to the Donnan membrane effect caused by D-001 as well as the specific interaction between TI（I） and HMO. The adsorbed TI（I） was partially oxidized into insoluble TI（III） by HMO at acidic pH, while negligible oxidation was observed at circumneutral pH. The exhausted HMO-001 was amenable to efficient regeneration by binary NaOH-NaC10 solution for at least 10-cycle batch runs without any significant capacity loss. Fixed-bed column test of Tl（I）-contained indus- trial effluent and natural water further validated that TI（I） retention on HMO-001 resulted in a conspicuous concentration drop from 1.3 mg/L to a value lower than 0.14 mg/L （maximum concentration level for industrial effluent regulated by US EPA） and from 1-4 μg/L to a value lower than 0.1 μg/L （drinking water standard regulated by China Health Ministry）, respectively.

Removal of lead from aqueous solution by hydroxyapatite/ manganese dioxide composite

A novel composite adsorbent, hydroxyapatite/ manganese dioxide （HAp/MnO2）, has been developed for the purpose of removing lead ions from aqueous solutions. The combination of HAp with MnO2 is meant to increase its adsorption capacity. Various factors that may affect the adsorption efficiency, including solution pH, coexistent substances such as humic acid and competing cations （Ca2＋, Mg2＋）, initial solute concentration, and the duration of the reaction, have been investigated. Using this composite adsorbent, solution pH and coexistent calcium or magnesium cations were found to have no significant influence on the removal of lead ions under the experi- mental conditions. The adsorption equilibrium was described well by the Langmuir isotherm model, and the calculated maximum adsorption capacity was 769 mg. gl. The sorption processes obeyed the pseudo-second-order kinetics model. The experimental results indicate that HAp/MnO2 composite may be an effective adsorbent for the removal of lead ions from aqueous solutions.

Effects of humic acid and surfactants on the aggregation kinetics of manganese dioxide colloids

The aggregation of common manganese diox- ide （MnO2） colloids has great impact on their surface reactivity and therefore on their fates as well as associated natural and synthetic contaminants in engineered （e.g. water treatment） and natural aquatic environments. Nevertheless, little is known about the aggregation kinetics of MnO2 colloids and the effect of humic acid （HA） and surfactants on these. In this study, the early stage aggregation kinetics of MnO2 nanoparticles in NaNO3 and Ca（NO3）2 solutions in the presence of HA and surfactants （i.e., sodium dodecyl sulfate （SDS）, and polyvinylpyrrolidone （PVP）） were modeled through time-resolved dynamic light scattering. In the presence of HA, MnO2 colloids were significantly stabilized with a critical coagulation concentration （CCC） of-300mmol · L-1 NaNO3 and 4 mmol.L-1 Ca（NO3）2. Electrophoretic mobility （EPM） measurements confirmed that steric hindrance may be primarily responsible for increasing colloidal stability in the presence of HA. Moreover, the molecular and/or chemical properties of HA might impact its stabilizing efficiency. In the case of PVP, only a slight increase of aggregation kinetics was observed, due to steric reactions originating from adsorbed layers of PVP on the MnO2 surface. Consequently, higher CCC values were obtained in the presence of PVP. However, there was a negligible reduction in MnO2 colloidal stability in the presence of 20 mg·L-1SDS.

Removal of Pb(Ⅱ) from aqueous solution by hydrous manganese dioxide:Adsorption behavior and mechanism

Hydrous manganese dioxide （HMO） synthesized by redox of potassium permanganate and hydrogen peroxide was used as an adsorbent for Pb（Ⅱ） removal.The specific surface area,pore volume and BJH pore diameter of the HMO were 79.31m2/g,0.07cm3/g and 3.38 nm,respectively.The adsorption equilibrium at 298K could be well described by the Langmuir isotherm equation with q max value of 352.55mg/g.The negative values of G and the positive values of H and S indicated the adsorption process was spontaneous and endothermic.The pseudo second-order equation could best fit the adsorption data.The value of the calculated activation energy for Pb（Ⅱ） adsorption onto the HMO was 38.23 kJ/mol.The uptake of Pb（Ⅱ） by HMO was correlated with increasing surface hydroxyl group content and the main adsorbed speciation was PbOH＋.The final chemical state of Pb（Ⅱ） on the surface of HMO was similar to PbO.HMO was a promising candidate for Pb（Ⅱ） removal from aqueous solution.

Manganese dioxide(MnO_(2))/Fullerene-C_(60)-Modified Electrodes for the Voltammetric Determination of Rifaximin

Rifaximin(RFX)is a broad-spectrum oral antibiotic with bactericidal actions against Gram-negative and Gram-positive bacteria.In the present work,a sensitive voltammetric assay for the RFX in pharmaceutical formulations is designed using nanostructured working electrodes.Surface functionalization with manganese dioxide(MnO_(2))/fullerene-C_(60) nanocomposite exhibited the highest electrochemical responses with a sharp oxidation peak at about 336 mV that was obtained using the differential pulse voltammetry(DPV).The cyclic voltammetry(CV)and electrochemical impedance spectroscopy(EIS)were applied,while the electrode matrix composition including types of nanomaterials,electroanalytical parameters,and pH eff ect were optimized.To that end,using the DPV,high sensitivity was obtained from the linear calibration curve ranged from 0.8 to 31.5μg·mL^(-1) with the correlation coe fficient of 0.99,limit of detection of 0.76μg·mL^(-1) and limit of quantification of 2.31μg·mL^(-1) .Accordingly,the designed approach is off ering a potential applicability towards the RFX determination in pharmaceutical preparations and its quality control.

From laboratory research to industrial application:a green technology of fluidized mineral processing for manganese dioxide ore reduction

The efficient utilization of manganese dioxide(MnO_(2))ore is essential for the sustainable development of manganese(Mn)industry.Confronting the great challenge of chemical engineering scale-up,a commercial fluidized reduction project of MnO_(2)ore with the capacity of 200,000 t a^(-1)is carried out based on deep experimental investigation,extensive kilogram-scale test and detailed engineering design.Compared with other production technologies and equipment,it is proved that the fluidized process shows distinguished advantages of lower energy consumption,higher production efficiency,larger automation degree and less environmental pollution.The comprehensive studies of experiment,modeling,simulation and optimization are required for a more promising development of fluidization engineering in the future.

Recent progress of advanced manganese oxide-based materials for acidic oxygen evolution reaction: Fundamentals, performance optimization,and prospects

The oxygen evolution reaction(OER) is the basis of various sustainable energy conversion and storage techniques,especially hydrogen production by water electrolysis.To realize the practical application of hydrogen energy and mass-scale hydrogen production via water electrolysis,several obstacles,such as the multi-electron transfer OER process with sluggish kinetics and overall high reaction barrier,should be overcome.Manganese oxide-based(MnOx) materials,especially MnO_(2),have emerged as promising non-noble electrocatalysts for water electro-oxidation under acidic conditions due to their wellbalanced properties between catalytic activity and stability.This review introduces the fundamental understanding of the catalytic OER process on MnOx-based materials,including the conventional adsorbate evolution mechanism(AEM) and emerging lattice oxygen oxidation mechanism(LOM).The rational screening and prediction of MnOx-based catalysts that can stably catalyze OER in acid are summarized based on Pourbaix diagram analysis and thermodynamic density functional theory(DFT) calculations.Then,the up-to-date progress of upgrading the OER catalytic performance of MnOx-based catalysts by composite construction is reviewed.Afterward,feasible strategies to improve the electrocatalytic activity and lifetime of MnOx-based catalysts are systemically discussed in terms of crystal structure control,reasonable setting of working potential and electrolyte environment,optimal selection of acid-stable conductive supports,and self-healing engineering.Finally,future scientific challenges and research directions are outlined to guide the construction of advanced MnOx-based electrocatalysts for OER in acid.