Investigations on Chemically Synthesized Pure and Doped Manganese Dioxide Nanoparticles for Dye Removal and Photocatalytic Applications

Pure and Mg2+, Ni2+, Cd2+ doped MnO2 nanoparticles were synthesized by chemical co-precipitation method. These samples were characterised by PXRD, SEM, EDX, FTIR, UV-Vis-NIR, PL, Antibacterial, Cyclic Voltammetry, Dye Degradation and Photocatalytic studies. From the powder XRD studies, the crystallite size of the particle was calculated using Scherer formula and found that the synthesized nanoparticles were in the range from 10 to 12 nm. The morphology of all the synthesized samples was viewed from SEM micrograph. The composition and purity of the samples were identified from EDX studies. In FTIR spectra metal-oxygen stretching and bending modes of vibrations were observed. From the absorption spectra of UV-Vis optical analysis values of absorption coefficient, extinction coefficient, refractive index, real and imaginary part of optical dielectric constant and optical conductivity were compared. The band gap energy obtained from Tauc's plot varies from 1.21 to 1.51 eV exhibits semiconducting behaviour of all the synthesized samples. Investigations on photoluminecsence spectrum reveals blue shift in wavelength for doped nanooxides compared to pure MnO2. Antimicrobial activity of synthesised samples against gram positive and gram negative bacteria was determined. The obtained results reveal very high bacterial resistance in Cd2+ doped MnO2 nanoparticles with higher activity towards bacterial resistance compared to standard drug. The specific capacitance values were determined from Cyclic Voltammetry studies. Using the batch method of dye removing technique the percentage of malachite green dye removal was calculated. Also the photocatalytic efficiency of all the synthesized MnO2 samples in removing malachite green dye was studied by exposing to sunlight for different dosage and contact time. Ni2+ doped MnO2 shows relatively higher % of dye degradation capacity about 93% for 0.1 g of dosage of photocatalysts.

Removal of Cadmium(II) by hydrated manganese dioxide: behaviour and mechanism at different pH

Homogeneous precipitation was proposed to prepare hydrated manganese dioxide (HMO) with KMnO4 as oxidant, NaCl as reductant and HNO3 as reaction auxiliary. HMO was applied to remove Cd(II) and the effect of contact time, initial concentration, adsorbent dose and pH value on adsorption efficiency were investigated. The removal mechanisms at various pH values were analysed in detail. Adsorption thermodynamics parameters were calculated as ΔG < 0, ΔH > 0 and ΔS > 0, which meant that the adsorption process was endothermic. The result of adsorption kinetics indicated the adsorption process conformed to pseudo-second-order kinetics. When adsorbing Cd(II) with initial concentration equaling 100 mg·L-1, the activation energy (Ea) was 62.740 kJ·mol-1. The Langmuir model could describe adsorption behaviour on HMO better than the Freundlich model, indicating that the adsorption sites of HMO were homogeneous and that single-layer adsorption was a dominant way in this process. The maximum adsorption capacity of Cd(II) on MnO2 calculated by the Langmuir model was 267 mg·g-1. The adsorbent HMO could be recycled and reused for several times with a high efficiency above 70% by adding HCl. SEM, EDS, FTIR and XPS were used to analyse the mechanisms of removal of Cd(II) at pH = 3,7 and 10. The mechanisms included electrostatic attraction, ion exchange and chemical precipitation. With pH increasing, the zeta potential decreased and the surface negative charge increased, promoting Cd(II) removal through enhanced electrostatic attraction. Meanwhile, ion exchange mechanisms including inner-sphere complexation and outer-sphere complexation occurred during adsorption process at different pH.

MnO2 -Based Materials for Environmental Applications

Manganese dioxide (MnO₂ ) is a promising photo-thermo-electric-responsive semiconductor material for environmental applications, owing to its various favorable properties. However, the unsatisfactory environmental purification efficiency of this material has limited its further applications. Fortunately, in the last few years, significant efforts have been undertaken for improving the environmental purification efficiency of this material and understanding its underlying mechanism. Here, the aim is to summarize the recent experimental and computational research progress in the modification of MnO₂ single species by morphology control, structure construction, facet engineering, and element doping. Moreover, the design and fabrication of MnO₂ -based composites via the construction of homojunctions and MnO₂ /semiconductor/conductor binary/ternary heterojunctions is discussed. Their applications in environmental purification systems, either as an adsorbent material for removing heavy metals, dyes, and microwave (MW) pollution, or as a thermal catalyst, photocatalyst, and electrocatalyst for the degradation of pollutants (water and gas, organic and inorganic) are also highlighted. Finally, the research gaps are summarized and a perspective on the challenges and the direction of future research in nanostructured MnO₂ -based materials in the field of environmental applications is presented. Therefore, basic guidance for rational design and fabrication of high-efficiency MnO₂ -based materials for comprehensive environmental applications is provided.

Internet of Things enabled portable thermal management system with microfluidic platform to synthesize MnO2 nanoparticles for electrochemical sensing

Evidently, microfluidic devices are proven to be one of the most effective and powerful tools for manipulating, preparing, functionalizing and producing new generation nanoparticles and nanocomposites. Their benefits include low solution/sample feeding, excellent handling of reagents, exceptional control of size and composition, compactness, easy to process with rapid thermal management and cost-effectiveness. Such advantages have led to the endorsement of nano-microscale fabrication methods to develop highly controllable and reproducible minuscule devices. This work aims to design and develop a microscale-based temperature control device with added features like low-cost, portability, miniaturized, easy-to-use, minuscule reaction volume and point-of-source system for the synthesis of nanoparticles. The device incorporates many features such as real-time data access with a GUI interface with a smartphone open-source app for Bluetooth and Database cloud for an Internet of Things module. The portable thermal device is then calibrated and is capable of achieving a maximum temperature of 250 °C in 25 min. The fabricated device is harnessed for the synthesis of manganese oxide (MnO2) nanoparticles. The synthesized nanoparticles were subjected to various characterization techniques like SEM and XPS to analyze the surface morphology. To test the applicability, as a proof of concept, the synthesized nanoparticles were tested for electrochemical sensing of hydrogen peroxide and dopamine. Overall, the portable device can be utilized for carrying out diverse temperature-controlled reactions in a microfluidic system in a user-friendly and automated manner.

Structural-Phase Catalytic Redox Reactions in Energy and Environmental Applications

The structure-property engineering of phase-based materials for redox-reactive energy conversion and environmental decontamination nanosystems, which are crucial for achieving feasible and sustainable energy and environment treatment technology, is discussed. An exhaustive overview of redox reaction processes, including electrocatalysis, photocatalysis, and photoelectrocatalysis, is given. Through examples of applications of these redox reactions, how structural phase engineering (SPE) strategies can influence the catalytic activity, selectivity, and stability is constructively reviewed and discussed. As observed, to date, much progress has been made in SPE to improve catalytic redox reactions. However, a number of highly intriguing, unresolved issues remain to be discussed, including solar photon-to-exciton conversion efficiency, exciton dissociation into active reductive/oxidative electrons/holes, dual- and multiphase junctions, selective adsorption/desorption, performance stability, sustainability, etc. To conclude, key challenges and prospects with SPE-assisted redox reaction systems are highlighted, where further development for the advanced engineering of phase-based materials will accelerate the sustainable (active, reliable, and scalable) production of valuable chemicals and energy, as well as facilitate environmental treatment.

Novel H2O2-MnO2 system for efficient physico-chemical cleaning of fouled ultrafiltration membranes by simultaneous generation of reactive free radicals and oxygen

The novel H₂O₂-MnO₂ system was developed to achieve highly efficient membrane cleaning for both fouled PVDF and PES membranes in this study. Compared with conventional chemical cleaning process in which the whole membrane module had to be soaked in highly concentrated solution of chemical reagent for long period of time, the H₂O₂-MnO₂ cleaning process conducting for only 5 min in 0.5 wt% H₂O₂ solution could achieve more than 95% recovery of permeate flux and almost total removal of the irreversible foulants. More importantly, the permeate flux and filtration efficiency of the membrane could be still kept stable after 6 runs of consecutive fouling and cleaning. Based on the systematic microscopic analyses, Electron Spin Resonance (ESR), Fourier Transform Infrared Spectroscopy (FTIR), as well as the quenching experiments with different free radical scavengers, the outstanding performance of H₂O₂-MnO₂ system was attributed to the generation of both free radicals and abundant oxygen simultaneously, leading to the physico-chemical membrane cleaning. Conclusively, the newly developed H₂O₂-MnO₂ system demonstrated noteworthy advantages on efficient membrane cleaning, and exhibited highly potential for the wide application in practical water treatment process.

Controllable Pulse Reverse Electrodeposition of Mesoporous Li xMnO2 Nano/Microstructures with Enhanced Electrochemical Performance for Li-Ion Storage

Given the ever-growing demand of electric vehicles and renewable energies, addressing the poor cyclic stability of lithium manganese dioxide is an urgent challenge. In this study, pulse reverse current as the driving force of a one-pot anodic electrodeposition was exploited to design the physicochemical and electrochemical characteristics of lithium manganese dioxides as cathode materials of Li-ion battery. The pulse reverse parameters, including the span of anodic and cathodic current application ( t_a and t_c) and frequency ( f'), were systematically modulated to determine the optimized values through monitoring the physicochemical properties using X-ray diffraction, thermogravimetric analysis/differential scanning calorimetry, field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive spectrometry, Raman spectroscopy, N₂ adsorption-desorption isotherms, and inductively coupled plasma-optical emission spectroscopy, as well as the electrochemical properties using cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge-discharge at different currents. Based on the results, Li_0.65MnO₂ synthesized using t_a = 95 ms, t_c = 5 ms, and f' = 8.33 Hz at the constant magnitude of anodic peak current density of 1 mA dm^-2 was determined as the optimized sample. The optimized lithium manganese dioxide rendered superior electrochemical performance with the initial discharge capacity of 283 mAh g^-1, which accounts for 96.4% of the theoretical discharge capacity, preserving 88.3% of this capacity after 300 cycles at 0.1 C and, in the meantime, was able to release a discharge capacity of 115 mAh g^-1 even after cycling at a higher current of 10 C. The superior electrochemical behavior of Li_0.65MnO₂ was attributed to the exclusive hierarchical urchin-like morphology as well as mesoporous nano/microstructures having a notably high Brunauer-Emmett-Teller surface area of 320.12 m² g^-1 alongside mixed-phase α/γ structure owing to the larger 2 × 2 tunnels, which offer more facile Li⁺ diffusion.

Synthesis of C@Ni-Al LDH HSS for efficient U-entrapment from seawater

In this paper, a double hollow spherical shell composite modified with layered double hydroxide (C@Ni-Al LDH HSS) was fabricated for uranium(VI) (U(VI)) adsorption. Various batch experiments were carried out to investigate the influence of pH, concentration, time and coexistence ion on extraction. The results showed that the adsorption processes of U(VI) onto C@Ni-Al LDH HSS were spontaneous and endothermic and closely followed pseudo-second-order and Langmuir isotherm models. The equilibrium time and maximum adsorption capacity of C@Ni-Al LDH HSS was 360 min and 545.9 mg g^-1. FT-IR and XPS analyses proved that the adsorption behavior was primarily attributed to the strong interaction between oxygen-containing functional groups and U(VI). Moreover, the extraction of trace U(VI) (μg L^-1) in artificial and natural seawater was also studied. The results showed that C@Ni-Al LDH HSS provided a promising application for the efficient extraction of U(VI) from seawater.

The controlled synthesis of complex hollow nanostructures and prospective applications†

Functionality in nanoengineered materials has been usually explored on structural and chemical compositional aspects of matter that exist in such solid materials. It is well known that the absence of solid matter is also relevant and the existence of voids confined in the nanostructure of certain particles is no exception. Indeed, over the past decades, there has been great interest in exploring hollow nanostructured materials that besides the properties recognized in the dense particles also provide empty spaces, in the sense of condensed matter absence, as an additional functionality to be explored. As such, the chemical synthesis of hollow nanostructures has been driven not only for tailoring the size and shape of particles with well-defined chemical composition, but also to achieve control on the type of hollowness that characterize such materials. This review describes the state of the art on late developments concerning the chemical synthesis of hollow nanostructures, providing a number of examples of materials obtained by distinct strategies. It will be apparent by reading this progress report that the absence of solid matter determines the functionality of hollow nanomaterials for several technological applications.

Doping strategy to boost electromagnetic property and gigahertz tunable electromagnetic attenuation of hetero-structured manganese dioxide

A facile and simple chemical route has been used to synthesize novel three-dimensional (3D) architectures of nickel-doped ε-MnO₂ without the addition of any surfactant or organic template.

Multi-functional MnO2 nanomaterials for photo-activated applications by a plasma-assisted fabrication route

Supported MnO2-based nanomaterials were fabricated on fluorine-doped tin oxide substrates using plasma enhanced-chemical vapor deposition (PE-CVD) between 100 °C and 400 °C, starting from a fluorinated Mn(ii) diamine diketonate precursor. Growth experiments yielded β-MnO2 with a hierarchical morphology tuneable from dendritic structures to quasi-1D nanosystems as a function of growth temperature, whose variation also enabled a concomitant tailoring of the system fluorine content, and of the optical absorption and band gap. Preliminary photocatalytic tests were aimed at the investigation of photoinduced hydrophilic (PH) and solid phase photocatalytic (PC) performances of the present nanomaterials, as well as at the photodegradation of Plasmocorinth B azo-dye aqueous solutions. The obtained findings highlighted an attractive system photoactivity even under visible light, finely tailored by fluorine content, morphological organization and optical properties of the prepared nanostructures. The results indicate that the synthesized MnO2 nanosystems have potential applications as advanced smart materials for anti-fogging/self-cleaning end uses and water purification.

Three-dimensional MnO2 porous hollow microspheres for enhanced activity as ozonation catalysts in degradation of bisphenol A

Three-dimensional (3D) MnO₂ porous hollow microspheres (δ- and α- MnO₂ PHMSs), with high adsorption and catalytic ozonation performance, were synthesized by a self-template (MnCO₃ microspheres) process at room temperature. The synthesized MnO₂ PHMSs were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) surface area. The results showed that PHMSs exhibit the excellent adsorption ability and catalytic activity owning to their hollow spherical structure, mesoporous shell and well-defined interior voids, leading to the strong adsorption for bisphenol A (BPA) and the retention of O₃ molecules on catalyst. Moreover, the catalytic performance of α-MnO₂ PHMSs was better than that of δ-MnO₂ PHMSs which was attributed to the richer lattice oxygen of α-MnO₂ PHMSs to accelerate O₃ decomposition by producing more reactive oxidative species. The degradation efficiency of BPA using 3D α-MnO₂ PHMSs was more than 90% in the presence of ozone within 30min reaction time. The probe tests for reactive oxidative species (ROSs) displayed that BPA degradation by catalytic ozonation is dominated by O₂^- and OH in our present study. Furthermore, the organic compounds as intermediates of the degradation process were identified by LC/MS.

Morphology and phase tuning of α- and β-MnO2 nanocacti evolved at varying modes of acid count for their well-coordinated energy storage and visible-light-driven photocatalytic behaviour

α and β of MnO₂ nanocacti (comprising nanowires with 1–10 nm diameter self assembled by ultrathin sheets) as well as MnO₂ nanorods (10–40 nm diameter) are synthesized without any seed or template.

One-pot synthesis and first-principles elasticity analysis of polymorphic MnO2 nanorods for tribological assessment as friction modifiers

XRD analysis of hydrothermally synthesized polymorphic MnO₂ nanorods and their frictional torque when added with palm oil as against pure palm oil.

Manganese dioxide core–shell nanostructure to achieve excellent cycling stability for asymmetric supercapacitor applications

This study present a facile and low-cost method to prepare core–shell nano-structured β-MnO₂@δ-MnO₂, in which β-MnO₂@nano-wires act as the cores to form 3D networks and δ-MnO₂ as the shells.

Formation of nickel-doped magnetite hollow nanospheres with high specific surface area and superior removal capability for organic molecules

A strategy for the formation of magnetic Ni _x Fe_3-x O₄ hollow nanospheres with very high specific surface areas was designed through a facile solvothermal method in mixed solvents of ethylene glycol and water in this work. The Ni/Fe ratios and the crystal phases of the Ni _x Fe_3-x O₄ hollow nanocrystals can be readily tuned by changing the molar ratios of Ni to Fe in the precursors. An inside-out Ostwald ripening mechanism was proposed for the formation of uniform Ni _x Fe_3-x O₄ hollow nanospheres. Moreover, the obtained Ni _x Fe_3-x O₄ hollow nanospheres exhibited excellent adsorption capacity towards organic molecules such as Congo red in water. The maximum adsorption capacities of Ni _x Fe_3-x O₄ hollow nanospheres for Congo red increase dramatically from 263 to 500 mg g^-1 with the increase of the Ni contents (x) in Ni _x Fe_3-x O₄ hollow nanospheres from 0.2 to 0.85. The synthesized Ni _x Fe_3-x O₄ nanoparticles can be potentially applied for waste water treatment.

Egg-shaped core/shell α-Mn2O3@α-MnO2 as heterogeneous catalysts for decomposition of phenolics in aqueous solutions

Novel uniform ellipsoid α-Mn2O3@α-MnO2 core/shell (McMs) nanocomposites were prepared via a hydrothermal process with a shape-control protocol followed by calcination at different temperatures. The properties of the composites were characterized by a number of techniques such as thermogravimetric analysis (TGA), X-ray diffraction (XRD), N2 adsorption, and scanning electron microscopy (SEM). The core/shell materials were much effective in heterogeneous oxone(®) activation to generate sulfate and hydroxyl radicals for degradation of aqueous phenol. The McMs composites demonstrated catalytic activity for 100% phenol decomposition in short duration varying between 20 and 120 min, much higher than that of homogeneous Mn(2+) system with 95% phenol degradation in 120 min. They also showed a higher activity than single-phase α-Mn2O3 or α-MnO2. The catalytic activity of phenol degradation depends on temperature, oxone(®) concentration, phenol concentration, and catalyst loading. The catalysts also showed a stable activity in several cycles. Kinetic study demonstrated that phenol degradation reactions follow a first order reaction on McMs catalysts giving activation energies at 32.1-68.8 kJ/mol. With the detection of radicals by electron paramagnetic resonance (EPR), the generation mechanism was proposed.

Size-Dependent Toxicity Differences of Intratracheally Instilled Manganese Oxide Nanoparticles: Conclusions of a Subacute Animal Experiment

Incomplete information on toxicological differences of micro- and nanometer-sized particles raised concerns about the effects of the latter on health and environment. Besides chemical composition, size and surface-to-volume ratio of nanoparticles (NPs) can affect toxicity. To investigate size-dependent toxicity differences, we used particles made of dioxide of the neurotoxic heavy metal manganese (Mn), typically found in inhaled metal fumes, in three size ranges (size A, 9.14 ± 1.98 nm; size B, 42.36 ± 8.06 nm; size C, 118.31 ± 25.37 nm). For modeling the most frequent route of exposure to Mn, NPs were given to rats for 6 weeks by intratracheal instillation. Of each NP size, 3 or 6 mg/kg body weight was given while control animals were vehicle treated. Neurotoxicity was assessed by measuring spontaneous locomotor activity in an open field and by recording spontaneous and evoked electrical activity from the somatosensory cortical area. Mn content of brain, lung, and blood, measured by ICP-MS, were correlated to the observed functional alterations to see the relationship between Mn load and toxic effects. Body weight gain and organ weights were measured as general toxicological indices. The toxicity of size A and size B NPs proved to be stronger compared to size C NPs, seen most clearly in decreased body weight gain and altered spontaneous cortical activity, which were also well correlated to the internal Mn dose. Our results showed strong effect of size on NP toxicity, thus, beyond inappropriateness of toxicity data of micrometer-sized particles in evaluation of NP exposure, differentiation within the nano range may be necessary.

Facile preparation of yolk–shell structured Si/SiC@C@TiO2 nanocomposites as highly efficient photocatalysts for degrading organic dye in wastewater

The prepared yolk–shell Si/SiC@C@TiO₂ nanospheres show a strong photon absorbance throughout the visible light region, and excellent photocatalytic performance for degrading methyl blue in water under UV and visible light irradiation.

Fabrication of a compressible PU@RGO@MnO2 hybrid sponge for efficient removal of methylene blue with an excellent recyclability

The fabricated compressible polyurethane@reduced graphene oxide@manganese dioxide hybrid sponge exhibits a high removal efficiency for MB with excellent recyclability.

Preparation of PEDOT/GO, PEDOT/MnO2, and PEDOT/GO/MnO2 nanocomposites and their application in catalytic degradation of methylene blue

The nanocomposite materials of poly(3,4-ethylenedioxythiophene)/graphene oxide (PEDOT/GO), poly(3,4-ethylenedioxythiophene)/MnO2 (PEDOT/MnO2), and poly(3, 4-ethylenedioxythiophene)/graphene oxide/MnO2 (PEDOT/GO/MnO2) were successfully prepared by facile and template-free solution method. The structure and morphology of nanonanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible absorption spectra (UV-vis), field emission scanning electron microscope (FESEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDX), respectively. The catalytic activities of nanocomposites were investigated through the degradation processes of methylene blue (MB) solution under dark, UV light, and nature sunlight irradiation, respectively. The results displayed that nanocomposites were successfully synthesized, and PEDOT/GO had higher conjugation length and doped degree than pure PEDOT. However, the introduction of MnO2 could lead to the reduction of conjugation length and doped degree in PEDOT/MnO2 and PEDOT/GO/MnO2 nanocomposites. The field emission scanning electron microscope (FESEM) analysis also showed that both MnO2 and GO had some effect on the morphology of nanocomposites. The catalytic activities of pure PEDOT and nanocomposites were in the order of PEDOT/GO/MnO2 > PEDOT/MnO2 > PEDOT/GO > pure PEDOT. Besides, the catalytic results also showed that the highest degradation efficiency of MB after 7 h occurred in the PEDOT/GO/MnO2 composite in three irradiation.

Manganese oxide nanostructures: low-temperature selective synthesis and thermal conversion

γ-MnOOH nanorods, δ-MnO₂ nanosheets, α-Mn₂O₃ nanocubes, and Mn₃O₄ nanoparticles were selectively prepared via a facile, high-yield and low-temperature reduction route.

Control of manganese dioxide crystallographic structure in the redox reaction between graphene and permanganate ions and their electrochemical performance

MnO₂ crystallographic structure was well controlled in the redox reaction between graphene and permanganate ions.

Facile one pot synthesis and Li-cycling properties of MnO2

MnO₂ compounds prepared by a molten salt method (MSM) using three different Mn-salts and studied for its electrochemical properties.

Multi-shelled hollow micro-/nanostructures

Recent advances in multi-shelled hollow micro-/nanostructures were reviewed, and the correlation between their geometric properties and specific performance was highlighted.

Anion-assisted one-pot synthesis of 1D magnetic α- and β-MnO2 nanostructures for recyclable water treatment application

The as-prepared MnO₂, especially β-MnO₂, exhibits superior degradation ability compared to the conventional adsorbents.

Do transition metal carbonates have greater lithium storage capability than oxides? A case study of monodisperse CoCO3 and CoO microspindles

As substitutions for transition metal oxides (MOs), transition metal carbonates (MCO3) have been attracting more and more attention because of their lithium storage ability in recent years. Is MCO3 better than MOs for lithium storage? To answer this question, monodisperse CoCO3 and CoO microspindles with comparable structures were synthesized and investigated as a case study. Excluding its structural effect, we found CoCO3 still exhibited reversible capacities and rate capabilities much higher than those of CoO. The reversible capacity of CoCO3 after 10 cycles was 1065 mAh g(-1), 48.2% higher than that (∼720 mAh g(-1)) of CoO. Furthermore, the greatly different electrochemical behaviors were investigated by analyzing the discharge-charge profiles, cyclic voltammetry curves, and Nyquist plots in depth. This work can improve our understanding of the lithium storage advantages of MCO3 against MOs and enlighten us in terms of developing high-performance MCO3 with favorable structures.

MnO2 prepared by hydrothermal method and electrochemical performance as anode for lithium-ion battery

Two α-MnO2 crystals with caddice-clew-like and urchin-like morphologies are prepared by the hydrothermal method, and their structure and electrochemical performance are characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), galvanostatic cell cycling, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). The morphology of the MnO2 prepared under acidic condition is urchin-like, while the one prepared under neutral condition is caddice-clew-like. The identical crystalline phase of MnO2 crystals is essential to evaluate the relationship between electrochemical performances and morphologies for lithium-ion battery application. In this study, urchin-like α-MnO2 crystals with compact structure have better electrochemical performance due to the higher specific capacity and lower impedance. We find that the relationship between electrochemical performance and morphology is different when MnO2 material used as electrochemical supercapacitor or as anode of lithium-ion battery. For lithium-ion battery application, urchin-like MnO2 material has better electrochemical performance.