Electrolytic Manganese Dioxide Samples Research Articles

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.

Heat-Treated Electrolytic Manganese Dioxide as an Efficient Catalyst for Oxygen Reduction Reaction in Alkaline Electrolyte

We developed an oxygen depolarized cathode (ODC) catalyst that can be employed for industrial chlor-alkali electrolysis by improving the oxygen reduction reaction (ORR) activity of commercially available electrolytic manganese dioxide (EMD). The ORR activity of EMD was systematically investigated by rotating disc electrode (RDE) measurements for EMD samples having different particle sizes and heat-treated at different temperatures. We found that the ORR activity of EMD became comparable to commercially available platinized carbon (Pt/C) when EMD with a median diameter of 0.5 μm was heat-treated at 500 °C. From XPS analysis, the EMD heat-treated at 500 °C contains many surface oxygen vacancies that were advantageous for adsorption of oxygen molecules. The obtained EMD sample was assembled into an ODC electrode and its ORR performance was evaluated under chlor-alkali electrolysis conditions (32.5 wt% NaOH, 88 °C). The heat-treated EMD showed an overpotential of ∼0.1 V smaller (at a current density of −1.0 A cm−2) than the benchmark catalyst, i.e., Ag particles. The catalyst we developed is therefore a most promising candidates to replace precious metal catalysts, owing to industrially valuable features such as low cost, simple synthesis method, and high ORR activity.

PH-Controlled Electrolysis of Electrolytic Manganese Dioxide (EMD) for Improved Cycle Life of Rechargeable MnO2/Zn Batteries

A systematic study of the effect of acid concentration (0.5–5 M H2SO4) on the electrolysis of electrolytic manganese dioxide (EMD or γ-MnO2) has been performed. All the samples were characterized for their phase and crystallinity, their structural water, the pyrolusitic-to-ramsdellite ratio, BET surface area, pore size range; and were examined for their electrochemical performance. Concentration of the electrolysis acid affects the structural water content and the pyrolusitic-to-ramsdellite ratio of the γ-MnO2 phase as well as the surface area and pore size. The best cycling performance was achieved for the samples prepared with an electrolysis bath containing an acid concentration of about 2 M H2SO4. Electrochemical performance over 100 cycles of the EMD prepared in 2 M H2SO4 has shown higher energy efficiency and improved longer term cycling performance compared to commercial EMD products. Post-mortem analysis of the cycled EMD samples show partial loss of the EMD phase, loss of water content, and growth of irreversible manganese dioxide phases.

PH-Controlled Electrolysis of Electrolytic Manganese Dioxide (EMD) for Improved Rechargeable MnO2/Zn Batteries

Alkaline batteries with the MnO2/Zn chemistry offer a number of advantages over other aqueous batteries (e.g., lead acid) including: a) high energy density, b) lower cost, and c) longer shelf life. The main active material used in the cathode electrode of these batteries is manganese dioxide, which has a low production cost, low toxicity, high specific capacity, low self-drain rate, and is abundant in nature. However, alkaline batteries cannot be easily recharged due to the rapid capacity loss and low energy efficiency of the MnO2 product used. An approach to improving the rechargeability of alkaline batteries may be synthesizing higher quality and/or modified manganese dioxide material. Manganese dioxide is a highly versatile substance that can grow into various crystal structures with different synthesis methods and be used in applications such as lithium-ion batteries, water oxidation electrocatalysts, etc. The preferred manganese dioxide used in alkaline batteries is electrolytic manganese dioxide (EMD) with a crystal structure which is an intergrowth of two different phases, pyrolusite and ramsdellite, which consist of arrays of MnO6 octahedra in 1 x 1 and 1 x 2 tunnels, respectively. The tunnels in the structure allow for the intercalation/deintercalation of protons during the discharge and charge processes. The EMD structure also contains protons (Ruetschi and Coleman protons) in the form of OH- complexes (also referred to as structural water) which provide a proton bridge, thus increasing the rate of proton diffusion into the lattice structure. The structural water content of EMD is an important parameter for the overall performance and has not been thoroughly reported before. Electrodeposition of EMD relies on the oxidation of Mn2+ to Mn4+ on a stable, conductive metal anode (e.g. titanium, nickel, etc.) in an acidic environment (typically H2SO4) which determines the water content. The EMD samples were electrodeposited by electrolysis of MnSO4 onto a titanium anode (4 cm × 14 cm × 2 mm) in an electrolyte solution containing 1.25 M MnSO4 and H2SO4 ranging from 0.5-5 M of H2SO4 at 95 oC using a current density of 115 A m-2. Electrosynthesis was performed for a period of 15 hours, thereafter, the deposits were chipped, grounded, washed, and filtered. The samples were then characterized using Thermogravemetric Analysis (TGA), X-Ray Diffraction (XRD), and Brunauer–Emmett–Teller (BET) surface area analysis techniques. Electrochemical properties of the EMD sample were examined with flat-plate cells using a zinc anode and a 9M KOH electrolyte solution and were cycled at a rate of C/10. Electrochemical impedance spectroscopy analysis was performed using a half-cell set-up using a nickel mesh as the counter electrode and an Hg/HgO reference electrode. The EMD samples synthesized with a manganese salt to acid ratio of 1.25:2 show a structural water content and surface area which are nearly twice that of the commercially available EMD products. Additionally, the ramsdellite fraction of the EMD samples increases by about 40%. EMD samples prepared in 2M acid solution exhibit improved cycling performance (see Figure) and energy efficiency when compared to commercial EMD products. The increase in water content is one possible explanation for the enhancement of the protonic conductivity of the in-house EMD as well as its improved physical characteristics. Synthesis and characterization of EMD samples and their electrochemical results will be presented Figure 1

Electrodeposition of Sea Urchin and Cauliflower‐like Nickel‐/Cobalt‐Doped Manganese Dioxide Hierarchical Nanostructures with Improved Energy‐Storage Behavior

AbstractTransforming the existing Zn–MnO2 primary battery into a secondary battery with enhanced storage behavior and a low cost is of significant interest. Such technology could underpin future energy‐storage development. To acquire this, doped electrolytic manganese dioxide (EMD) with hierarchical nanoarchitectures have been employed as a cathode in the Zn–MnO2 system. EMD is synthesized from manganese sulfate in a sulfuric acid bath with in situ doping of nickel and cobalt ions individually. Sea‐urchin‐shaped EMD has been obtained with nickel as a dopant, whereas cauliflower‐ and pyramidal‐shaped hierarchical nanostructures are observed with cobalt as a dopant, using a facile galvanostatic method without employing any template or surfactant. The structural studies indicated that all EMD samples (in the absence and presence of dopants) are predominantly composed of gamma‐type manganese dioxide; however, the peak intensity increased with increasing concentration of the dopants. The electrochemical results revealed that the Co‐doped EMD composite played a crucial role in increasing the storage capacity of the Zn–MnO2 battery, whereas the Ni‐doped EMD composite resulted in improved longevity compared the Co‐doped and undoped counterparts. The EMD composites individually doped with Ni and Co resulted in improved storage behaviors of 395 and 670 mA h g−1, respectively, against the undoped sample which is 220 mA h g−1, implying that the presence of Co3O4 and mesoporous nanostructured surfaces enhanced the fast kinetics of electrochemical reactions.

Faradaic and Non-Faradaic Contributions to the Power and Energy Characteristics of Electrolytic Manganese Dioxide for Electrochemical Capacitors

Step potential electrochemical spectroscopy (SPECS) has been applied to a range of different electrolytic manganese dioxide (EMD) samples to examine the changes in the charge storage mechanism as a function of the scan rate. The SPECS method allowed the charge storage contributions due to double layer and pseudo-capacitance to be decoupled. The charge storage mechanism has been shown to transition from predominantly pseudo-capacitive behavior to predominantly double layer behavior as the scan rate is increased. The relative contributions from each of these processes to the overall specific energy and power of each EMD samples has been analyzed and related to the properties of each material.

Dual Effect of Anionic Surfactants in the Electrodeposited MnO2 Trafficking Redox Ions for Energy Storage

The dual effect of in-situ addition of anionic surfactants, sodium octyl sulfate (SOS), sodium dodecyl sulfate (SDS) and sodium tetradecyl sulfate (STS) on the microstructure and electrochemical properties of electrolytic manganese dioxide (EMD) produced from waste low grade manganese residue is discussed. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), BET-surface area studies, thermogravimetry-differential thermal analysis (TG-DTA) and Fourier transform infrared spectroscopy (FTIR) were used to determine the structure and chemistry of the EMD. All EMD samples were found to contain predominantly γ-phase MnO2, which is electrochemically active for energy storage applications. FESEM images showed that needle, rod and flower shaped nano-particles with a porous surface and platy nano-particles were obtained in the case of EMD deposited with and without surfactant respectively. Thermal studies showed loss of structural water and formation of lower manganese oxides indicating high stability of the EMD samples. The cyclic voltammetry and charge – discharge characteristics implied the presence of surfactants enhances the energy storage within the MnO2 structure. Addition of the surfactant at its optimum concentration greatly increased the EMD surface area, which in turn improved the cycle life of the EMD cathode. EMD obtained in the presence of 25, 50, 25 ppm of SOS, SDS, and STS respectively showed an improved cycle life relative to the EMD obtained in the absence of surfactant. EMD obtained without surfactant showed a capacity fade of 20 mAh g−1 within 15 discharge-charge cycles, while surfactant modified samples showed stable cyclic behavior of capacity 95 mAh g−1 even after 15 cycles.

Influence of alternative alkali reagents on Fe removal during recovery of Mn as Electrolytic Manganese Dioxide (EMD) from Mn sludge

Flow sheet for recovery of Mn values from Mn sludge, a by-product obtained during processing of the Mn nodules through ammonia–ammonium sulphate–sulphur dioxide leaching process route as Electrolytic Manganese Dioxide (EMD) was developed. The unit operations include dissolution of Mn sludge with sulphuric acid in presence of activated charcoal, purification of liquor in two stages—removal of Fe by adjusting pH to ~4 followed by precipitation of other impurities as sulphides by addition of Na2S. The purified liquor was electrowinned for producing EMD. During first stage purification, Fe precipitation was carried out with CaO that resulted in loss of Mn due to its entrapment in the gypsum. The paper discusses use of alternative alkali reagents MgO and NaOH to minimise the Mn loss. Physico-electrochemical characteristics of the EMD produced from the purified MnSO4 solutions obtained by using CaO, MgO and NaOH for Fe removal during stage I purification and subsequent stage II purification of other impurities as sulphides was investigated and the discharge capacities of the EMD samples were found to be 267, 260 and 250mAhg−1 respectively.

Influence of the microstructure and its stability on the electrochemical properties of EMD produced from a range of precursors

The influence of the microstructure and the stable crystal structure on the electrochemical properties of the electrolytic manganese dioxide (EMD) produced from manganese cake (EMDMC), low-grade manganese ore (EMDLMO), and synthetic manganese sulfate solutions (EMDSMS) is reported. X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry/differential thermal analysis, field emission scanning electron microscopy (FESEM), and chemical analyses were used to determine the structural and chemical characteristics of the EMD samples. The charge–discharge profile was studied in 9 M KOH using a galvanostatic charge–discharge unit. All the samples were found to contain predominantly γ-phase MnO2, which is electrochemically active for energy storage applications. FESEM images show that preparation method significantly influences surface morphology, shape, and size of the EMD particles. In almost all cases, nanoparticles were obtained, with spindle-shaped nanoparticles for EMDMC, platy nanoparticles in the case of EMDLMO, and anisotropic growth of tetra-branched star-like nanoparticles of EMDSMS. These nanoparticles arrange themselves in a near net-like fashion, resulting in porosity of the flakes of EMD during electrochemical deposition. Thermal studies showed loss of structural water and formation of lower manganese oxides. The EMDMC showed superior discharge capacity of ~280 mAh g−1 as compared to EMDLMO (275 mAh g−1) and EMDSMS (245 mAh g−1).

Electrodeposition of manganese dioxide: effect of quaternary amines

The effect of quaternary ammonium salts (tetraethyl ammonium bromide, tetrapropyl ammonium bromide, and tetrabutyl ammonium bromide) on the structural, morphological, and electrochemical characteristics of electrolytic manganese dioxide (EMD) obtained from acidic aqueous sulfate solution has been investigated. Physical characterization of the EMD was achieved by X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, differential thermal analysis, and Fourier transform infrared spectroscopy. The charge–discharge profile of the materials was determined to evaluate their potential for alkaline battery applications. The presence of these quaternary ammonium salts as organic additives in the solution increased the current efficiency while decreasing energy consumption during electrochemical deposition of manganese dioxide (MnO2). All the additives influenced the discharge characteristics of the EMD samples significantly, producing a cathode material with increased cumulative discharge capacity relative to EMD prepared in the absence of additives. This is attributed to the ability of the additives to affect the particle size and morphology, and therefore electrochemical activity, of electrodeposited materials; the effects in the case of the additives investigated in this work were positive, producing a material with potential application to battery technology.

Heat Treated Electrolytic Manganese Dioxide for Li/MnO2 Batteries: Effect of Precursor Properties

The present study demonstrates that the properties of heat-treated electrolytic manganese dioxide (EMD) materials can be linked to the key properties of the precursor EMD used. The investigation holds particular significance for the informed selection of precursor EMD materials that result in superior performing heat treated materials in Li/MnO2 batteries. Kinetic analysis is used to determine the precise heating regime necessary to, theoretically, completely remove structural water from six different EMD samples. It was found that the oxidation of Mn(III) to Mn(IV) occurred to a greater extent for samples with initially high pyrolusite content and a low fraction of cation vacancies after heat treatment at low temperatures. This same Mn(III) to Mn(IV) conversion was also enhanced after high temperature treatment for those samples with a higher manganese content and low cation vacancy fraction. Additionally, at low heat treatment temperatures the parent γ-MnO2 structure and cation vacancies were better retained in samples with low starting BET surface area. Finally, this work determined that samples with high BET surface area tend to lose proportionally less of this value as a consequence of heat treatment, compared to those with low initial values.

Thermal Treatment Effects on Manganese Dioxide Structure, Morphology and Electrochemical Performance

Kinetic analysis is used to determine the required isothermal heating time at various temperatures to theoretically completely remove water from an electrolytic manganese dioxide (EMD) sample. The effect of the heat treatment regime on material structure, morphology and composition is investigated using various physical techniques, including X-ray diffraction and gas adsorption. Further, the electrochemical performance of heat treated EMD (HEMD) samples at a range of discharge rates finds that material properties such as retention of the γ-MnO2 structure and high surface area for the sample heat treated at 250°C, and extensive structural conversion and micro-pore closure in the case of the 350°C material, lead to higher capacity and power output. Conversely, significant amounts of structural water in the 200°C sample, and the compromise in structural rearrangement and surface area loss for the material prepared at 300°C, result in poor electrochemical behaviour, especially at high discharge rates. Particularly evident from this study is the complex interplay between the heat treatment regime, resulting HEMD properties and electrochemical performance.

Porosity Changes during Reduction of γ-MnO2 for Aqueous Alkaline Applications

In this work a structural and porosity analysis of a series of chemically reduced electrolytic manganese dioxide (EMD) samples has been carried out. EMD, or , for use in aqueous alkaline cathodes possesses an orthorhombic unit cell that progressively increases in size as reduction continues. This unit cell expansion is nonuniform, with dimensional changes being different in all three dimensions . The unit cell expansion is the direct result of the reduction process, with the discharge products ( and ) being larger than the corresponding ions in the host lattice ( and ). Gas adsorption isotherms on the same series of reduced EMD samples demonstrated that the Brunauer–Emmett–Teller surface area decreased considerably over the entire discharge compositional range. The calculated pore size distribution showed that microporosity was eliminated with reduction, but the mesopore volume increased. The origin of these changes in porosity is discussed in terms of the structural expansion, as is their effect on electrochemical performance.

Microporosity of heat-treated manganese dioxide

A structural and micro-pore analysis of a series of heat treated electrolytic manganese dioxide (EMD) samples has been conducted. In terms of crystal structure, the original EMD with γ-MnO 2 structure (orthorhombic unit cell) was found to progressively convert to β-MnO 2 (tetragonal unit cell) at elevated temperatures. The structural transition was kinetically limited, with the higher temperatures leading to a greater degree of transformation. The orthorhombic γ-MnO 2 unit cell was found to contract along the a and b axes, while along the c axis an expansion was observed only at the highest heat treatment temperatures. These changes occur as a result of manganese ion diffusion leading to the formation of a denser, more defect free material. The porosity of these heat treated EMD samples was also examined by N 2 gas adsorption combined with various interpretive techniques such as the Kelvin equation, MP method, Dubinin–Radushkevich method, Dubinin–Astakhov method and a more modern density functional theory based approach. Despite shortcomings associated with certain techniques, all clearly indicated that the EMD micro-pore volume decreased and the meso- and macro-pore volume increased as the heat treatment temperature was increased. This was justified as a result of manganese ion movement during the structural rearrangement causing the small pores to be progressively sintered shut, while the larger pores were formed as a result of stress-induced cracking in the denser final product.

Variation in the Adsorption of Lead(II) by a Range of Electrolytic Manganese Dioxides: Chemometric Examination of Correlation with Physical Properties

The adsorption of lead(II) by a range of ‘boutique’ electrolytic manganese dioxide (EMD) samples which differ in a range of physical properties has been followed at pH 5, 20°C and an ionic strength of 0.5, employing a wide range of initial lead ion concentrations from 5 × 10−5 mol/dm3 to 5 × 10−2 mol/dm3. Adsorption isotherms all fitted quite well to a simple Langmuir adsorption equation. The Langmuir parameters vary significantly for the different samples and good correlations between them and some physical properties (% water content, open circuit voltage and average crystallite size) are apparent. Further, Principal Component Regression (PCR) reveals excellent correlations between the lead(II) adsorption isotherms and some of the physical properties (water content, average crystallite size, density, total pore volume, electric conductivity, porosity, etc). A qualitative understanding of the relationship between the isotherms and the physical properties can be achieved. Adsorption of lead on partially chemically reduced EMD samples falls as the degree of reduction increases, associated with a drop in available hydrolysable surface groups with increasing degree of reduction.