Stability Of Manganese Research Articles

Synthesis and Thermal Stability of Manganese(III) Acetylacetonate

The dependence of the stability of Mn(C5H7O2)3 modifications on the properties of the solvent chosen for recrystallization is considered. Low-polarity solvents with a low dielectric permittivity enhance intermolecular interactions, which leads to the formation of the β-Mn(C5H7O2)3 modification during the synthesis of Mn(C5H7O2)3 from chloroform solutions. The use of mixtures of chloroform with petroleum ether makes it possible to control supersaturation, the rate of formation, and growth of phase nuclei due to the evaporation of chloroform under isothermal conditions. The use of polar solvents for recrystallization favors the formation of γ-Mn(C5H7O2)3. The composition of the thermal decomposition products of β‑Mn(C5H7O2)3 in a dry inert atmosphere has been determined by X-ray powder diffraction, IR spectroscopy, thermogravimetric and mass spectral analysis, and differential scanning calorimetry. In the temperature range 140–240°C, β-Mn(C5H7O2)3 melts to form Mn(C5H7O2)2. At temperatures of 500–550°С, Mn(C5H7O2)2 decomposes to a mixture of MnO, Mn3O4, Mn2O3, and carbon.

Synthesis and Thermal Stability of Manganese(III) Acetylacetonate

Synthesis and Thermal Stability of Manganese(III) Acetylacetonate

Stability of Manganese(II)-Pyrazine, -Quinoxaline or -Phenazine Complexes and Their Potential as Carbonate Sequestration Agents.

Carbonate sequestration technology is a complement of CO2 sequestration technology, which might assure its long-term viability. In this work, in order to explore the interactions between Mn2+ ion with several ligands and carbonate ion, we reported a spectrophotometric equilibrium study of complexes of Mn2+ with pyrazine, quinoxaline or phenazine and its carbonate species at 298 K. For the complexes of manganese(II)–pyrazine, manganese(II)–quinoxaline and manganese(II)–phenazine, the formation constants obtained were log β110 = 4.6 ± 0.1, log β110 = 5.9 ± 0.1 and log β110 = 6.0 ± 0.1, respectively. The formation constants for the carbonated species manganese(II)–carbonate, manganese(II)–pyrazine–carbonate, manganese(II)–quinoxaline–carbonate and manganese(II)–phenazine–carbonate complexes were log β110 = 5.1 ± 0.1, log β110 = 9.8 ± 0.1, log β110 = 11.7 ± 0.1 and log β110 = 12.7 ± 0.1, respectively. Finally, the individual calculated electronic spectra and its distribution diagram of these species are also reported. The use of N-donor ligand with π-electron-attracting activity in a manganese(II) complex might increase its interaction with carbonate ions.

Site Preference-Driven Mn4+ Stabilization in Double Perovskite Phosphor Regulating Quantum Efficiency from Zero to Champion.

The tetravalent-state stability of manganese is of primary importance for Mn4+ luminescence. Double perovskite-structured A2B'B″O6:Mn4+ has been recently prevalent, and the manganese ions are assumed to substitute for the B″(IV-VI)O6 site to stabilize at the tetravalent charge state to generate far-red emissions. However, some Mn-doped A2B'B″O6-type materials show no or weak luminescence such as typical Ca2MgWO6:Mn. In this work, a cation-pair co-substitution strategy is proposed to replace 2Ca2+ by Na+-La3+ to form Ca2-2xNaxLaxMgWO6:Mn. The significant structural distortion appears in the solid solution lattices with the contraction of [MgO6] but enlargement of [WO6] octahedron. We hypothesize that the site occupancy preference of Mn migrates from Mg2+ to W6+ sites. As a result, the effective Mn4+/Mn2+ concentration enhances remarkably to regulate nonluminescence to highly efficient Mn4+-related far-red emission. The optimal CaNa0.5La0.5MgWO6:0.9%Mn4+ shows an internal quantum efficiency of 94% and external quantum efficiency of 82%, reaching up to the top values in Mn4+-doped oxide phosphors. This work may provide a new perspective for the rational design of Mn4+-activated red phosphors, primarily considering the site occupancy modification and tetravalent-state stability of Mn.

Stability of Manganese(II) Phthalocyanine Films in Ambient Air

Stability of Manganese(II) Phthalocyanine Films in Ambient Air

Inhibiting manganese (II) from catalyzing electrolyte decomposition in lithium-ion batteries

A once overlooked source of electrolyte degradation incurred by dissolved manganese (II) species in lithium-ion batteries has been identified recently. In order to deactivate the catalytic activity of such manganese (II) ion, 1-aza-12-crown-4-ether (A12C4) with cavity size well matched manganese (II) ion is used in this work as electrolyte additive. Theoretical and experimental results show that stable complex forms between A12C4 and manganese (II) ions in the electrolyte, which does not affect the solvation of Li ions. The strong binding effect of A12C4 additive reduces the charge density of manganese (II) ion and inhibits its destruction of the PF6− structure in the electrolyte, leading to greatly improved thermal stability of manganese (II) ions-containing electrolyte. In addition to bulk electrolyte, A12C4 additive also shows capability in preventing Mn2+ from degrading SEI on graphite surface. Such bulk and interphasial stability introduced by A12C4 leads to significantly improved cycling performance of LIBs.

Release Characteristics of Manganese in Soil under Ion-absorbed Rare Earth Mining Conditions

ABSTRACT The use of high-concentration ammonium sulfate leaching agent for the mining of ion-absorbed rare earth ore will change the soil environment properties, thereby inducing the release of associated heavy metals. Serious manganese pollution has been observed in the environment of rare earth mining areas, but the environmental chemical process of manganese in the raw ore soil has not been fully recognized. In this study, a sequential extraction experiment showed that the manganese in the soil included acid extractable form, reducible form, oxidizable form, and residual form, among which residual form and reducible form were the main forms. According to the release kinetics experiment, the release process of manganese included the fast release and slow release, which was controlled by multiple diffusion mechanisms and could be optimally fitted with the Elovich equation. The treatment of ammonium sulfate leaching agent could reduce the proportion of reducible form and increase the proportion of residual form, but there was no significant change in other forms. In addition, batch release experiments indicated that leaching factors (the initial concentration and initial pH of leaching agent, and temperature) could affect the release of manganese. Lower pH and higher temperature were not conducive to the stability of manganese and significantly aggravated the release amount. Excessive initial concentration had a certain inhibitory effect on the release amount, but the effect was weak. Considering the significant effect of initial pH and temperature on the release of manganese, during the mining process of ion-absorbed rare earth, controlling the initial pH of leaching agent and reducing the mining scale in the hot summer are the key measures to manage the release risk of manganese.

Improving electrochemical properties and structural stability of lithium manganese silicates as cathode materials for lithium ion batteries via introducing lithium excess

The serious capacity decay caused by structural amorphization is still a major issue for polyanion-type lithium manganese silicates (Li2MnSiO4) as cathode material for lithium ion batteries. In this work, a new strategy for alleviating the structural instability via the introduction of excess lithium into the host crystal lattice is provided. A comprehensive study demonstrates that the required energy for the extraction/insertion of lithium ions into host crystal lattice was decreased as a result of changed local environment of cations in the compound after the excess lithium occupancy in lattice. Importantly, it was found that Li-rich samples deliver higher reversible capacity and increased average potential than pristine sample, indicating the improved energy density of polyanion-type Li2 + 2xMn1 − xSiO4/C. Additionally, the structure of Li2.2 sample was kept intact, while the Li2.0 sample was transformed to amorphous state at 200 mA h g−1 during the initial charging process by controlling the charge cut-off potential. As expected, the introduction of a certain amount of excess lithium into Li2MnSiO4 is explored as a route to achieving increased capacity with more movable lithium, while maintaining its structural stability and cyclic stability.

Preparation of manganese oxide/graphene oxide hydrogel for capacitive energy storage

Electrodepositing manganese oxide into graphene hydrogel provides a facile and effective way to make full use of structural features of the hydrogel and capacity advantage of manganese oxide. The electrodeposition conditions play a key role in the deposition of manganese oxide, but little is known about their effect on electrochemical properties of the hybrid electrodes. Here, we systematically clarify the influences of deposition parameters (including current density, deposition time, Mn2+ concentration and bath temperature) on the capacitive performance (including apparent capacitance, specific capacitance, rate capability, cycling stability and charge storage mechanism) of manganese oxide/graphene oxide hydrogel hybrid electrodes. Under the proper preparation conditions, the highest specific capacitance of 453.7 F g−1 is obtained, and 92.4% capacitance retention (419.2 F g−1) is maintained after 5000 charge/discharge cycles, indicating excellent charge storage capability and cycling stability.

On the thermal stability of manganese(II) sulfate and its reaction with zeolite A to form the sodalite Na6Mn2[Al6Si6O24](SO4)2

Thermal gravimetric analysis and in situ high-temperature powder X-ray diffraction (HT-PXRD) revealed that MnSO4 begins to thermally decompose under air at ~625 °C, which is significantly lower than the values reported in the literature. The reaction is kinetically sluggish and yields bixbyite, Mn2O3, ≳625 °C and hausmannite, Mn3O4, ≳850 °C. Na6Mn2[Al6Si6O24](SO4)2 was prepared as a novel sodalite-type phase by reacting zeolite A, Na6[Al6Si6O24], with MnSO4 as a compacted mixed-powder monolith at 650 °C under air. In situ HT-PXRD indicated that this reaction commenced at about 620 °C. Rietveld refinement of the PXRD data recorded at 20 °C showed that Na6Mn2[Al6Si6O24](SO4)2 crystallizes with a cubic cell, a = 0.89780(2) nm, and is isostructural (I4¯3m) with the mineral haüyne, Na6Ca2[Al6Si6O24](SO4)2. The product material contained traces of Mn2O3 which imparts a purplish-brown coloration; highlighting the problem of preparing Na6Mn2[Al6Si6O24](SO4)2 as a monophasic material within the narrow temperature ‘window’ available for this reaction.

Control of Size and Composition of Colloidal Nanocrystals of Manganese Oxide.

A comprehensive study on the effects of experimental parameters on the composition and size of manganese oxide nanocrystals was completed using colloidal chemistry. The reactions studied involved the thermolysis of Mn2+ acetate and Mn3+ acetylacetonate in oleylamine. Temperature was found to be the dominant factor affecting the composition and size of the products. Reactions completed below 200 °C favored the formation of nanocrystals smaller than 20 nm, with the presence of even impurity amounts of oxidizing agents leading to the formation of Mn3O4. Nanocrystals of MnO could only be synthesized below 200 °C if Mn2+ acetate was used, and the reaction was carefully controlled to have no O2 and H2O contamination. In turn, particle growth was rapid above this temperature. In this case, regardless of the oxidizing agents used or oxidation state of the Mn precursor, nanocrystals of MnO formed after annealing for at least 1 h at temperatures higher than 200 °C. This finding suggests the role of oleylamine as solvent, surfactant, and reducing agent at sufficiently high annealing temperatures. These results increase the understanding of redox stability of manganese during the colloidal synthesis of semiconductor metal oxide nanocrystals.

Boosting electrochemical water oxidation through replacement of Oh Co sites in cobalt oxide spinel with manganese.

The strikingly high catalytic performance and stability of manganese substituted cobalt oxide spinel (MnxCo3-xO4) over pristine cobalt oxide spinel (Co3O4) for the alkaline electrochemical water oxidation is reported. The different role of cations could be uncovered along with the detection of drastic surface-structural changes during the catalysis using spectroscopic and microscopic methods.

Oxygen atom transfer reactions from sterically encumbered brominated (oxo)manganese(V) corroles to styrene

Seven A3- and trans-A2B manganese(III) corroles (1–7-Mn) differing widely in their electronic and steric features were synthesized and transformed to their corresponding [Formula: see text]-brominated manganese(III) corroles derivatives (1a–7a-Mn). Their corresponding (oxo)manganese(V) corroles 1–7-Mn(oxo) and 1a–7a-Mn(oxo) were further prepapred by treating with iodosylbenzene (PhIO). The reactivity for the oxygen atom transfer from 1–7-Mn(oxo) to styrene followed the order of 1-Mn(oxo) > 2-Mn(oxo) > 7-Mn(oxo) > 4-Mn(oxo) > 3-Mn(oxo) > 6-Mn(oxo) [Formula: see text]5-Mn(oxo). The same pattern was observed for their [Formula: see text]-brominated analogs 1a–7a-Mn(oxo), albeit their reactivity was remarkably higher. The steric protection of [Formula: see text] moiety by ortho–ortho′-dibromophenyl substituents was found to enhance the stability of (oxo)manganese(V) corroles significantly.

Study on the hydrothermal and SO2 stability of Al2O3-supported manganese and iron oxide catalysts for lean CO oxidation

This paper addresses the hydrothermal stability and SO2 poisoning resistance of Al2O3-supported manganese and iron oxide catalysts for lean CO oxidation. Catalysts were used in the form of powders and coated cordierite monoliths. Bare catalysts mostly comprised Mn and Fe loadings of 20wt% and were prepared by impregnation and flame spray pyrolysis (FSP). The hydrothermal treatment was conducted at 700°C. Monolithic catalysts were evaluated toward CO oxidation, and powders were characterized by X-ray diffraction, N2 physisorption, X-ray absorption near-edge spectroscopy and transmission electron microscopy. Catalytic tests indicated higher hydrothermal stability of the FSP samples, whereas the corresponding Mn catalyst was most stable and most active. The superior stability of the FSP catalysts was associated with the maintenance of their nanocrystallinity and high active surface area. Furthermore, the hydrothermal treatment of the manganese oxide catalysts was accompanied by formation of the thermodynamically preferred Mn3O4.The SO2 poisoning of selected Mn-based powders was performed at 150°C and led to strong decrease in catalytic performance, likely due to formation of sulfate species on Mn sites and alumina surface. The FSP catalyst could be partially regenerated by annealing at 700°C, related to its thermal stability and homogeneous dispersion of the manganese moieties.

A Study on Structural and Electrochemical Properties of Co Fixed LiNi0.5+XCo0.2Mn0.3-XO2 (x=0, 0.1, 0.2) Using Synchrotron Based X-Ray Techniques

A recent attention in lithium ion battery research is focused on increasing its energy density and structural stability. As a result, the layered Li[NixCoyMnz]O2 (x+y+z=1) electrode materials have attracted a great deal of attention as an alternative of LiCoO2, due to its remarkable electrochemical properties. This three-component system shows high capacity of LiNiO2, layered character of LiCoO2, low cost and thermal stability of manganese in LiMnO2.[1,2] Recently, a lot of research is being carried out to improve the energy density by increasing the Ni content. However, there is always a trade-off between the benefits of large amount of Ni atoms and the risk of side effects, such as poor thermal stability and lower cyclability. In this study, the structural and electrochemical properties of Co fixed LiNi0.5+xCo0.2Mn0.3-xO2 (x=0, 0.1, 0.2) cathode material were investigated by using synchrotron based X-ray diffraction and absorption techniques to understand the effects of Ni and Mn components. The Rietveld refinement of diffraction data was performed by using R-3m model. Refinement results show that lattice parameters of LiNi0.5Co0.2Mn0.3O2 (x=0) are a=2.8697Å, c=14.2378Å, and by increasing the nickel content in LiNi0.5+xCo0.2Mn0.3-xO2 (x=0, 0.1, 0.2)lattice parameters “a” and “c” shrinkas shown in Table 1. Generally, it is believed that the Ni2+ content in the Li layer increase when the total amount of Ni component increase in the three component system. However, in the Co fixed LiNi0.5+xCo0.2Mn0.3-xO2 cathode material system, interestingly cation mixing decreases by increasing the nickel content. The NCM721 (x=0.2) electrode has lower Ni2+ ions in the lithium layer compared to NCM622 (x=0.1) which has even lower quantity of Ni2+ ions than that of NCM523 (x=0). In pristine electrode material, the theoretical value of average Ni oxidation state is Ni2.4+, Ni2.67+, Ni2.86+ for x=0, 0.1, 0.2 respectively and this trend is confirmed by Ni K-edge XANES spectra. The Ni K-edge XANES spectra show shift in energy position with change of nickel content in the electrode material. In NCM523, Ni K-edge position is close to that of Ni2+, while that of NCM721 is at higher energy position, indicating higher Ni valence (close to Ni3+) as shown in Figure 1. The increase of average Ni oxidation state in NCM721 pristine material suggests that Ni3+ component is predominant in its transition metal layer. Therefore, shrinking of lattice parameters by increasing the the nickel quantity can be explained on the basis of Ni3+ content in the transition metal layer. In the Co fixed system (rCo3 +=0.545Å), the unit cell dimensions in a hexagonal setting shrink by increasing the Ni content because of the difference in size between divalent and trivalent nickel ions (rNi2+=0.69Å and rNi3+=0.56Å). When the Ni3+ increases, the Ni2+ and the Mn4+ (rMn4 + =0.53Å) content decrease, net result is decrease in lattice parameters because the increment is small (rNi3+-rMn4+=0.03Å) compare to the decrement (rNi3+-rNi2+=-0.13Å). For the Ni2+ content in Li layer, we can also say that there is low opportunity for Ni2+ to go into the Li layer because the total amount of Ni2+ content decreases with increase of the Ni content. Consequently, these effects of nickel content in the layered structure would affect electrochemical properties such as capacity, cyclability and rate capability; hence their study can assist in designing safe and high performing electrode materials. The more detailed structural and electrochemical properties of Co fixed LiNi0.5+xCo0.2Mn0.3-xO2 cathode material will be presented at the time of meeting.[1] M.S. Whittingham, Chem. Rev. 104 (2004) 4271-4301[2] K.-W. Nam et al., Journal of Power Sources 189 (2009) 515-518

Structural Changes and Thermal Decomposition of Ni Based Cathode Materials for Li-Ion Batteries Studied By in-Situ XRD

The three-component system Li[NixCoyMnz]O2 has outstanding electrochemical properties due to advantage of the high capacity of LiNiO2, thermal stability and low cost of manganese in LiMnO2 and layered characteristics of LiCoO2. While capacity of Li[NixCoyMnz]O2 is similar to capacity of LiCoO2, it is a promising alternative in terms of performance, safety and cost. Various material combinations are being developed to achieve the higher capacity by increasing Ni content while retaining its advantages. Although higher Ni content contributes to better capacity in Li[NixCoyMnz]O2, but on the other hand, it tends to decrease the thermal stability of electrode material. Safety is one of the most important considerations in EV and HEV. First experimental condition is same state of charge with different Ni contents. Interesting phase transition behavior during heating is observed in Li0.66Ni0.5Co0.2Mn0.3O2 cathode material. Li0.66Ni0.5Co0.2Mn0.3O2 without electrolyte converts from layered (R-3m) structure to disordered LiM2O4-type spinel (Fd-3m) around 415 ºC. Upon further heating, M3O4-type spinel (Fd-3m) appears and co-exists with LiM2O4-type spinel (Fd-3m) from 497 ºC and remains in this structure up to 600 ºC. In the absence of electrolyte, no peaks of MO-type rock salt phase (Fm-3m) appear until 600 ºC whereas in the presence of electrolyte, further phase transition from M3O4-type spinel (Fd-3m) to MO-type rock salt phase (Fm-3m) takes place above 415 ºC. The electrolyte accelerates the thermal decomposition of charged cathode materials. The presence of electrolyte alters the paths of structural changes and lowers the onset temperatures of thermal decomposition reactions. In case of Li0.66Ni0.5Co0.2Mn0.3O2with electrolyte, more dramatic structural changes are observed in comparison with the one in the absence of electrolyte. The sample with electrolyte shows the structural decomposition to MO-type rock salt phase at 415 ºC, in the early stage of heating. Thermal behavior of Li0.33Ni0.6Co0.2Mn0.2O2 cathode material is similar to the one of Li0.66Ni0.5Co0.2Mn0.3O2. Li0.33Ni0.6Co0.2Mn0.2O2 without electrolyte converts from layered (R-3m) structure to disordered LiM2O4-type spinel (Fd-3m) around 374 ºC. Upon further heating, M3O4-type spinel (Fd-3m) co-exists with LiM2O4-type spinel (Fd-3m) from 497 ºC and maintains this structure up to 600 ºC. Presence of electrolyte initiates additional phase transitions in this cathode material. M3O4-type spinel (Fd-3m) starts to convert into MO-type rock salt phase (Fm-3m) at 374 ºC. Above 579 ºC, pure MO-type rock salt phase (Fm-3m) is observed. Second condition is same Ni contents in electrode material with different state of charge. The thermal behavior of Li0.66Ni0.5Co0.2Mn0.3O2 cathode material is mentioned above. Li0.33Ni0.6Co0.2Mn0.2O2 without electrolyte converts from layered (R-3m) structure to disordered LiM2O4-type spinel (Fd-3m) around 340 ºC. Upon further heating, M3O4-type spinel (Fd-3m) co-exists with LiM2O4-type spinel (Fd-3m) from 449 ºC and maintains this structure up to 600 ºC. Presence of electrolyte initiates additional phase transitions in this cathode material. M3O4-type spinel (Fd-3m) starts to convert into MO-type rock salt phase (Fm-3m) at 436 ºC. Above 560 ºC, pure MO-type rock salt phase (Fm-3m) is observed. In the presence of electrolyte, thermal induced phase transition of Li0.33Ni0.6Co0.2Mn0.2O2 shows conversion from LiM2O4-type spinel (Fd-3m) through M3O4-type spinel (Fd-3m) to MO-type rock salt phase (Fm-3m) step by step. On the other hand, thermal decomposition behavior of Li0.66Ni0.6Co0.2Mn0.2O2 shows phase transition to M3O4-type spinel (Fd-3m) and MO-type rock salt phase (Fm-3m) at the same time. This result of different thermal behavior of Li0.66Ni0.6Co0.2Mn0.2O2 and Li0.33Ni0.6Co0.2Mn0.2O2contributes towards better understanding for thermal stability of Ni-based cathode materials. Working on other samples and more detailed discussion will be presented at the time of meeting.Fig1. In-situ XRD patterns of the (a) 33% (b) 66% SOC LiNi0.6Co0.2Mn0.2O2 in the presence of electrolyte heated from 25℃ to 600℃

Significant electrochemical stability of manganese dioxide/polyaniline coaxial nanowires by self-terminated double surfactant polymerization for pseudocapacitor electrode

Manganese dioxide/polyaniline coaxial nanowire networks are prepared by using double surfactant approach. This approach improves the interaction between the two active materials which has been confirmed by FTIR and XPS measurements, and yields a controllable uniform thin coating of polyaniline on the well-dispersed manganese dioxide nanowires. This hybrid heteronanostructure enhances the conductivity and capacitive performance of the supercapacitor electrode. The electrochemical test delivers specific capacitance as high as 498 and 873 F g−1 at 2 and 0.25 A g−1, respectively. Good cycling stability of up to 5000 cycles (5% capacitive degradation) outperforms other currently available redox nanocomposite electrodes. This result shows that the interaction among the active materials and improved nanostructure design are the two important factors to boost up the electrochemical performance of the hybrid nanomaterials. This work illustrates a promising platform that can be adopted for a myriad of metal oxide-conducting polymer nanocomposites while reaping the benefit as low cost electrode material for supercapacitor application.

Cation inter-diffusion between LaMnO 3 and LaCoO 3 materials

Cation inter-diffusion between polycrystalline LaMnO 3 and LaCoO 3 pellets has been studied at 1373–1673 K in air by electron microprobe analysis. Inter-diffusion coefficients were evaluated by the Boltzman–Matano method from Mn 3+ to Co 3+ concentration profiles. The cation inter-diffusion is thermally activated and follows Arrhenius behaviour. The activation energies have been calculated and the mechanism for the B-site cation diffusion in La(Mn,Co)O 3 solid solution suggested. Cation diffusion coefficients in the end members LaMnO 3 and LaCoO 3 were estimated. Cation mobility in LaMnO 3 is higher than in LaCoO 3. It is suggested that higher cation diffusion in LaMnO 3 is due to the specific defect chemistry of this material, caused by the relative stability of manganese in a higher oxidation state (Mn 4+). The results are compared to previous reports on cation diffusion in perovskite oxides.

A mechanistic study on the disproportionation and oxidative degradation of phenothiazine derivatives by manganese(III) complexes in phosphate acidic media

The oxidative degradation of phenothiazine derivatives (PTZ) by manganese(III) was studied in the presence of a large excess of manganese(III)-pyrophosphate (P2O7 2−), phosphate (PO4 3−), and H+ ions using UV–vis. spectroscopy. The first irreversible step is a fast reaction between phenothiazine and manganese pyrophosphate leading to the complete conversion to a stable phenothiazine radical. In the second step, the cation radical is oxidized by manganese to a dication, which subsequently hydrolyzes to phenothiazine 5-oxide. The reaction rate is controlled by the coordination and stability of manganese(III) ion influenced by the reduction potential of these ions and their strong ability to oxidize many reducing agents. The cation radical might also be transformed to the final product in another competing reaction. The final product, phenothiazine 5-oxide, is also formed via a disproportionation reaction. The kinetics of the second step of the oxidative degradation could be studied in acidic phosphate media due to the large difference in the rates of the first and further processes. Linear dependences of the pseudo-first-order rate constants (k obs) on [MnIII] with a significant non-zero intercept were established for the degradation of phenothiazine radicals. The rate is dependent on [H+] and independent of [PTZ] within the excess concentration range of the manganese(III) complexes used in the isolation method. The kinetics of the disproportionation of the phenothiazine radical have been studied independently from the further oxidative degradation process in acidic sulphate media. The rate is inversely dependent on [PTZ+.], dependent on [H+], and increases slightly with decreasing H+ concentration. Mechanistic consequences of all these results are discussed.

Remarkable Stability of Supercapacitor Material Synthesized by Manganese Oxide Filled in Multiwalled Carbon Nanotubes

Improving the electrochemical stability of manganese oxide/multiwalled carbon nanotubes (MnO2/MWCNTs) nanocomposites is of great importance to many electrochemical supercapacitor applications. In this study, the electrochemical properties of MnO2 filled inside the cavity of MWCNTs were investigated for the first time. The prepared nanocomposite was characterized by means of X-ray photoelectron spectroscopy (XPS), X-ray diffraction patterns (XRD), transmission electron microscopy (TEM) images, scanning electron microscopy (SEM) together with energy dispersive X-ray spectroscopy (EDX) and thermogravimetric analyses (TGA). Electrochemical characterization has been performed using cyclic voltammetry (CV), galvanostatic charging/discharging (CD) test. The TEM image, XRD analysis confirmed the high structural stability and CD test complied the high electrochemical stability of the prepared nanocomposite. Besides, MnO2/MWCNTs nanocomposite supercapacitor showed superior cycling stability in the potential range of 0-1.0V due to the filling of the electroactive material inside the tubes and retained 96% of initial capacitance even over 200 cycles. Keywords: Carbon nanotubes, wet chemical, filling, nanocomposite, specific capacitance, stability, Supercapacitor Material, Manganese Oxide, Multiwalled Carbon Nanotubes, electric double-layer capacitors (EDLC), redox capacitor, double-layer capacitance, carbonaceous materials, porous nanotubes, metal oxides as hybrid supercapacitors, microstructures of the nanocomposites, fabricated nanocomposites, polytetrafluoroethylene (PTFE) solution, Solatron cell-test system, Supercapacitor Cell