Alkali metal ion-selective electrodes based on relevant alkali metal ion doped manganese oxides

Potentiometric properties of manganese oxides doped with alkali metal ions (Na⁺, K⁺, Rb⁺ and Cs⁺), which were prepared by heating mixed solutions (starting solution) of each alkali metal and Mn²⁺ ions, were examined. Electrodes based on mixed phases of Nao₄₄MnO₂/Mn₂O₃ and hollandite KMn₈O₁₆/M₂O₃ found by X-ray powder diffraction (XRD) exhibited Na⁺- and K⁺-selective responses with a near-Nernstian slope, respectively, when the molar ratio of alkali metal ion to Mn²⁺ ion in the starting solution was 0.1. When no alkali metal ions were added in the manganese oxide films, no significant potentiometric response was observed to any alkali metal ions. The selectivity coefficients of these electrodes were = 6.7 × 10^–2, = 7.1 × 10^–3, < 9 × 10^–4 and < 9x 10^–4 for the Na_0.44MnO₂/Mn₂O₃, and <4 × 10^–4 <4x 10^–4, =60 × 10^–2 ×10^–4, < 4 × 10^–4, for the KMn₈O₁₆/Mn₂O₃, respectively. Electrodes based on manganese oxides made from mixed solutions of Rb⁺/Mn²⁺ and Cs⁺/Mn²⁺ also responded to the respective primary ions, that is, Rb⁺ and Cs⁺ ions, although XRD patterns for the manganese oxides thus made did not show any peaks except for Mn₂O₃ (bixbyite); it was concluded in these cases that some amorphous type manganese oxides were formed in the Rb⁺/Mn²⁺ and Cs⁺/Mn²⁺ systems and they responded to the respective ions. Conditioning of these electrodes in an aerated indifferent electrolyte solution, 0.1M tetramethylammonium nitrate (TMA-NO₃), for relatively long time, typically more than 2 hours, was found to be a prerequisite for near-Nernstian response to the respective alkali metal ions. During this electrode conditioning, vacant sites (template) suitable in size for selective uptake of primary ions seemed to be formed by releasing the doped alkali metal ions from the solid phase into the adjacent electrolyte solution accompanying oxidation of the manganese oxide film.     

Die Kristallstrukturen von Mn5O8 und Cd2Mn3O8

The crystal structures of Mn₅O₈ and Cd₂Mn₃O₈ are determined from single crystal and high resolution X-ray powder data. Both structures have very similar monoclinic unit cells, space group C–C2/m, and are isotypic: Hence, the true formula of Mn₅O₈ is MnMnO₈. The crystal structure consists of pseudohexagonal Mn^IV sheets (bc) with similar oxygen sheets on either side, giving a distorted octahedral coordination to the Mn^IV. As every fourth Mn^IV is missing in these “main layers”, their composition becomes Mn₃O₈, and chains of coordination octahedra linked by common edges become distinct. Above and below the empty Mn^IV sites are either Mn^II or Cd^II completing the composition MnMnO₈ or Cd₂Mn₃O₈ respectively. Examples of similar “double layer” structures are given.     

Zum chemischen Transport im System Mn?O unter Berücksichtigng des Sauerstoffkoexistenzdruckes (I)

Chemical Transport in the System Mn? O in Consideration of the Oxygen Coexistence Pressure (I) The chemical transport of the coexistent phases Mn₂O₃? Mn₃O₄ and Mn₃O₄? MnO with Cl₂, Br₂, I₂, HCl, HBr, and HI was analysed thermodynamically and experimentally. The mentioned transport agents are able to transport the following phases:

1 Index (o) bedeutet obere, (u) untere Phasengrenze (index (o) – upper phase boundary, (u) – lower phase boundary).

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Phase equilibrium in the system Ln-Mn-O VI: Ln=Ho and Tb at 1100°C

Phase equilibria were established in Ho-Mn-O and Tb-Mn-O systems at 1100°C by varying the oxygen partial pressure from −log(P_O2/atm)=0-13.00, and phase diagrams for the corresponding Ln₂O₃-MnO-MnO₂ systems at 1100°C were presented. Stable Ln₂O₃, MnO, Mn₃O₄, LnMnO₃, and LnMn₂O₅ phases were found at 1100°C, whereas Ln₂Mn₂O₇, Ln₂MnO₄, Mn₂O₃, and MnO₂ were not found to be stable. Small nonstoichiometric ranges were found in the LnMnO₃ phase, with the composition of LnMnO₃ represented as functions of log(P_O2/atm), and . Activities of the components in the solid solution were calculated from these equations. The composition of LnMnO₃ may range from Ln₂O₃ rich to Ln₂O₃ poor, while MnO is slightly nonstoichiometric, being oxygen rich and LnMn₂O₅ seems to be nonstoichiometric. Lattice constants of LnMnO₃ quenched at different oxygen partial pressures and of LnMn₂O₅ quenched in air were determined. The standard Gibbs energy changes of the reactions appearing in the phase diagrams were also calculated. The relationship between the tolerance factor of LnMnO₃ and ΔG⁰of reaction, (1/2)Ln₂O₃+MnO+(1/4)O₂=LnMnO₃, is shown graphically.     

Über ein Oxotantalat mit teilgeordneter Korundstruktur: Mn0,6Mg3,4Ta2O9

About an Oxotantalate with Partly Ordered Corundum-Structure: Mn_0.6Mg_3.4Ta₂O₉ In the system of mixed crystals of the composition Mn_4?xMg_xTa₂O₉ single crystals with x = 3.4 were examined by X-ray methods (space group D–P3 c1; a = 5.2141; c = 14.178 Å; Z = 2). The point positions of the divalent metals are occupied in an ordered manner. Order and disorder are discussed in respect to Mn₂Zn₂Nb₂O₉, Mn₃ZnNb₂O₉, and oxotantalates (MM′)₄Ta₂O₉ [M, M′ = Zn, Ni, Mg].     

Kinetics of stepwise oxidation of manganese(II) by peroxodisulphate in phosphoric acid medium

Summary The oxidation of Mn^II by S₂O₈ ^2– to Mn^VII in phosphoric acid medium proceeds via a stable Mn^III and Mn^IV species. The reaction is catalysed by Ag⁺ and exhibits first order dependence on [S₂O₈ ^2–], [Ag⁺] and, is independent of [Mn^II]. The [H⁺] has no significant effect on the reaction. It is observed that the PO₄ ^3– ion stabilises the transient manganese(III) and manganese(IV) species by forming a stable and soluble phosphato-complexes. The activation parameters for the two stages of oxidation, namely Mn^II Mn^IV and Mn^IVMn^VII at 25° C are E_a=52 ±4 kJ mole^–1, S^*=–57±2 JK^–1 mole^–1 and E_a =56±4 kJ mole^–1, S^*=–44±2 JK^–1 mole^–1, respectively. A mechanism consistent with the experimental observations is proposed.Presented at the National Symposium on Reaction Kinetics and Mechanism, Department of Chemistry, University of Jodhpur, Jodhpur, India, Nov. 15–18, 1986.     

Electrochemical dissolution of Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> in acid solutions

The present study deals with the electrochemical reductive dissolution of Mn₃O₄, which was added to carbon-paste electroactive electrodes (CPEEs) in acid solutions. It was found that in the experimental conditions the thermodynamically stable form of manganese was . Kinetic features of the electrochemical reductive dissolution of Mn₃O₄, which was realized under potential cycling conditions (+1.0 V→−0.7 V→+1.0 V), were determined by the electrode polarization direction. It was shown that the cathodic reduction of Mn₃O₄ was accomplished in three stages. Manganese was dissolved in the supporting solution only at the third stage. The first two stages involved solid-phase reactions. The anodic cycling stage included an active dissolution of Mn₃O₄ and the lower manganese oxide (MnO) accumulated on the electrode surface during the cathodic reduction.     

Synthesis,structure and biological activity of the O,O′-diethylphosphorohydrazonothionate Schiff base and its complexes with transition metals

N-2-Hydroxy-3-methoxy-benzalmethylene-O,O-diethylphosphorohydrazonothionate (HL) and its six complexes (ML₂) with Cu^II, Zn^II, Ni^II, Fe^II, Co^II and Mn^II have been synthesized and characterized. The crystal structure of CuL₂ shows that the metal ion is tetracoordinated, bound to 2N from imine and 2O from hydroxybenzene to form a parallelogram. The effects on Stenostigma remota cells of complexes CuL₂, CoL₂ and MnL₂ have been determined by microcalorimetry, which indicates that the compounds inhibit the metabolism of the insect cells.     

Improving rate performance of cathode material Li<Subscript>1.2</Subscript>Mn<Subscript>0.54</Subscript>Co<Subscript>0.13</Subscript>Ni<Subscript>0.13</Subscript>O<Subscript>2</Subscript> via niobium doping

As a promising Li-ion battery cathode active material, lithium-rich manganese-based layer-structured oxides suffer from inferior cycle performance and poor rate capability. Herein, Nb-doped Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ is prepared by a sol-gel method, and the effects of Nb doping on its electrochemical performance are investigated. It is concluded that the Nb-doped Li_1.2Mn_0.54Ni_0.13Co_0.13O₂, has a good layered structure along c-axis independent on the amount of Nb dopant and little cationic mixing. Nb doping for Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ has no obvious influence on its morphology. It is found that Nb doping can enhance the electrochemical activity of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂, such as improved rate performance and cycle performance under high rate conditions. Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ doped with 0.015 Nb shows the best cycle performance under the high rate with the capacity maintenance of 95.4% after 100 cycles under 5 C rate, which is higher than that of the undoped one by 10.5%.

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Graphical abstract Rate performance of Li_1.2Mn_0.54-xCo_0.13Ni_0.13Nb _x O₂ materials

     

Solid-state electrochemical lithium cells with oxide electrodes and composite solid electrolyte

The LiClO₄-Al₂O₃ composite solid electrolyte and solid solutions LiFe _x Mn_2?x O₄ and Li₅Ti₄O₁₂ compositions are synthesized and their physicochemical properties are studied using the x-ray diffraction and electrical measurements. Based on composition 0.5LiClO₄-0.5Al₂O₃, whose conductivity is the highest, first experiments on the elaboration of model electrochemical solid-electrolyte lithium cells with LiMn₂O₄, LiFeMnO₄, LiFe_0.8Mn_0.2O₄, and Li₅Ti₄O₁₂ oxide spinel electrodes are performed.     

Synthesis,crystal structure and e.p.r. spectra of one-dimensional manganese(II) 3,5-dinitrobenzoate dihydrate

The crystal structure of catena-diaquatetrakis(₂-3,5-dinitrobenzoato-O,O)manganese(II) has been determined by X-ray diffraction. It consists of a chain with the 3,5-dinitrobenzoate group acting in the syn-anti ₂-O,O-bridging fashion, in which the Mn^II atom is octahedrally coordinated by two aqua ligands [2.162(3) Å] and four carboxy oxygen atoms [Mn—O = 2.114(3) and 2.221(3) Å]. The X-band e.p.r. spectra of this complex show a hyperfine structure due to Mn^II (I = 5/2) with a splitting factor (A) of 97 G at 5 K and 93 G at 19 K, respectively.     

Mn environment in layered Li[Mg0.5−xNixMn0.5]O2 oxides monitored by EPR spectroscopy

X-band and high-frequency EPR spectroscopy were used for studying the manganese environment in layered Li[Mg_xNi_0.5−xMn_0.5]O₂, 0?x?0.5. Both layered LiMg_0.5Mn_0.5O₂ and monoclinic Li[Li_1/3Mn_2/3]O₂ oxides (containing Mn⁴⁺ ions only) were used as EPR standards. The EPR study was extended to the Ni-substituted analogues, where both Ni²⁺ and Mn⁴⁺ are paramagnetic. For LiMg_0.5−xNi_xMn_0.5O₂ and Li[Li_(1−2x)/3Ni_xMn_(2−x)/3]O₂, an EPR response from Mn⁴⁺ ions only was detected, while the Ni²⁺ ions remained EPR silent in the frequency range of 9.23-285 GHz. For the diamagnetically diluted oxides, LiMg_0.25Ni_0.25Mn_0.5O₂ and Li[Li_0.10Ni_0.35Mn_0.55]O₂, two types of Mn⁴⁺ ions located in a mixed (Mn-Ni-Li)-environment and in a Ni-Mn environment, respectively, were registered by high-field experiments. In the X-band, comparative analysis of the EPR line width of Mn⁴⁺ ions permits to extract the composition of the first coordination sphere of Mn in layered LiMg_0.5−xNi_xMn_0.5O₂ (0?x?0.5) and Li[Li_(1−2x)/3Ni_xMn_(2−x)/3]O₂ (x>0.2). It was shown that a fraction of Mn⁴⁺ are in an environment resembling the ordered “α,β”-type arrangement in Li_1−δ1Ni_δ1[Li_{(1−2x)/3+δ1}Ni_2x/3−δ1)_α(Mn_(2−x)/3Ni_x/3)_β]O₂ (where and δ₁=0.06 were calculated), while the rest of Mn⁴⁺ are in the Ni,Mn-environment corresponding to the Li_1−δ2Ni_δ2[Ni_1−yMn_y]O₂ () composition with a statistical Ni,Mn distribution. For Li[Li_(1−2x)/3Ni_xMn_(2−x)/3]O₂ with x?0.2, IR spectroscopy indicated that the ordered α,β-type arrangement is retained upon Ni introduction into monoclinic Li[Li_1/3Mn_2/3]O₂.     

Darstellung und Kristallstruktur von Na2Mn3O7

Synthesis and Crystal-Structure of Na₂Mn₃O₇ Single crystals of Na₂Mn₃O₇ have been grown hydrothermally applying high oxygen pressure (p = 2 kbar). The new compound cystallizes triclinic; space group P1 ; a = 6.636(6) Å, b = 6.854(6) Å, c = 7.548(6) Å, α = 105.76(6)°, β = 106.86(6)°, γ = 111.60(6)°; Z = 2. The crystal structure has been solved and refined to R = 7.9% and R_w = 6.2% (diffractometer data, 1044 independent reflexions). The crystal structure consists of Mn₃O₇^2? anions with manganese coordinated octahedrally by oxygen. These layered anions are hold together by Na⁺ ions (coordination numbers 5 and 6).     

Co-precipitation spray-drying synthesis and electrochemical performance of stabilized LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode materials

In this paper, the LiNi_0.5Mn_1.5O₄ cathode materials of lithium-ion batteries are synthesized by a co-precipitation spray-drying and calcining process. The use of a spray-drying process to form particles, followed by a calcination treatment at the optimized temperature of 750 °C to produce spherical LiNi_0.5Mn_1.5O₄ particles with a cubic crystal structure, a specific surface area of 60.1 m² g^?1, a tap density of 1.15 g mL^?1, and a specific capacity of 132.9 mAh g^?1 at 0.1 C. The carbon nanofragment (CNF) additives, introduced into the spheres during the co-precipitation spray-drying period, greatly enhance the rate performance and cycling stability of LiNi_0.5Mn_1.5O₄. The sample with 1.0 wt.% CNF calcined at 750 °C exhibits a maximum capacity of 131.7 mAh g^?1 at 0.5 C and a capacity retention of 98.9% after 100 cycles. In addition, compared to the LiNi_0.5Mn_1.5O₄ material without CNF, the LiNi_0.5Mn_1.5O₄ with CNF demonstrates a high-rate capacity retention that increases from 69.1% to 95.2% after 100 cycles at 10 C, indicating an excellent rate capability. The usage of CNF and the synthetic method provide a promising choice for the synthesis of a stabilized LiNi_0.5Mn_1.5O₄ cathode material.

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Graphical Abstract Micro/nanostructured LiNi_0.5Mn_0.5O₄ cathode materials with enhanced electrochemical performances for high voltage lithium-ion batteries are synthesized by a co-precipitation spray-drying and calcining routine and using carbon nanofragments (CNFs) as additive.

     

Modeling water exchange on monomeric and dimeric Mn centers

Water exchange on Mn centers in proteins has been modeled with density functional theory using the B3LYP functional. The reaction barrier for dissociative water exchange on [Mn^IV(H₂O)₂(OH)₄] is only 9.6 kcal mol^–1, corresponding to a rate of 6×10⁵ s^–1. It has also been investigated how modifications of the model complex change the exchange rate. Three cases of water exchange on Mn dimers have been modeled. The reaction barrier for dissociative exchange of a terminal water ligand on [(H₂O)₂(OH)₂Mn^IV(-O)₂Mn^IV(H₂O)₂(OH)₂] is 8.6 kcal mol^–1, while the bridging oxo group exchange with a ring-opening mechanism has a barrier of 19.2 kcal mol^–1. These results are intended for interpretations of measurements of water exchange for the oxygen evolving complex of photosystem II. Finally, a tautomerization mechanism for exchange of a terminal oxyl radical has been modeled for the synthetic O₂ catalyst [(terpy)(H₂O)Mn^IV(-O)₂Mn^IV(O)(terpy)]³⁺ (terpy=2,2:6,2-terpyridine). The calculated reaction barrier is 14.7 kcal mol^–1.Contribution to the Björn Roos Honorary Issue     

Subsolidus phase equilibria and properties in the system Bi2O3:Mn2O3±x:Nb2O5

Subsolidus phase relations have been determined for the Bi-Mn-Nb-O system in air (750-900 °C). Phases containing Mn²⁺, Mn³⁺, and Mn⁴⁺ were all observed. Ternary compound formation was limited to pyrochlore (A₂B₂O₆O′), which formed a substantial solid solution region at Bi-deficient stoichiometries (relative to Bi₂(Mn,Nb)₂O₇) suggesting that ≈14-30% of the A-sites are occupied by Mn (likely Mn²⁺). X-ray powder diffraction data confirmed that all Bi-Mn-Nb-O pyrochlores form with structural displacements, as found for the analogous pyrochlores with Mn replaced by Zn, Fe, or Co. A structural refinement of the pyrochlore 0.4000:0.3000:0.3000 Bi₂O₃:Mn₂O_3±x:Nb₂O₅ using neutron powder diffraction data is reported with the A and O′ atoms displaced (0.36 and 0.33 Å, respectively) from ideal positions to 96g sites, and with Mn²⁺ on A-sites and Mn³⁺ on B-sites (Bi_1.6Mn²⁺_0.4(Mn³⁺_0.8Nb_1.2)O₇, (?227), a=10.478(1) Å); evidence of A or O′ vacancies was not found. The displacive disorder is crystallographically analogous to that reported for Bi_1.5Zn_0.92Nb_1.5O_6.92, which has a similar concentration of small B-type ions on the A-sites. EELS spectra for this pyrochlore were consistent with an Mn oxidation between 2+ and 3+. Bi-Mn-Nb-O pyrochlores exhibited overall paramagnetic behavior with negative Curie-Weiss temperature intercepts, slight superparamagnetic effects, and depressed observed moments compared to high-spin, spin-only values. At 300 K and 1 MHz the relative dielectric permittivity of Bi_1.600Mn_1.200Nb_1.200O₇ was ≈128 with tan δ=0.05; however, at lower frequencies the sample was conductive which is consistent with the presence of mixed-valent Mn. Low-temperature dielectric relaxation such as that observed for Bi_1.5Zn_0.92Nb_1.5O_6.92 and other bismuth-based pyrochlores was not observed. Bi-Mn-Nb-O pyrochlores were readily obtained as single crystals and also as textured thin films using pulsed laser deposition.     

Unique charge ordering of manganese in a new mixed valent phosphate

A new mixed-valent manganese phosphate, , has been synthesized using hydrothermal method. Its monoclinic C2/c structure (a=12.5506(16) Å, b=10.4816(18) Å, c=13.6723(10) Å, β=103.758(11)°) forms a 3D framework of MnO₆ octahedra, MnO₅ trigonal bipyramids, PO₄ and PO₃OH tetrahedra. The main structural feature of this phosphate deals with its [Mn₄O₁₆]_∞ chains running along , which are interconnected through PO₄ and PO₃OH tetrahedra, forming intersecting tunnels running along [110], and [001]. The geometry of the [Mn₄O₁₆]_∞ chains and the charge ordering of manganese in the latter are unique: they consist of trimeric units of divalent manganese “” alternating with single trivalent Mn^IIIO₆ octahedra along . In each “” unit one central Mn^IIO₆ octahedron shares two opposite edges with two Mn^IIO₅ trigonal bipyramids. Along , one Mn(II) octahedron alternates with one Mn(III) octahedron by sharing one corner. The relationships between the structure of this unique charge ordered phosphate and other manganese phosphates are discussed.