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Synchrotron X-ray diffraction of pyrolusite (MnO 2 ) and rutile (TiO 2 ) during heating to ~1000 °C
To compare thermal expansion behaviors in isomorphic structures with different redox behaviors, we separately heated pyrolusite (Mn 4+ O 2 ) and rutile (Ti 4+ O 2 ) powders from 25 to ~1000 °C at a rate of 0.05 °C/s at ambient pressure and analyzed them using synchrotron X-ray diffraction and Rietveld refinement. The pyrolusite exhibited two reduction-induced phase decompositions. Between 531 and 583 °C, pyrolusite decomposed to bixbyite (Mn 3+ 2 O 3 ), and between 972 and 998 °C, bixbyite decomposed to hausmannite (Mn 2+ Mn 3+ 2 O 4 ). The rutile experienced no phase decompositions or transitions over this same temperature interval. The refined bond lengths and angles for pyrolusite showed that the Mn 4+ coordination octahedron became more distorted near the phase decomposition to bixbyite due to the approach of two coordinating oxygen atoms. The 3d electrons of each Mn 4+ ion in pyrolusite make π bonds with the 2p electrons of the surrounding O 2- ions, whereas the Ti 4+ of rutile has no 3d electrons. Thus, π bonding between octahedral Mn 4+ and the surrounding O 2- anions increases the strength of the Mn–O bonds of pyrolusite relative to the Ti–O bonds of rutile. However, we observed a small decrease in O–O distances in pyrolusite before the decomposition, suggesting that at high temperature, increased π bonding between adjacent O anions precedes the release of O 2 and the reduction of Mn 4+ to Mn 3+ . Analogous behavior was observed for bixbyite before its reductive phase decomposition to hausmannite. In contrast, no anomalous changes in the O–O distances occurred for rutile. Our X-ray diffraction analyses provided accurate thermal expansion coefficients for these materials over a broader temperature range than reported in previous studies. The Mn–O bond lengths in pyrolusite were shorter and stronger than the Ti–O bonds of rutile; for example, at 60 °C, bond distances in pyrolusite refined to 1.8854(6) Å whereas the bond lengths of rutile were 1.9575(4) Å. Accordingly, the axial and volumetric thermal expansion coefficients refined for rutile were greater than those for pyrolusite. Further, the axial coefficients of thermal expansion (CTE) for pyrolusite were 96% (a-axis) and 69% (c-axis) of the corresponding values for rutile, and the volumetric CTE for pyrolusite was 85% of that for rutile.
Oxygen Loss on Disordered Li-Excess, Mn-Rich Li-Ion Cathode Li 2 MnO 2 F through First-Principles Modeling
Not Available
Framework Doping of Ni Enhances Pseudocapacitive Na-Ion Storage of (Ni)MnO[subscript 2] Layered Birnessite
Abstract not provided
Reversible Hydrogen-Induced Phase Transformations in La 0.7 Sr 0.3 MnO 3 Thin Films Characterized by In Situ Neutron Reflectometry
Not Available
Mechanistic Investigation of Redox Processes in Zn-MnO2 battery in Mild Aqueous Electrolytes
Zinc-MnO2 based batteries have acquired attention for grid-level applications, due to impressive theoretical performance, cost effectiveness and intrinsic safety. However, there are still many challenges that remain elusive due to the complex and controversial mechanisms of operation that hinders commercialization. In this work, the detailed redox processes that occur at the cathode during Zn-MnO2 battery operation are elucidated. Using a blend of structural and electrochemical techniques, the redox pairs that occur during operation are mechanistically studied while also showcasing the true impact of the electrolyte additive (0.1 M MnSO4) in a 1 M ZnSO4 electrolyte. An electrochemical quartz-crystal microbalance (EQCM) has been leveraged to reveal the effect of zinc hydroxy sulfate salt (Zn4SO4(OH)6·nH2O) and zinc manganese oxide (ZnxMnyOz) dissolution/deposition, which are believed to be major components during discharge and charge conditions. . These results provide insight not currently available, allowing a holistic view of the electrochemical reaction mechanisms during battery operation.
Growth and characterization of La 0.67 Sr 0.33 MnO 3 /YBa 2 Cu 3 O 7- δ bilayers
Understanding the interplay of ferromagnets and superconductors requires high quality interfaces. To this end, we have fabricated heterostructures of the cuprate superconductor YBa2Cu3O7-δ (YBCO) with the metallic ferromagnet La0.67Sr0.33MnO3 (LSMO) via pulsed laser deposition on SrTiO3 (STO) (001) and (LaAlO3)0.3(Sr2TaAlO6)0.7 (LSAT) (001) substrates. By varying the YBCO thickness from 1.7-13.6 nm while keeping the LSMO thickness at 12 nm, we have studied the interplay between ferromagnetism and superconductivity in the in-plane transport and magnetic properties of the bilayers. X-ray reflectivity data indicate the presence of a 2-3 nm thick interfacial layer between the LSMO and YBCO layers in all heterostructures. In-plane transport measurements exhibit suppression of the superconducting transition temperature from bulk YBCO values. Magnetometry measurements indicate high LSMO saturation magnetization values for samples grown on STO substrates and even higher (bulk-like) magnetization for bilayers grown on LSAT substrates. Together these results indicate that the interdiffused layer is largely attributed to a modified YBCO layer.
Family of anisotropic spin glasses Ba[subscript 1?x]La[subscript 1+x]MnO[subscript 4+delta]
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Bifunctional MnO x electrocatalysts for zinc–air batteries in alkaline electrolytes
The growing need for rechargeable zinc–air batteries has led researchers to look for low-cost and robust catalytic candidates. Furthermore, manganese oxides are promising for their low toxicity, natural abundance and low cost. In this review, we summarize the versatility of manganese oxides which is achievable by adjusting synthetic parameters. In addition, we highlight how manganese oxides impact zinc–air electrochemistry.
Enhanced cycle lifetime with gel electrolyte for MnO 2 nanowire capacitors
A nanowire energy storage device such as a nanowire battery or a capacitor having a cathode comprising a plurality of nanowires and an anode comprising a plurality of nanowires interlaced with the plurality of nanowires of the cathode, and embedded in a PMMA gel electrolyte.
Quantification of manganese for ChemCam Mars and laboratory spectra using a multivariate model
In this work, we report a new calibration model for manganese using the laser-induced breakdown spectroscopy instrument that is part of the ChemCam instrument suite onboard the NASA Curiosity rover. The model has been trained using an expanded set of 523 manganese-bearing rock, mineral, metal ore, and synthetic standards. The optimal calibration model uses the Partial Least Squares (PLS) and Least Absolute Shrinkage and Selection Operator (LASSO) multivariate techniques, with a novel “double blending” technique. We determined the detection limit for manganese is 82 ppm using a method blank procedure and is possibly as low as 27 ppm based on visual inspection of the spectra. Based on a representative test set consisting of measurements on 93 standards, the double blended multivariate model shows a Root Mean Squared Error of Prediction (RMSEP) accuracy of 1.39 wt% MnO for the full blended model. Employing a local RMSEP estimate where the model performance is evaluated based on nearby test samples, the accuracy is 0.03 wt% at the quantification limit (0.05 wt% MnO), 0.4 wt% accuracy at 1.0 wt% MnO, and 4.4 wt% accuracy at 100 wt% MnO. Precision is estimated using the standard deviation of the test set measurements, and is ±0.01 wt% MnO at the quantification limit, ±0.09 wt% MnO at 1.0 wt% MnO, and ± 2.1 wt% MnO at 100 wt% MnO (all 1 standard deviation). This new calibration is important for understanding the variation of manganese in the bedrock with the Curiosity rover on Mars, which provides insight into past redox conditions on Mars.
Secondary zinc-manganese dioxide batteries for high power applications
In an embodiment, a secondary Zn—MnO 2 battery comprises a battery housing, a MnO 2 cathode, a Zn anode, and an electrolyte solution. The MnO 2 cathode, the Zn anode, and the electrolyte solution are disposed within the battery housing, and the MnO 2 cathode comprises a MnO 2 cathode mixture and a current collector. The MnO 2 cathode mixture is in electrical contact with at least a portion of an outer surface of the current collector, and the MnO 2 cathode has a porosity of from about 5 vol. % to about 90 vol. %, based on the total volume of the MnO 2 cathode mixture of the MnO 2 cathode.
Nanoarray-Based Monolithic Adsorbers for SO 2 Removal
Nanoarray-based monolithic catalysts have been developed for various applications, including CO oxidation, hydrocarbon combustion, lean NO x trapping, and low-pressure CO 2 hydrogenation. In this work, SO 2 adsorption properties have been explored and evaluated on the cordierite honeycomb monoliths grown with zinc oxide nanoarray (ZnO), zinc oxide nanoarray washcoated by BaCO 3 nanoparticles (ZnO/BaCO 3 ), and manganese oxide nanowire array with cryptomelane structure (MnO x ) at a temperature range from 50 to 425 °C. All samples show temperature-dependent SO 2 adsorption behaviors. The adsorption results reveal the performance order: MnO x > ZnO/BaCO 3 > ZnO, with ~ 90% SO 2 adsorbed in MnO x at 425 °C. Washcoated BaCO 3 contributes to the improvement of SO 2 adsorption in ZnO nanoarray, and the best performance displayed in MnO x may be attributed to their high specific surface area. After regeneration, nanoarrays all exhibit good thermal stability during test-regeneration cycles. No additional phase is formed in regenerated ZnO nanoarrays (ZnO-R), while BaCO 3 is converted to BaSO 4 in the regenerated ZnO/BaCO 3 nanoarrays (ZnO/BaCO 3 -R), and the sulfur species (possibly MnSO 4 ) and Mn 2 O 3 are found in regenerated MnO x nanoarrays (MnO x -R). It is noted that a small amount of sulfur species (possibly MnSO 4 ) may promote the SO 2 adsorption of MnO x -R at a lower temperature, while the formed Mn 2 O 3 contributes to the deactivation of MnO x -R.
Molecular structure and catalytic promotional effect of Mn on supported Na 2 WO 4 /SiO 2 catalysts for oxidative coupling of methane (OCM) reaction
The structure and promotional effect of Mn in supported Mn-Na 2 WO 4 /SiO 2 catalysts for the oxidative coupling of methane (OCM) reaction has been debated for a longtime in the literature. In the current investigation, with the aid of multiple in-situ characterization studies, we show that the freshly calcined supported 1.2Mn-5Na 2 WO 4 /SiO 2 catalyst possesses crystalline Na 2 WO 4 , Mn 2 O 3 and SiO 2 (cristobalite phase) along with surface MnO x and Na-WO x sites at low temperature and oxidizing environments. Under the OCM reaction environment (T>800°C), the crystalline Na 2 WO 4 phase melts and Mn 2 O 3 phase reduces. In contrast, the surface MnO x and Na-WO x sites exhibit excellent thermal and chemical stability. Exposure of the 1.2Mn-5Na 2 WO 4 /SiO 2 catalyst to the OCM reaction environment redisperses the molten Na 2 WO 4 phase on the SiO 2 support to form new surface WO x sites. Interestingly, the stable MnO x species interacts with both molten Na 2 WO 4 phase and surface Na-WO x sites during OCM reaction. Controlled transient kinetic experiments in TAP and detailed steady state OCM fixed-bed reaction studies reveal the role and promotional effect of Mn in the 1.2Mn-5Na 2 WO 4 /SiO 2 catalyst. The W-oxides (both molten Na 2 WO 4 and surface Na-WO x sites) are the active sites for the catalytic OCM reaction and the MnO x species only function as promoters. The promotion of MnO x strongly depends on the gas phase O 2 partial pressure and the MnO x species act as mediators for oxygen exchange between the gas phase molecular O 2 and catalyst lattice oxygen. In conclusion, the temperature dependent MnO x promotion reveals that the MnO x species selectively promote the molten Na 2 WO 4 phase at lower reaction temperature and the surface Na-WO x sites at higher temperature.