Thermochemistry of Framework and Layer Manganese Dioxide Related Phases

Fritsch, Sophie; Post, Jeffrey E.; Suib, Steven L.; Navrotsky, Alexandra

doi:10.1021/cm970104h

Cited by 42 publications

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“…This structure phase analysis is in agreement with thermodynamics of hollandite phase since foreign ions like NH + 4 in structure channels decrease its free energy significantly [39] as a result of influence of entropic factor. Co 2+ , Fe 2+ are able to manganese substitution in oxide framework, whereas Cr 3+ causes the pillaring effect stabilising MnO x layers in birnessite structure [15].…”

Section: Resultssupporting

confidence: 86%

ORR Electrocatalysis on Cr³⁺, Fe²⁺, Co²⁺-Doped Manganese(IV) Oxides

et al. 2018

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The ionic dopant additives have different mechanisms of their influence upon MnO2 electrocrystallisation process and depending on dopants added the following polymorphs are stabilised: α-MnO2 (hollandite, I4/m) -NH + 4 ; γ-MnO2 (ramsdellite, P bnm) -Co 2+ , Fe 2+ ; layered polymorph δ-MnO2 (birnessite, C2/m) -Cr 3+ . The defect states of intergrowth method in ramsdellite matrix and twinning, OH groups studied by X-ray diffraction and the Fourier transform infrared mtehod, respectively, indicate their high content in case of Fe 2+ and Co 2+ -doped manganese dioxide. CVA oxygen reduction reaction peaks were established after experiments in alkaline electrolytes and dioxygen (argon, air) atmosphere. Activity of doped samples studied is comparable with other published data. Both doped with Co 2+ and Fe 2+ samples display maximal currents and some distinctive features in oxygen reduction reaction.

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Section: Resultssupporting

confidence: 86%

ORR Electrocatalysis on Cr³⁺, Fe²⁺, Co²⁺-Doped Manganese(IV) Oxides

et al. 2018

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“…This influence is seen most clearly for the potassium birnessites, where the values of ΔH°f -ox in kilojoules per formula containing 1 mol of manganese are −36.7 for x = 0.125 (12), −52.3 for x = 0.21 (this work), and −60.6 for x = 0.29 (12). The bulk sodium birnessite with x = 0.09 has more negative ΔH°f -ox* and ΔH°f -ox than the bulk potassium birnessite with x = 0.21 (Table 4).…”

Section: Resultsmentioning

confidence: 73%

“…Having more thermodynamically favorable standard formation enthalpies (Table 2), enthalpies of formation from the oxides (Table 2), and lower SE (Table 3), the birnessites (layer structure) are more stable relative to binary oxides than the cryptomelane (tunnel structure). Fritsch et al (12) also observed that birnessites are more thermodynamically stable than tunnel structure Mn oxides. The standard entropies (S°2 98 ) of the complex manganese oxides are not generally available.…”

Section: Resultsmentioning

confidence: 97%

“…Some calorimetric studies of enthalpies of formation of layer and tunnel manganese oxides have been reported (12), although their compositions in terms of AOS of manganese, and therefore oxygen content, were not measured and their particle sizes and surface areas were not characterized. These factors have recently been shown to be important in the thermodynamics of binary oxides in the Mn-O system (13) and probably play an equal or more important role in the complex layer and tunnel materials.…”

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confidence: 99%

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Thermodynamics of manganese oxides: Sodium, potassium, and calcium birnessite and cryptomelane

Birkner

Navrotsky

2017

Proc. Natl. Acad. Sci. U.S.A.

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Manganese oxides with layer and tunnel structures occur widely in nature and inspire technological applications. Having variable compositions, these structures often are found as small particles (nanophases). This study explores, using experimental thermochemistry, the role of composition, oxidation state, structure, and surface energy in the their thermodynamic stability. The measured surface energies of cryptomelane, sodium birnessite, potassium birnessite and calcium birnessite are all significantly lower than those of binary manganese oxides (Mn 3 O 4 , Mn 2 O 3 , and MnO 2 ), consistent with added stabilization of the layer and tunnel structures at the nanoscale. Surface energies generally decrease with decreasing average manganese oxidation state. A stabilizing enthalpy contribution arises from increasing counter-cation content. The formation of cryptomelane from birnessite in contact with aqueous solution is favored by the removal of ions from the layered phase. At large surface area, surface-energy differences make cryptomelane formation thermodynamically less favorable than birnessite formation. In contrast, at small to moderate surface areas, bulk thermodynamics and the energetics of the aqueous phase drive cryptomelane formation from birnessite, perhaps aided by oxidation-state differences. Transformation among birnessite phases of increasing surface area favors compositions with lower surface energy. These quantitative thermodynamic findings explain and support qualitative observations of phasetransformation patterns gathered from natural and synthetic manganese oxides.manganese oxides | birnessite | cryptomelane | calorimetry | thermodynamics C omplex manganese oxides, highly reactive fine-grained materials ubiquitous in nature, have served in a number of important capacities to benefit both the Earth and human society (1). These oxides have profoundly affected Earth's critical zone throughout geologic time, influencing the evolution of the atmosphere and the bioinorganic chemistry of organisms. They are effective in accumulation and recovery of economic ores and have recently inspired development of novel catalysts for green chemistry and energy sustainability technologies. Minerals based on MnO 2 include multiple classes, two of which are well known to geochemists: the 2 × 2 tunnel structure hollandite (the potassium -bearing variety is cryptomelane) and the layered structure phyllomanganates (e.g., birnessite) (2, 3). Layered Mn oxides, such as the mineral birnessite, derived from MnO 2 by inclusion of cations and water, with concomitant decrease in manganese average oxidation state (Mn AOS) from 4 to typical values between 3.5 and 3.9, with manganese in tetravalent, trivalent and sometimes divalent oxidation states, are among the most important Mn oxides in nature (4). These "nanosheet" Mn oxides readily transform among phases, influencing crucial environmental and technological processes, including biogeochemical cycles (1, 4, 5) water oxidation catalysis (6-8) and radionuclide confinement (9, ...

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“…However, the energetics and properties of the polymorphic phases of MnO 2 remain unresolved in first-principles calculations [17][18][19]. Experimentally, it is established that pyrolusite β-MnO 2 is the ground state of pure MnO 2 [9], but to our knowledge no nonempirical DFT method has stabilized β-MnO 2 as the ground state of the system. In this report we resolve this problem with the use of the recently reported SCAN meta-GGA [20] and show that the resolution of the ground state structure problem in the MnO 2 system also leads to a much more accurate representation of the basic physics of the material.…”

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Energetics ofMnO2polymorphs in density functional theory

et al. 2016

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We report the energetics and properties of the β, α, R, γ , λ, and δ polymorphs of MnO 2 within density functional theory, comparing the performance of the recently introduced SCAN functional with that of conventional exchange-correlation functionals and experiment. We find that SCAN uniquely yields accurate formation energies and properties across all MnO 2 polymorphs. We explain the superior performance of SCAN based on its satisfaction of all known constraints appropriate to a semilocal exchange-correlation functional and its accurate representation of all types of orbital overlap. DOI: 10.1103/PhysRevB.93.045132 First-principles thermodynamics has over the last decades matured into a reliable method for accessing the energetics of phase transitions and reactions in condensed matter systems. At the heart of this method lies Kohn-Sham density functional theory (DFT) [1], with its standard approximations to the exchange-correlation energy providing a reasonably accurate picture of electronic structure. One of the most basic results that can be derived from a set of DFT calculations is the ground-state structure of a given compound under some set of conditions, usually set as zero temperature and pressure. However, despite the importance of accurate first-principles structure determination for both materials and property analysis [2][3][4][5] this determination is often extremely difficult as the total energy differences between competing phases can be on the order of only a few meV per formula unit [6]. As a result, ground state structure selection is an attractive benchmark for verifying the adequacy of the physical model underlying a given approximation to the exchange-correlation energy.One particularly interesting system for investigating structure-transition energetics within DFT is the set of manganese oxides. The Mn-O system contains a diverse set of relatively well characterized structures both across a range of stoichiometries (MnO, Mn 3 O 4 , Mn 2 O 3 , and MnO 2 ), and within a single stoichiometry (pyrolusite β, ramsdellite R, hollandite α, intergrowth γ , spinel λ, layered δ MnO 2 ), as shown in Fig. 1. All the MnO 2 polymorphs share a common basic atomic structure-small Mn 4+ ions in a spin-polarized 3d 3 configuration and large, highly polarizable O 2-ions in a spin-unpolarized 2p 6 configuration, arranged in corner-and edge-sharing MnO 6 octahedra. The different packings of these octahedra form a variety of polymorphic structures, many of which have been studied extensively for applications in energy storage, catalysis, pigmentation, etc. [7][8][9][10][11][12][13][14][15]. * Corresponding author: gceder@berkeley.edu Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.The relative stability of the various oxidation states of Mn-O has been previously investigated within the PerdewBurke-Erzenhof (PBE) and...

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Thermochemistry of Framework and Layer Manganese Dioxide Related Phases

Cited by 42 publications

References 21 publications

ORR Electrocatalysis on Cr³⁺, Fe²⁺, Co²⁺-Doped Manganese(IV) Oxides

ORR Electrocatalysis on Cr³⁺, Fe²⁺, Co²⁺-Doped Manganese(IV) Oxides

Thermodynamics of manganese oxides: Sodium, potassium, and calcium birnessite and cryptomelane

Energetics ofMnO2polymorphs in density functional theory

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Thermochemistry of Framework and Layer Manganese Dioxide Related Phases

Cited by 42 publications

References 21 publications

ORR Electrocatalysis on Cr3+, Fe2+, Co2+-Doped Manganese(IV) Oxides

ORR Electrocatalysis on Cr3+, Fe2+, Co2+-Doped Manganese(IV) Oxides

Thermodynamics of manganese oxides: Sodium, potassium, and calcium birnessite and cryptomelane

Energetics ofMnO2polymorphs in density functional theory

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ORR Electrocatalysis on Cr³⁺, Fe²⁺, Co²⁺-Doped Manganese(IV) Oxides

ORR Electrocatalysis on Cr³⁺, Fe²⁺, Co²⁺-Doped Manganese(IV) Oxides