Structural evolution upon heating of sol–gel prepared birnessites

Prieto, O.; Arco, M. Del; Rives, V.

doi:10.1016/s0040-6031(02)00503-8

Cited by 19 publications

(11 citation statements)

References 45 publications

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“…From the weight decrease up to 200°C, the water composition is evaluated to be y = 0.40 in K 0.28 MnO 2 • yH 2 O. Similar TG-DTA curves have been reported by O. Prieto et al [8]. To investigate the details of structural change on heating, we have heat-treated the samples at several temperatures and have characterized them.…”

Section: As-prepared Samplementioning

confidence: 68%

“…It is also to be noted that the heat treatment of the xerogel at 600°C causes the formation of cryptomelane with 2×2 tunnel structure [8]. However, the relation of water and K compositions to the structural transformation, and also the mechanism of structural transformation are still uncertain, although a TEM study has been reported for the sample prepared by the precipitation from the aqueous solutions [9].…”

Section: Introductionmentioning

confidence: 99%

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Structure and Thermal Decomposition of KxMnO2・yH2O Prepared by Sol-Gel Method

Fujiwara

Akedo

Yusuke

et al. 2009

Trans. Mat. Res. Soc. Japan

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The birnessite-type K 0.28 MnO 2 hydrates with the average crystalline size of about 10-20 nm have been prepared by a sol-gel method using KMnO 4 and glucose aqueous solutions. Their crystal structure and thermal stability have been investigated by XRD, TG-DTA, and TEM-EDX. The dehydration reaction occurs at around 180°C. The samples heated in between 600 and 800°C transform into a cryptomelane-type phase with 2×2 tunnel type structure. Not so much change in the crystalline size due to the above phase transformation was observed. The heating at above 900°C causes the decomposition reaction into the tetragonal spinel-phase Mn 3 O 4 and the layered K-rich birnessite, K 0.31 MnO 2 , accompanied with the release of oxygen and the 4 times increase in the crystalline size.

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Section: As-prepared Samplementioning

confidence: 68%

Section: Introductionmentioning

confidence: 99%

Structure and Thermal Decomposition of KxMnO2・yH2O Prepared by Sol-Gel Method

Fujiwara

Akedo

Yusuke

et al. 2009

Trans. Mat. Res. Soc. Japan

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“…This charge is compensated by protons or interlayer cations: In our case, there are sodium cations and water molecules in the interlayer. The sample (further labeled NaBIR) was prepared by a sol−gel method − with a glucose/NaMnO 4 molar ratio of 1. It was characterized as described above for LDH samples.…”

Section: Methodsmentioning

confidence: 99%

Rotational Fluctuations of Water Confined to Layered Oxide Materials: Nonmonotonous Temperature Dependence of Relaxation Times

et al. 2007

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The rotational molecular dynamics of water confined to layered oxide materials with brucite structure was studied by dielectric spectroscopy in the frequency range from 10(-2) to 10(7) Hz and in a broad temperature interval. The layered double hydroxide samples show one relaxation process, which was assigned to fluctuations of water molecules forming a layer, strongly adsorbed to the oxide surface. The temperature dependence of the relaxation rates has an unusual saddlelike shape characterized by a maximum. The model of Ryabov et al. (J. Phys. Chem. B 2001, 105, 1845) recently applied to describe the dynamics of water molecules in porous glasses is employed also for the layered materials. This model assumes two competing effects: rotational fluctuations of water molecules that take place simultaneously with defect formation, allowing the creation of free volume necessary for reorientation. The activation energy of rotational fluctuations, the energy of defect formation, a pre-exponential factor, and the defect concentration are obtained as main parameters from a fit of this model to the data. The values of these parameters were compared with those found for water confined to nanoporous molecular sieves, porous glasses, or bulk ice. Several correlations were discussed in detail, such as the lower the value of the energy of defect formation, the higher the number of defects. The pre-exponential factor increases with increasing activation energy, as an expression of the compensation law, and indicates the cooperative nature of the motional process. The involvement of the surface OH groups and of the oxygen atoms of the interlayer anions in the formation of hydrogen bonds was further discussed. For the birnessite sample, the relaxation processes are probably overlaid by a dominating conductivity contribution, which is analyzed in its frequency and temperature dependence. It is found that the conductivity of birnessite obeys the characteristics of semiconducting disordered materials. Especially the Barton/Nakajima/Namikawa relationship is fulfilled. Analyzing the temperature dependence of the direct current (dc) conductivity sigma0 in detail gives some hint that sigma0(T) has also an unusual saddlelike form.

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“…oxidation of Mn 2+ in basic solution, the reduction of MnO 4in acidic solutions, or the redox reaction between Mn 2+ and MnO 4 -(redox precipitation processes) 37-40,49,52,64-67,72-94 by a sol-gel process 51,76,78,[95][96][97][98][99][100][101][102][103][104][105] or by an hydrothermal treatment from a manganese oxide compound 44,68,[106][107][108][109][110][111][112] or more recently by electrochemical deposition from a manganese sulfate solution. 25,26,29,30 The present study, which extends our recent investigations on crystallized MnO 2 compounds 4 as possible electrode materials for supercapacitors, presents an X-ray diffraction study performed on a magnesium-doped sodium-birnessite-type MnO 2 (layered structure) at various stages (oxidized and reduced) during charge/discharge cycles.…”

Section: Introductionmentioning

confidence: 99%

Variation of the MnO₂ Birnessite Structure upon Charge/Discharge in an Electrochemical Supercapacitor Electrode in Aqueous Na₂SO₄ Electrolyte

et al. 2008

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This paper provides new insight on the charge storage mechanism in crystallized Mg-doped sodium birnessite-type manganese dioxide used as active supercapacitor electrode material that involves the intercalation/deintercalation of cations between the sheets during electrochemical reduction/oxidation, respectively. An increase of the interlayer spacing from 0.710 to 0.720 nm upon electrochemical oxidation in the presence of Na+ cations in the electrolyte is associated with the deintercalation of Na+ and the intercalation of H2O between the layers. A progressive crystallinity loss of the material is also observed upon potential cycling between the oxidized and reduced states. Despite these structural changes, the birnessite electrode exhibits a stable capacitance of 145 F/g over 1100 cycles.

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Structural evolution upon heating of sol–gel prepared birnessites

Cited by 19 publications

References 45 publications

Structure and Thermal Decomposition of K<i><sub>x</sub></i>MnO<sub>2</sub>・<i>y</i>H<sub>2</sub>O Prepared by Sol-Gel Method

Structure and Thermal Decomposition of K<i><sub>x</sub></i>MnO<sub>2</sub>・<i>y</i>H<sub>2</sub>O Prepared by Sol-Gel Method

Rotational Fluctuations of Water Confined to Layered Oxide Materials: Nonmonotonous Temperature Dependence of Relaxation Times

Variation of the MnO₂ Birnessite Structure upon Charge/Discharge in an Electrochemical Supercapacitor Electrode in Aqueous Na₂SO₄ Electrolyte

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Structural evolution upon heating of sol–gel prepared birnessites

Cited by 19 publications

References 45 publications

Structure and Thermal Decomposition of K<i><sub>x</sub></i>MnO<sub>2</sub>・<i>y</i>H<sub>2</sub>O Prepared by Sol-Gel Method

Structure and Thermal Decomposition of K<i><sub>x</sub></i>MnO<sub>2</sub>・<i>y</i>H<sub>2</sub>O Prepared by Sol-Gel Method

Rotational Fluctuations of Water Confined to Layered Oxide Materials: Nonmonotonous Temperature Dependence of Relaxation Times

Variation of the MnO2 Birnessite Structure upon Charge/Discharge in an Electrochemical Supercapacitor Electrode in Aqueous Na2SO4 Electrolyte

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Variation of the MnO₂ Birnessite Structure upon Charge/Discharge in an Electrochemical Supercapacitor Electrode in Aqueous Na₂SO₄ Electrolyte