TEM-HRTEM study on the dehydration process of nanostructured Mg–Ca hydroxide into Mg–Ca oxide

Gomez-Villalba, L. S.; Sierra-Fernández, Aránzazu; Rabanal, M.E.; Fort, Rafael

doi:10.1016/j.ceramint.2016.03.007

Cited by 13 publications

(12 citation statements)

References 48 publications

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“…The SAED images show a typical pattern for LDH. The extra circles in SAED observed are due to the decomposition of hydroxides to oxides under strong electron beams . The enlarged TEM images (Figure g–i) present the lattice fringes of the (006) plane in each sample, showing a larger interlayer spacing of around 0.5 nm for CoMn-LDH-SO 4 , which also can be confirmed by the FFT image.…”

Section: Resultssupporting

confidence: 64%

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Enlarged Interlayer Spacing in Cobalt–Manganese Layered Double Hydroxide Guiding Transformation to Layered Structure for High Supercapacitance

Liu

Zhang

Gao

et al. 2019

ACS Appl. Mater. Interfaces

106

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Cobalt–manganese layered double hydroxide (CoMn-LDH) has been known as a highly desired cathode material used with an alkaline electrolyte. However, the layered double hydroxide structure is unstable and changes almost instantly in alkaline solution due to the instability of a manganese(III) ion. Thus, it is important to investigate the true active phase for designing efficient electrode materials. In this work, the metal–organic framework is used as a templating precursor to derive CoMn-LDH from three different manganese solutions, namely, MnSO4, Mn(NO3)2, and MnCl2. Anions in the solutions participate in the derivation process and strongly affect the layer structure, phase transformation process, and charge storage properties of the resulting materials. CoMn-LDH synthesized from manganese sulfate solution exhibits the largest interlayer spacing of 1.08 nm, and more interestingly, the layered structure can well be retained in KOH solution, while the other two synthesized from manganese chloride and nitrate solutions transform into the spinel structure. As a cathode material, it delivers a high areal capacity of 582.07 mC/cm2 at 2 mA/cm2 , which is about 100% higher than those of the other two samples. The present work explores the active phase of CoMn-LDH in the alkaline electrolyte and proposes a potential mechanism of the phase transformation, which provides insights into understanding and designing of the active electrode materials for stable and high-performing supercapacitors in an alkaline environment.

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Section: Resultssupporting

confidence: 64%

“…The extra circles in SAED observed are due to the decomposition of hydroxides to oxides under strong electron beams. 37 The enlarged TEM images (Figure 2g− (∼53 m 2 /g). 38 The interconnected 3D network morphology has effectively prevented the restacking of the LDH sheets, giving rise to the higher surface area of CoMn-LDH-SO 4 .…”

Section: Resultsmentioning

confidence: 99%

Enlarged Interlayer Spacing in Cobalt–Manganese Layered Double Hydroxide Guiding Transformation to Layered Structure for High Supercapacitance

Liu

Zhang

Gao

et al. 2019

ACS Appl. Mater. Interfaces

106

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“…The corresponding d-spacing of the {100} and {110} planes also decreased from 2.71 nm to 2.51 nm and 1.58 nm to 1.51 nm respectively. This indicates a dehydration of the material, although this interpretation can be difficult to discern from in-plane layer spacing changes 20,29 . The chemical and electronic structure of the Ni-Fe LDH was investigated using EELS, as shown in Fig.…”

Section: Results and Discussion Electron Irradiation Of Ni-fe Ldhs Atmentioning

confidence: 99%

TEM and EELS characterization of Ni–Fe layered double hydroxide decompositions caused by electron beam irradiation

et al. 2021

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Electron irradiation of Ni–Fe layered double hydroxides (LDHs) was investigated in the transmission electron microscope (TEM). The initial structure possessed a flat hexagonal morphology made up of crystalline domains with a well-defined hexagonal crystal structure. The Ni–Fe LDHs were susceptible to significant structural decompositions during electron irradiation. The generation of pores and crystallographic breakdown of the LDH routinely occurred. In addition, a compositional change was established by electron energy loss spectroscopy (EELS). During 300 kV irradiation, a pre-peak evolution in the oxygen K edge highlighted a transition to metal oxide species. In parallel, nitrogen K edge attenuation demonstrated interlayer mass-losses. It was found that TEM conditions profoundly affected the decomposition behaviours. At lower acceleration voltages, an increased dehydration rate of the LDH cationic layers is observed during irradiaton. Moreover, in situ specimen cooling revealed the retention of interlayer nitrates. An emphasis on the dehydroxylation processes and anionic mass-loss facilitation is discussed.

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“…The decomposition temperature of the mixed hydroxides deviates by only ≈15 °C from pure Mg(OH) 2 ( Figure S5, Supporting Information) (the dehydration mechanism of Mg(OH) 2 and a Ca-doped Mg 0.97 Ca 0.03 (OH) 2 was investigated in literature using transition electron microscopy [36] ).…”

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confidence: 99%

Calcium Doping Facilitates Water Dissociation in Magnesium Oxide

Müller

Knöll

Ruh

et al. 2017

Advanced Sustainable Systems

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is the most ubiquitously used form of energy, including in electricity generation, power plants, or industry. [5] In this context, in 2011, the International Energy Agency estimated in a report entitled "Solutions for a low-carbon energy future" that global energy loss through waste heat accounts for two-third of the overall energy production. [6] Therefore, methods suitable for reduction of waste heat or reutilization thereof could contribute significantly to a sustainable energy management. [7][8][9] Among the different approaches to this challenge, thermochemical energy storage (TCES) is a highly appealing concept, since by means of a reversible chemical reaction, a suitable material energy is converted from thermal to chemical energy. The charged material may be stored for any period of time without further losses or additional infrastructure (such as insulation), until, by addition of the proper reactant, the discharging reaction, releasing the stored energy in form of heat, is initiated. [2,[10][11][12] The economic benefit of implementing TCES cycles in the energy management was demonstrated by several economic feasibility studies, illustrating that, e.g., with the waste heat from Lenzing AG, [13] Calcium doping of magnesium oxide results in significantly increased water dissociation rates, thus enhancing both hydration rate and reaction completeness of hydration compared to pure MgO. For a series of mixed magnesiumcalcium oxides (Mg x Ca 1−x O) with varying Ca contents between 0% and 40%, the material of a composition Mg 0.9 Ca 0.1 O shows the fastest rehydration, transforming completely within 80 min to the mixed hydroxide. In consecutive dehydration/rehydration cycles, reasonable cycle stability is found. A "regeneration" of the aged material (reactivity reduced by excessive cycling) in liquid water re-establishes the initial rehydration reactivity. Density functional theory calculations support the experimental findings, confirming that calcium doping can reduce the energy of the rate limiting water dissociation reaction, exploiting both electronic and steric (size) effects. Three major requirements for future sustainable energy management have been established including reduction of greenhouse gas emissions, promotion and increased use of renewable energy sources, and enhancing the efficiency of energy use. [1,2] Whereas the first two issues are widely discussed and the subject of international treaties such as the Kyoto protocol [3] and the Paris agreement, [4] awareness of the poor overall efficiency of today's energy economy is rather limited. Heat

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TEM-HRTEM study on the dehydration process of nanostructured Mg–Ca hydroxide into Mg–Ca oxide

Cited by 13 publications

References 48 publications

Enlarged Interlayer Spacing in Cobalt–Manganese Layered Double Hydroxide Guiding Transformation to Layered Structure for High Supercapacitance

Enlarged Interlayer Spacing in Cobalt–Manganese Layered Double Hydroxide Guiding Transformation to Layered Structure for High Supercapacitance

TEM and EELS characterization of Ni–Fe layered double hydroxide decompositions caused by electron beam irradiation

Calcium Doping Facilitates Water Dissociation in Magnesium Oxide

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