Highly ordered and highly cooperative water with properties of both solid and liquid states has been observed by means of neutron scattering in hydrophobic one-dimensional channels with van der Waals ...diameter of 0.78 nm. We have found that in the initial stages of adsorption water molecules occupy niches close to pore walls, followed later by the filling of the central pore area. Intensified by confinement, intermolecular water interactions lead to the formation of well-ordered hydrogen-bonded water chains and to the onset of cooperative vibrations. On the other hand, the same intermolecular interactions lead to two relaxation processes, the faster of which is the spontaneous position exchange between two water molecules placed 3.2–4 Å from each other. Self-diffusion in an axial pore direction is the result of those spontaneous random exchanges and is substantially slower than the self-diffusion in bulk water.
Understanding the influence of electrode material’s morphology on electrochemical behavior is of great significance for the development of rechargeable batteries, however, such studies are often ...limited by the inability to precisely control the morphology of electrode materials. Herein, nanostructured titanium niobium oxides (TiNb
2
O
7
) with three different morphologies (one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D)) were synthesized via a facile microwave-assisted solvothermal method. The influence of the morphological dimension of TiNb
2
O
7
as electrode material on the electrochemical performance in Li-ion batteries (LIBs) and the underlying correlation with the electrochemical kinetics were studied in detail. 2D TiNb
2
O
7
(TNO-2D) shows a superior rate capability and cycling stability, associated with improved kinetics for charge transfer and Li-ion diffusion, compared to the 1D and 3D materials.
Operando
X-ray diffraction measurements reveal the structural stability and crystallographic evolution of TNO-2D upon lithiation and delithiation and correlate the Li-ion diffusion kinetics with the lattice evolution during battery charge and discharge. Moreover, carbon-coated TNO-2D achieves enhanced rate capability (205 mAh·g
−1
at 50 C) and long-term cycling stability (87% after 1000 cycles at 5 C). This work provides insights into the rational morphology design of electrode materials for accelerated charge transfer and enhanced fast-charging capability, pushing forward the development of electrode materials for high-power rechargeable batteries in future energy storage.
Kinetic‐quantum‐sieving‐assisted H2:D2 separation in flexible porous materials is more effective than the currently used energy‐intensive cryogenic distillation and girdle‐sulfide processes for ...isotope separation. It is believed that material flexibility results in a pore‐breathing phenomenon under the influence of external stimuli, which helps in adjusting the pore size and gives rise to the optimum quantum‐sieving phenomenon at each stage of gas separation. However, only a few studies have investigated kinetic‐quantum‐sieving‐assisted isotope separation using flexible porous materials. In addition, no reports are available on the microscopic observation of isotopic molecular transportation during the separation process under dynamic transition. Here, the experimental observation of a significantly faster diffusion of deuterium than hydrogen in a flexible pore structure, even at high temperatures, through quasi‐elastic neutron scattering, is reported. Unlike rigid structures, the extracted diffusion dynamics of hydrogen isotopes within flexible frameworks show that the diffusion difference between the isotopes increases with an increase in temperature. Owing to this unique inverse trend, a new strategy is suggested for achieving higher operating temperatures for efficient isotope separation utilizing a flexible metal–organic framework system.
An experimental observation of hydrogen isotope diffusion in flexible MIL‐53(Al) is demonstrated through quasielastic neutron scattering. Unlike rigid structures, the diffusion difference between the isotopes in the flexible MIL‐53(Al) increases with an increase in temperature. Owing to this unique inverse trend, a new strategy is suggested for achieving higher operating temperatures for efficient isotope separation utilizing a flexible metal–organic framework (MOF) system.
The self-diffusion mechanisms for adsorbed H2 in different porous structures are investigated with in situ quasi-elastic neutron scattering method at a temperature range from 50 K to 100 K and at ...various H2 loadings. The porous structures of the carbon materials have been characterized by sorption analysis with four different gases and the results are correlated with previous in-depth analysis with small-angle neutron scattering method. Thus, an investigation discussing the effect of pore shape and size on the nature of adsorbed H2 self-diffusion is performed. It is shown that H2 adsorbed in nanometer-scale pores is self-diffusing in two distinguishable timescales. The effect of the pore, pore wall shape and corrugation on the fraction of confined and more mobile H2 is determined and analyzed. The increased corrugation of the pore walls is shown to have a stronger confining effect on the H2 motions. The difference of self-diffusional properties of the two H2 components are shown to be smaller when adsorbed in smoother-walled pores. This is attributed to the pore wall corrugation effect on the homogeneity of formed adsorbed layers.
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•H2 adsorbed in porous CDCs diffuses in two distinguishable timescales.•Larger difference between the two H2 diffusional phases in corrugated pores.•Pore wall corrugation and shape influences H2 diffusivity.•Enhanced H2 confinement in corrugated pores compared to smoother-walled pores.
The title compound Cu
(NH
-(µ
-CN)
-Pd
(CN)
was prepared from the aqueous solution Cu
–
-tetraethylethane-1,2-diamine – Pd(CN)
, where the addition of excess amounts of ammonia caused the ...dissolution of the precipitate formed during reaction. Using this method, we prepared and structurally characterized the new complex of Cu(II) containing ammine ligand with tetracyanidopalladate(II) anion incorporated within the molecule. The crystal structure of compound is molecular; the unit cell contains centrosymmetric octanuclear molecules in which all central atoms lies on mirror plane. Generally, the structure of the molecule can be divided into central cyclic part and terminal pendants. The structure contains nitrogen atoms derived from the ammonia molecules coordinated to Copper(II) atoms. They are involved in the formation of N-H···N hydrogen bonds type.
The adsorption of water in one-dimensional channels in porous aluminophosphate material AlPO4-5 has been studied by a combination of gravimetric analysis techniques, neutron and X-ray diffraction and ...neutron spectroscopy. Molecular structure of AlPO4-5 consists of 12-membered rings of alternating, corner-sharing AlO4 and PO4 tetrahedra connected by oxygen bridges into sheets in the (a, b) plane. The sheets are connected by oxygen bridges along the c crystal axis and form one-dimensional channels of which the largest, formed by the 12-membered rings, have a van der Waals diameter of about 8.3 Å. Gradually increasing the amount of adsorbed water we could follow the evolution of the confined water mobility in a systematic way and identify the molecular mechanism of water adsorption. We focused particularly on the range of low and medium relative pressures up to p/p0 = 0.32, where a change from a hydrophobic behavior to a steep, capillary condensation like water intake has been observed. At the initial adsorption stages water occupies positions close to the pore walls causing the contraction of channels in the (a, b) plane and the prolongation of the channels along c axis in AlPO4-5. With the progressing intake water molecules form chains along the main channels. The cooperative interactions between water molecules lead to the onset of phonon-like cooperative modes and, surprisingly, to the increase of diffusive-like motion, which slow down only in the final adsorption stages when AlPO4-5 channels are completely filled.
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•Water sorption isotherm with a broad hysteresis has been observed in porous material AlPO4-5 with one-dimensional channels of about 8.3 Å in diameter. It shows changes from a hydrophobic behavior to a steep water intake in the medium range of relative pressures up to p/p0 = 0.32•X-ray and neutron diffraction studies reveal that in the initial adsorption stages water occupies positions close to the pore walls causing a structural contraction of channels in the plane across the pores and an elongation of the channels along the pores. With progressing intake water molecules form chains along the main channels.•These adsorption-induced structural changes can be one of the origins of the broad hysteresis observed in AlPO4-5.•Cooperative effects between confined water molecules lead to an increase of the mean square displacement for increasing hydration values up to relative pressures of p/p0 = 0.32 and are responsible for the major water intake.
In article number 2007412, Jitae T. Park, Hyunchul Oh, and co‐workers report a hydrogen‐isotope separation mechanism in the flexible framework of MIL‐53(Al) through a diffusion dynamics study by ...quasielastic neutron scattering measurements. The dynamic breathing of the flexible pores allows faster diffusion of the heavier isotope at high temperature, unlike in rigid frameworks.
Carbons are important in a multitude of applications, and thus, the reversible control of carbon structures is of high interest. Here we report the reversible formation of graphitic structures with ...three distinct interlayer distances in case of two carbide-derived carbons (CDCs) loaded under hydrogen pressure observed with in situ neutron scattering methods. The formation of these graphitic structures determined with in situ neutron diffraction is brought forth by the confinement of H2 in the porous structure when the temperature, T, is increased from T = 20 K–50 K under H2 loading from 68 mbar to 10 bar. The confinement of the desorbing H2 causes the pressure to increase inside the CDC structure and this increase of pressure is the cause for the reversible formation of graphitic domains. The confinement of H2 at T = 50 K is possible due to the presence of ultramicropores and suitable curved carbon structures. The three distinct formed graphitic domains correspond to a highly pressurized, conventional highly ordered graphitic, and disoriented graphitic domains with possible H2/H intercalation. In situ quasi-elastic neutron scattering and gas adsorption methods are used to determine the H2 transport properties and interactions with the CDCs.
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•Reversible formation of graphitic carbon structures.•Formation of structures in the presence of H2.•Structure formation caused by high-pressure H2 domains after temperature increase.•Curved and microporous carbons able to confine H2 pressure during heating.
Hydrogen adsorption in highly porous carbon with well-defined pores, with three different shapes, and different sizes ranging from sub-to nanometers is investigated. Using a combined approach of ...volumetric gas adsorption method and in-situ quasi-elastic neutron scattering method the relationship between final macroscopic intake properties, details of the local adsorbent structure and the molecular behaviour of confined hydrogen are established. It is shown that sub-nanometer pores of spherical and cylindrical shape strongly limit the diffusion of H2, and thus, enhance the H2 storage capability of carbons with well-tailored pore structure. In mesoporous carbide-derived carbon, the formation of a hydrogen layer with reduced mobility close to the pore walls is observed. With the increase in the amount of confined hydrogen and the occupation of the centre pore area, the mobility of confined hydrogen increases in a jump–like fashion. Surprisingly, the increase of hydrogen diffusion is also observed at higher hydrogen loadings, indicating that cooperative H2–H2 interactions might play a role.
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The large cell volume changes of switchable metal-organic frameworks (MOFs) render them as promising functional materials. Low-frequency phonon modes are known to influence the dynamic response of ...these materials. The pillared layer DUT-8(M) materials are prototypical examples of switchable MOFs, enabling switching between the closed and open pore phases, largely depending on the metal ions constituting the paddle wheel unit. However, the role of specific phonon modes in the softness of these materials is still rather unexplored. This study combines complementary spectroscopic techniques such as Raman spectroscopy, inelastic neutron scattering, and phonon acoustic spectroscopy (PAS) with density functional theory calculations (DFT) to unravel the vibrational properties of DUT-8(M) with different metal nodes (M = Ni, Co, Zn, Cu) to address these open questions. After analysis of the various experimental and theoretical spectroscopic data, the closed pore phase of DUT-8(Ni) appeared to be stiffer than that of the materials with Co and Zn. Experiments also show that the open pore phase of the Ni based compound is softer than those containing Zn and Co, although these findings could not be supported by theory. Nevertheless, DFT calculations could explain that changing the metal atom has mainly an impact on the phonon modes inducing changes in the paddle wheel unit. These results yield valuable insights into the role of the metal node on the observed flexibility in DUT-8(M) materials and can help to understand the mechanisms behind the phase transition in switchable MOFs.
The role of phonons in switchable DUT-8(M) MOFs involving Ni, Co, Zn, or Cu as metal (M) was studied by Raman spectroscopy, inelastic neutron scattering (INS), and phonon acoustic spectroscopy (PAS) and density functional theory (DFT) calculations.
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