Methane Sorption and Structural Characterization of the Sorption Sites in Zn-2(bdc)(2)(dabco) by Single Crystal X-ray Crystallography

Sorption isotherms of methane in Zn-2(bdc)(2)(dabco) are measured up to a pressure of 35 bar in the temperature range between 198-296 K. The methane sorption measurements at 296 K showed an uptake of 1.37 cm(3) cm(-3) at 35 bar. The enthalpy of methane adsorption for Zn-2(bdc)(2) (dabco) estimated by the virial equation is 13.6 kJ mol(-1) at zero coverage. X-ray structure analysis of methane-adsorbed Zn-2(bdc)(2)(dabco) by synchrotron radiation at 90 K revealed that methane molecules occupy three independent sorption sites (A, B, and C) with a stoichiometry of Zn2(bdc)2 (dabco)-6.69CH, which is consistent with the results of the gas sorption measurements at 198 K. In a cavity, eight symmetry-related methane sorption sites A are located near the {Zn-2 (CO2)(4)} paddle-wheel units, while four symmetry-related methane sorption sites B are near the center of the small windows along the a and b axes. Both A and B sites are half-occupied. Methane molecules occupying sites A are not only in van der Waals contact with the paddle-wheel units, but also interact with the phenyl rings of bdc ligands through partial pi-HC interactions. Methane molecules in B sites interact with the side of the phenyl rings through van der Waals interaction. The site C, located at the center of the cavity, is a secondary sorption site; methane molecules occupying sites C are in van der Waals contact with those in sites A and B.X115252sciescopu

Thermochemical Analysis of Hydrogenation of Pd-Containing Composite Based on TiZrVNbTa High-Entropy Alloy

The microcalorimetric hydrogen titration technique combined with conventional volumetric measurements has been used to reveal peculiarities of the hydrogenation of the single-phase TiZrVNbTa equiatomic high-entropy alloy. The alloy has been produced in the form of microfibers by the pendent drop melt extraction technique. Palladium coating of the fibers has been applied to enable first hydrogenation at room temperature without additional activation. An analysis of the obtained data allows us to evaluate the dependence of hydrogenation enthalpy on the hydrogen concentration in the alloy. Three concentration ranges, presumably related to the formation of the hydrogen solid solution, monohydride and dihydride phases, have been identified, and the corresponding ΔH values of about −100, −80 and −60 kJ/mol H2, respectively, have been determined

X-ray photoelectron study of the interaction of the uranyl group UO22+ with hydroxylapatite and fluoroapatite in aqueous solutions

The interaction of the uranyl group UO22+ in aqueous solutions with hydroxylapatite and fluoroapatite was studied by X-ray photoelectron spectroscopy. The apatite samples under study were found to contain CO32- groups. The reaction of uranyl nitrate with hydroxylapatite in aqueous solutions does not lend to U(IV)-containing compounds but forms U(VI)-containing uranyl compounds with equatorial hydroxyl or carbonate groups partly replaced by fluorine in the uranyl compounds in the case of fluoroapatite.. The interaction of the uranyl group with fluoroapatite in aqueous solutions is much more effective than the interaction with hydroxylapatite

Influence of Anion Composition on Gas Sorption Features of Cr-MIL-101 Metal–Organic Framework

A series of chromium­(III) terephthalates MIL-101 with different anion composition of the porous matrix have been synthesized and characterized in adsorption reactions with nitrogen, hydrogen, and methane by volumetric and calorimetric measurements at pressures up to 3.2 MPa. A peculiar local maximum of H₂ adsorption heat at concentrations of 0.7–0.9 mmol/g corresponding to the filling of nanosized supertetrahedra was found. It has been shown that the substitution of the fluorine anions by Cl^– strongly affected accessibility of these micropores toward gas molecules

Transition metal-based high entropy alloy microfiber electrodes: Corrosion behavior and hydrogen activity

This contribution reveals ultra-high corrosion resistance of high entropy alloys (HEAs), i.e. Ti$_{20}$Zr$_{20}$Nb$_{15}$V$_{15}$Hf$_{15}$Ta$_{15}$ of 1.85 µm yr$^{–1}$ in alkaline environment, adverting their use for battery/fuel cell components. Formation of several nanometers passive oxide layer confirmed by scanning transmission electron microscopy accounts for corrosion resistance which increases with TiOx content. Cathodic Tafel slope of 67 mV dec$^{–1}$ and large transfer coefficient of 0.82 obtained for Ti$_{20}$Zr$_{20}$Nb$_{20}$V$_{20}$Ta$_{20}$ suggest its use for hydrogen electrocatalysis. High amounts of hydrogen storage, 1.7 wt% in Ti$_{25}$Zr$_{20}$Nb$_{15}$V$_{15}$Ta$_{20}$, were confirmed by gas-solid reactions. This HEA also has high corrosion resistance in acidic and saline environments ideal for coatings and surgical tools/implants

Hydrogen storage performance of the multi-principal-component CoFeMnTiVZr alloy in electrochemical and gas-solid reactions.

The single-phase multi-principal-component CoFeMnTiVZr alloy was obtained by rapid solidification and examined by a combination of electrochemical methods and gas-solid reactions. X-ray diffraction and high-resolution transmission electron microscopy analyses reveal a hexagonal Laves-phase structure (type C14). Cyclic voltammetry and electrochemical impedance spectroscopy investigations in the hydrogen absorption/desorption region give insight into the absorption/desorption kinetics and the change in the desorption charge in terms of the applied potential. The thickness of the hydrogen absorption layer obtained by the electrochemical reaction is estimated by high-resolution transmission electron microscopy. The electrochemical hydrogen storage capacity for a given applied voltage is calculated from a series of chronoamperometry and cyclic voltammetry measurements. The selected alloy exhibits good stability for reversible hydrogen absorption and demonstrates a maximum hydrogen capacity of ∼1.9 wt% at room temperature. The amount of hydrogen absorbed in the gas-solid reaction reaches 1.7 wt% at 298 K and 5 MPa, evidencing a good correlation with the electrochemical results

Hydrogen storage performance of the multi-principal-component CoFeMnTiVZr alloy in electrochemical and gas-solid reactions.

Funder: Ministry of Science and Higher Education of the Russian FederationThe single-phase multi-principal-component CoFeMnTiVZr alloy was obtained by rapid solidification and examined by a combination of electrochemical methods and gas-solid reactions. X-ray diffraction and high-resolution transmission electron microscopy analyses reveal a hexagonal Laves-phase structure (type C14). Cyclic voltammetry and electrochemical impedance spectroscopy investigations in the hydrogen absorption/desorption region give insight into the absorption/desorption kinetics and the change in the desorption charge in terms of the applied potential. The thickness of the hydrogen absorption layer obtained by the electrochemical reaction is estimated by high-resolution transmission electron microscopy. The electrochemical hydrogen storage capacity for a given applied voltage is calculated from a series of chronoamperometry and cyclic voltammetry measurements. The selected alloy exhibits good stability for reversible hydrogen absorption and demonstrates a maximum hydrogen capacity of ∼1.9 wt% at room temperature. The amount of hydrogen absorbed in the gas-solid reaction reaches 1.7 wt% at 298 K and 5 MPa, evidencing a good correlation with the electrochemical results