X-ray and Synchrotron FTIR Studies of Partially Decomposed Magnesium Borohydride

Magnesium borohydride (Mg(BH4)(2)) is an attractive compound for solid-state hydrogen storage due to its lucratively high hydrogen densities and theoretically low operational temperature. Hydrogen release from Mg(BH4)(2) occurs through several steps. The reaction intermediates formed at these steps have been extensively studied for a decade. In this work, we apply spectroscopic methods that have rarely been used in such studies to provide alternative insights into the nature of the reaction intermediates. The commercially obtained sample was decomposed in argon flow during thermogravimetric analysis combined with differential scanning calorimetry (TGA-DSC) to differentiate between the H-2-desorption reaction steps. The reaction products were analyzed by powder X-ray diffraction (PXRD), near edge soft X-ray absorption spectroscopy at boron K-edge (NEXAFS), and synchrotron infrared (IR) spectroscopy in mid- and far-IR ranges (SR-FTIR). Up to 12 wt% of H-2 desorption was observed in the gravimetric measurements. PXRD showed no crystalline decomposition products when heated at 260-280 degrees C, the formation of MgH2 above 300 degrees C, and Mg above 320 degrees C. The qualitative analysis of the NEXAFS data showed the presence of boron in lower oxidation states than in (BH4)(-). The NEXAFS data also indicated the presence of amorphous boron at and above 340 degrees C. This study provides additional insights into the decomposition reaction of Mg(BH4)(2)

Role of extraframework metal sites for hydrogen adsorption into the pores of a zeolite: FT-IR study

In order to compare the adsorptive properties of nanoporous zeolites containing extraframework cations of different nature, we have studied the interaction of H2 with Na-A, Ca- A, and Co,Na-A zeolites. Low temperature Fourier transform infrared (FT-IR) spectroscopy was used for the investigation, as this technique is highly sensitive and responsive to the nature of the gas/surface interaction and can in addition allow for the estimation of the adsorption enthalpy. In all cases the spectra of adsorbed H2 have complex structure due to ortho/para splitting as well as to surface structural disorder. Na\ufe and divalent Ca2\ufe were found to induce almost similar perturbation on H2 molecule, resulting in the shift of the HeH vibrational frequency of 86 cm1 and 76 cm1 respectively (as compared to the Raman frequency of gaseous H2). The enthalpy of adsorption, estimated by the Variable Temperature Infrared (VTIR) method, is 13 1 kJ mol1 for the strongest adsorptive sites in Na-A and Ca-A samples. In the case of Co,Na-A the shift of the HeH frequency due to the formation of H2/Co2\ufe complexes is larger (ca. 180 cm1) suggesting that the interaction can involve some, although small, chemical contribution

Hydrogen cycling in ?-Mg(BH<inf>4</inf>)<inf>2</inf> with cobalt-based additives

Magnesium borohydride (Mg(BH&lt;inf&gt;4&lt;/inf&gt;)&lt;inf&gt;2&lt;/inf&gt;) is an attractive candidate as a hydrogen storage material due to its high hydrogen content and predicted favorable thermodynamics. In this work we demonstrate reversible hydrogen desorption in partially decomposed Mg(BH&lt;inf&gt;4&lt;/inf&gt;)&lt;inf&gt;2&lt;/inf&gt; which was ball milled together with 2 mol% Co-based additives. Powder X-ray diffraction and infrared spectroscopy showed that after partial decomposition at 285 °C, amorphous boron-hydride compounds were formed. Rehydrogenation at equivalent temperatures and hydrogen pressures of 120 bar yielded the formation of crystalline Mg(BH&lt;inf&gt;4&lt;/inf&gt;)&lt;inf&gt;2&lt;/inf&gt; in the first cycle, and amorphous Mg(BH&lt;inf&gt;4&lt;/inf&gt;)&lt;inf&gt;2&lt;/inf&gt; with other boron-hydrogen compounds upon the third H&lt;inf&gt;2&lt;/inf&gt; absorption. Reversibility was observed in the samples with and without Co-based additives, although the additives enhanced hydrogen desorption kinetics in the first cycle. X-ray absorption spectroscopy at Co K-edge revealed that all the additives, apart from Co&lt;inf&gt;2&lt;/inf&gt;B, reacted during the first desorption to form new stable species. This journal i

Vibrational Properties of MBH(4) and MBF(4) Crystals (M = Li, Na, K): A Combined DFT, Infrared, and Raman Study

In this work vibrational properties of alkaline-metal borohydrides and of the corresponding tetrafluorborates are studied by comparing DFT harmonic vibrational IR and Raman spectra of the crystals with the experimental ones, obtained by infrared attenuated total reflection and Raman techniques. The computed internal bending frequencies of the [BX(4)](-) anions are found to be in good agreement with the experiment, and the computed stretching frequencies of tetrafluorborates are slightly underestimated. As expected, due to the neglecting of anharmonicity in the DFT spectra, the computed stretching frequencies of borohydrides are overestimated. The peak assignment of the experimental spectra is carried out in terms of factor group theory. For borohydrides, it is mostly in agreement with previously published data but for a peak observed at ca. 1400 cm(-1). The peak assignment for KBF(4) and LiBF(4) was carried out for the first time in terms of factor group theory. This work is the first step on the way to determining the vibrational properties of the MBH(4) + MBF(4) solid solutions for hydrogen storage materials with enhanced H(2)-release/uptake properties and solid-state electrolytes

Exploits, advances and challenges benefiting beyond Li-ion battery technologies

International audienceThe battery market is undergoing quick expansion owing to the urgent demand for mobile devices, electric vehicles and energy storage systems, convoying the current energy transition. Beyond Li-ion batteries are of high importance to follow these multiple-speed changes and adapt to the specificity of each application. This review-study will address some of the relevant post-Li ion issues and battery technologies, including Na-ion batteries, Mg batteries, Ca-ion batteries, Zn-ion batteries, Al-ion batteries and anionic (F-and Cl-) shuttle batteries. MH-based batteries are also presented with emphasize on NiMH batteries, and novel MH-accommodated Li-ion batteries. Finally, to facilitate further research and development some future research trends and directions are discussed based on comparison of the different battery systems with respect to Li-ion battery assumptions. Remarkably, aqueous systems are most likely to be given reconsideration for intensive, cost-effective and safer production of batteries; for instance to be utilized in (quasi)-stationary energy storage applications

FTIR spectroscopy and thermodynamics of CO and H2 adsorbed on gamma-, delta- and alpha-Al2O3

The adsorption of CO and H2 at the surface of transitional (gamma and delta) and corundum (alpha) phases of Al2O3 is studied by means of FTIR spectroscopy at temperature variable in the 293\u201360 K (CO) and 293\u201320 K (H2) intervals with the aims of better clarifying the nature of the surface Lewis centres and evaluate the thermodynamics of the adsorption process

Experimental and computational characterization of phase transitions in CsB3H8

Metal hydroborates are versatile materials with interesting properties related to energy storage and cation conductivity. The hydrides containing B3H8- (triborane, or octahydrotriborate) ions have been at the center of attention for some time as reversible intermediates in the decomposition of BH4- (3BH4- \u2194 B3H8- + 2H2), and as conducting media in electrolytes based on boron-hydride cage clusters. We report here the first observation of two phase transitions in CsB3H8 prior to its decomposition above 230 \ub0C. The previously reported orthorhombic room temperature phase (here named \u3b1-CsB3H8) with the space group Ama2 changes into a new phase with the space group Pnma at 73 \ub0C (here named \u3b2-CsB3H8), and then into a face-centered cubic phase, here named \u3b3-CsB3H8, at 88 \ub0C. These phases are not stable at room temperature thus requiring in situ measurements for their characterization. The phase transitions and decomposition pathway of CsB3H8 were studied with in situ synchrotron powder X-ray diffraction (SR-PXD), in situ and ex situ vibrational spectroscopies (Raman and FTIR), and differential-scanning calorimetry combined with thermo-gravimetric analysis (DSC-TGA). The structure determination was validated by vibrational spectroscopy analysis and modeling of the periodic structures by density functional methods. In \u3b3-CsB3H8, a significant disorder in B3H8- positions and orientations was found which can potentially benefit cation conducting properties through the paddle mechanism

Hydrogen adsorption by delta and epsilon crystalline phases of syndiotactic polystirene aerogels

The H2 uptake from s-PS samples exhibiting different crystalline phases and different morphologies has been studied by gravimetric measurements at 77 K in the hydrogen pressure range from 0 up to 1.7 MPa and compared with molecular simulations relative to s-PS crystals. Gravimetric experiments show that the molecular hydrogen sorption is strongly dependent on the sample morphology and is maximum for low-density polymer aerogels. However, independently of the morphology, theH2 uptake is minimum for the dense \u3b2 and \u3b3 crystalline phases, intermediate for the channel-shaped nanoporous \u3b5 phase, and maximum for the cavity-shaped nanoporous \u3b4 phase. In particular, although the two nanoporous crystalline phases present essentially the same density (0.98 g/cm3), the hydrogen uptake from the \u3b4 phase is roughly double with respect to the uptake from the \u3b5 phase, both for powders and for aerogels. Infrared measurements and molecular simulations well agree with these quantitative sorption data and clearly indicate that, for both low and high pressure, the hydrogen molecules are preferentially adsorbed into the nanoporous crystalline phases. In particular, molecular simulations indicate that the maximum average hydrogen uptake is of nearly 3 molecules per cavity of the \u3b4 phase and of nearly 3.5 molecules per unit height of the channels of the \u3b5 phase