Search For Hydrogen Storage Materials Research Articles

Amorphized Defective Fullerene with a Single‐Atom Platinum for Room‐Temperature Hydrogen Storage

AbstractThe search for hydrogen storage materials allowing the storage of hydrogen in its molecular or atomic form at room temperature to meet the multistage targets such as the US Department of Energy (DOE) ultimate gravimetric and volumetric capacities of 6.5 wt% and 50 kg m‐3 is of global importance. Here, it is reported that an amorphized defective fullerene (C60‐x) offers a promising solution to this challenge. C60‐x immobilized with single‐atom platinum has ≈14‐fold higher surface area accessible for CH bonds compared to a crystalline C60, and its micro/meso pores give a ≈20‐fold larger volume for fast hydrogen transport. Indeed, hydrogen storage via spillover on C60‐x through pressure swing at room temperature is experimentally demonstrated to enable high reversible gravimetric (6.8 wt%) and volumetric (64.9 kg m‐3) capacities, hitherto the highest reversible capacities close to DOE targets at room temperature. Also, the density functional theory calculations show that a key to efficient hydrogen storage is the preservation of a curved sp2‐type local carbon geometry for spillover, which holds H radicals loosely for fast hydrogen migration. Moreover, H‐atom diffusion on the intact region of C60‐x is faster than that on the defect region. Furthermore, excellent capacity retention is achieved over repeated hydrogen adsorption/desorption cycles.

Electrochemical Performance and Hydrogen Storage of Ni–Pd–P–B Glassy Alloy

The search for hydrogen storage materials is a challenging task. In this work, we tried to test metallic glass-based pseudocapacitive material for electrochemical hydrogen storage potential. An alloy ingot with an atomic composition of Ni60Pd20P16B4 was prepared via arc melting of extremely pure elements in an Ar environment. A ribbon sample with a width of 2 mm and a thickness of 20 mm was produced via melt spinning of the prepared ingot. Electrochemical dealloying of the ribbon sample was conducted in 1 M H2SO4 to prepare a nanoporous glassy alloy. The Brunauer-Emmett-Teller (BET) and Langmuir methods were implemented to obtain the total surface area of the nanoporous glassy alloy ribbon. The obtained values were 6.486 m2/g and 15.082 m2/g, respectively. The Dubinin-Astakhov (DA) method was used to calculate pore radius and pore volume; those values were 1.07 nm and 0.09 cm3/g, respectively. Cyclic voltammetry of the dealloyed samples revealed the pseudocapacitive nature of this alloy. Impedance of the dealloying sample was measured at different frequencies through use of electrochemical impedance spectroscopy (EIS). A Cole-Cole plot established a semicircle with a radius of ~6 Ω at higher frequency, indicating low interfacial charge-transfer resistance, and an almost vertical Warburg slope at lower frequency, indicating fast diffusion of ions to the electrode surface. Charge-discharge experiments were performed at different constant currents (75, 100, 125, 150, and 200 mA/g) under a cutoff potential of 2.25 V vs. Ag/AgCl electrode in a 1 M KOH solution. The calculated maximum storage capacity was 950 mAh/g. High-rate dischargeability (HRD) and capacity retention (Sn) for the dealloyed glassy alloy ribbon sample were evaluated. The calculated capacity retention rate at the 40th cycle was 97%, which reveals high stability.

The binary boron lithium clusters B12Lin with n = 1-14: in search for hydrogen storage materials.

Molecular structures and properties of the binary clusters containing twelve boron atoms mixed with n lithium atoms, B12Lin with n = 1-14, were investigated using density functional theory with the TPSSh functional and the 6-311+G(d) basis set. Energetic parameters including relative energies, average binding energies and second-order energies of the entire series were predicted using the coupled-cluster theory (U)CCSD(T) in conjunction with the cc-pVTZ basis set. Several lowest-lying isomers were determined for each size B12Lin whose energies differ from each other by <3 kcal mol-1, except for n = 1, 2 and 4 (≤5 kcal mol-1), and particularly n = 8 (∼13 kcal mol-1). Electronic structure and chemical bonding in some specific sizes such as B12Li4, B12Li8 and B12Li14 were analyzed in detail. We established the electron shells of some magic clusters such as the B12Li4 cone for which we proposed a mixed cone-disk electron shell model. Thanks to both the phenomenological shell and Clemenger-Nilsson models, B12Li8 which contains a specific set of shells of 44 valence electrons is a high stability species. The arrangement of Li atoms around a fullerene B12 framework shows that the mixed B12Li8 emerges as the most suitable of this cluster series to adsorb molecular hydrogen. Up to 32 H2 molecules can strongly be attached to the B12Li8 cluster which is thus predicted to be a realistic candidate for hydrogen storage material with gravimetric density reaching up to a theoritical limit of 26 wt%. Attachment of the fifth H2 molecule to each Li atom of B12Li8 results in weaker average bonds but can give rise to a total of 40 H2 molecules, corresponding to 30 wt% of hydrogen.

Study of Ti, V and Their Oxides-Based Thin Films in the Search for Hydrogen Storage Materials

in the Search for Hydrogen Storage Materials Z. Tarnawski, K. Zakrzewska, N.-T.H. Kim-Ngan, M. Krupska, S. Sowa, K. Drogowska, L. Havela and A.G. Balogh Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, al. A. Mickiewicza 30, 30-059 Krakow, Poland Faculty of Computer Science, Electronics and Telecommunication, AGH University of Science and Technology, al. A. Mickiewicza 30, 30-059 Krakow, Poland Institute of Physics, Pedagogical University, 30-084 Krakow, Poland Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 12116 Prague, Czech Republic Institute of Materials Science, Technische Universitat Darmstadt, 64287 Darmstadt, Germany

How does the boron concentration affect hydrogen storage in lithium decorated zero- and two-dimensional boron–carbon compounds?

A balance between the hydrogen capacity and reversibility is a big challenge in the search for hydrogen storage materials. Using van der Waals-corrected density functional theory, we perform a detailed study of the hydrogen molecules adsorption on lithium (Li) decorated zero- and two-dimensional boron-carbon (B-C) compounds. It is found that not only the Li bond strength but also the number of adsorbed hydrogen molecules depends on the B concentration. First, the binding of Li on the B-C compounds strengthens with the increase of the B concentration due to the stronger hybridization between the lowest unoccupied molecular orbitals of the B-C compounds and Li 2p orbitals. Thus, Li atoms are not likely to form clusters, indicating a good reversible hydrogen storage. Second, higher B concentration results in weaker electric field produced by the charge transfer from Li to the B-C compounds. Therefore, one Li atom can adsorb up to 5H(2) molecules with the B concentration less than 50%. In contrast, the adsorption number of H(2) molecules is reduced to 4 when the B concentration is greater than or equal to 50%. Third, using a statistical model parametrized by the results of ab initio calculations, the adsorption and desorption of molecular hydrogens are calculated at ambient temperature and pressure. We find that the usable number of adsorbed H(2) per Li under ambient conditions decreases with the increase of B concentration. These results can serve as a guide in the design of new hydrogen storage materials based on B-C compounds.

Structural and optical properties of Mg yNi 1– yH x gradient thin films in relation to the as-deposited metallic state

Thin Mg y Ni 1− y H x films with a gradient in chemical composition are investigated by optical spectrophotometry, dc resistivity and X-ray diffraction measurements before and after exposure to hydrogen. In the metallic state crystalline Mg 2Ni is present for 0.6 ≤ y ≤ 0.8 and coexists with amorphous Mg and/or Ni. The hydride state is mainly characterized by the presence of Mg 2NiH 4 around the stoichiometric [Mg]/[Ni] = 2 composition and some MgH 2 on the Mg-rich side. The abrupt microstructural changes found in the as-deposited metallic state around the Mg–Mg 2Ni eutectic point correlate well with the compositional dependence of the optical properties in the hydride state. We conclude that the formation of the hydride depends directly on the detailed nature of the metallic parent phase. Furthermore, we demonstrate that high-throughput compositional screening via fiber-optic spectrophotometry is useful for hydride identification. When no structural long-range order is present, this provides a new tool for the search for hydrogen storage materials.

Ternary MgTiX‐Alloys: A Promising Route towards Low‐Temperature, High‐Capacity, Hydrogen‐Storage Materials

In the search for hydrogen-storage materials with a high gravimetric capacity, Mg(y)Ti((1-y)) alloys, which exhibit excellent kinetic properties, form the basis for more advanced compounds. The plateau pressure of the Mg--Ti--H system is very low (approximately 10(-6) bar at room temperature). A way to increase this pressure is by destabilizing the metal hydride. The foremost effect of incorporating an additional element in the binary Mg--Ti system is, therefore, to decrease the stability of the metal hydride. A model to calculate the effect on the thermodynamic stability of alloying metals was developed by Miedema and co-workers. Adopting this model offers the possibility to select promising elements beforehand. Thin films consisting of Mg and Ti with Al or Si were prepared by means of e-beam deposition. The electrochemical galvanostatic intermittent titration technique was used to obtain pressure-composition isotherms for these ternary materials and these isotherms reveal a reversible hydrogen-storage capacity of more than 6 wt. %. In line with the calculations, substitution of Mg and Ti by Al or Si indeed shifts the plateau pressure of a significant part of the isotherms to higher pressures, while remaining at room temperature. It has been proven that, by controlling the chemistry of the metal alloy, the thermodynamic properties of Mg-based hydrides can be regulated over a wide range. Hence, the possibility to increase the partial hydrogen pressure, while maintaining a high gravimetric capacity creates promising opportunities in the field of hydrogen-storage materials, which are essential for the future of the hydrogen economy.