Hydrogen Energy
This is an editorial that will appear in ChemPhysChem special issue.
Hirscher, Michael↗
Engineering topics
Orimo, Shin-ichi
Publications and source records attributed to Orimo, Shin-ichi.
Evidence of Intermediate Hydrogen States in the Formation of a Complex Hydride
A complex hydride (LaMg 2 NiH 7 ) composed of La 3+ , two Mg 2+ , [NiH 4 ] 4– with a covalently bonded hydrogen, and three H – was formed from an intermetallic LaMg 2 Ni via an intermediate phase (LaMg 2 NiH 4.6 ) composed of La, Mg, NiH 2 , NiH 3 units, and H atoms at tetrahedral sites. The NiH 2 and NiH 3 units in LaMg 2 NiH 4.6 were reported as precursors for [NiH 4 ] 4– in LaMg 2 NiH 7 [Miwa et al. J. Phys. Chem. C 2016, 120, 5926–5931]. To further understand the hydrogen states in the precursors (the NiH 2 and NiH 3 units) and H atoms at the tetrahedral sites in the intermediate phase, LaMg 2 NiH 4.6 , we observed the hydrogen vibrations in LaMg 2 NiH 4.6 and LaMg 2 NiH 7 by using inelastic neutron scattering. A comparison of the hydrogen vibrations of the NiH 2 and NiH 3 units with that of [NiH 4 ] 4– shows that the librational modes of the NiH 2 and NiH 3 units were nonexistent; librational modes are characteristic modes for complex anions, such as [NiH 4 ] 4– . Furthermore, the hydrogen vibrations for the H atoms in the tetrahedral sites showed a narrower wavenumber range than that for H – and a wider range than that for typical interstitial hydrogen. The results indicated the presence of intermediate hydrogen states before the formation of [NiH 4 ] 4– and H – .
36 MATERIALS SCIENCE↗
Comparison of Anion Reorientational Dynamics in MCB 9 H 10 and M 2 B 10 H 10 (M = Li, Na) via Nuclear Magnetic Resonance and Quasielastic Neutron Scattering Studies
The disordered phases of the 1-carba-closo-decaborates LiCB9H10 and NaCB9H10 exhibit the best solid-state ionic conductivities to date among all known polycrystalline competitors, likely facilitated in part by the highly orientationally mobile CB9H10- anions. We have undertaken both NMR and quasielastic neutron scattering (QENS) measurements to help characterize the monovalent anion reorientational mobilities and mechanisms associated with these two compounds and to compare their anion reorientational behaviors with those for the divalent B10H102- anions in the related Li2B10H10 and Na2B10H10 compounds. NMR data show that the transition from the low-T ordered to the high-T disordered phase for both LiCB9H10 and NaCB9H10 is accompanied by a nearly two-orders-of-magnitude increase in the reorientational jump rate of CB9H10- anions. QENS measurements of the various disordered compounds indicate anion jump correlation frequencies on the order of 1010-1011 s-1 and confirm that NaCB9H10 displays jump frequencies about 60% to 120% higher than those for LiCB9H10 and Na2B10H10 at comparable temperatures. The Q-dependent quasielastic scattering suggests similar small-angular-jump reorientational mechanisms for the different disordered anions, changing from more uniaxial in character at lower temperatures to more multidimensional at higher temperatures, although still falling short of full three-dimensional rotational diffusion below 500 K within the nanosecond neutron window.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Stabilizing Superionic-Conducting Structures via Mixed-Anion Solid Solutions of Monocarba- closo -borate Salts
Not Available
36 MATERIALS SCIENCE↗
Hydrogen release reactions of Al-based complex hydrides enhanced by vibrational dynamics and valences of metal cations
Hydrogen release from Al-based complex hydrides composed of metal cation(s) and [AlH4] – was investigated using inelastic neutron scattering viewed from vibrational dynamics. Here, the hydrogen release followed the softening of translational and [AlH4] – librational modes, which was enhanced by vibrational dynamics and the valence(s) of the metal cation(s).
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Unparalleled lithium and sodium superionic conduction in solid electrolytes with large monovalent cage-like anions
Solid electrolytes with sufficiently high conductivities and stabilities are the elusive answer to the inherent shortcomings of organic liquid electrolytes prevalent in today's rechargeable batteries. We recently revealed a novel fast-ion-conducting sodium salt, Na 2 B 12 H 12 , which contains large, icosahedral, divalent B 12 H 12 2– anions that enable impressive superionic conductivity, albeit only above its 529 K phase transition. Its lithium congener, Li 2 B 12 H 12 , possesses an even more technologically prohibitive transition temperature above 600 K. Here we show that the chemically related LiCB 11 H 12 and NaCB 11 H 12 salts, which contain icosahedral, monovalent CB 11 H 12 – anions, both exhibit much lower transition temperatures near 400 K and 380 K, respectively, and truly stellar ionic conductivities (>0.1 S cm –1 ) unmatched by any other known polycrystalline materials at these temperatures. Furthermore with proper modifications, we are confident that room-temperature-stabilized superionic salts incorporating such large polyhedral anion building blocks are attainable, thus enhancing their future prospects as practical electrolyte materials in next-generation, all-solid-state batteries.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Pulsed laser deposition of air-sensitive hydride epitaxial thin films: LiH
We report on the epitaxial thin film growth of an air-sensitive hydride, lithium hydride (LiH), using pulsed laser deposition (PLD). We first synthesized a dense LiH target, which is key for PLD growth of high-quality hydride films. Then, we obtained epitaxial thin films of [100]-oriented LiH on a MgO(100) substrate at 250 °C under a hydrogen pressure of 1.3 × 10{sup −2} Pa. Atomic force microscopy revealed that the film demonstrates a Stranski-Krastanov growth mode and that the film with a thickness of ∼10 nm has a good surface flatness, with root-mean-square roughness R{sub RMS} of ∼0.4 nm.
36 MATERIALS SCIENCE↗
Epitaxial thin film growth of LiH using a liquid-Li atomic template
We report on the synthesis of lithium hydride (LiH) epitaxial thin films through the hydrogenation of a Li melt, forming abrupt LiH/MgO interface. Experimental and first-principles molecular dynamics studies reveal a comprehensive microscopic picture of the crystallization processes, which sheds light on the fundamental atomistic growth processes that have remained unknown in the vapor-liquid-solid method. We found that the periodic structure that formed, because of the liquid-Li atoms at the film/MgO-substrate interface, serves as an atomic template for the epitaxial growth of LiH crystals. In contrast, films grown on the Al{sub 2}O{sub 3} substrates indicated polycrystalline films with a LiAlO{sub 2} secondary phase. These results and the proposed growth process provide insights into the preparation of other alkaline metal hydride thin films on oxides. Further, our investigations open the way to explore fundamental physics and chemistry of metal hydrides including possible phenomena that emerge at the heterointerfaces of metal hydrides.
36 MATERIALS SCIENCE↗
Development of bulk-type all-solid-state lithium-sulfur battery using LiBH{sub 4} electrolyte
Stable battery operation of a bulk-type all-solid-state lithium-sulfur battery was demonstrated by using a LiBH{sub 4} electrolyte. The electrochemical activity of insulating elemental sulfur as the positive electrode was enhanced by the mutual dispersion of elemental sulfur and carbon in the composite powders. Subsequently, a tight interface between the sulfur-carbon composite and the LiBH{sub 4} powders was manifested only by cold-pressing owing to the highly deformable nature of the LiBH{sub 4} electrolyte. The high reducing ability of LiBH{sub 4} allows using the use of a Li negative electrode that enhances the energy density. The results demonstrate the interface modification of insulating sulfur and the architecture of an all-solid-state Li-S battery configuration with high energy density.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Li{sub 4}FeH{sub 6}: Iron-containing complex hydride with high gravimetric hydrogen density
Li{sub 4}FeH{sub 6}, which has the highest gravimetric hydrogen density of iron-containing complex hydrides reported so far, is synthesized by hydrogenation of a powder mixture of iron and LiH above 6.1 GPa at 900 °C. In situ synchrotron radiation X-ray diffraction measurements reveal that while kinetics require high temperature and thus high pressure for the synthesis, Li{sub 4}FeH{sub 6} is expected to be thermodynamically stable slightly below room temperature at ambient pressure; further synthetic studies to suppress the kinetic effects may enable us to synthesize Li{sub 4}FeH{sub 6} at moderate pressures. Li{sub 4}FeH{sub 6} can be recovered at ambient conditions where Li{sub 4}FeH{sub 6} is metastable.
36 MATERIALS SCIENCE↗
Enhanced tunability of thermodynamic stability of complex hydrides by the incorporation of H{sup –} anions
First-principles calculations were employed to investigate hypothetical complex hydrides (M,M{sup ′}){sub 4}FeH{sub 8} (M = Na, Li; M{sup ′}=Mg, Zn, Y, Al). Besides complex anion [FeH{sub 6}]{sup 4–}, these materials contain two H{sup –} anions, which raise the total anionic charge state from tetravalent to hexavalent, and thereby significantly increasing the number of combinations of countercations. We have determined that similar to complex hydrides (M,M{sup ′}){sub 2}FeH{sub 6} containing only [FeH{sub 6}]{sup 4–}, the thermodynamic stability is tuned by the average cation electronegativity. Thus, the chemical flexibility provided by incorporating H{sup –} enhances the tunability of thermodynamic stability, which will be beneficial in obtaining optimal stability for hydrogen storage materials.
36 MATERIALS SCIENCE↗