Hydrogen-Release Reaction of a Complex Transition Metal Hydride with Covalently Bound Hydrogen and Hydride Ions |
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| Authors: | Dr. Toyoto Sato Dr. Luke L. Daemen Dr. Yongqiang Cheng Dr. Anibal J. Ramirez-Cuesta Dr. Kazutaka Ikeda Takuma Aoki Dr. Toshiya Otomo Prof. Shin-ichi Orimo |
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| Affiliation: | 1. Institute for Materials Research, Tohoku University, Sendai, Miyagi, 980-8577 Japan;2. Neutron Scattering Division, Spallation Neutron Source, Oak Ridge National Laboratory, Oak Ridge, Tennessee, 37831 USA;3. Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba, Ibaraki, 305-0801 Japan;4. Institute for Materials Research, Tohoku University, Sendai, Miyagi, 980-8577 Japan WPI-Advanced Institute for Materials Research (AIMR), Tohoku University, Sendai, Miyagi, 980-8577 Japan |
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| Abstract: | The hydrogen-release reaction of a complex transition metal hydride, LaMg2NiH7, composed of La3+, 2×Mg2+, [NiH4]4− and 3×H−, was studied by thermal analyses, powder X-ray, and neutron diffraction and inelastic neutron scattering. Upon heating, LaMg2NiH7 released hydrogen at approximately 567 K and decomposed into LaH2−3 and Mg2Ni. Before the reaction, covalently bound hydrogen (Hc°v.) in [NiH4]4− exhibited a larger atomic displacement than H−, although a weakening of the chemical bonds around [NiH4]4− and H− was observed. These results indicate the precursor phenomenon of a hydrogen-release reaction, wherein there is a large atomic displacement of Hc°v. that induces the hydrogen-release reaction rather than H−. As an isothermal reaction, LaMg2NiH7 formed LaMg2NiH2.4 at 503 K in vacuum for 48 h, and LaMg2NiH2.4 reacted with hydrogen to reform LaMg2NiH7 at 473 K under 1 MPa of H2 gas pressure for 10 h. These results revealed that LaMg2NiH7 exhibited partially reversible hydrogen-release and uptake reactions. |
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| Keywords: | complex transition metal hydride crystal structure inelastic neutron scattering neutron diffraction vibration |
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