Li4FeH6: Iron-containing complex hydride with high gravimetric hydrogen density

Abstract

Li4FeH6, 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, Li4FeH6 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 Li4FeH6 at moderate pressures. Li4FeH6 can be recovered at ambient conditions where Li4FeH6 is metastable.

Infrared Spectroscopic and Computational Studies on Li₄FeH₆ with High Gravimetric Hydrogen Density

“…Saitoh et al, reported that high temperature at around 900 C was necessary to obtain a high purity Li 4 FeH 6 in order to accelerate the reaction kinetics. 7) Hydrogen pressure higher than 6 GPa pressure was required to avoid subsequent decomposition of Li 4 FeH 6 during synthesis. Although the sample is not a single phase, the quality was good enough for the FTIR to access the hydrogen atomic motion in Li 4 FeH 6 .…”

“…7). The pellet, encapsulated in a pyrolytic boron nitride reaction capsule, was loaded together with a hydrogen source AlH 3 12,13) into a NaCl capsule with a diameter of 1.5 mm and a height of 3.5 mm.…”

“…Very recently, we have successfully synthesized a novel complex hydride, Li 4 FeH 6 , using a high pressure cubic-anvil-type apparatus based on a prediction by rst-principles calculations. 6,7) This is the rst complex hydride of which [FeH 6 ] 4− is counterbalanced by alkali metal elements, and has the highest gravimetric hydrogen density of 6.7 mass% in the Fe-based complex hydrides.…”

“…[1][2][3][4][5][6][7][8] In the complex hydrides, [FeH 6 ] 4− is generally counterbalanced by alkaline-earth metals (e.g. Mg 2 FeH 6 ) or mixed alkali/transition metals (e.g.…”

Raman and Infrared Spectroscopic Studies on Li₄RuH₆ Combined with First-Principles Calculations

“…Recently, novel Li 4 FeH 6 (6.7 mass%) was synthesized by hydrogenation of a mixture of LiH and Fe powders at high temperatures and high pressures, on the basis of the theoretical prediction of first-principles calculations. 5,6) Thus, owing to the high hydrogen density, Li 4 T H 6 has potential as a hydrogen storage material.…”