Synthesis of novel hydride Li₃AlFeH₈ at high temperature and pressure

Iron-containing complex hydrides are a fascinating class of materials for hydrogen storage applications because they consist of abundant iron and usually contains [FeH₆]⁴⁻ complexes, resulting in high hydrogen densities. In this study, we synthesized theoretically predicted Li₃AlFeH₈, which has the highest gravimetric hydrogen density of all transition metal complex hydrides, through a hydrogenation reaction of LiH, AlH₃, and pure iron powder mixture under high pressure. The reaction process was observed in situ using a synchrotron radiation x-ray diffraction technique to clarify its reaction kinetics. The reaction temperature and pressure were changed to optimize reaction conditions for obtaining single phase Li₃AlFeH₈. Unfortunately, we did not obtain single phase Li₃AlFeH₈ because the reaction was slow. In addition, there were other phases with similar thermodynamic stabilities to that of Li₃AlFeH₈. Another novel hydride, LiAlFeH₆, was found to be synthesized above 850 °C at 9 GPa.