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

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 Li ₄FeH₆ at moderate pressures. Li₄FeH₆ can be recovered at ambient conditions where Li₄FeH₆ is metastable.