Hydrogen storage of a novel combined system of LiNH2–NaMgH3: synergistic effects of in situ formed alkali and alkaline-earth metal hydrides

Abstract

Bimetallic hydride NaMgH₃ is used for the first time as a vehicle to enhance hydrogen release and uptake from LiNH₂. The combination of NaMgH₃ with LiNH₂ at a molar ratio of 1 : 2 can release about 4.0 wt% of hydrogen without detectable NH₃ emission in the temperature range of 45 °C to 325 °C and exhibiting superior dehydrogenation as compared to individual NaH and/or MgH₂ combined with LiNH₂. A high capacity retention of about 75% resulting from the introduction of NaMgH₃ is also achieved in LiNH₂ as well as re-hydrogenation under milder conditions of 180 °C and 5 MPa H₂ pressure. These significant improvements are attributed to synergistic effects of in situ formed NaH and MgH₂via the decomposition of NaMgH₃ where a succession of competing reactions from the cyclic consumption/recovery of NaH are involved and serve as a “carrier” for the ultra-rapid conveyance of the N-containing species between the [NH₂]⁻ amide and the resulting [NH]²⁻ imide complexes.