Hydrogen storage properties of a Mg-La-Fe-H nano-composite prepared through reactive ball milling

Abstract

In the present work, a Mg-La-Fe-H nano-composite was prepared through reactive ball milling of the mixture of MgH2, Fe and La powders. The phase components, microstructure and hydrogen sorption properties of the composite powders were carefully investigated. After milling, an unsaturated hydride LaH2.3 formed in the Mg-La-Fe-H composite. It is observed that since Mg(102) and α-Fe(110) planes have the similar interplanar spacing, Mg grains preferentially nucleate at the interface of MgH2/α-Fe when MgH2 transforms to Mg. Based on the Pressure-Composition-Temperature measurements, the hydrogenation enthalpy of the Mg-La-Fe-H composite is determined to be −72.0 kJ/mol H2. Meantime, the hydrogen absorption kinetics can be significantly improved and the hydrogen desorption temperature can be reduced in the Mg-La-Fe-H composite when compared to those in the Mg-La-H or Mg-Fe-H composites. This is especially promising for the Mg-La-Fe-H composite, which can absorb 5.0 wt% of hydrogen within 8 h at room temperature and desorb hydrogen at 463 K. Such rapid absorption kinetics at low temperatures can be attributed to the synergetic catalytic effects from both LaH2.3 and α-Fe. The above results indicated that simultaneous addition of La and Fe to MgH2 through the reactive ball milling can effectively improve the hydrogen sorption kinetic properties of MgH2.