Hydrogen Absorption-Desorption Properties of Mg-(TiFe_0.8Mn_0.2)-Graphite Composites

Abstract

This study deals with the assessment of the hydrogen absorption-desorption properties of Mg-based composites containing TiFe_0.8Mn_0.2, Fe, and graphite (Mg-10Gr, Mg-10TFM-10Fe, Mg-10TFM-10Gr, Mg-10Fe-10Gr, and Mg-5TFM-5Fe-10Gr) that were gotten with ball milling under Ar atmosphere. The TiFe_0.8Mn_0.2 and Fe were used as catalysts for improving hydrogen absorption-desorption properties of Mg and the graphite to prevent them from oxidizing. We conducted hydrogenation, X-ray diffraction (XRD) analyses, differential scanning calorimetries (DSC), and Pressure-Composition-Temperature (PCT) measurements for the samples. MgH₂ was observed in Mg-10TFM-10Gr, Mg-10Fe-10Gr, and Mg-5TFM-5Fe-10Gr with XRD analyses after hydrogenation at 200℃ under hydrogen pressure of 2.5–2.6 MPa. It might be that the added graphite prevented from oxidizing from the samples and consequently enhanced the catalytic effects of TiFe_0.8Mn_0.2 and Fe. These samples desorbed hydrogen around 275–350℃ in DSC processes. Mg-10TFM-10Gr, Mg-10Fe-10Gr, and Mg-5TFM-5Fe-10Gr stored hydrogen up to 2.5 wt.%, 3.5 wt.%, and 4.0 wt.%, respectively at 200℃ under hydrogen pressure of 2.6 MPa on PCT measurements without any activation process, and Mg-5TFM-5Fe-10Gr stored hydrogen up to 4.1 wt.% at 200℃ and 4.8wt.% at 280℃ under hydrogen pressure of 2.6 MPa after activation.