Improved hydrogen storage properties of Ti-doped Mg 95 Ni 5 powder produced by hydriding combustion synthesis
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Ti was added to Mg–Ni alloy (Mg95Ni5) by a novel hydriding combustion synthesis (HCS) process. The effect of Ti on hydrogen absorption/desorption kinetics of Mg95Ni5 was investigated. The results showed that Ti had superior catalytic effects on hydrogen storage properties of Mg95Ni5, which required only 80 s to reach its saturated hydrogen absorption capacity of 6.29 wt% at 473 K and released 5.49 wt% hydrogen within 900 s at 553 K. Based on an Arrhenius analysis, the activation energy of the hydrogen desorption process was 80.8 kJ mol1 for the main phase of MgH2 in the Ti-doped Mg95Ni5. The excellent hydriding/dehydriding properties were related to the existence of TiH1.924, which improved the efficiency of mechanical milling and was helpful in the refinement of the crystallite size of MgH2, resulting in more fresh surface area and grain boundary area. Besides, it was thought to restrain the Mg particles from growth during the hydrogenation/dehydrogenation cycles.
I. INTRODUCTION
A safe, economical, and efficient hydrogen storage material is urgently needed for the future hydrogen economy.1 Metal hydrides are considered as having the greatest potential for hydrogen storage due to their superior properties in storage capacity and safety. Among metal hydrides, MgH2 has been the subject of intense study due to its low cost, low environmental impact, abundant resources, and high capacity for hydrogen storage (;7.6 wt%).2 However, proper strategies are required to overcome the unfavorable thermodynamic and kinetic barriers for the formation of MgH2. The hydrogen desorption peak temperature of MgH2 is above 350 °C. A commonly successful method is to use various elements3–5 or compounds6–8 as the catalysts to enhance the hydrogen storage performance of MgH2. Zhou et al.9 added TiMn2 to MgH2, demonstrating a hydrogen absorption capacity of more than 4.5 wt% at 373 K within 240 min under 0.1 MPa hydrogen pressure. After mechanical milling with TiF3, MgH2 could absorb 3.8 wt% hydrogen at 423 K within 30 s under 2.0 MPa hydrogen pressure and release about 3.0 wt% hydrogen at 553 K within 25 min under 0.01 MPa hydrogen pressure.10 Composites of 90 wt% MgH2–10 wt% MeSi2 (Me 5 Ti, Cr) were synthesized by Grigorova et al.,11 which showed fast kinetics and hydrogen sorption capacity higher than 6 wt% within 60 min above Contributing Editor: Gary L. Messing a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.62 J. Mater. Res., Vol. 30, No. 7, Apr 14, 2015
573 K. Zhang et al.12 studied the synergistic effects of Ti and F co-doping on dehydrogenation properties of MgH2. In recent years, Ti has been usually used to improve the hydrogen storage properties of MgH2. In our previous work, hydriding combustion synthesis (HCS) was used to synthesize Mg-based hydrogen storage materials.13 The HCS has the advantages of low energy consumption, high activity of the product, and short processing time, which is regarded as an innovative process for the preparation of Mg-based materials. We have prepared
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