Effects of Zn(BH<sub>4</sub>)<sub>2</sub>, Ni, and/or Ti Doping on the Hydrogen-Storage Features of MgH<sub>2</sub>

Abstract

In the present work, MgH2 was doped with Zn(BH4)2, Ni, and/or Ti to improve its hydrogen absorption and release features. Samples were prepared by grinding in a planetary ball mill in a hydrogen atmosphere. To increase the hydrogen absorption and release rates without significantly sacrificing hydrogenstorage capacity the additive percentages were less than 10 wt%. The activation of these samples was not necessary. M2.5Z2.5N had the largest quantity of hydrogen absorbed in 60 min, Qa (60 min), at the number of cycles, NC, of one (NC=1), followed in descending order by M5Z2.5N2.5T and M1Z. M5Z2.5N2.5T had the highest initial release rate, followed in descending order by M2.5Z2.5N and M1Z. M5Z2.5N2.5T had the highest initial release rate and M1Z had the largest quantity of hydrogen released in 60 min, Qd (60 min) at NC=2. The sample without Ni (M1Z) had the lowest initial release rate at NC=2. Among these samples, M2.5Z2.5N had the best hydrogen absorption and release properties. Grinding MgH2 with Zn(BH4)2, Ni, and/ or Ti in hydrogen is believed to create defects, induce lattice strain, generate cracks, and reduce the particle sizes. The formed hydrides β-MgH2, γ-MgH2, and TiH1.924 are believed to help produce finer particles in the sample by being pulverized during grinding in hydrogen. The formed Zn and TiH1.924 and the NaCl remained unreacted during cycling. It was deemed that the formed Mg2Ni phase contributed to the increases in the initial hydrogen absorption and release rates and the improvement in cycling performance by absorbing and releasing hydrogen itself.