Improvement of the hydrogen storage characteristics of MgH2 with a flake Ni nano-catalyst composite.

Abstract

Magnesium hydride (MgH2) is considered to be one of the most promising hydrogen storage materials owing to its safety profile, low cost and high hydrogen storage capacity. However, its slow kinetic performance and thermal stability limit the possibility of practical applications. Herein, it is confirmed that the hydrogen storage performance of MgH2 can be effectively improved via doping with a flake Ni nano-catalyst. According to experimental results, a MgH2 + 5 wt% Ni composite begins to dehydrogenate at almost 180 °C and could dehydrogenate 6.7 wt% within 3 min at 300 °C. After complete dehydrogenation, hydrogen can be absorbed below 50 °C, and 4.6 wt% H2 can be absorbed at 125 °C within 20 min at a hydrogen pressure of 3 MPa. In addition, the activation energies of MgH2 hydrogen absorption and dehydrogenation decreased by 28.03 and 71 kJ mol-1, respectively. Cycling stability testing showed that the hydrogen storage capacity decreases significantly in the first few cycles and decreases slightly after 10 cycles. Furthermore, it was found that Mg2Ni/Mg2NiH4 was formed initially during the hydrogen absorption or desorption reaction on the surface of Mg/MgH2, which acted as a "hydrogen pump", accelerating the rates of hydrogen absorption and desorption.