Nano-inducement of Ni for low-temperature dominant dehydrogenation of Mg–Al alloy prepared by HCS+MM

Abstract

Magnesium hydride is one of the most ideal solid hydrogen storage materials (HSMs). However, its sluggish absorption/desorption kinetics and undesirable thermodynamics create a burden for industrial-scale applications. In this paper, the effects of micro-Ni and nano-Ni on the dehydrogenation properties of Mg–Al alloys were compared and studied. All the samples were prepared by hydriding combustion synthesis (HCS) and mechanical milling (MM). Temperature programmed desorption (TPD) and differential scanning calorimeter (DSC) analyses showed that the catalytic effect of nano-Ni was vastly superior to that of micro-Ni and the catalytic effect of Ni was more excellent than Al3Ni2 on the dehydrogenation of Mg–Al alloy. Mg90Al10-5nanoNi-MM exhibited the best dehydrogenation property, in which, two dehydrogenation peaks at 260 °C and 343 °C in the DSC curve (10 °C/min) were observed and the main dehydrogenation occurred at the lower temperature. The apparent activation energy for dehydrogenation of MgH2 was reduced from 144.8 kJ/mol to 88.8 and 65.5 kJ/mol for the two dehydrogenation peaks. Ex-situ X-ray differential (XRD) and high resolution transmission electron microscope (HRTEM) were conducted to understand the microstructure evolution during dehydrogenation. Nano-inducement of nano-Ni dramatically promotes the regulation of Al on MgH2 thus improving the dehydrogenation performance.