Rapid, ambient temperature hydrogen generation from the solid state Li–B–Fe–H system by mechano-chemical activation synthesis

Abstract

A novel processing method promoting a rapid hydrogen generation from the solid state Li–B–Fe–H system is presented. The Li–B–Fe–H system is quite remarkable since the mechanical dehydrogenation rate at the ambient temperature is much higher than the thermal dehydrogenation rate at the 100–250 °C range. The quantity of 4.02 wt.% H2 is desorbed after barely 0.5 h of ball milling with a very low energy input of 36.4 kJ/g while at 250 °C, after the same desorption time, only 3.2 wt.% H2 is desorbed. Thus this system is a rapid, solid state H2 generator at the ambient temperature. X-ray diffraction after ball milling shows the presence of the crystalline LiCl diffraction peaks. The Fourier transform infrared spectroscopy (FT-IR) measurements show a spectrum characteristic of the disordered Fe(BH4)2 hydride. Samples milled under varying energy inputs are attracted to a permanent magnet. It is shown that the thermal dehydrogenation behavior of the pre-milled samples is initially fast but then quickly slows down. The pre-milled samples after thermal dehydrogenation are also attracted to a permanent magnet. Diffraction peaks of α-Fe are clearly observed after thermal desorption of powders at 100 and 250 °C. For the sample dehydrogenated at 250 °C the crystallite size of the α-Fe phase, estimated from its diffraction peak breadths, is within a nanometric range of 27–47 nm.