Preparation and dehydrogenation properties of two cobalt-based ammine borohydrides: CoCl3·3NH3/3LiBH4 and CoCl2·3NH3/2LiBH4

• Cobalt-based ammine borohydrides were synthesized via a simple ball milling process.
• 5.2 wt.% pure hydrogen can be evolved within 45 min at 80 °C from CoCl3·3NH3/3LiBH4.
• CoCl2·3NH3/2LiBH4 shows certain advantage over CoCl2/2LiBH4 as hydrogen storage material.

Two new cobalt-based ammine borohydrides were prepared via ball milling of LiBH4 and CoCln·3NH3 (n = 3, 2) with molar ratios of 3:1 and 2:1, respectively. X-ray diffraction (XRD) results revealed the as-prepared composites having amorphous state. Thermogravimetric analysis-mass spectrometry (TG-MS) measurements showed that the two composites mainly release H2, concurrent with the evolution of a small amount of NH3. Further results showed that the excessive addition of LiBH4 can suppress the liberation of NH3, resulting in the release of H2 with a high purity (>99 mol.%). By combination with the temperature-programmed-desorption (TPD) results, the CoCl3·3NH3/4LiBH4 and CoCl2·3NH3/3LiBH4composites can release 7.3 wt.% (4.2 wt.% including LiCl) and 4.2 wt.% (2.0 wt.% including LiCl) pure hydrogen, respectively, in the temperature range of 25–300 °C. Isothermal dehydrogenation results reveal that CoCl3·3NH3/3LiBH4 shows favorable dehydrogenation rate at low temperatures, releasing about 5.2 wt.% (2.9 wt.% including LiCl) of hydrogen within 45 min at 80 °C.