Cobalt chloride

The starting chemicals of cobalt chloride (CoCl₂·6H₂O, purity 99.99%), nickel chloride (NiCl₂·6H₂O, purity 99.3%), and hexamethylenetetramine (C₆H₁₂N₄, purity 99%) were purchased from Alfa Aesar and used without further purification. First, CoCl₂·6H₂O, NiCl₂·6H₂O, and hexamethylenetetramine were dissolved in 1,000 ml of deionized water at different weight ratios and then refluxed for 6 h under nitrogen protection with continuous magnetic stirring. The light-pink precipitate was recovered by filtration and washed with deionized water and anhydrous ethanol in turn. Finally, it was air-dried at room temperature. By changing the starting mixing ratio of CoCl₂·6H₂O and NiCl₂·6H₂O, different kinds of Co/Ni(OH)_x precursors can be obtained according to the above process.
The precursor and graphene were first mixed manually at an optimized weight ratio of 7:3, and then the mixed powders were ball-milled on a planetary ball mill at 300 rpm with a ball-to-sample weight ratio of 60:1 for 6 h under an argon atmosphere. The catalyst powders were then thermally annealed at ~800°C for 5 h. Subsequently, the catalyst obtained was used to dope MgH₂ by mixing them at a weight ratio of 95:5 for 2 h under a 0.5 MPa hydrogen atmosphere by using a planetary mill at 400 rpm with a 20:1 ball-to-powder ratio and are denoted as Ni/Co@G-doped MgH₂ composites.

Cobalt chloride (CoCl₂·6H₂O) and nickel chloride (NiCl₂·6H₂O) were purchased from Alfa Aesar. Polyacrylonitrile (PAN, Mw = 150,000) and Thiourea were purchased from Sigma-Aldrich.