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.
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.