Hollow Ni–SiO2 nanosphere-catalyzed hydrolytic dehydrogenation of ammonia borane for chemical hydrogen storage

Nickel clusters contained within silica nanospheres (20–30 nm) were synthesized by using a Ni(NH3)6Cl2 crystal template method in a polyoxyethylene–nonylphenyl ether/cyclohexane reversed micelle system followed by an in situ reduction in aqueous NaBH4/NH3BH3 solutions. Metallic nickel clusters exist inside the SiO2 nanospheres prepared by the method while oxidized nickel clusters prepared by the conventional impregnation method were supported on the outer surface of silica as shown in the results of transmission electron microscope (TEM)/energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) measurements. The nickel clusters inside of silica nanospheres show higher catalytic activity for hydrolysis of ammonia borane to generate stoichiometric amount of hydrogen than the supported nickel catalysts.