Ni nanoparticles supported on carbon as efficient catalysts for the hydrolysis of ammonia borane

We report on the preparation of three kinds of Ni nanoparticles supported on carbon (Ni/C) and their application in the catalytic hydrolysis of ammonia borane (AB). Three Ni/C catalysts were prepared from a Ni metal-organic framework (Ni-MOF) precursor by reduction with KBH₄, calcination at 700 ℃ under Ar, and a combination of calcination and reduction, the products being denoted as Ni/C-1, Ni/C-2, and Ni/C-3, respectively. The structure, morphology, specific surface area, and element valence were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption-desorption measurements, and X-ray photoelectron spectra (XPS). The results demonstrate that Ni/C-1 is composed of amorphous Ni particles agglomerated on carbon, Ni/C-2 is characteristic of crystalline Ni nanoparticles (about 10 nm in size) supported on carbon with Ni oxidized on the surface, while the surface of the Ni particles in Ni/C-3 is less oxidized. The specific surface areas of Ni-MOF, Ni/C-1, Ni/C-2, and Ni/C-3 are 1239, 33, 470, and 451 m²·g^-1, respectively. The catalytic hydrolysis of AB with Ni/C-3 shows a hydrogen generation rate of 834 mL·min^-1·g^-1 at room temperature and an activation energy of 31.6 kJ/mol. Ni/C-3 shows higher catalytic activity than other materials, which can be attributed to its larger surface area of crystalline Ni. This study offers a promising way to replace noble metal by Ni nanoparticles for AB hydrolysis under ambient conditions.