Highly active Ni- and Co-based bimetallic catalysts for hydrogen production from ammonia-borane

Abstract

Ammonia-borane is one of the most promising candidates for hydrogen carriers. A series of Ni- and Co-based bimetallic catalysts supported on SiO 2 (Ni-M/SiO 2 and Co-M/SiO 2 ; M = Ga, Ge, Sn, Zn) was prepared and tested as catalysts for hydrogen production from ammonia-borane (AB) in water or methanol. Ni-Zn/SiO 2 and Co-Ge/SiO 2 exhibited catalytic activities much higher than those of monometallic Ni/SiO 2 and Co/SiO 2 , respectively. Ni-Zn/SiO 2 showed a high catalytic activity when water was used as a solvent, where the reaction was completed within 6 min at room temperature with a specific reaction rate of 4.3 ml min -1 mmol-cat -1 mM-AB -1 . To the best of our knowledge, this is the highest value among those reported using 3d metal-based catalysts. Co-Ge/SiO 2 afforded a five-fold higher reaction rate than that of the corresponding monometallic Co/SiO 2 . XRD, TEM, and HAADF-STEM-EDS analyses revealed that Ni 0.75 Zn 0.25 and Co 0.8 Ge 0.2 solid-solution alloys were formed with high phase purities. An XPS study showed that Co atoms in Co 0.8 Ge 0.2 were electron-enriched due to electron transfer from Ge to Co, which may be the origin of the improved catalytic activity.