Porously hierarchical Cu@Ni cubic-cage microstructure: Very active and durable catalyst for hydrolytically liberating H2 gas from ammonia borane

By adjusting various Cu/Ni molar ratios, a series of Cu0Ni1.0, Cu0.2Ni0.8, Cu0.4Ni0.6, Cu0.6Ni0.4, Cu0.8Ni0.2 and Cu1.0Ni0 bi-metal catalysts have been fabricated by one-step solvothermal reduction route. The morphology, phase makeup and chemical states of the catalyst were systematically analyzed by scanning and transmission electron microscopy, x-ray powder diffraction, x-ray photoelectron spectroscopy, and inductively coupled plasma mass spectrometry, respectively. The catalytic activity was evaluated via hydrolytically releasing H2 from ammonia borane. The as-synthesized products have porously hierarchical cubic-cage microstructure with microsized Cu cubes claded by Ni nanospheres. The charge transfer from Cu to Ni gives rise to synergistic effect between Cu and Ni component, thus endowing the bimetal catalysts with better catalytic performance. The catalytic activity for the bimetal catalysts follows Cu0.8Ni0.2 > Cu0.6Ni0.4 > Cu0.2Ni0.8 > Cu0.4Ni0.6, each of which is higher than that of the single metal Ni or Cu. The catalyst Cu0.8Ni0.2 can fully release H2 in 8 min with the apparent activation energy of 40.53 kJ/mol, which can still retain 78% initial catalytic activity after reusing 5 times. Theoretically, the unique microstructure building strategy could be also extended to other metal systems for fabricating highly active multi-metal nano/micro catalysts.