Amorphous nickel catalysts derived from nickel halides (NiF2, NiCl2, NiBr2, NiI2) were in situ synthesized in an aqueous solution of NaBH4/NH3BH3. The halide anions have effects on the formation of Ni(0) catalysts, which can further affect the catalytic activities and activation energies of the catalysts for the hydrolysis of ammonia borane. The PVP stabilized catalysts have higher hydrogen evolution rates and durabilities than bare Ni catalysts for the hydrolysis of ammonia borane. The catalysts derived from NiBr2 stabilized by PVP present the highest catalytic activity and the lowest activation energy, which has been measured to be 25.58 kJ/mol. This value is lower than most of reported Ni-based catalysts and even noble-metal containing catalysts. The results of mercury poisoning experiment reveal that Ni(0) catalysts derived from NiBr2 are heterogeneous catalysts in the hydrolysis of ammonia borane.