Monodisperse 1.9 nm Ni nanoparticles (NPs) were in-situ synthesized by simple mechanical stirring of solvent-free mixtures of a nickel(II) chloride and dimethylamine borane (DMAB) under inert gas atmosphere at 25.0 +/- 0.1 degrees C. They were found to be highly active catalyst in hydrogen generation from the solvent-free dehydrogenation of DMAB; totally one equivalent of hydrogen gas per DMAB were generated at low catalyst loading at room temperature. 11B-NMR study of the reaction showed that hydrogen evolution likely takes place through the formation of BH2(mu-Me2N)(A-H)BH2 (dimethylamino diborane) and (Me2N)(2)BH (bis(dimethylamino) borane). In this reaction, DMAB was used as both reducing and stabilizing agent. The detailed kinetics of the solvent-free dehydrogenation of DMAB catalyzed by monodisperse Ni NPs were shown to be dependent on catalyst and substrate loading and temperature. (C) Copyright 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.