Only one H atom is extracted from a single H2O molecule in a usual reaction for hydrogen generation. In this study, a three-step reaction has been identified for completely extracting H-2 from H2O molecule with the catalysis of a small Al6Cu cluster, based on the first principles calculations. All the reactants, products, and transition states are determined by optimization calculation and confirmed by frequency analysis. The intrinsic reaction coordinate is also calculated to validate the reaction process. Results show that the whole reaction is an endothermic reaction. The charge distribution is used to understand the novel reaction. It is found that Al6Cu cluster can strongly capture H2O molecule and extract the H-2 molecule completely, which may present a more efficient way to generate H-2 from a single H2O molecule. (C) 2016 Elsevier Ltd. All rights reserved.