Molecular dynamics simulation on reaction and kinetics isotope effect of nano-aluminum and water

摘要

Molecular dynamics simulation on the reaction of nano-aluminum particle and water were performed by ReaxFF force field. The different reaction rates of aluminum with H2O and D2O indicate that the effect of kinetic isotope effect (KIE) is obvious. The generation rate of H-2 is 20% higher than that of D-2. The mechanism of formation and consumption of AlH3 as well as the generation of Al2O3 are elucidated. Specifically, the most frequent reaction pathways throughout the full period are clarified based on the changes of numbers of intermediate and final products. The reactions in the early period are endothermic and release isolated H atoms, which involves Al + 3H(2)O - Al(OH)(3) + 3H and 3Al + 2H(2)O - 2AlO + AlH3 + H. Afterwards, the reactions release a large amount of energy and generate H-2 molecules in the later period, in accordance with the equations of 2AlO + H2O - Al2O3 + H-2, Al(OH)(3) + AlH3 - Al2O3 + 3H(2) and 2AlH(3) + 3H(2)O - Al2O3 + 6H(2). The initial pathways are in agreement with early DFT investigations. The diffusion coefficients of the different atoms show that the replacement of H2O by D2O reduces the diffusion rate of all the atoms (5%) in the system. The KIE is confirmed, and the results agree with experiments. In addition, the simulations were performed under different maximum temperatures. Results show that the solid residues become more disperse in space as the temperature increase. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.