THE STUDY OF HYDROGEN INTERACTION WITH PALLADIUM AND NICKEL NANOPARTICLES BY THE METHOD OF MOLECULAR DYNAMICS

Hydrogen interaction with Pd and Ni nanoparticles was studied by the method of molecular dynamics. The metal particle in the model was created by cutting a ball from the fcc crystal. The interaction of metal atoms with each other was described with the aid of the multiparticle Cleri-Rosato potential, constructed within the tight binding model. To describe the interactions of hydrogen atoms with metal atoms and with each other, the Morse potential was used, the parameters of which were calculated from the experimental data of absorption energy, activation energy of the above-barrier diffusion of hydrogen in the metal (at normal and high temperatures), binding energy with the vacancy and dilatations. Temperatures from 300 to 1100 K were considered. During the computer experiment the temperature in calculation block was constant. The concentration of hydrogen atoms introduced into the calculation block corresponded to a pressure of 10 and 20 MPa. The initial positions of the hydrogen atoms in the calculation block (in the metal particle or outside it) did not affect the final equilibrium distribution of hydrogen, which was established after some time of the computer experiment, depending on the temperature. As it was shown by the molecular dynamics simulation, nanoparticles are effective hydrogen accumulator having a high velocity of reversible sorption-desorption process of hydrogen. At room temperature, Pd and Ni nanoparticles sorb substantially all hydrogen which is unevenly distributed in the particle volume in an effort to form aggregates containing a few tens of hydrogen atoms. In the case of Ni particles hydrogen predominantly is located near the surface. In the Pd particles, by contrast, hydrogen strongly connected with the Pd lattice, and at increasing temperature it form larger aggregates. Intensive evaporation of hydrogen from the Pd and Ni particles occurs at temperatures above 700 K. At the same time, according to the obtained data, hydrogen is more strongly associated with the particles of Pd than with Ni particles, and the work that needs to be spent for hydrogen evacuation (desorption) in the case of Pd particles is higher than for Ni particles. 

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