Development of a ReaxFF reactive force-field modeling for magnesium nanoparticles and water system

The Mg/O/H ReaxFF force field was developed based on the JAX-ReaxFF framework of the gradient descent algorithm to elucidate the intricate interactions and hydrogen production mechanisms of Mg nanoparticles and H2O. The ReaxFF parameters were optimized based on a quantum mechanical training set, which included the interactions between Mg/O/H, as well as the equation of state of MgH2 and Mg(OH)2 crystals. Molecular dynamics simulations were conducted to simulate the structural evolution of Mg nanoparticles in an H2O atmosphere at high temperatures. Results show that H2O dissociates on the surface of Mg nanoparticles to form Mg-H, Mg-OH, and Mg-O bonds. Structural evolutions of Mg nanoparticles depend on the temperature and the density of H2O. The inward diffusion rate of H atoms surpasses that of O atoms, resulting in the formation of a Mg hydride core and a Mg oxide shell. Chemical bond analysis demonstrates a correlation between H2 production and H2O consumption, with H2 production trailing H2O consumption. The inward diffusion of O atoms and the outward diffusion of Mg atoms lead to the release of H2 from the magnesium hydride. The ReaxFF protocol stands as a valuable tool for studying the hydrogen production in magnesium-water systems at the atomic level.