Enhancing combustion performance, hydrogen evolution stability and sintering resistance of AlH3-nanoparticles via Ni coating

Surface coating is an effective approach for addressing the poor stability of AlH3. In this study, the influence of chemical bonding, atomic diffusion dynamics, as well as the thermodynamic and structural properties of AHNPs coated by Al2O3, Ni, along with uncoated counterparts during the ignition and combustion processes are investigated using ReaxFF-MD method. In the ignition period, Ni-coated AHNP displays a markedly diminished proportion of O atoms that penetrate oxide shell and bond with core-AlH3 compared to Al2O3-coated, which leads to the combustion temperature of Ni-coated AHNP exceeding that of Al2O3-coated. The combustion stages of three types of AHNPs can be divided into surface combustion, slow combustion, and self-sustained combustion. The bonding interaction between Al atoms within core region (cAl) and O atoms within the environment (eO) plays a crucial role in surface combustion, therefore, the uncoated AHNP combusts immediately after ignition. Ni coating exerts a weaker inhibitory effect on the inward diffusion of eO atoms in comparison to Al2O3 shell during the combustion phase. Therefore, Ni-coated AHNP exhibits a reduced ignition delay time and accelerated rapid temperature rise rate compared to Al2O3-coated AHNP. Furthermore, under identical heating rates and combustion temperatures, Al2O3-coated AHNPs undergo sintering, whereas Ni-coated AHNPs remain separated.