Mechanistic Insight into H2-Mediated Ni Surface Diffusion and Deposition to form the Branched Ni Nanocrystals: A Theoretical Study

Present work systematically investigates the kinetic role of H2 molecule played during Ni surface diffusion and deposition to generate the branched Ni nanostructures by employing density function theory (DFT) calculations and ab initio molecule dynamic (AIMD) simulations. The Ni surface diffusion results unravel that in comparison to the scenarios of Ni(110) and Ni(100), both the subsurface and surface H hinder the Ni surface diffusion over Ni(111) especially under the surface H coverage of 1.5 ML displaying the lowest Ds values, which greatly favors the trapping of the adatom Ni and subsequent overgrowth along direction. The Ni deposition simulations by AIMD further suggest that both the H2 molecule (in solution) and surface dissociatively-adsorbed atomic H can promote Ni depositions. Moreover, a cooperation effect between H2 molecule and surface atomic H can be clearly observed, which synergically favors Ni depositions. Additionally, in addition to working as the solvent, the liquid C2H5OH can also interact with the Ni(111) to produce the surface atomic H, which then favors the Ni deposition. Finally, the Ni deposition rate predicted by deposition constant (Ddep) is found to be much higher than its surface diffusion rate predicted by Ds for Ni(111) and Ni(110), which quantitatively verified overgrowth along and directions to produce the branched Ni nanostructures.