Kinetic Understanding of Hydrogen-Mediated Ni Growth: From Metal Precursor Reduction to Branched Nanostructure Formation

Small gas molecule such as H 2 has been widely reported to be used as the structure-directing agent that assists synthetic processes of diverse structured metal nanocrystals. Herein, we systematically investigated the H 2 -mediated growth mechanisms of branched Ni (Ni-BN) using a combined experimental and theoretical approach (molecular dynamics). Two types of kinetic models describing Ni precursor reduction and Ni nuclei overgrowth forming branched Ni-BN have been established, which quantitatively illustrate kinetic roles of H 2 played during Ni-BN synthesis. On one hand, the H 2 significantly promoted Ni precursor reduction rate with the value being about two times higher than that without H 2; on the other hand, the dissociatively adsorbed atomic H on Ni nuclei greatly affected the deposition kinetics (deposition rate and deposition equilibrium) of the reduced Ni atoms. Synergistically, the faster Ni precursor reduction rate associated with enhanced Ni atom deposition kinetics resulted in the overgrowth of Ni nuclei along the ⟨111⟩ direction and eventually generating the branched nanostructures. Finally, a MATLAB program was further developed, which can well simulate nanostructure Ni-BN. Present work quantitatively illustrated H 2 -mediated Ni-BN growth mechanism at the atomic level, which contributes to shedding more light on small gas molecule directed metal nanocrystals (MNCs) growth.