First Principles Calculations of Atomic Nickel Redox Potentials and Dimerization Free Energies: A Study of Metal Nanoparticle Growth

The redox potentials and dimerization free energies of transient transition metal cations in water shed light on the reactivity of species with unusual charge states and are particularly pertinent to understanding the mechanism and feasibility of radiolysis-assisted metal nanoparticle growth from salt solutions. A combination of quasi-chemical theory and ab initio molecular dynamics thermodynamic integration methods are applied to calculate these properties for nickel. The reduction potential for Ni2+ (aq) is predicted to be between -1.05 to -1.28 V, which is substantially lower than previous estimates. This suggests that Ni2+ reduction may possibly occur in the presence of organic radical anion electron scavengers and hydrogen atoms, not just hydrated electrons. In contrast, Ni+ is found to be stable against disproportionation. The formation of dimers Ni-2 and Ni-2(+) from Ni and Ni+ are predicted to be favorable in water.