Hydrogen diffusion behavior and vacancy interaction behavior in OsO2 and RuO2 by ab initio calculations

Abstract

The behavior of atomic hydrogen in osmium dioxide and ruthenium dioxide is investigated through ab initio calculations using density functional theory. Interstitial hydrogen behaves as a donor in both metal oxides and only has one stable interstitial position, bonding with an O atom to form an OHO defect. The rates of diffusion parallel to the c-axis are estimated to be 3.95 × 10−7exp(−0.793/kBT) m2/s and 3.64 × 10−7exp(−0.659/kBT) m2/s in OsO2 and RuO2, respectively. The rates of diffusion perpendicular to the c-axis are estimated to be 1.80 × 10−6exp(−0.941/kBT) m2/s and 1.10 × 10−6exp(−1.21/kBT) m2/s in OsO2 and RuO2, respectively. Additionally, the binding energy of multiple H atoms in (O, Os, Ru) vacancies have been calculated. High binding energies of hydrogen in metal vacancies result in multiple H atoms associating with a single metal vacancy. In RuO2, the binding energy of multiple H atoms outweighs the formation energy of a single Ru vacancy as well as that of a Ru–O divacancy.