The effect of oxygen-containing species on corrosion behavior of Ta (1 1 0) surface: A DFT study with an experimental verification

• Oxygen is the main species responsible for tantalum passivation. • Adsorption of H 2 O molecules reduces the work function of Ta. • H 2 O molecule adsorption promotes corrosion of tantalum. Adsorption of oxygen-containing species on the surface of tantalum (Ta) electrode significantly affects its electrochemical corrosion behavior. Density-functional theory (DFT) is employed to investigate the adsorption energies, structural properties and electronic structures of atomic oxygen (O) and molecular water (H 2 O) on Ta (1 1 0) surface. The adsorption behavior of H 2 O at room temperature is also studied based on ab initio molecular dynamics (AIMD). We find the passivation of Ta metal is mainly attributed to the strong adsorption of oxygen atoms. Thermodynamic results show that bulk Ta 2 O 5 is easily formed at room temperature, which is the fundamental reason for the spontaneous passivation of Ta (1 1 0) surface. The formation of an oxygen monolayer (1.00 ML) on Ta (1 1 0) surface dramatically increases the work function, making the equilibrium potential of Ta electrode move in the positive direction, thus slowing down the corrosion rate of Ta metal. However, the adsorption of H 2 O causes a negative work function change, which promotes its anodic dissolution. The electrochemical impedance spectra (EIS) of tantalum foil in three different NH 4 F-methanol electrolytes (pure, 0.01 M water and oxygen saturated) shows that the charge transfer resistance increases in the sequence R H2O < R pure < R oxygen , which can be well explained by the results of DFT calculations.