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

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 (H₂O) on Ta (1 1 0) surface. The adsorption behavior of H₂O 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 Ta₂O₅ 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 H₂O causes a negative work function change, which promotes its anodic dissolution. The electrochemical impedance spectra (EIS) of tantalum foil in three different NH₄F-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.