Passivity of Holmium Studied Theoretically by Potential-pH Diagrams for Selection of Electrolytes and Experimental Proof of the Formation of Ultra-Thin Anodic Films

We present an efficient strategy to identify anodizing electrolytes by coupling conventional Eh–pH diagrams with first-principles density functional theory calculations. Herein, the growth of ultra-thin films having a thickness 10–20 nm is successfully demonstrated on thermally evaporated holmium. Considering only thermodynamic basis, simulated Eh-pH diagrams, and solubility analysis, different compositions pH values are suggested for anodic films. The modified incorporation oxide–forming species in such way appreciably extend stability domain. predicted showed strong agreement experimental observations provide better understanding Ho–H2O based aqueous systems can serve as guide other rare-earth elements anodizing. Grown film properties investigated using electrochemical impedance studies which disclose linear increase inverse capacitance formation voltage indicating uniform irrespective electrolyte selection. Formation factor, k, grown up 10 V varies from 1.16 1.95 V−1 selected electrolytes. k greater than unity may contribute at values.