298 K下离子液体BMIMPF6 中电沉积制备镧金属薄膜

Preparation of La Thin Film in BMIMPF6 Ionic Liquid at 298 K by Electrodeposition

摘要:

以无水硝酸镧、1-丁基-3-甲基咪唑六氟磷酸（BMIMPF₆）和助溶剂丙酮为电解液，在室温（298 K）下电沉积制得镧金属薄膜。电解液BMIMPF₆的电化学窗口为-2.5~1.5 V vs. Pt，La³⁺还原为La²⁺发生于-1.7 V vs. Pt，La²⁺还原为La⁰发生于-2.1 V vs. Pt。BMIMPF₆的低吸湿性有利于在空气气氛下电沉积镧。使用扫描电子显微镜和光学显微镜观察到所制备的薄膜织构致密，经能量色散谱和X射线光电子能谱对沉积薄膜进行了表征，确定了薄膜中含有大量镧元素。通过探究电压扫描速率和硝酸镧浓度对La³⁺的电化学行为的影响，证明La³⁺的还原反应是一个受物质扩散控制的不可逆过程，La³⁺在BMIMPF₆中的扩散系数为1.47×10^-9 cm²·s^-1。本研究为获得金属镧薄膜和镧氧化物薄膜提供了一种简便的方法，并且有望用于电沉积制备其它镧系元素薄膜。

Abstract:

Lanthanum (La) thin film was electrodeposited at room temperature (298 K) using lanthanum nitrate, ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF₆) and cosolvent acetone as the electrolyte. Results show that the reduction from La³⁺ to La⁰ involves the transformation of La³⁺→La²⁺ occurring at around -1.7 V vs. Pt and La²⁺→La⁰ occurring at around -2.1 V vs. Pt. The electrolyte BMIMPF₆ exhibits an electrochemical window from -2.5 V vs. Pt to 1.5 V vs. Pt. The low hygroscopic property of BMIMPF₆ allows La electrodeposition under air atmosphere. The precipitate films were observed by scanning electron microscopy and metallographic microscope, showing a dense texture. Then the films were characterized by energy dispersive spectrometry and X-ray photoelectron spectroscopy, confirming therein a large amount of La. The electrochemical tests of changing voltage scan rate and the concentration of lanthanum nitrate reveal that the reduction of La³⁺ is an irreversible process. The diffusion coefficient of La³⁺ in BMIMPF₆ is calculated as 1.47×10^-9 cm²·s^-1. This research provides a simple approach to obtain La thin film, which can be used for the electrodeposition of other lanthanides thin film.