Electric Double Layer in the Electrodeposition of Aluminium from Ionic Liquids

Electric Double Layer in the Electrodeposition of Aluminium from Ionic Liquids

Yong Zheng, Yongjun Zheng, Huichao Lv, Dayong Tian, Yinyin Liu

(College of Chemical and Environmental Engineering, Anyang Institute of Technology, Anyang 455000, Henan, China)

Since the end of 19th century, the production of aluminium has been mainly conducted by the Hall-Heroult electrolytic process. However, this method suffers from many problems, including high operating temperature, high energy consumption and high CO₂ emission. Therefore, it's necessary to develop new methods for the low-temperature and low-energy electrolysis of aluminium. Ionic liquids (ILs) are labeled as room-temperature molten salts, which have a bright prospect in this field[1, 2]. During the electrolysis, electric double layer of electrode interface/IL plays an important role in the formation and morphology of aluminium deposits.

From above background, this work mainly focuses on the composition and structure of electric double layer formed in some typical chloroaluminate ILs, such as [Emim]Cl/AlCl₃ (1-ethyl-3-methylimidazolium chloroaluminate), [Bmim]Cl/AlCl₃ (1-butyl-3-methylimidazolium chloroaluminate) and [Amim]Cl/AlCl₃ (1-allyl-3-methylimidazolium chloroaluminate). Firstly, systematic measurements of cyclic voltammetry, chronoamperometry and impedance spectroscopy were performed to get a deeper insight into the electrochemical behavior of these ILs. On the basis of density functional theory calculations, the effect of ILs' composition, structure and cation-anion interaction on the electric double layer was analyzed. Experimental results show that the polarity and alkyl chain of imidazolium cation, as well as interaction energy between ions is key to aluminium electrodeposition process.

Figure 1 Electrochemical impedance spectroscopy of Pt electrode in Lewis acidic [Emim]Cl/AlCl₃

References:

[1] Giridhar P., Zein El Abedin S., Endres F. Electrochim. Acta, 2012, 70: 210-214.

[2] Armand M., Endres F., MacFarlane D R., et al. Nat. Mater., 2009, 8: 621-629.

Acknowledgements: This work was supported by the National Natural Science Foundation of China (No.21406002), Government Decision-making Subject of Henan Province (No.2014351) and Doctoral Scientific Research Foundation of Anyang Institute of Technology.