Electrodeposition of Bright Al Coatings from 1-Butyl-3-Methylimidazolium Chloroaluminate Ionic Liquids with Specific Additives

Abstract

The electrodeposition of aluminum (Al) on copper (Cu) substrate was investigated in [Bmim]Cl/AlCl 3 (33.3/66.7 mol%) ionic liquid using three pyridine derivatives, nicotinic acid, methyl nicotinate, and 3-methyl pyridine as additives at 303 K, respectively. It was found that bright Al coatings could be electrodeposited with nicotinic acid and methyl nicotinate as additives. SEM and XRD characterizations revealed that the bright coatings were very smooth, composed of nanocrystalline and with a strong (200) preferential orientation. By contrast, a matte and lusterless Al coating was obtained from the ionic liquid with 3-methyl pyridine. Furthermore, the effect of the three additives was investigated by means of cyclic voltammetry, chronopotentiometry and Raman spectroscopy. It was demonstrated that nicotinic acid and methyl nicotinate could absorb on electrode surface more easily and thus served as very effective brighteners producing highly uniform and smooth Al coatings. However, 3-methyl pyridine had no such effect. Al coatings have attracted wide research interest due to the excellent properties, such as non-toxic, low density and corrosion resistance. Conventionally, Al coatings are prepared by thermal spraying, 1 hot dipping, 2 sputter deposition, 3 vapor deposition 4 and electrodeposition.5 Among them, only the electrodeposition method does not need high temperature and has no damage to substrates. However, Al is an active metal that cannot be electrodeposited from aqueous solutions. Al coatings have been prepared from organic solvents or inorganic molten salts, but the former electrolyte suffers from narrow electrochemical window, low conductivity, strong volatile and easy combustion, while the latter needs high operating temperature, causing large energy consumption, rapid equipment corrosion and high environment pollution. 5,6 In contrast, ionic liquids, as a new medium for electrodeposition, have shown many inherent advantages, such as low vapor pressure, high conductivity and wide electrochemical window. 7 The first ionic liquid used for deposition of Al was the mixture of N-ethylpyridinium bromide and AlCl 3 by Hurley and Wier in 1951.8 Since then, a series of research works have been carried out in this field.9-11 Until now, the chloroaluminate ionic liquids prepared by mixing organic chloride salts with AlCl 3 are more favored. The Lewis acidity of these ionic liquids can be adjusted by varying the molar percentage of AlCl 3 , and Al can only be deposited from the Lewis acidic chloroaluminate ionic liquids in which the molar percentage of AlCl 3 is over 50%. Among the Al-containing species in these ionic liquids, only [Al 2 Cl 7 ]− anion is reducible and responsible for the deposition. The cations of these ionic liquids are mainly alkyl pyridine, alkyl imidazole, and quaternary ammonium.12-16 Among them, the most frequently studied systems are those ionic liquids with alkyl imidazole as cations due to their higher conductivity, lower viscosity, and better stability, in which, 1-ethyl-3-methylimidazo...

Robust Aluminum Electrodeposition from Ionic Liquid Electrolytes Containing Light Aromatic Naphta as Additive

“…The presence of the co‐solvent promotes lower viscosity and higher conductivity in the electrolyte, in comparison with bare melts, facilitating the plating process. Regarding the use of organic additives as brighteners, nicotinic acid and methyl nicotinate (2.0 to 8.0 mmol) have given good results on small flat surfaces (10 mm×10 mm) whereas 1,10‐phenantroline (27.7 mmol) was tested on car wheel bolts.…”

Effect of Sodium Bromide on the Electrodeposition of Sn, Cu, Ag and Ni from a Deep Eutectic Solvent-Based Ionic Liquid

“…Some additives can increase the polarization of the cathode. [57,58,74,75] The adsorption of additives on the electrode surface can change the cathode potential, thus resulting in an increase in current density and the corresponding increase in current efficiency. However, there are some additives that can decrease cathodic polarization, such as pyridine derivatives.…”

Electrodeposition in Ionic Liquids

“…Recently, we found nicotinamide and methyl nicotinate were effective leveling agents and brighteners for Al deposition based on the results of cyclic voltammetry and AFM. Through comparison, it was concluded that pyridine derivatives with electron‐withdrawing groups have stronger adsorption ability, enabling them to tailor Al deposition and producing better Al deposits . Moreover, the function mechanism of these additives was proposed as shown in Figure .…”