J Solid State Electrochem (2014) 18:257–267 DOI 10.1007/s10008-013-2269-y

ORIGINAL PAPER

Effect of nicotinamide on electrodeposition of Al from aluminium chloride (AlCl3)-1-butyl-3-methylimidazolium chloride ([Bmim]Cl) ionic liquids Qinqin Zhang & Qian Wang & Suojiang Zhang & Xingmei Lu

Received: 13 June 2013 / Revised: 15 September 2013 / Accepted: 22 September 2013 / Published online: 5 October 2013 # Springer-Verlag Berlin Heidelberg 2013

Abstract The effect of nicotinamide on the electrodeposition of Al was first investigated in the ionic liquid [Bmim]Cl/AlCl3 (40.0/60.0, mol%) by means of cyclic voltammetry and chronopotentiometry. Cyclic voltammograms indicated that nicotinamide produced an inhibiting effect on Al deposition, which can be attributed to the adsorption of nicotinamide on the electrode surface. Galvanostatic deposition experiments revealed that nicotinamide served as a very effective leveling agent, resulting in highly uniform and smooth Al deposits. The effects of temperature and current density on the surface morphologies and crystal orientations of Al deposits were also studied. As the temperature was increased from 30 to 70 °C, the grain size of Al deposits increased but the intensity of the preferred (200) crystallographic plane weakened. By contrast, the opposite applied just with increasing current density from 3.4 to 9.4 mA cm−2. Keywords Ionic liquid . Aluminium . Electrodeposition . Nicotinamide . Additive

Introduction Al is widely used as a surface coating for various materials due to its admirable properties of non-toxic, low density, Q. Zhang : Q. Wang : S. Zhang (*) : X. Lu Beijing Key Laboratory of Ionic Liquids Clean Process, State Key Laboratory of Multiphase Complex Systems, Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China e-mail: [email protected] Q. Zhang College of Chemistry and Chemical Engineering, University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China

attractive luster, and excellent corrosion resistance. Several methods such as electrodeposition [1], vapor deposition [2], hot dipping [3], and thermal spraying [4] have been developed to prepare such coating. Compared with the other methods, electrodeposition is a preferred method because of its incomparable advantages such as mild operating conditions, better control of the thickness of the coatings, and slight damage to substrates. However, Al coatings cannot be electrodeposited in aqueous solutions due to the large negative standard potential of Al(III)/Al couple (−1.67 V vs. NHE). Hence, a number of non-aqueous media [1] including organic solvents, inorganic molten salts, and ionic liquids have been studied for Al electrodeposition. Compared with the other media, ionic liquids exhibit many unique features such as negligible vapor pressure and wide electrochemical potential window and thus are considered as promising media for Al deposition [5, 6]. Electrodeposition of Al in ionic liquids has received considerable attention since Hurley and Wier [7] first reported that Al could be obtained from the mixture of ethylpyridinium bromide and AlCl3. Several kinds of ionic liquids have been tried so far for Al deposition. They are mixtures of anhydrous aluminium halides with N -alkylpyridinium halides [8], N,N′dialkylimidazolium halides [9–15], trialkyl-arylammonium halides [16], and N -alkylpyrrolidinium halides [17–21], respectively. Among them, ionic liquids formed by mixing AlCl3 with N,N′-dialkylimidazolium chloride such as AlCl31-ethyl-3-methylimidazolium chloride ([Emim]Cl) and AlCl3-1-butyl-3-methylimidazolium chloride ([Bmim]Cl) have been considered as the most promising electrolytes, due to their liquid state over a wider composition range, relatively higher electrical conductivities and lower viscosity. However, Al deposits obtained from them are non-uniform and insufficient in smoothness. In particular, when increasing the thickness and/or the current density, a rough and dendritic forms, which is easily peeled off. A suitable solution to this problem is the introduction of additives into these systems.

258

Additives are essential to most aqueous electroplating systems as leveling agents and brighteners. However, there are a few reports describing the effects of additives on the electrodeposition of Al from ionic liquids. Endres et al. [22] obtained uniform and nanocrystalline Al deposit from the ionic liquid [Emim]Cl/AlCl3 (45/55 mol%) with the addition of nicotinic acid. Abbott et al. [23] found that LiCl had an opposite effect on the electrodeposition of Al, resulting in a dark grey Al deposit with large crystallites. Caporali et al. [24] showed that bright Al layers could be electrodeposited from the ionic liquid [Bmim]Cl/AlCl3 (33.3/66.7 mol%) with 1, 10phenanthroline as a brightener. Recently, Liu et al. [25] obtained uniform and compact Al deposits using LaCl3 as an additive. It is clear that additives significantly affect the electrodeposition of Al in ionic liquids and the quality of Al deposits can be improved by the addition of proper additives. In this work, nicotinamide was first used as an additive to improve the quality of the Al deposits obtained from the ionic liquid [Bmim]Cl/AlCl3 (40.0/60.0 mol%). Its effect on the surface morphology, crystal orientation and deposition mechanism of Al was systematically investigated. In addition, the effects of temperature and current density on the electrodeposition of Al in the presence of nicotinamide were also studied.

J Solid State Electrochem (2014) 18:257–267

mirror finish, and then cleaned in an ultrasonic bath. After the pretreatment, a part of each substrate was covered with kapton tape so that a square area (10 mm×10 mm) was exposed. The anode was an Al plate (40 mm×15 mm, 99.99 %, General Research Institute for Nonferrous Metals), which was polished and rinsed with deionized water and acetone before use. The distance between the substrate and the anode was about 20 mm. The reference electrode was an Al wire (Alfa, 99.99 %) immersed in the ionic liquid [Bmim]Cl/AlCl3 (40.0/ 60.0 mol%) and was isolated from the bulk electrolyte with a porosity glass frit. Electrodeposition experiments were carried out under controlled-current condition and the same charge density of 20 C cm−2 was used for all deposits. After electrodeposition, the deposits were immediately removed from the glove box, rinsed in succession with acetone, ethanol, and deionized water and then dried with N2. All the deposits were characterized with scanning electron microscopy (SEM, XL30 S-FEG), energy dispersive X-ray spectrometry (EDS), and X-ray diffraction (XRD, PANalytical ) techniques using Cu Kα radiation (λ =0.15405 nm).

Results and discussion Cyclic voltammetry

Experimental The electrolyte preparation and subsequent electrochemical experiments were both carried out in an argon-filled glove box (MIKROUNA Co., China). BmimCl (Henan Lihua Pharmaceutical Co., AR) was dried under vacuum condition at 55 °C for 48 h to remove residual moisture before use. Anhydrate AlCl3 (Sinopharm Chemical Reagent Co., AR) was used as received. The ionic liquid [Bmim]Cl/AlCl3 (40.0/60.0 mol%) was prepared as described in a previous article [15]. The prepared ionic liquid was purified by electrolysis. Then, precise quantities of nicotinamide (Sinopharm Chemical Reagent Co., BR) were added to the ionic liquid with continuous stirring until a transparent liquid was obtained. All the electrochemical experiments were carried out using an electrochemical workstation (CHI660D) in a threeelectrode cell. For cyclic voltammetry, Teflon-sheathed Cu disk and Pt disk electrodes (99.9 %, Beijing Chemical Reagents Company, 2 mm diameter) were used as working electrodes. Prior to each experiment, these electrodes were polished with aqueous slurry of 0.3 and 0.05 μm alumina, cleaned in an ultrasonic bath for 5 min, and then dried with N2. A Pt plate (99.99 %, General Research Institute for Nonferrous Metals) was employed as the counter electrode, which was directly immersed in the bulk ionic liquids. For electrodeposition, Cu foils (40 mm×10 mm) were used as substrates. Prior to electrodeposition, the substrates were polished to a

Figure 1 shows the cyclic voltammograms recorded on a Cu electrode in the ionic liquid [Bmim]Cl/AlCl3 (40.0/60.0, mol%) with various concentrations of nicotinamide at 30 °C. The electrode potential was scanned from the open circuit potential at a scan rate of 50 mV s−1. As shown in Fig. 1, the bulk deposition of Al starts at ca. 0.000 V in the neat ionic liquid. A close examination of Fig. 1 reveals that there is an additional small peak at 0.174 V. Figure 2 shows a systematic

Fig. 1 Cyclic voltammograms recorded on a Cu electrode in [Bmim]Cl/ AlCl 3 (40.0/60.0, mol%) containing a 0.0, b 2.0, c 4.0, and d 8.0 mmol dm−3 nicotinamide at 30 °C. Scan rate: 50 mV s−1

J Solid State Electrochem (2014) 18:257–267

Fig. 2 A series of cyclic voltammograms revealing UPD of Al on Cu electrodes in [Bmim]Cl/AlCl3 (40.0/60.0, mol%) ionic liquid at 30 °C. Scan rates: (a ) 50 mV s−1, (b ) 100 mV s−1, (c ) 200 mV s−1, (d ) 300 mV s−1, (e) 400 mV s−1. The inset graph shows the peak current (i pc) of UPD as a function of the scan rate (ν)

study of this peak at various scan rates. It can be seen that the voltammogram is quite reproducible and the peak current density is proportional to the scan rate (the inset graph of Fig. 2). Based on these results, the peak is attributed to the underpotential deposition (UPD) of Al on Cu. Kolb– Gerischer's UPD correlation [12] predicts a UPD shift (△E p) corresponding to half of the difference between the work functions Φ of the substrate (sub) and adsorbate (ads) in their bulk forms, i.e., △E p =1/2(Φ sub−Φ ads). According to the work functions reported in the literature (Φ Al =4.28 eV, Φ Cu = 4.65 eV) [26], △E p would be 0.185 V for Al UPD on Cu. As shown in Fig. 2, the reversible underpotential deposition potential is ca. 0.240 V, which is consistent with the value expected from Kolb–Gerischer's rule. Previously, the UPD of Al on Cu(111) in Lewis acidic [Emim]ClAlCl3 ionic liquid was reported [27]. Thus, it is concluded that the UPD of Al on Cu in our system is indeed involved. The charges under each of the UPD deposition peaks are found between 0.54 and 0.69 mC cm−2 as the scan rate is varied from 50 to 400 mV s−1. These charges correspond to approximately one monolayer of Al if it is assumed that Al atom (r = 1.43 Å) is packed closely on the electrode surface. When nicotinamide is added, the shape of the small peak at 0.174 V is almost the same as that in the neat ionic liquid, suggesting an ignorable influence of nicotinamide on the UPD of Al on Cu. As shown in Fig. 1, in the ionic liquid [Bmim]Cl/AlCl3 (40.0/60.0, mol%) containing 2.0 mmol dm−3 nicotinamide, the bulk deposition of Al also starts at ca. 0.000 V. However, the deposition current is smaller than that in the neat ionic liquid and changes slightly with the electrode potential varied from 0.000 to −0.250 V. As the electrode potential

259

is below −0.250 V, the deposition current increases rapidly. For brevity, the potential range, in which the deposition current is small and changes slightly, is defined as the “inhibition region.” As the concentration of nicotinamide is increased, the deposition current decreases gradually, but the width of this region increases slightly. From an EDS analysis, pure Al has been detected on all the deposits obtained at −0.150 V from [Bmim]Cl/AlCl3 (40.0/60.0, mol%) with various concentrations of nicotinamide, indicating that the deposition current in the inhibition region corresponds to the deposition of Al. Cyclic voltammograms recorded at a Pt electrode in the ionic liquid [Bmim]Cl/AlCl3 (40.0/60.0, mol%) with various concentrations of nicotinamide are shown in Fig. 3. The electrode potential was scanned from 1.300 V at a scan rate of 50 mV s−1. As shown in Fig. 3, the voltammetric behavior observed on Pt electrode is different from that observed on Cu electrode. In the neat ionic liquid, the onset of the cathodic current is at ca. −0.096 V, and a typical current loop is observed in the potential range from −0.096 to −0.180 V, which is not observed on Cu electrode. This current loop indicates that overpotential is required to initiate the nucleation and subsequent growth of Al on Pt electrode. With the addition of 2.0 mmol dm−3 nicotinamide, the initial deposition potential of Al moves to ca. −0.190 V. With the further increase in concentration of nicotinamide, the initial deposition potential becomes more negative. From the above results, it can be concluded that nicotinamide produces an inhibiting effect on the deposition of Al. In aqueous solutions, additives are thought to function by two mechanisms: (1) by complexing the metal ions and decreasing their reduction potential to make it more difficult to nucleate metal clusters, or (2) by adsorption of an organic species on the electrode surface blocking nucleation and hindering

Fig. 3 Cyclic voltammograms recorded on a Pt electrode in [Bmim]Cl/ AlCl3 (40.0/60.0, mol%) containing (a) 0.0, (b) 2.0, (c) 4.0, and (d) 8.0 mmol dm−3 nicotinamide at 30 °C. Scan rate: 50 mV s−1

260

Fig. 4 Potential observed during the galvanostatic deposition on a Cu electrode in [Bmim]Cl/AlCl3 (40.0/60.0, mol%) containing (a) 0.0, (b) 2.0, (c) 4.0, (d) 6.0, and (e) 8.0 mmol dm−3 nicotinamide at 30 °C. Current density: −3.4 mA cm−2 Fig. 5 SEM images of the Al deposits obtained from [Bmim]Cl/AlCl3 (40.0/60.0, mol%) containing a 0.0, b 2.0, c 4.0, d 6.0, and e 8.0 mmol dm−3 nicotinamide at 30 °C. Current density: −3.4 mA cm−2

J Solid State Electrochem (2014) 18:257–267

growth [28]. These mechanisms may also be applicable in ionic liquids. The adsorption of nicotinamide on electrode surface in aqueous solutions has been confirmed by electrochemical method [29]. It is observed that the color of the electrolyte does not change with the addition of nicotinamide. Furthermore, there is no obvious difference between the 27Al NMR spectra (not shown) of [Bmim]Cl/AlCl3 (40.0/60.0, mol%) with and without nicotinamide. These indicate that nicotinamide has no influence on the coordination environment of Al(III). Thus, the inhibiting effect of nicotinamide in the present study could be attributed to the adsorption of nicotinamide on the electrode surface. Because the UPD of Al occurs both on Cu electrode and on Pt electrode [8], nicotinamide actually interacts with the deposited Al. However, the UPD of Al on Pt, which is attributed to alloy formation, is different from that on Cu. Hence, the different surface properties of electrodes should be responsible for the different voltammetric behavior observed on Cu and Pt electrodes.

J Solid State Electrochem (2014) 18:257–267

261

Fig. 6 XRD patterns of the Al deposits obtained at −3.4 mA cm−2 from [Bmim]Cl/ AlCl3 (40.0/60.0, mol%) containing (a) 0.0, (b) 2.0, (c) 4.0, (d) 6.0, and (e) 8.0 mmol dm−3 nicotinamide at 30 °C. The diffraction peaks of the Cu substrate are denoted by solid circles

Table 1 Texture coefficients of the Al deposits prepared at various conditions

Deposition condition

TC(111)

TC(200)

TC(220)

TC(311)

Concentration of nicotinamide (mmol dm−3)

Temperature (°C)

Current density (mA cm−2)

0.0

30

3.4

0.3

1.9

0.6

1.2

2.0 4.0 6.0 8.0 8.0 8.0 8.0 8.0

30 30 30 30 50 70 70 70

3.4 3.4 3.4 3.4 3.4 3.4 6.4 9.4

0.5 0.9

0.8 0.6 4.0 4.0 1.8 1.5 1.8 4.0

2.1 1.6

0.6 0.9

0.8 0.6 0.6

0.5 0.6 0.6

0.8 1.3 1.1

262

Fig. 7 Potential observed during the galvanostatic deposition on a Cu electrode in [Bmim]Cl/AlCl3 containing 8.0 mmol dm−3 nicotinamide at temperatures of (a) 30 °C, (b) 50 °C, and (c) 70 °C. Current density: −3.4 mA cm−2

Electrodepositon and characterization of Al deposits Effect of the concentration of nicotinamide Figure 4 shows the potential-time curves observed during the galvanostatic deposition on a Cu substrate in [Bmim]Cl/AlCl3 (40.0/60.0, mol%) containing various concentrations of nicotinamide. It is clear that the cathodic electrode potential during

Fig. 8 SEM images of the Al deposits obtained from [Bmim]Cl/AlCl3 (40.0/60.0, mol%) containing 8.0 mmol dm−3 nicotinamide at temperatures of a 30 °C, b 50 °C, and c 70 °C. Current density: −3.4 mA cm−2

J Solid State Electrochem (2014) 18:257–267

the galvanostatic deposition with nicotinamide is more negative than that without nicotinamide. Furthermore, the electrode potential becomes more negative with an increase in the concentration of nicotinamide. These agree well with the results of the above voltammograms and the consensus that the adsorption of an organic species usually increases the overpotential of electrodeposition [30, 31]. SEM images of the Al deposits obtained from [Bmim]Cl/ AlCl3 (40.0/60.0, mol%) with various concentrations of nicotinamide are shown in Fig. 5. Deposition from [Bmim]Cl/ AlCl3 (40.0/60.0, mol%) without the addition of nicotinamide produces large uneven prismoid-like particles (Fig. 5a). A dense deposit of uniform particle size is obtained with the addition of 2.0 mmol dm−3 nicotinamide (Fig. 5b). The deposit obtained with the addition of 4.0 mmol dm−3 nicotinamide shows the most special morphology of tetrahedron-like clusters (Fig. 5c). As the concentration of nicotinamide is increased to 6.0 mmol dm−3, a highly smooth and flat Al deposit with fine grains is obtained (Fig. 5d). A smoother deposit with smaller grain size is observed with the addition of 8.0 mmol dm−3 nicotinamide (Fig. 5e). It is obvious that the appearance of the deposits obtained with nicotinamide is smoother and less granular than that without nicotinamide, which can be explained by the adsorption of nicotinamide on the surface of the substrate and deposits. The arrival rate of nicotinamide at the projecting parts is greater than that at the caved parts. Because the adsorption of nicotinamide hinders the electrodeposition of Al, the deposition rate at the

J Solid State Electrochem (2014) 18:257–267

263

Fig. 9 XRD patterns of the Al deposits obtained at −3.4 mA cm−2 from [Bmim]Cl/ AlCl3 (40.0/60.0, mol%) containing 8.0 mmol dm−3 nicotinamide at temperatures of (a) 30 °C, (b) 50 °C, and (c) 70 °C. The diffraction peaks of the Cu substrate are denoted by solid circles

projecting parts is slower than that at the caved parts, resulting in a decrease in the roughness of the deposit [32]. EDS examination (not shown) reveals that these deposits are elemental Al with quite a small amount of aluminium oxide which is due to the exposure of deposits to air. No signals of chloride are detected in the deposit obtained from the neat ionic liquid. However, a weak signal of chloride is observed in both deposits produced with 2.0 and 4.0 mmol dm−3 nicotinamide. As the concentration of nicotinamide is further increased, the signal of chloride becomes stronger. The chloride content in the deposits obtained with 6.0 and 8.0 mmol dm−3 nicotinamide is determined to be 5.9 and 7.0 at.%, respectively. The detected signals of chloride indicate the entrainment of electrolytes in deposits. It is believed that the high viscosity of the electrolyte due to the presence of nicotinamide should increase the amount of entrained electrolytes.

XRD patterns of these Al deposits are shown in Fig. 6. Diffraction peaks attributed to pure Al with a face-centered cubic (fcc) structure are clearly detected in the deposit obtained from the neat ionic liquid. Similar patterns are observed for both deposits obtained with 2.0 and 4.0 mmol dm−3 nicotinamide. However, the crystallographic textures of them are different, which can be examined by analyzing the results of XRD. Texture coefficients, TC (hkl), of the (111), (200), (220), and (311) crystallographic planes are calculated by using the following expression (Eq. (1)) [9], I hkl =I r;hkl

T C ðhklÞ ¼ 1  X I

hkl =I r;hkl

ð1Þ

n

where I hkl is the peak intensity of the (hkl) crystallographic plane for the obtained deposits, I r,hkl is the peak intensity of

264

Fig. 10 Potential observed during the galvanostatic deposition on a Cu electrode in [Bmim]Cl/AlCl3 (40.0/60.0, mol%) containing 8.0 mmol dm−3 nicotinamide at (a ) −3.4 mA cm−2, (b ) −6.4 mA cm−2, and (c ) −9.4 mA cm−2. Temperature: 70 °C

the (hkl) crystallographic plane for the JCPDS card no. 00004-0787, and n is the total number of crystallographic planes being considered. The calculated texture coefficients of the Al deposits obtained with various concentrations of nicotinamide are listed in Table 1. It can be seen that the deposit obtained from the neat ionic liquid has a preferred (200) crystallographic orientation. The intensity of the (311) plane is essentially equal to that of a randomly oriented sample, and the (111) and (220) planes are relatively weak. With the increase in concentration of nicotinamide from 0.0 to 4.0 mmol dm−3, the Fig. 11 SEM images of the Al deposits obtained from [Bmim]Cl/AlCl3 (40.0/60.0, mol%) containing 8.0 mmol dm−3 nicotinamide at a −3.4 mA cm−2, b −6.4 mA cm−2, and c −9.4 mA cm−2. Temperature: 70 °C

J Solid State Electrochem (2014) 18:257–267

intensity of the (200) plane decreases and becomes weaker than that of a randomly oriented sample. Both deposits obtained with 2.0 and 4.0 mmol dm−3 nicotinamide display a preferred (220) orientation. As the concentration of nicotinamide is increased to 6.0 and 8.0 mmol dm−3, the (200) plane becomes very intense, whereas all other diffraction peaks vanish. This indicates that both deposits have a strong preferred (200) orientation. Furthermore, the (200) diffraction peak is quite broad. According to the Scherrer equation, the average crystalline size of the deposits obtained with 6.0 and 8.0 mmol dm−3 nicotinamide is determined to be 20 and 14 nm, respectively. Similar nanocrystalline Al deposits were previously obtained from ionic liquids containing pyrrolidinium cation [17]. Endres et al. [21] proposed that the pyrrolidinium cation might adsorb on the substrates and on the growing nuclei, thus hindering the further growth of crystals. In addition, nanocrystalline Al deposits were also obtained from partially decomposed imidazolium-based ionic liquids [33] and 1-(2-methoxyethyl)-3-methylimidazolium chloride-AlCl3 ionic liquids [34]. Effect of temperature The effect of temperature on Al deposition was investigated in [Bmim]Cl/AlCl3 (40.0/60.0, mol%) containing 8.0 mmol dm−3 nicotinamide. Variation of the cathodic potential during galvanostatic deposition as a function of temperature is shown in Fig. 7. It is clear that the cathodic potential becomes positive with increasing temperature from 30 to 70 °C. This could be

J Solid State Electrochem (2014) 18:257–267

explained from two aspects. On one hand, an increase in temperature will enhance the charge transfer of the electroactive species, thus weakening the electrochemical polarization. On the other hand, the weaker adsorption of nicotinamide at higher temperatures [35] further lowers the electrochemical polarization. Hence, the cathodic overpotential decreases with temperature increase. SEM images of the Al deposits obtained at various temperatures are shown in Fig. 8. It is obvious that the grain size of the deposits gradually increases with increasing temperature from 30 to 70 °C. The grain size of the deposit is determined by the competition between the nucleation rate and the growth rate of nuclei [36]. The higher the nucleation rate during deposition, the finer are the grains of the deposit. The nucleation rate depends mainly on the overpotential. As shown in Fig. 7, an increase in the temperature results in a lower overpotential that Fig. 12 XRD patterns of the Al deposits obtained at 70 °C from [Bmim]Cl/AlCl3 (40.0/60.0, mol%) containing 8.0 mmol dm−3 nicotinamide at (a) −3.4 mA cm−2, (b) -6.4 mA cm-2, and (c) −9.4 mA cm−2. The diffraction peaks of the Cu substrate are denoted by solid circles

265

decreases the nucleation rate. In the dynamics aspect, the growth rate of nuclei is positively related to temperature. Hence, smooth Al deposits with fine grains are obtained at low temperatures, whereas deposits with large granules are produced at high temperatures. EDS examination reveals a decrease of the chloride content in the deposits with increasing temperature from 30 to 70 °C. It is believed that the low viscosity of electrolytes at high temperature can reduce the amount of entrained electrolytes. XRD patterns of these deposits are shown in Fig. 9. All the characteristic diffraction peaks of Al are detected in both deposits prepared at 50 and 70 °C. In consistent with the gradually increased grain size (Fig. 8), the peak width decreases with temperature increased. According to Eq. (1), the texture coefficients of the Al deposits obtained at different temperatures are listed in Table 1. All of the deposits have a

266

preferred (200) crystallographic orientation. Furthermore, the intensity of the (200) plane decreases with increasing temperature from 30 to 70 °C. Effect of current density The effect of current density on Al deposition was investigated in [Bmim]Cl/AlCl 3 (40.0/60.0, mol%) containing 8.0 mmol dm−3 nicotinamide. Figure 10 shows the potentialtime curves recorded at three different current densities. It is apparent that the cathodic potential becomes negative with an increase in current density. This agrees well with the Butler– Volmer equation [36], which indicates that the overpotential increases with current density increase. In addition, a potential step is observed in the curve recorded at 9.4 mA cm−2. This phenomenon is easily understood. At high current density, the consumption rate of the electroactive species [Al2Cl7]− near the cathode surface will exceed its supplement rate. As [Al2Cl7]− near the cathode surface is depleted, mass transfer dominates, and then the concentration polarization increases sharply. The potential step at 9.4 mA cm−2 can be attributed to such concentration polarization. SEM images of the deposits prepared at three current densities are shown in Fig. 11. It is evident that the grain size of the deposits decreases with increasing current density from 3.4 to 9.4 mA cm−2, which is consistent with the previous report [37]. Current density plays an important role in the grain size of deposits. As shown in Fig. 10, an increase in the current density results in a higher overpotential, which increases the nucleation rate and promotes the grain refinement. EDS examination (not shown) reveals that the chloride content in the deposits increases with current density increase. The chloride content in the deposit obtained at 9.4 mA cm−2 is 6.41 at.%. It is believed that the high deposition rate at high current density can enhance the entrainment of electrolytes. XRD patterns of the three Al deposits are shown in Fig. 12. The texture coefficients of them are also calculated according to Eq. (1). As shown in Table 1, all deposits exhibit a preferred (200) orientation. Furthermore, the intensity of the (200) plane increases with increasing current density from 3.4 to 9.4 mA cm−2. At 9.4 mA cm−2, the intensity of the (200) plane is very strong, whereas all other diffraction peaks vanish. This indicates that the deposit obtained at 9.4 mA cm−2 has a strong preferred (200) orientation. Furthermore, the (200) diffraction peak is quite broad, and the average crystalline size is calculated to be 15 nm.

Conclusions The effect of nicotinamide on the electrodeposition of Al was studied in the ionic liquid [Bmim]Cl/AlCl3 (40.0/60.0 mol%). The cyclic voltammograms recorded on Cu and Pt both

J Solid State Electrochem (2014) 18:257–267

showed that nicotinamide produced an inhibiting effect on Al deposition, which is probably attributed to the adsorption of nicotinamide on the electrode surface. Al deposits obtained with the addition of nicotinamide were flatter and less granular than that without nicotinamide. Highly uniform and smooth Al deposit with average crystalline size of 14 nm was obtained with the addition of 8 mmol dm−3 nicotinamide at 30 °C. The effects of temperature and current density on the surface morphologies and crystal orientations of Al deposits were also investigated. As the temperature was increased from 30 to 70 °C, the grain size of Al deposits increased gradually, the chloride content in the deposits decreased, and the intensity of the preferred (200) crystallographic plane decreased. In contrast, an opposite trend was observed with increasing current density from 3.4 to 9.4 mA cm−2. Acknowledgements The authors gratefully acknowledge the financial support from the National Basic Research Program of China (2013CB632606), National Key Technology Research and Development Program of the Ministry of Science and Technology of China (2012BAF03B01), and Program of National Natural Science Foundation of China (51274181).

References 1. Zhao YG, VanderNoot TJ (1997) Electrochim Acta 42:3–13 2. Charrier C, Jacquot P, Denisse E, Millet JP, Mazille H (1997) Surf Coat Technol 90:29–34 3. Wang DQ, Shi ZY (2004) Appl Surf Sci 227:255–260 4. Paredes RSC, Amico SC, d'Oliveira A (2006) Surf Coat Technol 200: 3049–3055 5. Bardi U, Caporali S, Craig M, Giorgetti A, Perissi I, Nicholls JR (2009) Surf Coat Technol 203:1373–1378 6. Yue G, Lu X, Zhu Y, Zhang X, Zhang S (2009) Chem Eng J 147(1): 79–86 7. Hurley FH, Wier TP (1951) J Electrochem Soc 98:207–212 8. Robinson J, Osteryoung RA (1980) J Electrochem Soc 127:122–128 9. Liao Q, Pitner WR, Stewart G, Hussey CL, Stafford GR (1997) J Electrochem Soc 144:936–943 10. Lee JJ, Bae IT, Scherson DA, Miller B, Wheeler KA (2000) J Electrochem Soc 147:562–566 11. Liu QX, El Abedin SZ, Endres F (2006) Surf Coat Technol 201: 1352–1356 12. Jiang T, Brym MJC, Dube G, Lasia A, Brisard GM (2006) Surf Coat Technol 201:1–9 13. Chang J-K, Chen S-Y, Tsai W-T, Deng M-J, Sun IW (2007) Electrochem Commun 9:1602–1606 14. Chang J-K, Chen S-Y, Tsaia W-T, Deng M-J, Sun IW (2008) J Electrochem Soc 155:C112–C116 15. Yue G, Zhang S, Zhu Y, Lu X, Li S, Li Z (2009) AIChE J 55:783–796 16. Jiang T, Brym MJC, Dube G, Lasia A, Brisard GM (2006) Surf Coat Technol 201:10–18 17. El Abedin SZ, Moustafa EM, Hempelmann R, Natter H, Endres F (2005) Electrochem Commun 7:1111–1116 18. El Abedin SZ, Moustafa EM, Hempelmann R, Natter H, Endres F (2006) ChemPhysChem 7:1535–1543 19. Moustafa EM, El Abedin SZ, Shkurankov A, Zschippang E, Saad AY, Bund A, Endres F (2007) J Phys Chem B 111:4693–4704

J Solid State Electrochem (2014) 18:257–267 20. Atkin R, El Abedin SZ, Hayes R, Gasparotto LHS, Borisenko N, Endres F (2009) J Phys Chem C 113:13266–13272 21. Giridhar P, El Abedin SZ, Endres F (2012) Electrochim Acta 70:210– 214 22. Endres F, Bukowski M, Hempelmann R, Natter H (2003) Angew Chem Int Ed 42:3428–3430 23. Abbott AP, Qiu F, Abood HMA, Ali MR, Ryder KS (2010) Phys Chem Chem Phys 12:1862–1872 24. Barchi L, Bardi U, Caporali S, Fantini M, Scrivani A (2010) Prog Org Coat 68:120–125 25. Liu L, Lu X, Cai Y, Zheng Y, Zhang S (2012) Aust J Chem 65:1523– 1528 26. Tierney BJ, Pitner WR, Mitchell JA, Hussey CL, Stafford GR (1998) J Electrochem Soc 145:3110–3116 27. Stafford GR, Kongstein OE, Haarberg GM (2006) J Electrochem Soc 153:C207–C212

267 28. 29. 30. 31. 32. 33. 34. 35. 36. 37.

Abbott AP, McKenzie KJ (2006) Phys Chem Chem Phys 8:4265–4279 Milkowska M, JurkiewiczHerbich M (1996) Pol J Chem 70:783–794 Cheng CC, West AC (1997) J Electrochem Soc 144:3050–3056 Mimani T, Mayanna SM, Munichandraiah N (1993) J Appl Electrochem 23:339–345 Fukui R, Katayama Y, Miura T (2011) Electrochim Acta 56:1190– 1196 Liu QX, El Abedin SZ, Endres F (2008) J Electrochem Soc 155: D357–D362 El Abedin SZ, Giridhar P, Schwab P, Endres F (2010) Electrochem Commun 12:1084–1086 Vazquez-Arenas J, Cruz R, Mendoza-Huizar LH (2006) Electrochim Acta 52:892–903 Budevski E, Staikov G, Lorenz WJ (2000) Electrochim Acta 45: 2559–25 Tang J, Azumi K (2011) Electrochim Acta 56:1130–1137