Effect of dichloromethane and toluene on the structure, property, and Al electrodeposition in 1-butyl-3-methylimidazolium chloroaluminate ionic liquid
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摘要: 離子液體電沉積鋁技術具有廣闊的應用前景,而添加劑是提高鋁鍍層性能的有效方法,但相關作用機制還有待明確。本文應用量子化學和分子動力學模擬研究了二氯甲烷(DCM)和甲苯(C7H8)對氯化-1-丁基-3-甲基咪唑/三氯化鋁([BMIM]Cl/AlCl3)體系的微觀結構、物理化學性質和鋁電沉積的影響。發現DCM易與陰、陽離子形成氫鍵,分布在陰陽離子之間使得陰陽離子間距離增加、相互作用能減小, 導致陰陽離子擴散能力增強、鋁配離子更傾向以
${\rm{A}}{{\rm{l}}_2}{\rm{Cl}}_7^ -$ 形式存在,體系黏度降低電導率增加,因而對體系電化學性質提升很大,而且DCM起到了晶粒細化和整平作用,從而可以得到鏡面光亮的沉積層,所得結果與實驗值吻合較好。C7H8主要分布在陽離子周圍,與陽離子有較強相互作用,在沉積過程中吸附于電極表面的凸出部分,抑制了電活性離子的還原而主要起到整平作用,其對陰離子和陽離子之間的相關作用的影響比DCM小,因而體系電化學性質提升不如DCM。Abstract: The electrodeposition of aluminum in ionic liquid has broad application prospects, and additives are an effective way to improve the performance of the aluminum coating. However, the relevant mechanism behind this remains to be clarified. In the present work, the effects of dichloromethane (DCM) and toluene (C7H8) on the microstructure, physicochemical properties, and aluminum electrodeposition with 1-butyl-3-methylimidazolium chloride/aluminum chloride ([BMIM]Cl/AlCl3) were studied using quantum chemistry and molecular dynamics simulation. It is found that DCM easily forms hydrogen bonds with anions and cations of ionic liquids. Since DCM is distributed between anion and cation, the distance between the anion and cation increases, and the interaction energy decreases. As a result, the diffusion ability of anions and cations is enhanced, and the aluminum complex anions tend to exist in the form of${\rm{A}}{{\rm{l}}_2}{\rm{Cl}}_7^ - $ . The viscosity of the system decreases, and the conductivity increases, so the electrochemical properties of the system are significantly improved, which are in good agreement with the experimental values. C7H8 is adsorbed on the protruding part of the electrode surface in a flat way, which plays a leveling role and results in a flat white coating. Alternatively, DCM easily interacts with the electroactive ion${\rm{A}}{{\rm{l}}_2}{\rm{Cl}}_7^ - $ , which makes it difficult to reduce this electroactive ion. At the same time, the concentration of the electroactive ion decreases as the concentration of the additive is increased, which leads to a large overpotential in the electrochemical process, resulting in a decrease in the electrode reaction rate that plays a role in grain refinement. Moreover, the interaction between DCM and cations is also strong, and they can be adsorbed on the protruding part of the electrode surface during the electrochemical process, playing a certain leveling role. Therefore, the addition of DCM can obtain specular gloss deposits. The effect of C7H8 on the interaction between anions and cations is not as good as DCM, which consequently results in inferior electrochemical properties compared to DCM. Therefore, DCM is more favorable for the electrodeposition of aluminum than the aromatic hydrocarbon C7H8.-
Key words:
- ionic liquids /
- aluminum electrodeposition /
- additives /
- dichloromethane /
- toluene /
- first principles /
- molecular dynamics
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圖 4 MD模擬計算得到體系中離子間的徑向分布函數gA-B(r)。(a)[BMIM]+與
${\rm{Al}}_{x} {\rm{Cl}}_y^{3x-y} $ ;(b)${\rm{Al}}_{x} {\rm{Cl}}_y^{3x-y} $ 與Cl?;(c)[BMIM]+與M(M=DCM、C7H8);(d)${\rm{Al}}_{x} {\rm{Cl}}_y^{3x-y} $ 與M(M=DCM、C7H8)Figure 4. Calculated radial distribution functions gA-B(r) for particle A and B from MD simulation: (a) [BMIM]+-
${\rm{Al}}_{x} {\rm{Cl}}_y^{3x-y} $ ; (b)${\rm{Al}}_{x} {\rm{Cl}}_y^{3x-y} $ -Cl?; (c) [BMIM]+-M(M = DCM, C7H8); (d)${\rm{Al}}_{x} {\rm{Cl}}_y^{3x-y} $ -M(M = DCM、C7H8)圖 5 計算得到的三維空間分布圖。(a)[BMIM]+周圍Cl?(綠色)、C7H8(黃色)、DCM(紅色)、
${\rm{Al}}_{x} {\rm{Cl}}_y^{3x-y} $ (藍色)的三維空間分布;(b)${\rm{Al}}_{x} {\rm{Cl}}_y^{3x-y} $ 周圍Cl?(綠色)、DCM(紅色)、C7H8(黃色)空間分布Figure 5. Spatial distribution from simulation: (a) Cl? (green),
${\rm{Al}}_{x} {\rm{Cl}}_y^{3x-y} $ (blue), DCM (red), and C7H8 (yellow) around the [BMIM]+; (b) Cl? (green), DCM (red), C7H8 (yellow) around${\rm{Al}}_{x} {\rm{Cl}}_y^{3x-y} $ 圖 6 DCM和C7H8對體系中各粒子均方根位移(MSD)和擴散系數的影響。(a)[BMIM]+的MSD;(b)
${\rm{Al}}_{x} {\rm{Cl}}_y^{3x-y} $ 的MSD;(c)DCM和C7H8的MSD; (d) 各粒子的擴散系數Figure 6. Effects of DCM and C7H8 on the root-mean-square displacement MSD and diffusion coefficient of particles: (a) MSD of [BMIM]+; (b) MSD of
${\rm{Al}}_{x} {\rm{Cl}}_y^{3x-y} $ ; (c) MSD of DCM and C7H8; (d) diffusion coefficient表 1 B3LYP/6-311++G(d,p)方法得到的體系中各粒子間的相互作用能
Table 1. Interaction energy in the system with B3LYP/6-311++G(d,p) method
M Interaction energy/(kJ·mol?1) [BMIM]+ and M ${\rm{A}}{{\rm{l}}_2}{\rm{Cl}}_7^ - $ and M [BMIM]+M and ${\rm{A}}{{\rm{l}}_2}{\rm{Cl}}_7^ - $ C7H8 ?27.69 ?7.27 ?260.76 DCM ?22.29 ?21.28 ?267.99 表 2 B3LYP/6-311++G(d,p)方法得到的體系的相關量化參數
Table 2. Quantitative parameters of the system from B3LYP/6-311++G(d,p) method
Type μ/
(10?30 ℃·m)EHOMO/
eVELUMO/
eVΔE/
eVχ/
eVC7H8 1.343 ?9.9132 ?4.8584 5.0548 7.3858 DCM 6.081 ?8.5991 ?0.9064 7.6927 4.7528 [BMIM]Al2Cl7 51.152 ?8.0239 ?1.9718 6.0521 4.9978 [BMIM]Al2Cl7/C7H8 49.127 ?9.3491 ?4.8725 4.4766 7.1108 [BMIM]Al2Cl7/DCM 44.482 ?8.1412 ?1.9195 6.2217 5.0303 表 3 計算所得體系中主要粒子的配位數
Table 3. Calculated coordination number of the main particles in the system
Type ${\rm{C}}{{\rm{N}}_{({\rm{A}}{{\rm{l}}_x}{\rm{Cl}}_y^{3x - y} - {\rm{C}}{{\rm{l}}^ - })}}$ ${\rm{C}}{{\rm{N}}_{({{[{\rm{BMIM}}]}^ + } - {\rm{A}}{{\rm{l}}_x}{\rm{Cl}}_y^{3x - y})}}$ [BMIM]Cl/AlCl3 0.99 2.88 [BMIM]Cl/AlCl3/C7H8 0.85 1.81 [BMIM]Cl/AlCl3/DCM 0.68 1.54 表 4 計算得到的303.14 K和0.1 MPa下體系的黏度(η)與電導率(κ)
Table 4. Viscosity (η) and conductivity (κ) of the system from MD simulation at 303.14 K and 0.1 MPa
Type η/(mPa·s) κ/(mS·cm?1) [BMIM]Cl/AlCl3/C7H8 11.61 7.59 [BMIM]Cl/AlCl3/DCM 2.48 48.55 www.77susu.com -
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