1-丁基-3-甲基咪唑硫酸氢盐与乙酸钠混合电解液中三价铬电镀的研究

doi:10.13208/j.electrochem.180326

摘要/Abstract

摘要： 本文研究了Cr³⁺在1-丁基-3-甲基咪唑硫酸氢盐（[BMIM]HSO₄）电解液中的电沉积反应以及添加剂NaOAc对电镀铬的影响. 含Cr³⁺电解液的循环伏安结果表明，Cr(III)还原为Cr(II)的峰电位是-1.5 V (vs. Pt)，峰电位和峰电流均满足Rendle-Sevcik扩散方程，由该方程计算得到Cr³⁺的扩散系数为1.6 × 10^-8 cm²·s^-1. 铬镀层的X射线衍射和扫描电子显微镜表征结果表明镀层由纳米球状的单质铬颗粒聚集而成，其平均粒径为0.87 μm. 在电解液中添加NaOAc后，Cr³⁺的还原峰电位正移了约0.25 V. 同时EDS结果表明，在NaOAc的作用下镀层中Cr/O摩尔比由4.48增加至6.28，这说明OAc^-有利于单质铬的电沉积. 当电解液中NaOAc-[BMIM]HSO₄-CrCl₃-H₂O的摩尔比为0.075:1:0.5:6时，所得的镀层最厚(63 μm)与电流效率最高(33.5%).

关键词: 电镀, 1-丁基-3-甲基咪唑硫酸氢盐, 醋酸钠, 三价铬, 铬镀层

Abstract: Using trivalent chromium ions (Cr(III)) as the chromium source for chromium electrodeposition has attracted much attention since it can reduce the toxicity of the whole process. Even though the chromium deposition in Cr(III)-based ionic liquid bath can avoid the most hydrogen evolution problem, CrCl₃·6H₂O is widely used as the Cr(III) precursor, which still contains water and has the stable octahedral structure. As a result, it is difficult to deposit Cr and there is still hydrogen evolution reaction (HER). Moreover, the hydroxyl ions (OH^-) produced during HER react with Cr³⁺ to form Cr(OH)₃, which will affect the performance and property of the Cr layer. To avoid the formation of Cr(OH)₃, 1-butyl-3-methylimidazolium hydro sulfate ([BMIM]HSO₄) aqueous solution was used as the electrolyte in this work. To enhance the depositing ability and to lower the reduction onset potential of Cr(III), NaOAc was used as the additive. Electrochemical measurements such as cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were made to test the electrochemical performance in different electrolytes. Chromium layers were electrodeposited on copper plates at a constant potential of -3.0 V (vs. Pt). The Cr thickness and current efficiency were calculated based on the gravimetric method. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX) techniques were used to study the surface morphology, crystalline structure and elemental composition of the deposited Cr layer, respectively. The cyclic voltammetric results showed that the reduction of Cr(III) to Cr(0) is a two-step process. First, Cr(III) reduced to Cr(II) at -1.50 V (vs. Pt). Then, Cr(II) further reduced to Cr(0) at -2.10 V (vs. Pt). Both of the peak current and peak potential followed the Rendle-Sevcik equation, by which the diffusion coefficient of Cr³⁺ at 40 ℃ was calculated to be 1.6 ×10^-8 cm²·s^-1. The XRD and SEM characterizations indicated that the Cr coating layers were composed of Cr nanoparticles with an average particle size of 0.87μm. The NaOAc effect on the electrodeposition of Cr was also studied. After adding NaOAc, the reduction peak potential of Cr(III)shifted to positive direction, indicating less energy required to reduce Cr³⁺. Additionally, the molar ratio of Cr:O in the coating layer increased from 4.48 to 6.28, indicating that OAc- was helpful for the electrodeposition of Cr metal. This was because the addition of OAc- could break the stable octahedral structure of CrCl₃·6H₂O. Overall, the best coating thickness (63 μm) and highest current efficiency (33.5%) were obtained when the molar ratio of NaOAc-[BMIM]HSO₄-CrCl₃-H₂O electrolyte was 0.075:1:0.5:6. Based on this study, it can be concluded that [BMIM]HSO₄-NaOAc aqueous electrolyte might be benefited to electrodeposit pure Cr, instead of Cr(OH)₃, with relatively high current efficiency and low reduction onset potential.

Key words: electrodeposition, 1-butyl-3-methylimidazolium hydro sulfate, sodium acetate, trivalent chromium, chromium coating

中图分类号:

O646

刘德英，罗维，张文娟，胡硕真，徐衡，张新胜. 1-丁基-3-甲基咪唑硫酸氢盐与乙酸钠混合电解液中三价铬电镀的研究[J]. 电化学（中英文）, 2018, 24(5): 538-545.

LIU De-ying，LUO Wei，ZHANG Wen-juan，HU Shuo-zhen，XU Heng，ZHANG Xin-sheng. Electrochemical Deposition of Cr from Cr(III)-Based [BMIM]HSO₄ and NaOAc Electrolyte[J]. Journal of Electrochemistry, 2018, 24(5): 538-545.

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