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Journal of Electrochemistry ›› 2020, Vol. 26 ›› Issue (6): 859-867.  doi: 10.13208/j.electrochem.191009

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Effect of 18-Crown-6 Additive on Chromium Electrodeposition in Ionic Liquid

WANG Yi-jie, NIU Dong-fang, ZHANG Xin-sheng*()   

  1. State Key Laboratory of Chemical Engineering, East China University of Science and Technology,Shanghai 200030, China
  • Received:2019-10-15 Revised:2020-02-27 Online:2020-12-28 Published:2021-01-07
  • Contact: ZHANG Xin-sheng E-mail:xszhang@ecust.edu.cn


Trivalent chromium ion (Cr3+) is used for electrodeposition due to its low toxicity. Electrodeposition in ionic liquids can greatly solve for hydrogen evolution problem. However,as a widely used Cr(III) precursor, chromium chloride hydrate (CrCl3·6H2O), still contains water. In the presence of water, Cr3+ will form a complex coordination structure with water molecules ([Cr(H2O)6]3+), which is a stable octahedral structure and is difficult to be directly reduced to chromium metal. Therefore, coordination agents should be added into the bath. In this work, the effect of 18-Crown-6 additive on chromium electrodeposition was investigated in CrCl3/[BMIM]HSO4/H2O plating solution. The UV-Vis spectra showed that 18-Crown-6 formed a complex with Cr3+, destroyed the stable coordination structure formed by Cr3+ and water molecules, making a red shift in the maximum absorption wavelength. The cyclic voltammograms indicated that the electroreduction of Cr3+ occurred in a two-step process, namely, Cr3+ + e → Cr2+ and Cr2+ + 2e → Cr0. Both of the peak potential and initial reduction potential of Cr3+ had positive shifts by 220 mV after adding 18-Crown-6. The reason for this phenomenon was that when 18-Crown-6 was added to the plating solution, the stable structure of [Cr(H2O)6]3+ was destroyed, Cr3+ became more readily to be reduced, thereby, lowered the reduction potential of Cr3+. The EDS data showed that the chromium content in the coating was increased under the action of 18-Crown-6. The improvement indicated that 18-Crown-6 was beneficial to the chromium electrodeposition. The SEM characterizations indicated that the coating obtained in 18-Crown-6/CrCl3/[BMIM]HSO4/H2O plating solution had a larger particle size. Tafel curves suggested that the corrosion resistance of chromium coating was better than that of brass substrate. The optimized process in 18-Crown-6/CrCl3/[BMIM]HSO4/H2O plating solution could be proceeded at the temperature of 50 oC, pH of 3.5, current density of 1200 A·m-2, and plating time of 1.5 h. The thickness of the chrome plating reached 72.5 μm and the current efficiency was 42.3%.

Key words: trivalent chromium, 1-butyl-3-methyl imidazole sulfate, 18-Crown-6, chromium electrodeposition, current efficiency

CLC Number: