Electrodeposition Behavior of Chromium in Ionic Liquid [BMIM]PF6†

doi:10.7503/cjcu20130278

Abstract

Abstract:

1-Butyl-3-methylimidazolium hexafluorophosphate([BMIM]PF₆) ionic liquid was synthesized by 1-chlorobutane, N-methylimidazole and KPF₆. The structure of ionic liquid was investigated by IR spectrum. The electrochemical window of [BMIM]PF₆ was determined to be 4.7 V at 85 ℃ by cyclic voltammetry. The electrochemical behavior of the[BMIM]PF₆-Cr(Ⅲ) electrolyte was studied. The reduction of chromium from Cr(Ⅲ) to Cr(0) in the solution is a one-step irreversible growth process which is controlled by diffusion. The cathodal transfer coefficient(α) is 0.023 and the cathode diffusion coefficient(D₀) is 1.142×10^-6 cm²/s. The electrodeposition of chromium on copper substrate from [BMIM]PF₆-Cr(Ⅲ) were experimented by potentiostatic method at -1.5 V. The surface morphology of chromium coating was characterized by means of scanning electron microscopy(SEM) and its morphology was granular structure. The size of granulae increase with the increase of deposition time. The chemical composition and structure of chromium coating were tested by energy dispersive spectrometry(EDS) and X-ray diffraction(XRD). The results indicate that the coating consist of amorphous metallic chromium.

Key words: Chromium, Ionic liquid, Cyclic voltammetry, Electrochemical window, Electrodeposition

CLC Number:

O646

TrendMD:

HASIMU Yushanjiang, LIU Ruiquan, MI Hongyu. Electrodeposition Behavior of Chromium in Ionic Liquid [BMIM]P $F 6 †$ [J]. Chem. J. Chinese Universities, 2014, 35(1): 140.

Figures/Tables 11

Scheme 1 Synthesis of [BMIM]PF6 ionic liquid

Fig.1 Schematic diagram of electrochemical device

Fig.2 FTIR spectrum of [BMIM]PF6 ionic liquid

Fig.3 Electrical conductivities of [BMIM]PF6(a) and [BMIM]PF6-Cr(Ⅲ)(b)

Fig.4 Electrochemical window of ionic liquid

Fig.5 Cathodic polarization curves of [BMIM]PF6-Cr(Ⅲ)

Table 1 Data of cathodic polarization of [BMIM]PF6-Cr(Ⅲ)(0.1 mol/L) with various scan rates at 85 ℃

ν/(mV?s^-1)	I_pc/μA	E_pc/V	E_pc/2/V	∣E_pc-E_pc/2∣/V	ν^1/2/(mV?s^-1)^1/2	α
50	-1.52	-1.50	-0.765	0.735	7.071	0.026
80	-3.04	-1.61	-0.771	0.839	8.944	0.023
100	-3.74	-1.65	-0.775	0.875	10.000	0.022
120	-4.51	-1.69	-0.800	0.890	10.954	0.022
180	-6.26	-1.77	0.875	0.895	13.416	0.022
Average						0.023

Fig.6 Relationship between Epc and lgν

Fig.7 Relationship between Ipc and ν1/2

Fig.8 SEM images of Cr deposits from [BMIM]PF6-Cr(Ⅲ) electrolyte at 85 ℃, -1.50 V on Cu substrate (A—C) 0.1 mol/L Cr(Ⅲ); (A'—C') 0.4 mol/L Cr(Ⅲ). Deposition time/min: (A), ( A') 30; (B), (B') 60; (C), (C') 120.

Fig.9 EDS analysis of Cr deposits from [BMIM]PF6-Cr(Ⅲ) on Cu substrate

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