离子液体中对苯醌的电化学行为

doi:10.7503/cjcu20130724

摘要/Abstract

摘要：

采用循环伏安法(CV)和现场光谱电化学方法从分子水平上研究了对苯醌(BQ)在4种离子液体中铂电极上的电化学氧化还原过程. 基于在298.15~343.15 K温度范围内对苯醌的伏安曲线, 获得了不同温度下对苯醌的扩散系数(D), 进而求得其扩散活化能(E_a). 利用现场红外光谱电化学循环伏吸及导数循环伏吸法同时跟踪电化学过程中反应物、中间体及产物随时间(电位)的变化. 光谱电化学结果表明, 苯醌在1-丁基-3-甲基咪唑四氟硼酸盐(BMIMBF₄)和1-丁基-3-甲基咪唑六氟磷酸盐(BMIMPF₆)中与在乙腈中类似, 先生成苯醌阴离子自由基, 随后进一步还原为二价阴离子.

关键词: 离子液体, 对苯醌, 现场红外光谱电化学, 扩散系数, 活化能

Abstract:

The reduction of 1,4-benzoquinone(BQ) on Pt electrode was investigated in various ionic liquids by cyclic voltammetry(CV). Over a wide range of scan rates, two couples of redox peaks were clearly observed in cyclic voltammogram, showing a quasi reversible diffusion process of BQ with the two-step electrochemical reduction. Diffusion coefficient and activation energy were obtained from cyclic voltammogram, which displayed the increase of diffusion coefficient accompanying temperature rise from 298.15 K to 343.15 K. The techniques of cyclic voltammetry, in situ FTIR spectroelectrochemistry(FTIR), cyclic voltabsorptometry(CVA) and derivative cyclic voltabsorptometry(DCVA) were used to investigate the electrochemical behavior of BQ in ionic liquids, BMIMBF₄ and BMIMPF₆. The results support that BQ undergoes two successive one-electron reductions, corresponding to the formation of a radical anion intermediate and then the dianion, in ionic liquids, while presenting a different shape of cyclic voltammogram compared to anhydrous acetonitrile solvent.

Key words: Ionic liquid, 1,4-Benzoquinone, In-situ Fourier transform infrared spectroelectrochemistry, Diffusion coefficient, Activation energy

中图分类号:

O646.54

TrendMD:

李彤, 金葆康. 离子液体中对苯醌的电化学行为. 高等学校化学学报, 2014, 35(4): 847.

LI Tong, JIN Baokang. Electrochemical Redox of Benzoquinone in Ionic Liquids^†. Chem. J. Chinese Universities, 2014, 35(4): 847.

图/表 10

Fig.1 Cyclic voltammogram of 0.005 mol/L BQ in BMIMBF4 at Pt working electrode using various scan ratesScan rate/(mV·s-1): a. 20; b. 40; c. 50; d. 100; e. 200.

Fig.2 Plots of Ip vs. v1/2 from cyclic vohammogram of 0.005 mol/L BQ in BMIMBF4a. ipa1 vs. v1/2; b. ipa2 vs. v1/2; c. ipc2 vs. v1/2; d. ipc1 vs. v1/2.

Fig.3 Cyclic voltammogram of BQ at various temperatures in BMIMPF6(scan rate: 100 mV/s)Temperature/K: a. 298.15; b. 303.15; c. 313.15; d. 323.15; e. 333.15; f. 343.15.

Table 1 Values of diffusion coefficient D of BQ in BMIMPF6 at different temperatures

T/K	I_pc1/μA	I_pc2/μA	10⁷D/(cm²·s^-1)	T/K	I_pc1/μA	I_pc2/μA	10⁷D/(cm²·s^-1)
298.15	6.897	3.950	2.671	323.15	9.991	5.847	6.075
303.15	7.285	4.023	3.030	333.15	11.540	7.894	8.356
313.15	8.524	4.505	4.285	343.15	13.140	9.535	11.160

Fig.4 Plot of lnD vs. 1/T of BQ in BMImPF6

Table 2 Values of activation energy Ea of BQ in ionic liquids

Ionic liquid	Slope	E_a/(kJ·mol^-1)	R^*	Ionic liquid	Slope	E_a/(kJ·mol^-1)	R^*
BMIMBF₄	-2401.77	19.97	-0.996	HMIMBF₄	-2583.76	21.48	-0.990
BMIMPF₆	-3313.19	27.55	-0.999	HMIMPF₆	-4734.50	39.36	-0.991

Table 3 Parameters ofcyclic voltammogram for 0.025 mol/L BQ in ionic liquids and CH3CN solution

Solution	E_pc1/V	E_pa1/V	E_pc2/V	E_pa2/V	ΔE_p1/V	ΔE_p2/V	(E_1/2)₁/V	(E_1/2)₂/V	ΔE_1/2/V
BMIMBF₄	-0.542	-0.102	-0.753	-0.468	0.440	0.280	-0.322	-0.611	0.289
BMIMPF₆	-0.578	-0.078	-0.804	-0.409	0.500	0.395	-0.328	-0.607	0.279
CH₃CN	-0.563	-0.389	-0.959	-0.747	0.174	0.212	-0.476	-0.853	0.377

Fig.5 Cyclic voltammogram(A1—A3) and the corresponding 3D spectra(B1—B3) of 0.025 mol/L BQ in BMIMBF4(A1,B1), BMIMPF6(A2,B2) and CH3CN containing 0.1 mol/L TBAP(A3,B3)(scan rate: 5 mV/s)

Fig.6 CVAs(A) and selected DCVAs(B)(smoothing with a fast Fourier transform smoothing algorithm) for the BQ electrochemical reaction in BMIMBF4 ν˙/cm-1: (A) a. 1233, b. 1310, c. 1341, d. 1487, e. 1503, f. 1656; (B) a. 1487, b. 1503, c. 1656.

Fig.7 CVAs(A) and selected DCVAs(B)(smoothing with a fast Fourier transform smoothing algorithm) for the BQ electrochemical reaction in BMIMPF6 ν˙/cm-1: (A) a. 1241, b. 1310, c. 1341, d. 1479, e. 1503, f. 1656; (B) a. 1479, b. 1503, c. 1656.

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