Electrochemical Redox of Benzoquinone in Ionic Liquids†

doi:10.7503/cjcu20130724

Abstract

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

CLC Number:

O646.54

TrendMD:

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

Figures/Tables 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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