全钒氧化还原液流电池用石墨毡电极的分步氧化活化

doi:10.13208/j.electrochem.190714

摘要/Abstract

摘要：

石墨毡电极是组成钒电池的关键材料,其较低的电化学活性是造成钒电池功率密度较低的关键因素之一. 本论文采用一种简便的石墨毡电极分步氧化活化法,先将石墨毡在高锰酸钾溶液中进行氧化,后置于活化溶液中激发其反应活性. 通过对处理后的石墨毡进行循环伏安、交流阻抗测试、XPS以及SEM表征,发现氧化时间和活化溶液组成是影响电极性能的因素,在本文中,先经过3天氧化时间,后在配比为3:1的活化溶液中处理的电极,较其他方法处理的电极,电荷传递电阻明显降低,其与溶液之间的接触电阻最低,为7.33 Ω·cm ²,氧化还原峰值比更接近于1,有效提高了反应的活性与可逆性,经X射线光电子能谱分析发现性能提高的原因与表面含氧官能团数目增加有关. 单电池性能测试结果进一步证实,利用该方法处理的石墨毡为电极的单电池,较未经处理的电池相比性能更优,有更高的放电容量和能量效率,在100 mA·cm ^-2电流密度下,能量效率较未处理电极高出7.47%. 与热处理法、酸处理法及电化学氧化法相比较,该方法不需要辅助设备,不消耗能源.

关键词: 钒电池, 石墨毡, 分步氧化活化, 反应活性

Abstract:

As a well-known electrode material of the vanadium redox flow battery (VRFB),graphite felt electrode is the frequently-used electrode material in VRFB, and its low electrochemical activity is one of the key factors for the low power density of VRFB. In this work, we proposed a step-by-step modification method, which used KMnO₄ to oxidize graphite felt first and then placed in an activation solution to excite its reactivity, to improve the electrochemical performance of the graphite felt electrode. According to the results from cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) characterizations of the treated graphite felts, it was found that the oxidation time and the composition of the activation solution are factors affecting the electrode performance. In this paper, the charge transfer resistance of the electrode treated in the activation solution with a volume ratio of H₂SO₄:H₂O₂ = 3:1 after oxidation in KMnO₄ for 3 days, was significantly lower than that of the electrode treated by other methods, showing the lowest contact resistance (7.33 Ω·cm ²). The redox peak current density ratio (I_pa/I_pc) was closer to 1, which effectively increased the activity and reversibility of the redox reactions. In addition, the XPS data showed that the excellent electrochemical performance of the treated graphite felt might be related to the increase in the number of surface oxygen-containing functional groups. The charge/discharge testing results demonstrated that the all-vanadium redox flow battery employing the modified graphite felt electrodes exhibited the enhanced performance with higher battery efficiency and favorable discharge capacity. Moreover, the all-vanadium redox flow battery with the treated graphite felt as an electrode delivered the energy efficiency of 7.47%, which was higher than that of the untreated electrode at a current density at 100 mA·cm ^-2. Compared with heat treatment, acid treatment and electrochemical oxidation, the step-by-step modification method requires no auxiliary equipment and consumes no energy.

Key words: vanadium redox flow battery, graphite felt, step-by-step modification, activity

中图分类号:

TM911
O646

娄景媛, 尤东江, 李雪菁. 全钒氧化还原液流电池用石墨毡电极的分步氧化活化[J]. 电化学（中英文）, 2020, 26(6): 876-884.

LOU Jing-yuan, YOU Dong-jiang, LI Xue-jing. Step-by-Step Modification of Graphite Felt Electrode for Vanadium Redox Flow Battery[J]. Journal of Electrochemistry, 2020, 26(6): 876-884.

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Sample	Oxidation time in KMnO₄/day	Mixed activation solution ratio/(V:V)
N	0	0
A1	1	3:1
A2	1	2:1
A3	1	1:1
B1	3	3:1
B2	3	2:1
B3	3	1:1

Sample	I_pa/(mA·cm^-2)	I_pc/(mA·cm^-2)	E_pa/V	E_pc/V	I_pa/I_pc
N	12.06	5.02	0.94	0.86	2.40
A1	36.60	24.50	0.94	0.88	1.49
A2	21.20	12.90	0.93	0.89	1.64
A3	17.96	7.48	0.93	0.87	2.39
B1	39.70	28.50	0.93	0.87	1.39
B2	36.15	25.78	0.92	0.82	1.40
B3	20.5	13.8	0.94	0.86	1.49

Sample	R_s/(Ω·cm²)	R₁/(Ω·cm²)	R₂/(Ω·cm²)
N	0.40	21.06	299.60
A1	0.32	10.64	255.90
A2	0.32	9.41	273.30
A3	0.33	11.41	266.50
B1	0.38	7.33	198.30
B2	0.34	10.64	203.30
B3	0.38	10.95	253.10

Sample	Atomic concentration/%		O1s/C1s
Sample	O1s	O1s	O1s/C1s
N	93.20	6.86	0.07
A1	73.12	27.88	0.39
A3	84.87	15.13	0.18
B1	58.60	41.40	0.71
B3	75.06	24.94	0.33

Current density/ (mA·cm^-2)	N			B1
Current density/ (mA·cm^-2)	CE/%	VE/%	EE/%	CE/%	VE/%	EE/%
50	92.61	80.55	74.59	95.93	84.27	80.84
80	94.58	69.67	65.90	96.61	74.84	72.30
100	95.19	61.90	58.92	97.33	68.21	66.39
150	-	-	-	98.55	52.82	52.05