Few-layer graphene via electrochemically cathodic exfoliation for micro-supercapacitors

doi:10.11949/0438-1157.20200259

Abstract

Abstract:

The use of graphite as a raw material for efficient, green, and low-cost preparation of few-layer graphene is of great significance for the large-scale production and application of graphene. However, the efficient exfoliation of graphite to graphene without use of strong oxidants and acids is still a great challenge. Herein, we developed a green and scalable aqueous-based electrochemical cathodic exfoliation approach, in which graphite as negative electrode can be electrochemically charged and expanded in an electrolyte of 6 mol·L^-1 potassium hydroxide (KOH) under high current density and exfoliated efficiently into few-layer graphene sheets with the aid of sonication. The obtained few-layer graphene has low oxygen content [1.27% (mass)], few defects (I_D/I_G <0.035), a plate size of 5—10 μm, high conductivity of >200 S·cm^-1, and good solution additivity. Moreover, such electrochemically exfoliated graphene (EG) nanosheets are readily used to produce highly solution-processable ink (1 mg·ml^-1) in ethanol without the need of any surfactants, allowing for the production of large-area EG microelectrodes for EG based micro-supercapacitors (EG-MSCs). Furthermore, the as-fabricated aqueous EG-MSCs show ultrahigh scan rate of 100000 mV·s^-1 and short time constant of only 24 ms. More importantly, using ionic liquids-based electrolyte of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide with bis(trifluoromethanesulfonyl)imide lithium salt (EMIMTFSI/LiTFSI), EG-MSCs can work at a high voltage of 4.0 V, and show high volumetric energy density of 113 mW·h·cm^-3, outperforming the most reported MSCs (<50 mW·h·cm^-3).

Key words: electrochemical, cathode exfoliation, graphene, graphite, micro-supercapacitors

摘要：

以石墨为原料高效、绿色、低成本制备少层石墨烯，对石墨烯的规模化生产和应用具有非常重要的意义。电化学阴极剥离法是一种高效制备少层石墨烯的方法，但已有的报道均采用有机溶液体系，成本高且不够绿色环保。开发了一种绿色的水溶液电化学剥离方法，在6 mol·L^-1 KOH溶液中，将石墨作为阴极进行快速剥离制备出少层石墨烯。获得的少层石墨烯具有含氧量低[1.27%(质量)]、缺陷少(I_D/I_G< 0.035)、片径尺寸为5~10 μm、高电导率(大于200 S·cm^-1)以及良好溶液可加性等特点。基于此，采用叉指型掩模板辅助过滤的方法可以高效制备出图案化石墨烯基平面微电极，在硫酸-聚乙烯醇凝胶电解液中，构筑的准固态微型电容器在没有金属集流体存在的情况下，表现出高扫描速率，达到了100000 mV·s^-1，弛豫时间常数低至24 ms；以1-乙基-3甲基-咪唑双(三氟甲基磺酰基)亚胺和双(三氟甲基磺酰基)亚胺锂盐的混合液为电解液，所构建的微型超级电容器的工作电压达4.0 V，体积能量密度为113 mW·h·cm^-3，远高于目前报道的微型超级电容器的电化学性能(<50 mW·h·cm^-3)。

关键词: 电化学, 阴极剥离, 石墨烯, 石墨, 微型超级电容器

CLC Number:

TQ 028.8

Feng ZHOU, Lijun TIAN, Lei GAO, Zhongshuai WU. Few-layer graphene via electrochemically cathodic exfoliation for micro-supercapacitors[J]. CIESC Journal, 2020, 71(6): 2724-2734.

周锋, 田利军, 高磊, 吴忠帅. 电化学阴极剥离制备少层石墨烯及其微型超级电容器[J]. 化工学报, 2020, 71(6): 2724-2734.

Figures/Tables 11

Fig.1 Schematic diagram of electrochemical exfoliation cell

Fig.2 Photograph of the exfoliated graphite flakes after electrochemical exfoliation

Fig.3 Schematic of the fabrication of EG-MSCs

Table 1 Summary of electrolytes investigated in the electrochemical cathodic exfoliation of graphite

电解质	浓度	槽电压/V	时间/min	结果
氢氧化钾	6 mol·L^-1	10	30	高效剥离
氢氧化钾	3 mol·L^-1	10	30	低效剥离
氢氧化钾	0.5 mol·L^-1	10	30	无剥离
氢氧化钠	6 mol·L^-1	10	30	高效剥离
硫酸钠	饱和	10	30	无剥离
氯化钾	饱和	10	30	有效剥离
溴化钾	饱和	10	30	有效剥离
碘化钾	6 mol·L^-1	10	30	高效剥离

Fig.5 TEM image of EG

Fig.4 SEM image of EG

Table 2 EDS of EG

Element	Mass/%	Atomic/%
C	98.45	98.95
O	1.27	0.96
K	0.28	0.09

Fig.6 AFM, Raman and XRD pattern of EG

Fig.7 Electrochemical characterization of EG-MSCs in PVA-H2SO4

Fig.8 Electrochemical characterization of EG-MSCs in ionic liquids

Fig.9 Electrochemical characterization of EG-MSCs in EMIMTFSI+LiTFSI

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