Abstract This work reports the electrochemical properties of graphene supercapacitors that employ flexible graphene electrodes (FGEs) coated by V2O5 (VOx) or carbon nanotubes (CNTs)/VOx layers. According to scanning electron microscopy images, the morphology of VOx consists in micro-ribbons with lengths of 20–45 μm and widths from 5 to 12 μm. The CNTs form interconnected long fibers, which were functionalized with carboxylic groups for producing defects. We demonstrated that the gel electrolyte used for the supercapacitors produces V4+-oxygen vacancies (VO) defects. Both, the CNTs and V4+-VO defects act as redox centers, which delay the current discharge in the supercapacitors. The presence of the carboxylic groups, defects in CNTs, defects in VOx, and oxidation states (V4+ and V5+), were confirmed by the UV–Vis, XPS, and FTIR techniques. The electrochemical characterization of the supercapacitors indicated that the devices made with FGEs coated by VOx or CNTs/VOx layers produced constant voltages of 0.14 V and 0.38 V during 535 and 593 min, respectively. The increase of voltage is explained by the increase of surface area and by the extra redox centers (defects) introduced by the CNTs. The results indicated that the CNTs/VOx layer increases the voltage and discharge times of the graphene supercapacitors, which can be of interest for the development of graphene systems with high charge storage capabilities.

中文翻译：

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提高石墨烯超级电容器在其电极上沉积 CNT/V2O5 层的电压和放电时间

摘要 这项工作报告了石墨烯超级电容器的电化学特性，该电容器采用由 V2O5 (VOx) 或碳纳米管 (CNT)/VOx 层涂覆的柔性石墨烯电极 (FGE)。根据扫描电子显微镜图像，VOx 的形态包括长度为 20-45 μm、宽度为 5-12 μm 的微带。碳纳米管形成相互连接的长纤维，这些长纤维被羧基官能化以产生缺陷。我们证明了用于超级电容器的凝胶电解质会产生 V4+-氧空位 (VO) 缺陷。CNT 和 V4+-VO 缺陷都充当氧化还原中心，延迟超级电容器中的电流放电。UV-Vis、XPS 和 FTIR 技术证实了羧基的存在、CNT 中的缺陷、VOx 中的缺陷和氧化态（V4+ 和 V5+）。超级电容器的电化学特性表明，用 VOx 或 CNTs/VOx 层涂覆的 FGE 制成的装置分别在 535 和 593 分钟内产生了 0.14 V 和 0.38 V 的恒定电压。电压的增加可以通过表面积的增加和由 CNT 引入的额外氧化还原中心（缺陷）来解释。结果表明，CNTs/VOx 层增加了石墨烯超级电容器的电压和放电时间，这对于开发具有高电荷存储能力的石墨烯系统很有意义。电压的增加可以通过表面积的增加和由 CNT 引入的额外氧化还原中心（缺陷）来解释。结果表明，CNTs/VOx 层增加了石墨烯超级电容器的电压和放电时间，这对于开发具有高电荷存储能力的石墨烯系统很有意义。电压的增加可以通过表面积的增加和由 CNT 引入的额外氧化还原中心（缺陷）来解释。结果表明，CNTs/VOx 层增加了石墨烯超级电容器的电压和放电时间，这对于开发具有高电荷存储能力的石墨烯系统很有意义。