氧化还原依赖的石墨烯和石墨台阶边缘空间分辨电化学
Redox-Dependent Spatially Resolved Electrochemistry at Graphene and Graphite Step Edges
作者:Aleix G. Güell;Anatolii S. Cuharuc;Yang-Rae Kim;Guohui Zhang;Sze-yin Tan;Neil Ebejer;Patrick R. Unwin;
关键词:graphene,graphite,edges,electrochemistry,electron transfer,HOPG
DOI:https://doi.org/10.1021/acsnano.5b00550
发表时间:2015年
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摘要
在水溶液中,使用Ru(NH3)63 / 2作为氧化还原探针,研究了机械剥离的石墨烯和高度定向热解石墨(HOPG)的电化学(EC)行为,具有高空间分辨率。其标准电位接近于石墨烯和石墨的本征费米能级。当扫描电化学细胞显微镜(SECCM)数据与应用于同一样品区域的补充技术(原子力显微镜,微喇曼)相结合时,基面和台阶边缘之间显示出不同的时间相关的EC活性。相比之下,其他氧化还原偶(二茂铁衍生物)其电位与石墨烯和石墨的本征费米能级进一步分离,显示出uniform and high activity(接近扩散控制)。在不同环境中进行的宏观伏安法测量揭示了在HOPG剥离后的时间相关行为,不特别与任何表面污染物相关,而是合理地归因于HOPG随时间自发剥离来创建部分耦合的石墨层,由导电原子力显微镜测量进一步支持。这个过程对石墨烯和石墨边缘的态密度产生了重大影响,尤其是在Ru(NH3)63 / 2最敏感的本征费米能级。通过使用改进的SECCM伏安法模式,我们制作了HOPG活性的电位分辨和空间分辨片段,揭示了在Ru(NH3)63 / 2中台阶边缘的增强活性是微妙的效果。这些研究使我们能够提出一个微观模型来解释石墨烯(基面和边缘)和老化HOPG的EC响应,考虑到其非平凡的电子能带结构。
Abstract
The electrochemical (EC) behavior of mechanically exfoliated graphene and highly oriented pyrolytic graphite (HOPG) is studied at high spatial resolution in aqueous solutions using Ru(NH3)63+/2+ as a redox probe whose standard potential sits close to the intrinsic Fermi level of graphene and graphite. When scanning electrochemical cell microscopy (SECCM) data are coupled with that from complementary techniques (AFM, micro-Raman) applied to the same sample area, different time-dependent EC activity between the basal planes and step edges is revealed. In contrast, other redox couples (ferrocene derivatives) whose potential is further removed from the intrinsic Fermi level of graphene and graphite show uniform and high activity (close to diffusion-control). Macroscopic voltammetric measurements in different environments reveal that the time-dependent behavior after HOPG cleavage, peculiar to Ru(NH3)63+/2+, is not associated particularly with any surface contaminants but is reasonably attributed to the spontaneous delamination of the HOPG with time to create partially coupled graphene layers, further supported by conductive AFM measurements. This process has a major impact on the density of states of graphene and graphite edges, particularly at the intrinsic Fermi level to which Ru(NH3)63+/2+ is most sensitive. Through the use of an improved voltammetric mode of SECCM, we produce movies of potential-resolved and spatially resolved HOPG activity, revealing how enhanced activity at step edges is a subtle effect for Ru(NH3)63+/2+. These latter studies allow us to propose a microscopic model to interpret the EC response of graphene (basal plane and edges) and aged HOPG considering the nontrivial electronic band structure.
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