Redox-Dependent Spatially Resolved Electrochemistry at Graphene and Graphite Step Edges
Redox-Dependent Spatially Resolved Electrochemistry at Graphene and Graphite Step Edges
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DOI：
10.1021/acsnano.5b00550
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发表时间：
2015-04-01
期刊：
影响因子：
17.1
通讯作者：
Unwin, Patrick R.
中科院分区：
文献类型：
--
作者：
Gueell, Aleix G.;Cuharuc, Anatolii S.;Unwin, Patrick R.
以Ru（NH3）（6）（3+/2+）为氧化还原探针，在水溶液中以高空间分辨率研究了机械剥离石墨烯和高取向热解石墨（HOPG）的电化学行为。当扫描电化学电池显微镜（SECCM）的数据与互补技术（原子力显微镜，显微拉曼）施加到相同的样品区域，不同的时间依赖性EC活动之间的基础平面和步骤的边缘被揭示。相比之下，其他氧化还原对（二茂铁衍生物），其电位进一步从石墨烯和石墨的本征费米能级移除，显示出均匀和高的活性（接近扩散控制）。在不同环境中的宏观伏安测量揭示了HOPG裂解后的时间依赖性行为，Ru（NH3）（2）（3+/2+）特有的，与任何表面污染物没有特别的关联，但合理地归因于HOPG随时间的自发分层以产生部分耦合的石墨烯层，进一步由导电AFM测量支持。该过程对石墨烯和石墨边缘的态密度有重大影响，特别是在Ru（NH3）（6）（3+/2+）最敏感的本征费米能级处。通过使用改进的SECCM伏安模式，我们产生了电位分辨和空间分辨HOPG活性的电影，揭示了在阶跃边缘增强的活性是如何对Ru（NH3）（6）（3+/2+）产生微妙的影响。这些后者的研究使我们能够提出一个微观模型来解释的EC响应的石墨烯（基面和边缘）和老化的HOPG考虑到非平凡的电子能带结构。
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)(6)(3+/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)(2)(3+/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)(6)(3+/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)(6)(3+/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.