Redox Reaction on the Surface/Edge Strturtures of Graphene/Graphite

Graphene, a single atomic layer of graphite, has been widely studied because of its unique electrical, optical, electrochemical, and elastic properties. With respect to the electrochemical property, it is also expected for energy harvesting and storage applications such as hydrogen generation for fuel cells and ion transport for secondary batteries. Indeed, the graphene’s exotic phenomena come from its ideal structure such as edge states, two-dimensional surface, defects. To understand their intrinsic mechanism due to structure effects, it is required to analyze and visualize their electrochemical reaction by a spatially resolved electrochemical analysis technique at microscopic scale. In general, electrochemical analytical tools are conducted at mesoscopic scale. Scanning probe microscopies have been also utilized for analyzing their properties to satisfy the issue in resolution. Scanning tunneling microscopy and conductive atomic force microscopy can analyze at atomic scale precisely, but their information is mainly limited to electronic properties which do not directly reflect to their electrochemical properties. In this study, to overcome the issue, scanning electrochemical cell microscopy with sub-micrometer resolution, i.e. nanoSECCM, was utilized as a direct technique for electrochemical reactions [1]. A glass nano-pipette was applied as a probe. The pipettes were filled electrolyte and a reference electrode (5 mM hexaammineruthenium chloride and 25 mM KCl in phosphate buffer or deionized water for electrolyte, Ag/AgCl for a reference electrode). The nanoSECCM was applied to cleaved graphite or graphene on silicon substrates. When the pipette was approached to the sample surface, a meniscus was created as an electrochemical cell. Through the cell, redox reaction of ruthenium ion inside electrolyte was measured. By scanning the pipette with the same process at next measurement location, redox reaction on the graphene/graphite surface were visualized as shown in Fig 1. [1] Y. Takahashi, A. Kumatani et al. Nat. Comm. 5:6450 (2014). Figure 1