Apr 20th, 1:00 PM - 4:00 PM
Intercalation Process of Acidic Ions into Graphite Atomic Steps Studied by Electrochemical-Scanning Tunneling Microscopy
Highly oriented pyrolitic graphite (HOPG) and perchloric acid (HClO4) were adopted as a model host and a model guest, respectively, in graphite intercalation compounds. In this type of compound, the graphite layers of HOPG remain largely intact and the guest molecules of perchloric acid are located in between. We investigate the electrochemical anion intercalation process in the graphite layer by using cyclic voltammetry and electrochemical scanning tunneling microscopy (EC-STM) to understand the interaction between the host and the guest. The cyclic voltammetry data shows four peaks at the potentials of working electrode between 0V and 1.0 V with respect to the silver quasi reference electrode (Ag-Qref) in a 2M solution. The data suggests that the intercalation process has four different stages in which each stage compound has different ratio between the host layer and the guest ions. Every host layer is not necessarily occupied by guest ions between two graphite layers in the graphite intercalation compound. EC-STM was performed subsequently in the same electrochemical cell to obtain topographic information for each stage. The change of step height between two terraces of the HOPG surface supports this intercalation process. Further cyclic voltammetry measurements were performed over several potential scan cycles on the graphite surface as a function of the acid concentration from 0.1 M to 6 M with varying scan rates from 10 mV/s to 1000 mV/s to see the concentration dependence and the response time for the intercalation reaction. The cyclo-voltammetry and EC-STM data of gold (Au) sample in 0.05 M solution of sulfuric acid (H2SO4) will be discussed as a comparison system.