M-H. Choi, S-J. Cho, L.A. Baker, S. Kaemmer
Park Systems inc.,
Keywords: HOPG, SECCM, Local Electrochemical Activity
Summary:HOPG is a popular substrate for scanning probe microscopy (SPM) research due to its flatness, uniformity, and ordered layered structure. It is used in various SPM techniques, including Scanning Tunneling and Atomic Force Microscopy. HOPG has been extensively used as a model electrode substrate for developing and optimizing electrocatalytic materials and reactions, playing a key role in energy conversion processes.1-4 The highly ordered structure and high electrical conductivity of HOPG make it an ideal substrate for investigating electrocatalysis at the atomic and molecular level. By studying the electrochemical behavior, one can gain insights into the fundamental mechanisms of electrocatalysis and design more efficient catalysts for various applications. From a microscopic viewpoint, the basal plane and edge of the HOPG surface exhibit heterogeneous electro- and electrocatalytic characteristics due to differences in their electronic and structural properties.5 Conventionally, scanning electrochemical microscopy (SECM) is employed to study the electrochemical heterogeneity at a surface allowing for the visualization of electrochemical processes 6 By using a microelectrode probe, SECM measures the electrochemical activity of local areas, providing information of electrocatalytic properties. Subsequently, the development of scanning electrochemical cell microscopy (SECCM) by the Unwin group has significantly advanced the field.7,8,9 SECCM offers higher spatial resolution measurements compared to SECM, which can only provide information on the average electrochemical activity over a local area due to its in-situ imaging principle. This is achieved by using a small meniscus formed at the pipette tip as a probe and electrochemical cell, allowing for precise delivery of reactants to a specific location on the surface. The map of electrochemical activity measured by SECCM was correlated with AFM topography to identify the step edge from the basal plane where showed a higher electrochemical activity on the HOPG.8 This study demonstrates the visualization of the heterogeneity in the electrochemical activities of HOPG using a customized SECCM setup which allowed for the simultaneous acquisition of topography and electrochemical activity maps.10. The HOPG grade 2 uses in this study possesses an intermediate quality between grade 1 and 3 making it suitable for both extensive use and high-resolution imaging purposes. Series of electrochemical maps at different potential applied to HOPG substrate were acquired by operating SECCM in AC-mode. Details will be discussed in the poster.