(30d) High Resolution Measurement of Potential-Dependent Electrochemical Activities on HOPG Using Scanning Electrochemical Cell Microscopy (SECCM)

HOPG is widely used as a substrate for scanning probe microscopy (SPM) research due to its flatness, uniformity, and ordered layered structure, making it ideal for various SPM techniques such as Scanning Tunneling and Atomic Force Microscopy. It is also commonly used as a model electrode substrate for developing and optimizing electrocatalytic materials and reactions, playing a vital role in energy conversion processes. HOPG's highly ordered structure and high electrical conductivity make it an excellent substrate for investigating electrocatalysis at the atomic and molecular level, providing insights into the fundamental mechanisms of electrocatalysis and designing more efficient catalysts for various applications. However, the HOPG surface exhibits heterogeneous electro- and electrocatalytic characteristics on its basal plane and edge due to differences in their electronic and structural properties.

Traditionally, scanning electrochemical microscopy (SECM) is employed to study the electrochemical heterogeneity at a surface, allowing for the visualization of electrochemical processes. SECM measures the electrochemical activity of local areas using a microelectrode probe, providing information on the electrocatalytic properties. However, the Unwin group has developed scanning electrochemical cell microscopy (SECCM), which offers higher spatial resolution measurements than SECM. SECCM achieves this by using a small meniscus formed at the pipette tip as a probe and electrochemical cell, enabling precise delivery of reactants to a specific location on the surface. The map of electrochemical activity measured by SECCM is correlated with AFM topography to identify the step edge from the basal plane, which exhibits higher electrochemical activity on the HOPG.

In this study, the heterogeneity in the electrochemical activities of HOPG was visualized using a customized SECCM setup that allowed for the simultaneous acquisition of topography and electrochemical activity maps. The HOPG grade 2 substrate used in this study possesses an intermediate quality suitable for both extensive use and high-resolution imaging purposes. A series of electrochemical maps at different potentials applied to the HOPG substrate were acquired by operating SECCM in AC-mode. Further details will be discussed in the poster.