Correlative SECCM and AFM Microscopy Study of Local Electrochemical Activity in HOPG
Authors: Choi Myunghoon(Brian) , Schoenek Ben , Min Gilbert , Kaemmer Stefan 
Published: December 2024

Highly-oriented pyrolytic graphite (HOPG) is a favored substrate in scanning probe microscopy (SPM) research due to its flatness, uniformity,and structured layers. Extensively employed as a model electrode substrate, HOPG facilitates the development and optimization of electrocatalytic materials and reactionsthat are crucial in driving energy conversion processes.1-4 HOPG's exceptional structural organization and electrical conductivity position it as an ideal substrate for investigating electrocatalysis at the atomic and molecular scale. At the microscopic level, the basal plane and edges of the HOPG surface reveal heterogeneous electro- and electrocatalytic traits owing to variances in their electronic and structural attributes.5

Scanning electrochemical cell microscopy (SECCM) is a valuable technique for investigating behavior at atomic-scale structural features (such as defects and step edges) and their electrochemical activities within two-dimensional (2D) materials.6,7,8,9 SECCM allows for localized cyclic voltammetry (CV) measurements on with higher spatial resolution. This is achieved by using a small meniscus formed at the pipette tip as both a probe and an electrochemical cell. This confined volume enables precise delivery of reactants to a specific location on the surface. Previously, maps of electrochemical activity measured by SECCM were co-localized with AFM topography to identify the step edge from the basal plane with higher electrochemical activity on HOPG.8 SECCM leaves behind electrolyte residue “footprints” that indicate the size of the electrode formed by individual electrolyte contact events on the surface of 2D material. Atomic force microscopy (AFM) topography enables precise estimation of footprint dimensions. These footprints vary due to differences in electrolyte dispersity resulting from hydrophobic or hydrophilic interactions and surface geometry.10

This study demonstrates the qualitative investigation of the heterogeneity in the electrochemical activities of HOPG using correlative SECCM and AFM microscopy. Estimation of the electrode for each cyclic voltammetry from SECCM allows for accurate current density calculations, improving standardization in electrochemical analysis. Understanding the variation in footprints assists in the selective quantification and qualification of SECCM data from a metrological standpoint. This highlights the importance of not simply assuming that footprints are identical in size to pipette tips. More details will be discussed in the poster.
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