Surface Interrogation with Hybrid Scanning Electrochemical Probe Microscopy for Quantitative Imaging of Adsorbed Hydrogen

Abstract Surface-interrogation scanning electrochemical microscopy (SI-SECM) can quantify adsorbed electrocatalytic intermediates by transient redox titration, but conventional implementations require a probe/substrate size match and are therefore largely restricted to point interrogation. Here, we develop surface-interrogation SECM implemented in an SECCM-confined local cell (SCSI-SECM) within an integrated SECCM-SECM architecture. In this method, a localized SECCM meniscus defines the wetted substrate area, while an integrated carbon electrode performs mediator-based surface-interrogation readout. Using adsorbed hydrogen (Hads) on polycrystalline Pt as a model intermediate, we validate the approach by finite-element simulation, feedback-mode characterization, and single-point SCSI-SECM measurements. Correlative SCSI-SECM and electron backscatter diffraction (EBSD) imaging further resolves crystallographic variations in local Hads charge density on polycrystalline Pt. This strategy preserves the quantitative strength of SI-SECM while adding microscale spatial resolution, providing a route for mapping surface intermediates at heterogeneous electrocatalytic interfaces.