Probing Graphene Interfacial Reactivity via Simultaneous and Colocalized Raman-Scanning Electrochemical Microscopy Imaging and Interrogation.

Abstract

Addressing challenges in interfacial electrochemistry requires multimodal approaches that correlate the local structure and reactivity of materials with high spatial and temporal versatility. Here, we introduce spatiotemporally correlated Raman spectroscopy and scanning electrochemical microscopy (SECM) to study the impact that structural heterogeneities, interfacial decomposition products, and layer number have on the electron-transfer properties of graphene electrodes. By colocalizing the SECM probe and laser line, we successfully obtained congruent SECM and Raman images at a rate of 5 s per pixel with sub-10 μm resolution, obtaining full spectra per pixel at a signal-to-noise ratio as high as ∼20. SECM imaging of a micropatterned graphene electrode showed its reactivity to be highly dependent on the intensity of the G peak, an indicator of the number of graphene layers. We further monitored the impact of excursions to positive potentials using the [Fe(CN)6]3-/4- redox pair as mediator. Raman-SECM allowed us to decouple the contributions to the redox response of different structural effects including exfoliation, increase in defect density, and surface film formation, on the same site and in real time. The coupling of in situ Raman spectroscopy and SECM provides a powerful surface-sensitive analytical approach to elucidate interfacial properties relevant to energy, catalysis, and sensing.