Localized Spectroelectrochemical Identification of Basal Plane and Defect-Related Charge-Transfer Processes in Graphene

It is well-known that structural defects play a decisive role in electrochemical behavior of atomically thin materials, where all the defects are directly accessible by the electrolyte. However, the vast majority of experimental techniques do not allow disentanglement of the processes at the edges/defects from those at the intact basal plane. Therefore, to address this issue, we introduce a localized spectroelectrochemical method featuring a microdroplet electrochemical cell with simultaneous Raman spectroscopy monitoring. The electrochemical and spectral responses of the basal planes of monolayer graphene samples with varying levels of disorder were compared. Two contributions, stemming from the intact and defective areas on the surface, respectively, were discovered both in the Raman G band shifts and cyclic voltammetry using the hexaammineruthenium complex. Consequently, two independent electron transfer processes of slower and faster rates coexist in one sample, but they are restricted to the defect-free and defect-rich areas, respectively.