Abstract
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.
Highlights
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
The sample preparation and treatment is defining for the electrochemistry of graphene, which is extremely sensitive to adventitious contamination, surface type, and domain size.[6,7]
The best example of such a discrepancy is the dependence of the electron transfer kinetics on the number of graphene layers: increase, decrease, as well as independence were all argued for.[8−10] Sample heterogeneity can be efficiently tackled using a measurement in a microdroplet electrochemical cell, which facilitates electrochemical characterization or electrolyte gating of precisely defined surface regions.[11]
Summary
This comparison corroborates the general understanding of the electron transfer kinetics on graphene/ graphite: the defect-free basal plane, approximated here by the pristine exfoliated graphene with k0 of 0.8 × 10−4 cm s−1 has slower kinetics than defected surfaces, approximated here by the CVD graphene with k0 of 1.8 × 10−4 cm s−1. The differing behavior of the two surface types manifests in the Raman spectral response by an apparent G band splitting with the applied potential, as well as in the cyclic voltammograms using an outer-sphere redox mediator Both observations point to different charge transfer processes with varying rates, which take place at the defect-free and defect-rich regions at the surface.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
