Interfacial capacitance of graphene: Correlated differential capacitance and in situ electrochemical Raman spectroscopy study

The origin of the low interfacial capacitance of carbon-based materials is a long standing puzzle. The space charge capacitance and the quantum capacitance models have been proposed to interpret the phenomena. However, the physical origin of the capacitance is still unclear. In this study, we performed the differential capacitance and in situ electrochemical Raman spectroscopic measurement of single layer graphene in aqueous solutions to study the origin of the interfacial capacitance of graphene. The capacitance was found to have a minimum value of ∼4.5 μF cm−2 in NaCl solutions and increased linearly with respect to both sides of the minimum. The Raman parameters of single layer graphene, including the frequency and band width of the G band, the frequency of the 2D band and the intensity ratio of 2D to G bands (I2D/IG), show the similar potential dependent behavior as the capacitance curve. The clear correlation between the Raman parameters and the capacitance can be understood by the same physical origin of carrier concentration (n) of graphene. This study shows that the carrier concentration is a decisive factor that determines the quantum capacitance and thus the total capacitance of graphene in the electrochemical systems.