When graphene meets electrolyte: how does graphene sense proton (H⁺)?

Graphene has been extensively used as electrodes in electrochemical applications [1,2,3]. Despite its relevance for these various applications of graphene, the effect of electrolyte solutions on the electronic properties, specifically conductivity, of graphene remains poorly understood. In the few available studies using graphene field effect transistors (FETs) for ionic sensing, conflicting results have been reported [4,5]. One major challenge is to separate contributions to the overall FET conductance from bulk electrolyte conductivity and from graphene itself, as the FET contacts are typically also exposed to the electrolyte. Here we introduce THz spectroscopy as a contact-free, all optical means to track the intrinsic carrier conductivity of silica-graphene in contact with protons (H⁺) in water. Our report provides new insight on the graphene’s proton sensing mechanism, and highlights the importance and impact of proton transfer though graphene and interfacial charge screening on the graphene conductivity enhancement.


References
1 G. Kucinskis et al J. Power Sources 240, 66 (2013).
2 X. Wang et al Nano Lett. 8, 323 (2008).
3 Z. Wenig et al Adv. Energy Mater. 1, 917 (2011).
4 P. K. Ang et al J. Am. Chem. Soc. 130, 14392 (2008).
5 W. Fu et al Nano Lett. 11, 3597 (2011).