Electrochemistry in a drop: a study of the electrochemical behaviour of mechanically exfoliated graphene on photoresist coated silicon substrate†
A micro apparatus for electrochemical studies on individual high quality graphene flakes is presented. A microinjection-micromanipulator system has been employed to deposit droplets of aqueous solutions containing redox-active species directly on selected micro-scale areas of mechanically exfoliated graphene layers on polymer coated silicon wafers. This approach allows the clear distinction between the electrochemical activity of pristine basal planes and the edges (defects) or steps to be measured. Voltammetric measurements were performed in a two-electrode configuration, and the standard heterogeneous electron transfer rate (k°) for reduction of hexachloroiridate (IrCl62−) was estimated. The kinetics of electron transfer were evaluated for several types of graphene: mono, bi, and few layer basal planes, and the k° was estimated for an edge/step between two few layer graphene flakes. As a comparison, the kinetic behaviour of graphite basal planes was measured for the deposited aqueous droplets. The appearance of ruptures on the graphene monolayer was observed after deposition of the aqueous solution for the case of graphene on a bare silicon/silicon oxide substrate.