Comparative Study of Screen-Printed Electrodes Modified with Graphene Oxides Reduced by a Constant Current

Abstract

A comparative study of several screen-printed electrodes modified with electrochemically reduced graphene oxides (ERGO) by means of a constant current has been carried out. The ERGOs were produced from graphene oxides (GO) with different controlled functional groups contents and locations. The experimental reduction conditions were optimized for each particular GO to generate ERGO-modified electrodes with the aim of improving the performance of the dopamine redox process. The ERGO-modified electrodes exhibited a larger electroactive area, a higher reversibility of the redox process, faster kinetics, and greater double-layer capacitance. Analysis of the reduction degree and residual functional groups by means of X-ray photoelectron spectroscopy (XPS) after and before reduction enabled us to determine the relation between the electrochemical behavior and morphology of the electrodes. A hydrazine-reduced graphene oxide showed the best analytical performance with a higher sensitivity (0.259 μA/μM vs. 0.090 μA/μM in the case of a bare electrode), and a linear range from 1-100 μM. It was found that both the experimental reduction conditions and starting graphene material are critical for obtaining a modified electrode with a suitable electrochemical behavior and properties and that a constant current is a suitable technique for the reduction of graphene oxides, especially for screen-printed electrodes.Graphene, a two-dimensional carbon material with highly useful properties including a large surface area and high mechanical, thermal and chemical stabilities, has emerged as a very interesting material for electrochemical applications, especially in (bio)sensors due to its excellent properties such as high electron conductivity, fast heterogeneous electron-transfer rate at the graphene sheet edges and basalplane defect sites, large surface area and good biocompability. 1-4 The most suitable graphene material for modifying electrochemical sensors is graphene oxide (GO) due to its high capacity to be dispersed in aqueous solvents that allows a more efficient electrode modification. GO is usually produced by the oxidation of graphite, a methodology based on the Hummers 5 or Brodie method, 6 which is considered to be the best alternative for the preparation of graphene on a large scale. 7 Additionally, the preparation of GO can be modified by using graphites with different crystalline structures or by different preparation methods 8 giving rise to graphene materials of different sheet size, structure and properties, variables that can also be tuned to improve the electrochemical performance of electrodes.Although several studies on GO improving electrode properties have been reported, 9,10 in most cases a previous GO reduction is carried out in order to decrease the number of oxygen-based functional groups to obtain better electrochemical properties. 11,12 And again the properties of the reduced graphene oxides are influenced not only by the parent GO but also by the reduction process followed. 13 Several authors have report...

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