Graphene Nanoelectrodes: Fabrication and Size-Dependent Electrochemistry

Abstract

The fabrication and electrochemistry of a new class of graphene electrodes are presented. Through high-temperature annealing of hydrazine-reduced graphene oxides followed by high-speed centrifugation and size-selected ultrafiltration, flakes of reduced graphene oxides (r-GOs) of nanometer and submicrometer dimensions, respectively, are obtained and separated from the larger ones. Using n-dodecanethiol-modified Au ultramicroelectrodes of appropriately small sizes, quick dipping in dilute suspensions of these small r-GOs allows attachment of only a single flake on the thiol monolayer. The electrodes thus fabricated are used to study the heterogeneous electron transfer (ET) kinetics at r-GOs and the nanoscopic charge transport dynamics at electrochemical interfaces. The r-GOs are found to exhibit similarly high activity for electrochemical ET reactions to metal electrodes. Voltammetric analysis for the relatively slow ET reaction of Fe(CN)6(3-) reduction produces slightly higher ET rate constants at r-GOs of nanometer sizes than at large ones. These ET kinetic features are in accordance with the defect-dominant nature of the r-GOs and the increased defect density in the nanometer-sized flakes as revealed by Raman spectroscopic measurements. The voltammetric enhancement and inhibition for the reduction of Ru(NH3)6(3+) and Fe(CN)6(3-), respectively, at r-GO flakes of submicrometer and nanometer dimensions upon removal of supporting electrolyte are found to significantly deviate in magnitude from those predicted by the electroneutrality-based electromigration theory, which may evidence the increased penetration of the diffuse double layer into the mass transport layer at nanoscopic electrochemical interfaces.

Electrochemistry at highly oriented pyrolytic graphite (HOPG): lower limit for the kinetics of outer-sphere redox processes and general implications for electron transfer models

“…Although it was suggested that the higher k 0 for Ru(NH 3 ) 6 3+/2+ on Pt compared to macroscopic electrodes could be due to diffuse double layer (Frumkin) effects, which may be more pronounced on nanoscale electrodes, 78 it is interesting to note that the highest reported k 0 values for Ru(NH 3 ) 6 3+/2+ on distinctly different electrodes are -in fact -rather similar, e.g. 10 ± 5 cm s -1 on metallic single walled carbon nanotubes, 49 9 cm s -1 on the basal surface of HOPG (free from defects), 8 9 -10 cm s -1 on reduced graphene oxide, 78 13.5 ± 2 cm s -1 on Au and 17.0 ± 0.9 cm s -1 on Pt.…”

“…10 ± 5 cm s -1 on metallic single walled carbon nanotubes, 49 9 cm s -1 on the basal surface of HOPG (free from defects), 8 9 -10 cm s -1 on reduced graphene oxide, 78 13.5 ± 2 cm s -1 on Au and 17.0 ± 0.9 cm s -1 on Pt. 103 This similarity in values is especially striking in view of the large difference in DOS, electronic structure and the different electrode configurations studied experimentally.…”

Autophagic flux induced by graphene oxide has a neuroprotective effect against human prion protein fragments

“…15,18,20,[22][23][24] Significantly, GO has abundant oxygen functional groups, including hydroxyl, epoxy, carbonyl, and carboxyl groups. 25 The effect of GO can be modulated by modification of its oxygen moieties as well as altering chemical functionality on graphene layers. 25 Some studies suggest that GO promotes differentiation of neural stem cells and neural outgrowth.…”

Time-Resolved Detection and Analysis of Single Nanoparticle Electrocatalytic Impacts

“…[1][2][3] An interesting approach for observing the electrochemical properties of catalytic NPs is to monitor their impact (or landing) from solution onto a collector electrode, as introduced by Bard et al, 4,5 and developed by several groups. [6][7][8][9][10][11][12] In order to resolve such impacts, the use of a small-sized ultramicroelectrode (UME) is mandatory to reduce both background currents and the impact frequency.…”