Patterning and Imaging of Oxides on Glassy Carbon Electrode Surfaces by Scanning Electrochemical Microscopy

Abstract

The scanning electrochemical microscope (SECM) is used to form and characterize patterns of oxides on glassy carbon (GC) surfaces. Chemically specific imaging of oxides present on these surfaces was demonstrated by taking advantage of differential heterogeneous electron-transfer rates for the Fe(II/III) reaction occurring at unoxidized and oxidized GC electrodes. Localized generation of surface oxides was demonstrated using both the microreagent and direct modification modes of the SECM. The microreagent mode was used to perform a chemical oxidation of the surface by generating the strong oxidant Ag(II) at the ultramicroelectrode tip while positioned close to the carbon surface. However, this technique had poor reproducibility. Direct mode oxidation was much more versatile toward generating complex patterns of oxides on carbon surfaces. The reproducibility of the direct mode technique depended heavily on the solution resistance. “Charge dose” studies, followed by reaction-rate imaging, qualitatively show that the electron-transfer rate for the Fe(II/III) system scales with the amount of charge “injected” in each oxidation experiment, indicating a correlation between surface oxide density and electron-transfer rate. © 2003 The Electrochemical Society. All rights reserved.