SOLID-STATE ANALYTICAL CHARACTERIZATION OF ELECTROCHEMICALLY MODIFIED GLASSY-CARBON ELECTRODES

Glassy carbon electrodes were electrochemically modified in sulfate, phosphate and carbonate media (and attempts at modification were tried in perchlorate media) by cycling to high positive potentials, yielding electrodes capable of incorporating cations. Unmodified and modified electrodes (with and without ruthenium-hexaammine or copper-tetraammine incorporation) were examined by scanning electrode microscopy (SEM), energy dispersive x-ray analysis (EDX), secondary ion mass spectrometry (SIMS) and x-ray photoelectron spectroscopy (XPS). Examination of electrodes by SEM has shown that the sulfate-modified electrodes contained irregularly shaped regions (ca. 2-20-mu-m in size and < 5% of total area) that disappeared on uptake of the Ru or Cu complexes. EDX and SIMS revealed these areas contained large amounts of sulfur and sulfate, respectively. The use of SIMS also indicated that the modified electrodes had been altered to a depth of 100-300 nm (for electrodes cycled for 10 min). Also, XPS of the carbon core-level spectra for modified electrodes showed varying extents of functionalization depending on the modification media. However, on incorporation of redox active cations, the surface appeared less oxidized. The mechanism and structure for the formation of modified electrodes are discussed.