Sb. Basame et Hs. White, Scanning electrochemical microscopy: Measurement of the current density atmicroscopic redox-active sites on titanium, J PHYS CH B, 102(49), 1998, pp. 9812-9819
Absolute values of the current density at microscopic electroactive sites o
n polycrystalline Ti electrodes have been measured with a scanning electroc
hemical microscope (SECM). The active sites on the oxide-film-coated Ti ele
ctrode have radii ranging from 3.3 to 28.6 mu m and are randomly distribute
d at a surface density of similar to 180 sites/cm(2). Localized current den
sities as large as 0.14 A/cm(2) are observed for the oxidation of Br- in aq
ueous solution, approximately 4 orders of magnitude larger than the average
current density based on the geometrical area of the electrode. Quantitati
ve analysis of large-area SECM images demonstrates that at least similar to
65% of the total current during Br- oxidation is associated with sites tha
t occupy a minuscule fraction (0.01-0.1%) of the total exposed electrode ar
ea. The SECM data also suggest that the rate of Br- oxidation approaches th
e diffusion-limited value at sites having radii less than similar to 10 mu
m; a precipitous decrease in the electron-transfer rate is observed at elec
troactive sites of slightly larger dimensions.