Scanning electrochemical microscopy: theory and application of the transient (chronoamperometric) SECM response.

A study of the transient (chronoamperometric) response of the scanning electrochemical microscope (SECM) is presented. SECM transients were simulated digitally with a novel integrator based on a Krylov algorithm. The transients observed with planar electrodes (PE), microdisks (MD), and thin-layer cells (TLC) are shown to be limiting cases that fit the simulated SECM transients at very short, intermediate, and long times, respectively. A procedure is established that, provided the tip radius is known, allows the determination of the diffusion coefficient of the species in solution independent of its concentration and the number of electrons transferred in the electrode reaction. Experimental SECM transients are reported for the electrochemical oxidation of Fe(CN)6(4-) in KCl; the diffusion coefficient of Fe(CN)6(4-) was found to agree very well with the literature value.