Scanning Electrochemical Microscopy in Substrate Generator/Tip Collector Mode

Scanning electrochemical microscopy (SECM) has two principal modes of operation: feedback mode and generator/collector mode. When the substrate is the generator and the tip microelectrode is the collector, this is designated substrate generator/tip collector mode (SG/TC). This Demonstration shows the current at the tip and the concentration profile as functions of the tip-substrate distance and time.

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At the substrate, oxidation takes place: . The resulting oxidant will diffuse in one dimension according to the PDE equation: = ,
with initial and boundary conditions: , ; , ; , . is the concentration of the reduced form, , while for the oxidized form, .
At the tip microelectrode, reduction takes place: . When the tip (the red electrode) moves close to the substrate, it can capture more so that the current is increased.
Note that positive feedback effect is not considered here. The increase of tip current depends only on the gradient of the concentration profile.
For further information, see: A. J. Bard and M. V. Mirkin, eds., Scanning Electrochemical Microscopy, 2nd ed., New York: CRC Press, 2001.
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