Shielding of a Microdisc Electrode Surrounded by an Adsorbing Surface

Microdisc electrodes are usually made by surrounding a metal wire with a diameter of a few microns in a flat insulating sheath made of glass or another insulating material. The sheath is generally assumed to play no role in the voltammetry at the microdisc electrode. However, in some cases, and especially for experiments with nanoparticles, significant adsorption can occur onto the sheath, perturbing the current response measured at the disc. We report theoretical calculations of the effect of shielding by the insulating sheath of microelectrodes and show that it can significantly influence the magnitude of the current, even for relatively small levels of adsorption, not least because of the typically very large area of the insulation relative to the electrode size. Working curves are provided to permit the analysis of experimental data. Sheath shielding: It is shown that if significant adsorption occurs on the sheath used to insulate a microdisc electrode, then it can have a high impact on the measured current–time data because of a considerable shielding effect. Chronoamperograms are simulated as a function of the sheath‐to‐disc electrode radius ratio and the rate constant for adsorption onto the sheath.