Blocking of two-electron reduction of non-charged species in the absence of supporting electrolyte at nanoelectrodes

1,4-Benzoquinone (BQ) and tetracyanoquinodimethane (TCNQ), which are reduced consecutively to mono-anions and dianions under conventionally voltammetric conditions, cannot be reduced up to the dianions without supporting electrolyte in acetonitrile solution. Effects of the IR-drop and the electrostatic force in low concentrations of supporting electrolyte are examined by use of the first reduction waves. They apply to the analysis of the second waves. Voltammograms without supporting electrolyte at microelectrodes with the diameters less than 0.4 μm do not include noticeably IR-drop. The large overpotential for the anions cannot be explained in terms of the electric migration which has been estimated from solutions of the Nernst–Planck equation and the Laplace equation. With an increase in the conductivity of the solution by addition of electrolyte, the second reduction wave appears, involving the potential shift. The electrolyte does not influence the first reduction waves but varies the second one. The salt effect specific to the second wave is ascribed to non-stoichiometric association of the redox anion with the salt cation.