Determination of electrochemical electron-transfer reaction standard rate constants at nanoelectrodes: Standard rate constants for ferrocenylmethyltrimethylammonium(III)/(II) and hexacyanoferrate(III)/(II)

The most common approximation of electroneutrality is inappropriate for analyzing the voltammetric response of nanoelectrodes. Therefore, the microelectrode theory for extracting the standard rate constant k(0) for electron transfer from steady-state voltammograms is invalid for nanoelectrodes. Unlike previous approaches, we considered the influence of the interfacial potential distribution caused by the absence of electroneutrality. We estimated the magnitude of the error at low overpotential incurred as a result of ignoring the absence of electroneutrality and found that it was small. In this region, electrochemical reaction appears to be limited by the rate of electron transfer. Under these conditions, k(0) can be obtained from steady-state voltammogram data in a low overpotential region according to an approximate form of the Butler-Volmer equation. This procedure can greatly simplify analysis and calculation of the rate constant k(0) at nanoelectrodes. Steady-state voltammogram of equal-concentration hexacyanoferrate(III)/(II) (Fe(CN)(6)(3-)/Fe(CN)(6)(4-)) and ferrocenylmethyltrimethylammonium(III)/(II) (FcTMA(2+)/FcTMA(+)) redox couples were investicated at Pt-Ir nanoelectrodes in the presence of a support electrolyte. k(0) for Fe(CN)(6)(3-)/Fe(CN)(6)(4-) and FcTMA(2+)/FcTMA(+) at Pt-Ir nanoelectrodes were evaluated.