A simulation analysis of errors in the measurement of standard electrochemical rate constants from phase-selective impedance data

Abstract

A digital simulation analysis is presented of the coupled effects of solution resistance and lock-in amplifier damping upon the evaluation of standard rate constants, k s ob, for rapid electrode reactions using phase-selective ac impedance measurements with positive-feedback iR compensation. These two effects combine so to yield “apparent” (i.e. measured) rate constants, k s ob(app), evaluated using the conventional frequency-dependent analysis, that are generally smaller than the actual values, k s ob(true). The extent to which these systematic errors depend on experimental conditions is explored for various values of k s ob(true), the uncompensated and specific solution resistances, the amplifier filter time constant, the double-layer capacitance, and other relevant parameters. A simple scheme employing theses simultations is outlined by which k s ob(true) values can be extracted from k s ob(app) measurements. Some experimental verification of these effects is also presented.