Reliability of standard rate constants for rapid electrochemical reactions

Abstract

A method is outlined for testing the reliability of standard rate constants, k^s, for rapid electrode reactions evaluated by using electrochemical perturbation techniques. This entails monitoring the response of the apparent values of k^s to systematic alterations of the double-layer structure caused by the addition of specifically adsorbed anions. These rate responses are compared with those observed at the same potential for structurally similar, yet irreversible reactions for which reliable rate constant-potential data can be obtained by using conventional dc methods. The procedure is applied to rate data obtained for Ru(III/II) ammine redox couples by comparing the measured rate increases resulting from the addition of p-toluenesulfonate anions with the corresponding rate increases seen for the irreversible reduction of Co(III) ammines. Ruthenium(III/II) ammine couples, especially Ru-(NH3)6^(3+/2+), are proposed as "reference reactions" with which to test the capabilities of different perturbation techniques for evaluating rapid standard rate constants and for intercomparing rate data obtained in different laboratories.