Significance of Nonsteady-State A-C and D-C Measurements in Electrochemical Adsorption Kinetics

Abstract

Information obtainable from nonsteady‐state electrochemical studies is examined with particular reference to the determination and significance of capacitance associated with adsorbed intermediates in consecutive reactions. The frequency dependence of the capacity in a‐c measurements is related to the rise‐time dependence in d‐c charging transients and the concept of an equivalent frequency in d‐c measurements is proposed. The nonsteady‐state kinetics for a galvanostatic charging process is examined for a reaction sequence involving adsorbed intermediates, and it is shown how the capacitance behavior depends on the charging current density. Applications to the triangular voltage sweep method are made, and it is shown that for this case where neither steady‐current nor steady‐state kinetics apply, care must be exercised in interpretation of results derived from this method. The nonsteady‐state kinetics for this case are derived and the dependence of the capacity on sweep‐rate is deduced. The differential galvanostatic method leads to results which can be much more explicitly analyzed in a rigorous kinetic manner, for irreversible charging processes. Applications to experimental results which support the treatment given are discussed.