General equations are derived for the overvoltage of two stepwise-proceeding electrode reactions for the transient regime under galvanostatic conditions. Two shapes of η-t curves have been found depending on the mechanism and i values: for iO1 > iO2 and i > icritical, the η-t curves are peak shaped; for iO1 > iO2 and i ≤ icritical, the η-t curves gave the usual form of monotone increasing η toward the steady-state value. At the same time, the intermediate ion concentration increases, following an S-shape curve: for iO1 = iO2 and iO1 < iO2, the ·-t curves have the same form as for the iO1 > iO2 and i < icritical case, but the intermediate ion concentration remains constant and equal to the equilibrium concentration for iO1 = iO2 and decreases below the equilibrium concentration for iO1 < iO2. The relationships concerned are of some help in assigning a mechanism and under specific conditions in calculating the exchange currents of both steps by using them in conjunction with experimental results. © 1969, The Electrochemical Society, Inc. All rights reserved.
