General equations are derived for the overvoltage of two stepwise-proceeding electrode reactions for the transient regime under galvanostatic conditions. Two shapes of ~-t curves have been found depending on the mechanism and i values: for ioi > io2 and i > /critical, the ~-t curves are peak shaped; for iol > io2 and i --~ /critical, the ~-t curves gave the usual form of monotone increasing ~ toward the steady-state value. At the same time, the intermediate ion concentration increases, following an S-shape curve: for iol = io2 and iol ~ io2, the ~-t curves have the same form as for the iol > io2 and i ~ /critical case, but the intermediate ion concentration remains constant and equal to the equilibrium concentration for ioi = io2 and decreases below the equilibrium concentration for iol ~ 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.
The previous system of equations derived for the kinetics of two stepwise‐proceeding electrode reactions under galvanostatic conditions is extended for the case when both concentration polarization and mass transfer of the intermediate and final ion are taken into account.
The transient regime of the anodic dissolution of a three‐valent metal, proceeding in two steps under galvanostatic conditions, is studied for the particular case when
z1=1
,
z2=2
and
i01>i02
. It has been found in going from low to high current densities that the
η−t
curve changes its shape, namely: for
i>inormaler1
, monotone increasing η toward the steady state; for
inormalcr1inormalcr2
, monotone increasing η toward the steady state again. Under particular conditions of
false[M+]normalo
values, the overvoltage peak may disappear for
inormalcr1
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