KINETICS OF ROUGHNESS RELAXATION AT GOLD ELECTRODES

Roughness relaxation of thin columnar Au electrodeposits in NaF and K2 SO4 aqueous solutions at 298 K has been followed through the change of both the roughness factor (R), measured from the O adatom voltammetri c electrodesorption charge, and the electrode capacitance (C) at const ant potential (E) determined at different frequencies. After a certain relaxation time (t), R and C fit the R is-proportional-to t(-k) and C is-proportional-to t(-k') proportionality, respectively, where k = 1/ 4 and k' < 1/4. Otherwise, the proportionality C is-proportional-to A( n) has been found, where A denotes the electrodeposit real surface are a. When C was measured in concentrated solutions in the 165 to 1070 Hz range or in dilute solutions at low frequencies, k' --> k and n --> 1 . As t increased C(d), the specific capacitance, vs. E plots shifted u pward approaching the behavior of a smooth Au electrode, without any a ppreciable change in the value of E associated with the minimum value of C(d). These results were interpreted through a porous model with a time-dependent average pore radius.