S. Taguchi et al., KINETIC-STUDY OF UNDERPOTENTIAL DEPOSITION OF ZINC IONS ON PD(111) INACIDIC PHOSPHATE SOLUTION, Journal of electroanalytical chemistry [1992], 435(1-2), 1997, pp. 55-61
The formation and desorption kinetics of Zn2+ ion underpotential depos
ition (upd) on Pt(111) were investigated with respect to the effects o
f specifically adsorbed anions in the solution by potential sweeping a
nd potential step methods. Results by both methods are consistent with
each other; in phosphate solution, Zn2+ upd formation took place acco
rding to the Langmuir adsorption kinetics, while on the addition of Br
- in the solution the kinetic mechanism of Zn2+ upd formation was chan
ged to that of a two-dimensional phase transformation, although the de
sorption processes of Zn2+ upd always seemed to take place according t
o the nucleation-growth mechanism, being indifferent to the presence o
f Br-. This indicates that the Zn underpotentially deposited on Pt(111
) becomes somewhat ordered with the increase of its coverage, and deso
rbs according to a nucleation-growth mechanism. In the absence of Br-
in the phosphate solution, Zn upd formation obeys the Langmuir adsorpt
ion mechanism, which corresponds to the mechanism of phosphate desorpt
ion that takes place at the potential where Zn2+ upd occurs. Random Zn
2+ upd formation seems to be induced by the random desorption of the a
dsorbed phosphate. On the addition of Br- ions, the Zn2+ ion upd poten
tial shifts 0.12V to a more negative potential. The desorption of spec
ifically adsorbed anions is suggested to trigger upd of Zn. These fact
s are discussed with regard to the adsorbed anions that are likely to
play the role of a 'footprint' for upd; empty sites available to upd o
f Zn2+ ions are the sites which were just occupied by specifically ads
orbed anions. This means that the desorption of the anions guides the
upd of Zn2+ as a 'footprint'. (C) 1997 Elsevier Science S.A.