S. Taguchi et A. Aramata, CORRELATION OF THE UNDERPOTENTIAL DEPOSITION (UPD) OF ZINC IONS ON PT(111), PT(100), AND PT(110) WITH ANION-SPECIFIC ADSORPTION, Journal of electroanalytical chemistry [1992], 457(1-2), 1998, pp. 73-81
We report two roles of the adsorbed anions in the underpotential depos
ition (upd) of zinc ions giving cooperative and competitive interactio
n with the upd metals under different circumstances. The effect of spe
cifically adsorbed anions on Zn upd was investigated systematically at
Pt(111), Pt(100), and Pt(110) in solutions of pH 1-4.6 by cyclic volt
ammetry, where the anions were (bi)sulfate, phosphate, chloride, bromi
de, and iodide anions. Zn upd hardly occurred on Pt(111) in acidic sol
utions of pH 1. However, the growth of sharp Zn upd voltammetric waves
was observed on Pt(111) in phosphate solutions with pH increase in th
e pH range of 2-4.6. In sulfate and perchlorate solutions, such behavi
or was not observed on Pt(111) with pH increase. On the other hand, at
Pt(110), the Zn upd was clearly observed in phosphate solution of pH
1. In 0.1 M KH2PO4 (pH 4.4) with 10(-3) M halides, the onset potential
of Zn upd on Pt(111) shifted negatively according to the order of the
adsorption strength of Cl- < Br- < I-. The negative shift of 0.02 V b
y Cl- adsorption on Pt(111) was smaller than that of 0.10 V on Pt(100)
. These results are discussed and correlated to the strength of anion
adsorption at the onset potentials of Zn upd, in terms of cooperative
and competitive interaction of the adsorbed anion with the upd Zn; ads
orbed phosphate anions on Pt facilitate the Zn upd kinetically by the
desorption action, but halides tightly adsorbed at the Pt surface obst
ruct the initiation of Zn upd. (C) 1998 Elsevier Science S.A. All righ
ts reserved.