Kinetic study of underpotential deposition of zinc ions on Pt(111) in acidic phosphate solution

• Published in: Journal of electroanalytical chemistry (Lausanne, Switzerland) Vol. 435; no. 1; pp. 55 - 61
• Main Authors: Taguchi, Satoshi, Fukuda, Toshihiro, Aramata, Akiko
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.09.1997; Elsevier Science
• Subjects: Chemistry; Electrochemistry; Electrodeposition; Exact sciences and technology; General and physical chemistry; Nucleation-growth process; Random process; Study of interfaces; Underpotential deposition kinetic mechanism; Zinc underpotential deposition; Random process; Zinc underpotential deposition; Underpotential deposition kinetic mechanism; Pt; Nucleation-growth process; Phosphates; Crystal orientation; Transition metal; Zinc Ions; Experimental study; Buffer solution; Electrodes; Adsorption; Medium effect; Platinum; Growth mechanism; Bromides; Electrodeposition; Kinetics; Electrochemical reaction
• ISSN: 1572-6657; 1873-2569
• DOI: 10.1016/S0022-0728(97)00129-0

The formation and desorption kinetics of Zn 2+ ion underpotential deposition (upd) on Pt(111) were investigated with respect to the effects of specifically adsorbed anions in the solution by potential sweeping and potential step methods. Results by both methods are consistent with each other: in phosphate solution, Zn 2+ upd formation took place according to the Langmuir adsorption kinetics, while on the addition of Br − in the solution the kinetic mechanism of Zn 2+ upd formation was changed to that of a two-dimensional phase transformation, although the desorption processes of Zn 2+ upd always seemed to take place according to the nucleation-growth mechanism, being indifferent to the presence of Br −. This indicates that the Zn underpotentially deposited on Pt(111) becomes somewhat ordered with the increase of its coverage, and desorbs according to a nucleation-growth mechanism. In the absence of Br − in the phosphate solution, Zn upd formation obeys the Langmuir adsorption mechanism, which corresponds to the mechanism of phosphate desorption that takes place at the potential where Zn 2+ upd occurs. Random Zn 2+ upd formation seems to be induced by the random desorption of the adsorbed phosphate. On the addition of Br − ions, the Zn 2+ ion upd potential shifts 0.12 V to a more negative potential. The desorption of specifically adsorbed anions is suggested to trigger upd of Zn. These facts 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 of Zn 2+ ions are the sites which were just occupied by specifically adsorbed anions. This means that the desorption of the anions guides the upd of Zn 2+ as a ‘footprint’.