Thermodynamic evidence for K+-SO4 2- ion pair formation on Pt(111). New insight into cation specific adsorption

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Authors

Colleges, School and Institutes

Abstract

This work contributes to the understanding of cation specific effects on platinum electrochemistry by means of a thorough thermodynamic analysis of potassium adsorption on Pt(111) in sulfuric acid solutions. It is concluded that potassium specific adsorption is better described as the adsorption of the K+-SO2-4 ion pair. From the evaluation of the potassium sulfate concentration, it is found that potassium specific adsorption only takes place in the presence of coadsorbed sulfate species. Within the main sulfate adsorption state, for ∼0.3 V < E < ∼0.4 V (vs. SHE), the extent of potassium specific adsorption is small, reaching ∼0.1 × 10 14 species per cm2 for cK+ > 0.1 M. Then, at higher potentials, E > 0.55 V (vs. SHE), a second potassium adsorption process takes place, concomitant with the second sulfate adsorption process (associated to the small voltammetric feature called "the hump"). This last process involves the adsorption of an equal amount of potassium and sulfate species, leading to the adsorption of ∼0.5 × 1014 ion pair species per cm2 (∼0.03 ion pair species per platinum surface atom). Furthermore, the results of the formal partial charge numbers corroborate that potassium adsorption involves sulfate cooperative coadsorption, in such a way that the effective adsorbing species is anionic, rather than cationic. In conclusion, this work evidences that cation specific effects may originate from the formation of surface ion pairs, which is probably related to the presence of ion pairs in solution.

Details

Original languageEnglish
Pages (from-to)12146-12152
Number of pages7
JournalPhysical Chemistry Chemical Physics
Volume12
Issue number38
Early online date9 Aug 2010
Publication statusPublished - 14 Oct 2010