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Platinum surfaces in sulfuric acid: Pt(111) – sulfate

  • M. NowickiEmail author
  • K. Wandelt
Part of the Condensed Matter book series (volume 45B)

Abstract

In this chapter the experimental results on adsorption of sulfate ion on Pt(111) surface is described.

The interaction of sulfate anions with Pt(111) electrodes is one of the most studied electrochemical systems. SO42− adsorption on Pt(111) was studied in 0.05 M H2SO4, (0.5 – x) M HClO4 + x M H2SO4 (with x varying between 10−4 and 0.2 M) and 0.1 M HClO4 + x mMH2SO4 solutions, using CV, in situ STM, thermodynamic studies, radioactive labeling, and theoretical methods.

Like on Au(111) SO42− forms a (√3 × √7)R19.1° (or \( \left(\begin{array}{cc}2& 1\\ {}\overline{1}& 2\end{array}\right) \) structure) on Pt(111) between 0.5 and 0.7 V (RHE). CV shows two well-defined features between 0.3 and 0.6 V and between 0.65 and 0.9 V (SHE = Standard Hydrogen Electrode). The (√3 × √7)R19.1° structure is identified as a co-adsorption structure of specifically adsorbed SO4 anions and solvent (water) molecules corresponding to an SO42− coverage of 20% of a monolayer. This coverage or packing density is supported by the integrated charge of the cyclic voltametric curves as well as by a radioactive labeling method. The co-adsorbed water/hydronium species play the role of a 2D hydration “sphere,” reducing the electrostatic repulsion between the anions.

The charge on the anions varies with potential in that bisulfate (HSO4) dissociates to sulfate with increasing potential. At saturation a surface concentration vs. electrode potential plot suggests partially discharged SO42− anions of charge −1.7e. With increasing potential, also the nature of the co-adsorbed species varies from H3O+ to H2O. Both H3O+ and H2O act as 2D hydration “sphere” and shield the anionic charges from each other [1, 2, 3, 4, 5, 6].

Symbols and abbreviations

Short form

Full form

2D

two dimensional

RHE

reference hydrogen Electrode

SHE

standard hydrogen Electrode

STM

scanning tunneling microscopy

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Copyright information

© Springer-Verlag GmbH Germany 2018

Authors and Affiliations

  1. 1.Institute of Experimental PhysicsUniversity of WroclawWroclawPoland
  2. 2.Institute of Physical and Theoretical ChemistryUniversity of BonnBonnGermany

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