Regensburg 2013 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 76: Focussed Session: Solid-liquid Interfaces II
O 76.2: Vortrag
Donnerstag, 14. März 2013, 16:30–16:45, H31
Broadband SFG Spectroscopy of Specific Anion Adsorption at Pt(111)-Electrolyte Interfaces — •Björn Braunschweig — University of Erlangen-Nuremberg, Institute of Particle Technology (LFG)
Vibrational broadband sum-frequency generation (SFG) synchronized with cyclic voltammetry (CV) was applied to study the electrochemical adsorption of (bi)sulfate and formate anions on ordered Pt(111) electrodes. SFG spectra of Pt(111) immersed in 0.1 M H2SO4 reveal an intense vibrational band at 1270 cm−1 for potentials >0.21 V vs. Ag/AgCl. A close comparison of SFG spectra with in-situ STM images and the CV reveals that this potential corresponds to a surface transformation from a disordered (bi)sulfate adlayer to an ordered layer with large domains of closed-packed (√3×√7)R19.1∘ superstructures [1,2]. Changing the electrode potential results in significant Stark tuning of the (bi)sulfate band and to a second abrupt change in SFG amplitude, bandwidth and Stark tuning rate at 0.5 V that is indicative for a second surface transformation.
In addition to experiments in blank H2SO4 dilutions, the adsorption of formate during the electrochemical oxidation of 0.5 M formic acid on Pt(111) has been studied with SFG. For potentials <0.3 V, CO is the dominant surface-adsorbed species, while potentials >0.3 V lead to co-adsorption of formate. Oxidative removal of CO at potentials >0.5 V leads to predominant adsorption of formate.
[1] Braunschweig, Dlott, Wieckowski et al.; JACS, 132, 14036 (2010)
[2] Braunschweig and Daum; Langmuir 25, 11112 (2009)