In situ Fourier transform infrared spectroelectrochemical study of bisulfate and sulfate adsorption on gold, with and without the underpotential deposition of copper

Abstract

In situ surface infrared (IR) spectroelectrochemistry is used to investigate the adsorption of sulfate (S01") and bisulfate (HSO4-) ions on polycrystalline gold surfaces in sodium sulfate and sulfuric acid, and also during copper underpotential deposition in sulfuric acid medium. In sodium sulfate solution, IR peaks due to surface sulfate and bisulfate are observed at potentials within the double-layer region on gold, and the ratio of IR peak intensities for sulfate to bisulfate increases as the applied potential is made more negative. In sulfuric acid, surface IR spectra indicate that adsorbed sulfate is favored at more positive potentials, while adsorbed bisulfate is prevalent at more negative voltages; also, a potential-dependent reorientation of water is observed in the spectra. IR spectroelectrochemical data from a sulfuric acid system containing copper sulfate indicate that adsorbed sulfate is preaent on gold at more positive potentials, and its coverage increases when underpotentially deposited (UPD) copper is preaent on the gold substrate surface. When the applied potential is sufficiently negative to effect full discharge of UPD copper, IR spectroelectrochemistry shows a loss of adsorbed sulfate and an increase in surface bisulfate species, with a concomitant reorientation of adsorbed water molecules. The resulta are explained in terms of surface electrostatic considerations during UPD of copper, and ale0 in terms of potential4epeadent pH changes at the interface. To our knowledge, this is the f i t reported infrared spectrodectrochemid study of interfacial changes occurring during metal underpotential deposition processes.

Underpotential deposition of Cu on Au(111) in sulfate-containing electrolytes: A theoretical and experimental study

“…The UPD of Cu on Au(111) in sulfate-containing electrolytes has been extensively studied, both by in situ techniques like CV [7,8,10,11,[45][46][47][48][49][50][51], chronocoulometry [45][46][47][48][49][50][51], scanning tunneling microscopy (STM) [9,45,52,53], atomic-force microscopy (AFM) [54], Fourier-transform infrared spectroscopy (FTIR) [55], X-ray-absorption spectroscopy (EX-AFS and XANES) [56][57][58], surface X-ray scattering [59,60], quartz crystal microbalance (QCM) [47,59], and by ex situ techniques, such as LEED, RHEED (reflection high-energy electron diffraction) and AES [10,11,[61][62][63]. Electrolyte compositions used in several CV experiments (including the present work) are listed in Table I, together with potential scan rates and observed current-peak separations.…”

Molecular Dynamic Simulations in Interfacial Electrochemistry

“…Infrared reflection-absorption spectroscopy, 89 surface-enhanced Raman scattering, 2,90 and second harmonic generation 91 have been used to investigate the structure of water at different metal surfaces, but the pictures emerging from all these studies are not always consistent, partially because of surface modification and chemical adsorption, which complicate the analysis.…”

Structure transitions between copper-sulphate and copper-chloride UPD phases on Au(111)

“…[28][29][30][31][32] The various adlayer structures were characterized by electron diffraction, 33,34 X-ray techniques, 24,29,[35][36][37][38][39][40] infrared absorption 26,[40][41][42][43] and Auger electron 44 spectroscopies as well as by electrochemical STM [45][46][47][48][49][50][51][52][53][54] and atomic force microscopy (AFM). 55,56 The experimental studies are complemented by theoretical modelling employing statistical mechanics, Monte Carlo simulations, density functional and/or molecular dynamics approaches.…”