Early Stages of Copper Electrocrystallization:  Electrochemical and in Situ X-ray Absorption Fine Structure Studies of Coadsorption of Copper and Chloride at the Au(111) Electrode Surface

Abstract

Cu K-edge X-ray absorption spectra (XAS) recorded in situ using glancing incidence and fluorescence detection have been employed to study the codeposition of copper and chloride ions on a Au(111) surface under an electrolyte solution. Chronocoulometric measurements provided information about the composition of the overlayer and about the number of electrons flowing to the interface per adsorbed copper ion. The XAS displays a remarkable dichroism consistent with a bilayer in which the Cu adatoms are covered by chloride ions. Previous scanning tunneling microscopy (STM) measurements suggested either a (5 × 5) long-range structure similar to that of the (111) plane of a CuCl crystal or to (4 × 4)-based structures. FEFF 6.01 multiple scattering calculations of the XAS were performed on five different model structures derived from the STM proposals. A unique solution could not be obtained. The results indicate that there is a large degree of static disorder. They rule out high-symmetry structures in which there are narrow distributions of Cu−Cl, Cu−Au, and Cu−Cu distances and bond angles.

Underpotential deposition of Cu on Au(111) from neutral chloride containing electrolyte

“…Both standing wave and computational data favour the structural model where an incommensurate (5×5) Cl layer seen by STM is adsorbed on top of a (1×1) commensurate layer of Cu. Thus, it contrasts studies on Cu-UPD in an acidic environment which conclude either an incommensurate (5x5) CuCl adlayer structure 31,62 or a structure exhibiting significant disorder 40 . Thus adding to the puzzle of Cu-UPD in chloride containing electrolytes, this calls for a detailed comparative study which fully assesses the adsorbate system through a combination of structurally sensitive techniques.…”

“…31,37,62,63 This is contrasted by a study using X-ray absorption spectroscopy (XAS) which finds that neither the zincblende structure nor the commensurate layer give satisfactory agreement with the experimental data. 40 The XAS data rule out a narrow distribution of bond distances including the Cu-Cl bond which is not consistent with the models concluded from the STM studies. Suggesting a significant degree of static disorder, the authors surmise that the Cu atoms could be shifted from high symmetry positions.…”

“…Note that distances are determined by P modulo 1 because of the periodic nature of the wavefield planes. Since the chloride is located above the Cu layer 40,62 the P value of 0.56 corresponds to a value of 3.68 Å above the Au(111) surface plane. Compared to Cu and Au, the coherent fraction of the chloride is pronouncedly smaller, which suggests that Cl exhibits a substantially wider distribution normal to the surface, i.e.…”

Development and application of in situ/operando soft X-ray transmission cells to aqueous solutions and catalytic and electrochemical reactions

“…XAS in the hard X-ray region is applied to electrochemical reactions in order to study the local electronic structure of electrolytes in aqueous solutions [216][217][218][219][220]. Hard X-ray photoelectron spectroscopy is applied to investigate potential-induced Si oxide growth in water at the Si membrane surface [221].…”

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

“…15,16). The effect of chloride on Cu UPD on Au(111), for example, was studied by voltammetry and chronocoulometry, 22,[64][65][66] low energy electron diffraction spectroscopy, 67 X-ray absorption spectroscopy, 24,65 , electrochemical STM 45,[48][49][50]53,[68][69][70] and AFM. 56 In situ STM experiments in sulfuric or perchloric acid revealed that trace amounts of chloride ions lead to the formation of an incommensurate (5 × 5)-like Cu-Cl UPD structure at high potentials.…”