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

TL;DR

This study combines computational modeling and experiments to analyze the underpotential deposition of copper on gold electrodes in sulfate electrolytes, revealing phase behavior and interaction energies.

Contribution

It introduces a combined theoretical and experimental approach to understand Cu underpotential deposition, including a lattice-gas model with detailed interactions.

Findings

Identification of a mixed R3xR3 phase with 2/3 Cu and 1/3 sulfate coverage

Agreement between model predictions and experimental voltammetry data

Estimation of effective electrovalences and lateral interaction energies

Abstract

We study the underpotential deposition of Cu on single-crystal Au(111) electrodes in sulfate-containing electrolytes by a combination of computational statistical-mechanics based lattice-gas modeling and experiments. The experimental methods are in situ cyclic voltammetry and coulometry and ex situ Auger electron spectroscopy and low-energy electron diffraction. The experimentally obtained voltammetric current and charge densities and adsorbate coverages are compared with the predictions of a two-component lattice-gas model for the coadsorption of Cu and sulfate. This model includes effective, lateral interactions out to fourth-nearest neighbors. Using group-theoretical ground-state calculations and Monte Carlo simulations, we estimate effective electrovalences and lateral adsorbate--adsorbate interactions so as to obtain overall agreement with experiments, including both our own and those of other groups. In agreement with earlier work, we find a mixed R3xR3 phase consisting of 2/3 monolayer Cu and 1/3 monolayer sulfate at intermediate electrode potentials, delimited by phase transitions at both higher and lower potentials. Our approach provides estimates of the effective electrovalences and lateral interaction energies, which cannot yet be calculated by first-principles methods.