Statics and Dynamics of Halide Sub-Monolayer Electrosorption on Silver: Computer Simulations with Comparison to Experiments

• Other Authors: Abou Hamad, Ibrahim (authoraut)
• Format: Others
• Language: English; English
• Published: Florida State University
• Subjects: Physics
• Online Access: http://purl.flvc.org/fsu/fd/FSU_migr_etd-0103

This dissertation investigates equilibrium and dynamical properties of submonolayer chemical adsorption of Br and Cl on single-crystal Ag(100) electrodes. Computational methods, such as Monte Carlo simulations with First-order Reversal Curve analysis, are used along with experimental data. Monte Carlo simulations of a two-dimensional lattice-gas approximation for the adlayer are used to explore equilibrium properties of the system. Lateral interaction energies between adsorbates, as well other system parameters like the electrosorption valency, are determined by fitting simulations to experimental chronocoulometry isotherms. While neither the electrosorption valency nor the lateral interactions show any dependence on the adsorbate coverage for the Br/Ag(100) system, a model in which both are coverage dependent is required to adequately describe the Cl/Ag(100) system. A self-consistent, entirely electrostatic picture of the lateral interactions with coverage dependence is developed, and a relationship between the lateral interactions and the electrosorption valency is investigated for Cl on Ag(100). The adsorbates form a disordered adlayer at low electrochemical potentials. At a more positive electrochemical potential the adlayer undergoes a disorder-order phase transition to an ordered c(2x2) phase. This phase transition produces a peak in the current density observed in cyclic-voltammetry experiments. Kinetic Monte Carlo studies of the lattice-gas model are used to simulate cyclic-voltammetry experiments. The scan-rate dependence of the separation between positive- and negative-going peaks in cyclic-voltammetry simulations are compared to experimental peak separations. This dynamics study identifies the inverse Monte Carlo attempt frequency with a physical timescale. Although kinetic Monte Carlo simulations can provide long-time simulations of the dynamics of physical and chemical systems, this identification is not yet possible in general. To further investigate the dynamics, First-order Reversal Curve (FORC) analysis---a method that was recently developed and used for magnetic systems---is applied to simulations of electrochemical submonolayer adsorption in systems with first- and second-order phase transitions. Not only does this method highlight differences between the two kinds of phase transitions, but it can also be used to recover the equilibrium behavior for systems with a second-order phase transition and slow equilibration from dynamic reversal curves. === A Dissertation submitted to the Department of Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy. === Degree Awarded: Spring Semester, 2006. === Date of Defense: April 3, 2006. === Monte Carlo, Phase Transitions, Halide Electrosorption, Electrochemistry, First-Order Reversal Curve Analysis, Lattice Gas Odel === Includes bibliographical references. === Per Arne Rikvold, Professor Directing Dissertation; Joseph B. Schlenoff, Outside Committee Member; Jorge Piekarewicz, Committee Member; Huan-Xiang Zhou, Committee Member; Linda Hirst, Committee Member.