Computational Studies in Electrochemical Materials Science by Statistical-Mechanical and Ab-Initio Methods

Florida State University, Tallahassee FL

Investigators

Abstract

0240078 Rikvold This grant supports a theoretical project investigating surface electrochemistry. Surface electrochemistry contributes to the welfare of society in many ways, including metal production, electroplating, corrosion protection, energy storage, and heterogeneous catalysis for the chemical and pharmaceutical industries and environmental protection. Despite these diverse and economically important applications, it is only in the last two decades that experimental methods have become available that permit observation and manipulation of electrode/electrolyte interfaces on an atomic scale without removing the electrode to an ultra-high vacuum environment. These new, nanoscopic in situ methods include scanning probe microscopies, such as scanning tunneling microscopy and atomic force microscopy, and X-ray diffraction using high-brilliance synchrotron sources. In combination with the traditional, macroscopic methods of electrochemistry, such as cyclic voltammetry and chronocoulometry, these new techniques have ushered in a new era of atomic-scale electrochemical surface science. As a consequence, electrochemical methods to manufacture high-tech materials and devices that derive their properties from structure on the nanometer scale are being developed and have the potential to become cost-effective alternatives to current high-vacuum techniques. These impressive experimental developments are paralleled by spectacular progress in computer hardware and software. Calculations that required supercomputers a decade ago are now performed on personal computers, while today's fastest computers and algorithms can handle billions of atoms. This research will apply results and techniques from recent NSF-supported computational and theoretical studies of dynamical phenomena in electrochemical materials science to study the dynamics of anions that are electrochemically adsorbed on single-crystal electrodes. These results and techniques include theoretical models for specific electrochemical systems, highly efficient dynamic multiscale simulation algorithms, and ab initio quantum mechanical methods. The methods will be used and developed further in investigations of halides electrochemically adsorbed on silver and gold, and the dynamics of phase transformations of gold surfaces under rapidly pulsed potential. The results will be compared with experiments in collaboration with experimental groups. In addition to studies of specific systems, the research will include work of more general scope on effects of diffusion of adsorbed atoms on the adsorbate structure, on dynamics of adsorbate systems under conditions of rapidly varying electrode potentials, and on methods to include the effects of electric fields and to explicitly include water molecules in ab initio calculations. Work will also continue to develop simulation algorithms that faithfully represent the effects of adsorption, desorption, and lateral diffusion that occur on atomic time scales of less that 10-10 seconds, while enabling simulation of processes on a scale of seconds or longer. This problem of bridging time scales will be addressed in a hierarchical manner, using studies of small continuum systems to determine parameters for input in simulations that can reach macroscopic times with the application of modern algorithms. This research is expected to result in improved understanding of nonequilibrium processes at electrode/electrolyte interfaces, and thereby contribute to the development of new, electrochemistry-based processes to manufacture nanoparticles, ultrathin films, and other nanostructured materials. The research is ideal for involving students at all levels in the discovery process. %%% This grant supports a theoretical project investigating surface electrochemistry. Surface electrochemistry contributes to the welfare of society in many ways, including metal production, electroplating, corrosion protection, energy storage, and heterogeneous catalysis for the chemical and pharmaceutical industries and environmental protection. Despite these diverse and economically important applications, it is only in the last two decades that experimental methods have become available that permit observation and manipulation of electrode/electrolyte interfaces on an atomic scale without removing the electrode to an ultra-high vacuum environment. These new, nanoscopic in situ methods include scanning probe microscopies, such as scanning tunneling microscopy and atomic force microscopy, and X-ray diffraction using high-brilliance synchrotron sources. In combination with the traditional, macroscopic methods of electrochemistry, such as cyclic voltammetry and chronocoulometry, these new techniques have ushered in a new era of atomic-scale electrochemical surface science. As a consequence, electrochemical methods to manufacture high-tech materials and devices that derive their properties from structure on the nanometer scale are being developed and have the potential to become cost-effective alternatives to current high-vacuum techniques. These impressive experimental developments are paralleled by spectacular progress in computer hardware and software. Calculations that required supercomputers a decade ago are now performed on personal computers, while today's fastest computers and algorithms can handle billions of atoms. This research will apply results and techniques from recent NSF-supported computational and theoretical studies of dynamical phenomena in electrochemical materials science to study the dynamics of anions that are electrochemically adsorbed on single-crystal electrodes. These results and techniques include theoretical models for specific electrochemical systems, highly efficient dynamic multiscale simulation algorithms, and ab initio quantum mechanical methods. The methods will be used and developed further in investigations of halides electrochemically adsorbed on silver and gold, and the dynamics of phase transformations of gold surfaces under rapidly pulsed potential. The results will be compared with experiments in collaboration with experimental groups. In addition to studies of specific systems, the research will include work of more general scope on effects of diffusion of adsorbed atoms on the adsorbate structure, on dynamics of adsorbate systems under conditions of rapidly varying electrode potentials, and on methods to include the effects of electric fields and to explicitly include water molecules in ab initio calculations. Work will also continue to develop simulation algorithms that faithfully represent the effects of adsorption, desorption, and lateral diffusion that occur on atomic time scales of less that 10-10 seconds, while enabling simulation of processes on a scale of seconds or longer. This problem of bridging time scales will be addressed in a hierarchical manner, using studies of small continuum systems to determine parameters for input in simulations that can reach macroscopic times with the application of modern algorithms. This research is expected to result in improved understanding of nonequilibrium processes at electrode/electrolyte interfaces, and thereby contribute to the development of new, electrochemistry-based processes to manufacture nanoparticles, ultrathin films, and other nanostructured materials. The research is ideal for involving students at all levels in the discovery process. ***