RUI: Mesoscale Methods for Electrochemistry: Confronting the Complexity of Ion and Electron Transfer

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Project AbstractProfessor Ryan Jorn of Villanova University is supported by an award from the Chemical Theory, Models, and Computational Methods program in the Division of Chemistry. Professor Jorn develops methods to study the transport of electrons and ions at electrode surfaces, with particular focus on the reactive interfaces present in rechargeable batteries. While rechargeable batteries are essential to powering personal electronics, they may also play a significant role in reducing carbon emissions by powering cars. Several technical challenges to energy storage for transportation remain, including loss of storage capacity over time and poor rates of recharge. These challenges are intimately connected to the transport of ions and electrons at the molecular level. Unfortunately, charge transport mechanisms are poorly understood. Few experiments can access sufficiently small length and time scales at the electrode surface. Most computer simulations are also inadequate to describe the multiple length scales at work during battery operation. Studying the behavior of electrons requires using quantum mechanics to properly treat their wave-like nature. Such calculations, however, are only feasible for a relatively small numbers of atoms. Accurately capturing the evolution of the interface through which the electron travels requires accounting for thousands of atoms for very long times. Professor Jorn's research uses a multi-scale approach to study these problems. He and his coworkers compute molecular forces from quantum mechanics. They then use these forces to describe the classical motion of ions and molecules at the electrode surface. His work at Villanova University relies heavily on the involvement of undergraduate students who are trained on state-of-the-art simulation software and high-performance computing platforms. Professor Jorn also uses his research to introduce first generation and under-represented college students to computational modeling through the Center for Access, Success, and Advancement at Villanova University. Molecular simulations of electrochemical interfaces have previously relied on ab initio molecular dynamics (AIMD) to study chemical reactions, and classical molecular dynamics (CMD) to explore solvation phenomena. Regarding the former, limitations on the time scales of simulation render description of transport phenomena intractable. On the other hand, it is widely recognized that "off-the-shelf" force fields used in CMD fail to accurately capture polarization effects and interface structure. Professor Jorn's research addresses these deficiencies by employing a force-matching approach that uses information from quantum AIMD simulations to train classical molecular force fields. His research group explores how best to build force fields at interfaces by exploring different functional forms for intermolecular interactions and sampling high-energy configurations. In addition to developing force fields for interfacial processes, Professor Jorn's work includes developing enhanced sampling methods to describe the exchange of species across the electrolyte/electrode interface. By using a unique combination of replica exchange umbrella sampling and collective variables, his approach allows for the study of single defect migration as well as correlated mechanisms involving ion "knock-off". Regarding the motion of electrons, Professor Jorn's work employs a Newns-Anderson Hamiltonian coupled with ensemble scattering theory to describe the classical force on molecules during reduction. In adding electron transfer to classical simulations, Professor Jorn is developing a framework to study electrochemistry at a molecular level.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.