(4fk) Understanding Electrochemical Systems across Length and Time Scales

Electrolyte solutions and electrochemical interfaces are ubiquitous in physiology, energy storage technologies, and myriad other applications, yet many fundamental aspects of thermodynamics and transport in these systems remain poorly understood. Central to many of the open questions in this area is the issue of multiscale understanding: we require theories to describe how macroscopic behavior arises from collective molecular fluctuations at the mesoscale, and how these fluctuations arise from the detailed chemical structure of the electrolyte and electrode constituents. Efforts to describe these phenomena are complicated by the presence of both long-range electrostatic forces and short-range specific chemical interactions, as well as the fact that many electrochemical systems of interest operate out of equilibrium, where gradients in concentration, electric potential, pressure, and temperature can cause the physical properties of the system to vary in space and time. I am interested in developing theory and computational methods to work towards a comprehensive understanding of electrochemical systems across a broad range of length and time scales. Such understanding has the potential to enable the design of transformative technologies for a sustainable future, including efficient water desalination materials, next-generation batteries and fuel cells, and more.

Research Experience:

As a faculty member, I will build upon the theoretical tools I developed in my doctoral research at UC Berkeley working with Kristin Persson, Bryan McCloskey, and Kranthi Mandadapu. Here, I developed theory for studying ion transport in liquid electrolytes at both the molecular and continuum levels. The key accomplishments of this theory are as follows:

• Through the integration of continuum mechanics, electromagnetism, and nonequilibrium thermodynamics, I derived governing equations that fully capture the coupled transport of charge, mass, momentum, and heat in electrolytes. These governing equations provide a continuum-level description of complex electrochemical systems subject to multiple driving forces away from equilibrium.
• I established a quantitative mapping between the transport coefficients emerging from these continuum-level governing equations and microscopic correlations in ion motion. This mapping between micro- and macro-scale transport behavior provides a powerful lens for interpreting macroscopic transport properties such as the conductivity and transference number at an atomistic level.
• I derived relations to directly compute ion correlations in electrolytes using molecular simulations. This allows us to easily calculate transport properties that may be challenging to characterize experimentally. I have published freely-available code which makes these calculations widely accessible to the scientific community.

My work to apply this transport framework has focused on electrolytes for Li-ion batteries, with emphasis on polyelectrolyte solutions and polymerized ionic liquids. Using molecular dynamics simulations, I have shown that ion correlations (non-idealities) can drastically impact the bulk transport properties of these electrolytes, such that the ideal solution approximations commonly used to analyze these systems in both experiment and simulation lead to qualitatively misleading results. These efforts have thus called into question some of the conventional paradigms for intuitively understanding and characterizing transport phenomena in polyelectrolytes.

Future Research:

My research group will integrate techniques from quantum chemistry, statistical mechanics, and continuum mechanics to develop predictive understanding of electrochemical systems across length and time scales. Using molecular simulation methods and theories at both the classical and quantum levels, we will consider problems such as (i) developing analytical theories to predict electrolyte transport coefficients beyond the dilute regime, (ii) elucidating the transport behavior in electrolytes with novel or unconventional ion transport mechanisms, such as glassy electrolytes and superconcentrated solvent-in-salt systems, and (iii) modeling ion adsorption, desolvation, and transport at interfaces and in electrolytes under confinement. Furthermore, my group will develop theory to couple these molecular-level insights to continuum-level finite element models. We will work towards understanding how changes in microscopic ion interactions manifest in the macroscopic behavior of electrochemical systems subject to external driving forces such as electromagnetic fields and convective flow. This multiscale approach will be a powerful tool to probe the bulk and interfacial phenomena governing electrophoretic separations, selective ion transport in channels, electrosorption methods such as capacitive deionization, and electrocatalysis. These models will inform design principles for new systems to meet pressing needs in sustainable water treatment as well as energy storage and conversion.

Teaching Interests:

Throughout my undergraduate and graduate studies, I have continuously sought out opportunities to deepen my engagement with teaching. As an undergraduate at Stanford, I worked as a teaching assistant for the Introduction to Chemical Engineering course as well as a three-week intensive summer class on the chemistry of art materials. At UC Berkeley, I have served as a graduate student instructor for two semesters in the introductory transport phenomena course, receiving the Outstanding Graduate Student Instructor Award both years. Beyond these teaching assistant roles, I also had the opportunity to redesign part of the pedagogy class taught to all first-year graduate students in my department. One of the most meaningful parts of this project was presenting at both the American Society for Engineering Education and the American Institute of Chemical Engineers national meetings to share my work and learn about exciting initiatives being developed at other schools. I plan to leverage the connections I made at these conferences to stay engaged with the engineering education community as a faculty member.

My background in chemical engineering has prepared me to teach any core course in the undergraduate or graduate curriculum. Furthermore, I am interested in developing (i) an undergraduate-level course introducing the basic techniques of molecular modeling for solving problems in chemical engineering, and (ii) a course for graduate students or advanced undergraduates on transport and thermodynamics in electrochemical systems. I am committed to creating a diverse, inclusive culture in the classroom and my research group, where students can grapple with difficult concepts without fear of failure. I will actively use my leadership role as a professor to advocate for the support and retention of underrepresented minorities in STEM, both within my university and in the broader community.

Selected Awards:

• Berkeley Fellowship for Graduate Study, 2020-2022
• NSF Graduate Research Fellowship, 2017-2020
• Outstanding Graduate Student Instructor, UC Berkeley, 2019, 2020
• Women in Chemical Engineering Travel Award, AIChE, 2019
• Churchill Scholarship, 2016-2017
• Henry Ford II Scholar, Stanford University, 2016
• Firestone Medal for Excellence in Undergraduate Research, Stanford University, 2016
• The Deans’ Award for Academic Achievement, Stanford University, 2016
• Barry Goldwater Scholarship, 2014

Selected Publications: (4 of 19)

1. K. D. Fong, J. Self, B. D. McCloskey, K. A. Persson. “Ion Correlations and Their Impact on Transport in Polymer‑Based Electrolytes.” Macromolecules, 2021, 54, 6: 2575‑2591.
2. K. D. Fong, J. Self, B. D. McCloskey, K. A. Persson. “Onsager Transport Coefficients and Transference Numbers in Polyelectrolyte Solutions and Polymerized Ionic Liquids.” Macromolecules, 2020, 53, 21: 9503‑9512.
3. K. D. Fong, H. K. Bergstrom, B. D. McCloskey, K. K. Mandadapu. “Transport Phenomena in Electrolyte Solutions: Non‑Equilibrium Thermodynamics and Statistical Mechanics.” AIChE Journal, 2020, 66, 12: e17091.
4. K. D. Fong, J. Self, K. M. Diederichsen, B. M. Wood, B. D. McCloskey, and K. A. Persson. “Ion Transport and the True Transference Number in Nonaqueous Polyelectrolyte Solutions for Lithium‑Ion Batteries.” ACS Central Science, 2019, 5: 1250‑1260.