(4pc) Unleashing Electrochemical Flow Reactors By Engineering the Membrane-Electrolyte System

Electrochemical flow reactors are a versatile platform for new unit operations to electrify the chemical industry, to remediate and valorize waste, and to unleash large-scale energy storage. My aim is to approach pressing grand challenges in electrochemical engineering for sustainability with a use-informed orientation, posing fundamental research questions based on the context-specific details for envisioned technologies. My research group will direct electrochemical principles toward delivering exceptionally selective separations and reactivity with reactors that utilize Earth-abundant materials and aqueous solvents, and can demonstrate durable operation under practical conditions.

Research Experience

During my PhD I developed a framework for understanding a crucial interface in electrochemical flow reactors: the interactions between ion exchange membranes and the flowed electrolyte. I applied this membrane-electrolyte system approach toward applications spanning redox flow batteries and electrodialysis-based CO₂ capture.

I demonstrated that state-of-the-art membranes for redox flow batteries exhibit transport properties that are highly dependent on the electrolyte environment, including the concentration of redox-active reactants and charge-carrying counterions, and on thermal and chemical pretreatment history. Through this work, I showed that under certain conditions the crossover of flow battery reactants (which causes capacity fade) can be completely suppressed, and that tradeoffs exist between battery energy density and power density due to membrane properties. I further established, coordinating a three-institution collaboration with another battery group and a polymer chemistry lab, how a new membrane design can deliver crossover-free flow batteries with improved power by improving potassium-ion conductivity.

Toward the development of long-lifetime aqueous flow batteries with organic reactants, I studied the influence of redox reactant molecular structure on both transport properties through charged membranes and on chemical stability. Through this research, I applied the membrane-electrolyte system approach to point toward opportunities for the synergistic design of redox reactants and membranes, making use of steric and coulombic effects to simultaneously promote transport selectivity and resistance to chemical decomposition for durable flow reactors.

I designed a redox-mediated electrodialysis reactor to generate high-concentration acid and base through bipolar membrane water dissociation and devised a scheme to use the alkaline stream to directly capture atmospheric CO₂ as dissolved ions and to subsequently release the pure CO₂ for sequestration by combining with the acidic stream. The process operates in a closed loop with energy provided as potentially renewable electricity.

The performance of electrodialysis for CO₂ capture, along with other bipolar membrane flow reactors for myriad applications, depends on the speciation of ions at the bipolar interface. My study of this membrane-electrolyte system has uncovered ion-exchange processes by which the compositions of impure electrolytes determine membrane polarization characteristics. In this work, I combined electrochemical measurements and 1D continuum modeling to illustrate mechanisms governing bipolar membrane phenomena.

These research endeavors each illustrate how specific technological use cases inform fundamental research questions that reveal underlying phenomena which, in turn, translate across applications. For example, the presence of supporting salt or ocean water in a BPM electrodialyzer for CO₂ capture inspired my study of BPM ion exchange processes in impure electrolytes, and the resulting understanding of transport and equilibrium processes in membranes points towards new electrochemical engineering approaches to long-lifetime acid/base flow batteries and wastewater treatment.

Future Research

My research group will expand the traditional chemical engineering toolbox of thermodynamics, kinetics, and transport to leverage the effects of both chemical and electrostatic charge in diverse electrochemical flow reactors. The promise of electrochemical systems for uniquely selective reactions and separations can be realized by building a comprehensive understanding of the interplay between charged reactants, ion-selective membranes, polarized electrodes, and the convection and (electro)osmosis of the solvent. The balance of these complex interactions is dependent on specific chemical and electrochemical conditions, which will be constrained by technological needs, from which we will work to resolve universal principles and establish general design rules.

In particular, we will focus on systems with concentrated, impure, non-ideal electrolytes of practical importance, such as brines for lithium extraction, municipal and agricultural wastewater for valorization of nitrates, phosphates, and organic waste, and energy-dense electrolytes for redox flow batteries. We will combine in situ sensors, operando spectroscopy, and device-level electrochemical diagnostics and modeling to investigate coupled phenomena of redox reactions and ion transport across time- and length-scales. Further, we will develop highly sensitive electroanalytical techniques and accelerated stress testing protocols to rigorously evaluate the durability of devices and components under realistic conditions to drive technological advancement. These interdependent research approaches will reveal both the origins of device performance bottlenecks and the mechanisms of long-term failure, and will inform engineering strategies for overcoming these challenges. Overall, our efforts will support broadening the applications of electrochemical flow reactors for deep decarbonization and environmental sustainability.

Teaching Interests

I am prepared to teach any course in the core chemical engineering curriculum to meet departmental needs. In particular, I am motivated to teach chemical engineering because this and subsequent generations of chemical engineers will rise to the great challenge and opportunity of engineering design for a sustainable future. The call for energy transition is what brought me into the field of chemical engineering and inspired my ongoing research in electrochemical engineering, and my teaching experiences so far have introduced me to increasing numbers of students who are similarly motivated by sustainability and especially interested in electrochemistry. Electrochemical engineering draws on core chemical engineering principles of thermodynamics, transport phenomena, and chemical reaction engineering. The interfacial nature of electrochemical reactions means that topics in electrochemistry can be leveraged to synthesize elements of the curriculum. In addition to working to include electrochemical engineering topics throughout the core curriculum, I am interested in developing a new undergraduate electrochemical engineering course and graduate-level electives such as electrochemical separations, which are courses that will provide important training for the next-generation workforce.

In the core chemical engineering curriculum, I am especially interested in teaching thermodynamics, transport phenomena, and mass and energy balances or a first-year chemical engineering seminar. I am interested in designing curricula and classroom practices that draw upon the students’ existing knowledge and motivations, to foster a sense of personal agency and determination, so that students are learning the chemical engineering skills to address the challenges that are important to them and to their communities. I explored curriculum design toward these goals in a research project on first-year chemical engineering education, and presented the resulting paper at a meeting of the American Society of Engineering Education.

I am committed to maintaining a practice of continual reflection and development of my own teaching, and I am interested in growing a community of teaching practice among chemical engineering faculty. As a pedagogy fellow at Harvard, I have worked as a mentor to other graduate teaching assistants, guiding them to build a reflective teaching practice through feedback sessions on recorded videos of their teaching. In this role I have also organized department-wide teaching training, and socials for teaching assistants to discuss how things are going in the classroom. As part of my development as an educator, I am committed building the necessary skills to encourage equitable student participation through active learning strategies, and to create a classroom environment in which students with diverse backgrounds, identities, and accessibility needs are all welcomed and included.

Selected Awards

Derek Bok Center Fellowship – Harvard (2023)

Certificate of Distinction in Teaching – Harvard (2020)

NSF Graduate Research Fellowship (2019)

Outstanding Chemical Engineering Student - AIChE Boston Section (2018)

AIChE Student Conference Best Poster: Fuels, Petrochemicals and Energy Division 2 (2018)

Harry West Student Poster Award – AIChE (2018)

Selected Publications (4 of 16)

* Denotes equal contribution † Undergraduate or masters student mentee

1. T. Y. George, I. C. Thomas†, N. O. Haya†, J. P. Deneen†, C. Wang†, and M. J. Aziz, “Membrane-electrolyte system approach to understanding ionic conductivity and crossover in alkaline flow cells,” ACS Applied Materials & Interfaces, vol. 15, 49 2023.
   
   
2. B. H. Robb*, T. Y. George*, C. M. Davis, Z. Tang, C. Fujimoto, M. J. Aziz, and M. P. Marshak, “Sulfonated Diels-Alder poly(phenylene) membrane for efficient ion-selective transport in aqueous metalorganic and organic redox flow batteries,” Journal of The Electrochemical Society, vol. 170, 3 2023.
   
   
3. T. Y. George, E. F. Kerr, N. O. Haya†, A. M. Alfaraidi, R. G. Gordon, and M. J. Aziz, “Size and charge effects on crossover of flow battery reactants evaluated by quinone permeabilities through Nafion,” Journal of The Electrochemical Society, vol. 170, 4 2023.
   
   
4. T. Y. George, A. S. Klein, and K. B. Wendell, “First impressions: Engaging first-year undergraduates in chemical engineering design,” American Society of Engineering Education, 2020.