Elucidating Degradation Mechanisms of High-Potential Redox Electrolytes in Nonaqueous Redox Flow Batteries

Renewable energy sources, such as solar and wind energy, are promising alternatives to reduce the energy and environmental risks associated with fossil fuels. However, these naturally occurring renewable energy sources are intermittent, meaning that the energy cannot be produced constantly or respond to meet demand levels. Therefore, it is necessary to store energy for release when needed.

Redox flow batteries (RFBs) use solution-based materials for energy storage and have attracted remarkable attention due to their low cost and reliability, yet their widespread application is hindered by their low energy density and instability. The objective of this proposal is to develop novel metal-free compounds for RFBs to enhance their energy density.

Specifically, the investigators aim to develop a new family of compounds, namely bipyridine and tetrathiafulvalene (TTF), with the necessary combination of (1) high solubility in organic solvents, (2) extended redox potentials for high battery voltage, and (3) high electrochemical reversibility for long cycling lifetime. Using the research outcomes as the basis for outreach activities, the investigators will engage a diverse body of students and the general public to enhance their understanding of renewable energy science and, more broadly, chemistry for sustainability.

Furthermore, the proposed outreach activities will help the public understand the connection between fundamental research in laboratories and renewable energy in daily lives while increasing their scientific literacy and will provide opportunities for undergraduate and graduate students to develop their science communication skills.

This proposed project aims to achieve two goals: (1) design, synthesize, and characterize the physical and redox properties of molecular, high-redox-potential, metal-free bipyridine and TTF derivatives, and (2) investigate their application in nonaqueous redox flow batteries (NRFBs) and elucidate their potential decomposition mechanisms using in situ cyclic voltammetry as well as operando UV-Vis and Fourier-transform infrared spectroscopies. The investigator hypothesizes that the electronic and steric properties of the derivates, as well as their thermodynamics and electrokinetics, can be finetuned using molecular engineering, thus improving their stability and cycling efficiency in NRFBs.

This research will advance the frontiers of knowledge in design principles that guide the synthesis of redox-active compounds with high redox potentials, great electrochemical reversibility, enhanced mass transfer coefficients, and high electron transfer rates. The work done in this proposal will fill the knowledge gap between the development of promising NRFBs and the lack of ideal redox electrolytes, as well as generate key fundamental insights into ideal redox-active compounds.

The conclusions drawn from this research will have a profound impact on battery performance enhancement design.

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.