Collaborative Research: Designing Solid Boosters and Electrolytes for Redox-Targeting Flow Batteries

University Of Massachusetts Lowell, Lowell MA

Investigators

Abstract

Redox flow batteries (RFBs) are considered one of the most promising energy storage technologies to enable the transition toward a carbon-neutral electricity grid. RFBs offer many benefits for grid applications, including ability to decouple energy and power ratings, the associated, unprecedented scalability, and the cost-effectiveness in long-duration storage. However, low solubility of the redox active species in the electrolyte have so far presented challenges. One promising approach to address this limitation is the utilization of solid charge storage (booster) materials in the tanks to reversibly reduce or oxidize dissolved species in the electrolyte via indirect redox-targeting reactions. In this way, the capacity is no longer dependent on the concentration of soluble species but rather the quantity of solids in the tanks. This concept demonstrates the promise for exploiting the unique benefits of solid- and liquid-phase redox chemistry, combining the high-energy-density of the former with the scalability and safety of the latter. Successful implementation of the research will contribute to addressing the key obstacles to widespread adoption of RFBs. This will enable greater utilization of renewable sources and reduce energy related emissions. It will provide grid resilience and flexibility by effectively managing unwanted fluctuations with decoupled energy demand and supply. The research project includes pedagogical aspects of beneficial societal impact. Its integrated, interdisciplinary nature will aid in training a diverse energy science and engineering workforce to be literate in multiple aspects of materials research. Curriculum enhancements and outreach will benefit the education of a range of undergraduate and graduate students and mentor secondary and community college students, especially those of underrepresented minority groups, toward STEM careers in the strategic area of sustainable energy. This research project will provide an in-depth understanding of the nature of indirect redox targeting reactions by investigating the fundamental principles, i.e., thermodynamics, reaction kinetics, and mass and charge transport. Two specific principles underpinning the approach are: (1) Metal hexacyanometallates (MHCMs) possess both coarse and fine adjustments to reduction potential (E°), which can be tuned to minimize the gap in reduction potential between mediators and boosters, (2) because the energy density of redox targeting flow batteries is set by the quantity of booster material, rather than the concentration of active materials in the electrolyte, moderate concentration of both anolyte and catholyte can be used in a compositionally symmetric electrolyte. The effects of intercalation cations on E° will be probed, and thermodynamic and kinetic information from these studies will be implemented in a computational model to provide first-principles knowledge. The resulting knowledge will also provide insights into other electrochemistry-related fields utilizing the indirect redox targeting reactions, such as water electrolysis and fuel cells. 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.