Building an experimental platform for flow battery research presents many challenges. In this talk, I will share the lessons and insights gained from establishing a junior research group from scratch, with a focus on redox targeting strategies to boost energy density and chelate design for high-power aqueous flow batteries.

The limited solubility of redox-active species in flow batteries can be addressed by adding solid capacity boosters to the electrolyte tanks. A soluble redox mediator is charged or discharged in the electrochem-ical cell and subsequently reacts chemically with the booster, allowing the use of solid materials whose charge-storage capacities far exceed what is practically attainable by dissolving active species in water. Lithium iron phosphate, for instance, works well as a booster paired with ferrocyanide as the mediator. Although reproducible fabrication of booster granules turned out to be harder than expected, we recently showed that swapping fluorinated binders for biodegradable alternatives improves mediator-solid inter-actions thanks to the lower hydrophobicity of the composite, tripling the reaction rate between mediator and booster.^[1]

For all-liquid designs, we revalidated KCrPDTA as a benchmark negative electrolyte for high-power flow batteries and ran into challenges spanning precursor purity, chromium olation, and recrystallization, as well as membrane ruptures and flow fields absorbing electrolyte. In the process, we found that thermal activation of carbon paper electrodes strongly influences the morphology of bismuth electrocatalysts, which in turn affects parasitic hydrogen evolution and Coulombic efficiency, illustrating how electrode treatments can shift the balance between kinetics and stability.^[2,3]

At the molecular level, we investigated how small structural changes in chelating ligands alter the elec-tronic structure of transition-metal complexes. Adding a hydroxyl group to the PDTA backbone (yielding CrPDTA-OH) introduces subtle geometric distortions that sharply slow electron transfer, emphasizing how important a stable hexacoordinate geometry is for fast, reversible redox processes with these che-lates.^[4]

Taken together, these studies link system-level design principles with molecular-level control, offering lessons on how chemistry, processing, and reproducibility intersect in advancing next-generation flow battery materials.

1. Lorenzetti, J., Ziemiański, P., Kupferschmid, C., Reber, D. PFAS-free Capacity Boosters for High Energy Density Redox Flow Batteries, ACS Materials Letters, 2026, 8, 889–895.
2. Liu, Q., Kimbell, G., Ahn, J., Camenisch, L., Celik, R., Echeverria, T., Virk, B., Battaglia, C., Reber, D. Revalidating KCrPDTA as flow battery electrolyte, submitted
3. Echeverria, T., Bernasconi, F., Ziemiański, P., Reber, D. Impact of Thermal Electrode Activa-tion on Electrocatalyst Performance in KCrPDTA/K4Fe(CN)6 Flow Batteries, Batteries & Su-percaps, 2024, e202400696
4. Thurston, J.R., White, K.P., Kudisch, M., Kitsu Iglesias, L., Lorenzetti, J., Bernasconi, F., Toney, M.F., Marshak, M.P., Reber, D. Electronic Structure Distortions in Chromium Chelates-Impair Redox Kinetics in Flow Batteries, Batteries & Supercaps 2025, e202500250