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Title: Mediating Anion-Cation Interactions to Improve Aqueous Flow Battery Electrolytes

Journal Article · · Applied Materials Today

The limited solubility of electrolyte active materials has impeded the development of energy dense aqueous redox flow batteries. Here, we report on the solubilizing effect urea has on metal-organic complexes chelated by aminopolycarboxylate ligands. Upon addition of urea, solubility enhancements of up to 60% or 125% are observed for chromium ethylenediaminetetraacetate (CrEDTA) and chromium 1,3-propylenediaminetetraacetate (CrPDTA) salts, respectively, resulting in maximum solubilities of e.g., 1.5 M for KCrPDTA and 2.2 M for NaCrEDTA. We investigate the mechanism behind enhanced solubility of aminopolycarboxylate chelates, revealing strong hydrogen bonding between urea and anions, resulting in eutectic-like destabilization of the solid phase. We study the impact of urea on the electrochemical performance of near neutral pH flow batteries and demonstrate 50% higher anolyte capacities, up to 40 Ah L-1, than previously reported for this promising class of materials. In capacity balanced full cells, using ferrocyanide catholytes, we observe excellent Coulombic efficiencies >99.6% and voltage efficiencies >78% at average discharge voltages of ca. 1.5 V when cycling at 100 mA cm-2. Peak discharge power densities of >400 mW cm-2 further highlight the potential of our facile and cost-effective approach. Finally, we discuss avenues for future work to further exploit the solubilizing effect described herein.

Research Organization:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Organization:
USDOE Advanced Research Projects Agency - Energy (ARPA-E)
DOE Contract Number:
AC36-08GO28308
OSTI ID:
1872581
Report Number(s):
NREL/JA-5900-83186; MainId:83959; UUID:cd3b058e-77a0-4b1d-9951-7262715f3676; MainAdminID:64680
Journal Information:
Applied Materials Today, Vol. 28
Country of Publication:
United States
Language:
English

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