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Waters, Scott E.

Publications and source records attributed to Waters, Scott E..

6 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

High‐Energy‐Density Chelated Chromium Flow Battery Electrolyte at Neutral pH

Abstract High‐concentration operation of redox flow batteries (RFBs) is essential for increasing their energy‐storage capacity, but non‐acidic electrolytes struggle to achieve the high concentrations of metal ions dissolved in acid, limiting the development of energy‐dense neutral pH electrolytes. We report neutral pH RFB operation of chromium 1,3‐propylenediaminetetraacetate (CrPDTA) at concentrations of 1.2 M at room temperature and 1.6 M at 40 °C, demonstrating 60% higher negolyte capacity, up to 42.9 Ah L −1 , than previously reported for non‐additive‐utilizing solutions of this promising material. With extended full cell cycling, we demonstrate the importance of buffer selection and pH when using the Fumasep E‐620(K) membrane. Finally, we expand the pH operation range of CrPDTA to pH 7, which when cycled at 100 mA cm −2 against a ferrocyanide posolyte demonstrated excellent coulombic efficiencies >99.7% and energy efficiencies >87%, while operating at almost 700 mV more negative than the thermodynamic hydrogen evolution window.

Chemistry↗
DOE OSTI2022

Transport of Ligand Coordinated Iron and Chromium through Cation-Exchange Membranes

Fluxes of negatively charged ligand-coordinated iron, Fe(CN) 6 3/4- , and chromium, CrPDTA 1/2− , through two promising commercial cation-exchange membranes, Aquivion E87–05S and Fumasep E-620(K), were measured as functions of current density. The magnitude of the partial current density reached a maximum of − 43 μ A cm −2 at the maximum applied current density magnitude of − 43 mA cm −2 for Fe(CN) 6 3/4− transport through Aquivion, or 0.1% of the total current density. Fumasep E-620(K) blocks practically all crossover of both compounds. Both membranes sorb more Fe(CN) 6 3/4− and CrPDTA 1/2− than predicted by Donnan equilibrium, and low crossover rates can be attributed mainly to slow diffusion, not charge-based rejection of co-ions. The magnitude of the diffusion coefficient appears to correlate with hydraulic permeability. Although Aquivion E87–05S and Fumasep E-620(K) have significant and observable differences in membrane crossover rates, cells built with the DI-soaked membranes offer similarly high coulombic efficiency, indicating the relatively small contribution that crossover makes to inefficiency over a single cycle.

25 ENERGY STORAGE↗
DOE OSTI2021

Holistic design principles for flow batteries: Cation dependent membrane resistance and active species solubility

Cation dependent resistance of a commercial cation exchange membrane, Nafion™ 212, as well as the solubility of select active materials are investigated, demonstrating practical consequences of cation choice on redox flow battery (RFB) performance. The conductivity of alkali and methyl- or -alcohol substituted ammonium cations through pretreated Nafion™ 212 reveal that cation size is the dominant factor affecting ionic transport. Among the alkali series the resistance increases with larger ionic radii and similarly, with increasing steric bulk through substitution on ammonia. The solubility of ferrocyanide, a commonly used redox flow battery posolyte (or catholyte), as well as iron, cobalt, and chromium metal-organic compounds are determined for the same series of cations. Full cells are assembled using various cation mixtures and membrane pre-treatments to demonstrate practical effects of each variable. Here, we highlight the need to carefully select the correct cations for efficient electrolyte design, since certain cations may lead to high conductivity but low solubility, or vice versa, and provide design principles for RFBs using Nafion™ 212.

25 ENERGY STORAGE↗
DOE OSTI2020

Evaluating aqueous flow battery electrolytes: a coordinated approach

Here, we outline some basic pitfalls in the electrochemical investigation of aqueous metal complexes and advocate for the use of bulk electrolysis in redox flow cells for electrolyte analysis. We demonstrate the methods of operation and performance of a lab scale redox flow battery (RFB), which is assembled from unmodified, commercially available material and cycled with a vanadium electrolyte in order to provide a comparative baseline of expected performance. Common misconceptions about the thermodynamic window for water splitting are addressed and further express the need to develop next-generation aqueous redox flow battery electrolytes. Although non-aqueous electrolytes are a popular approach, they suffer from distinct challenges that limit energy and power density in comparison with aqueous electrolytes. Expanding the scope of aqueous electrolytes to include metal–chelate complexes allows electrolytes to be as tailorable as organic species, while maintaining robust metal-based redox processes. A flow battery assembly and operation guide is provided to help facilitate the use of flow battery testing in the evaluation of next-generation electrolytes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗