Evaluating aqueous flow battery electrolytes: a coordinated approach

Robb, Brian H.; Waters, Scott E.; Marshak, Michael P.

doi:10.1039/d0dt02462g

Cited by 18 publications

(22 citation statements)

References 68 publications

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“…The results of ″in flow″ potentiodynamic bulk electrolysis (″in flow″ CV) 66,67 are in accordance to insights into the host−guest behavior retrieved from NMR titration studies. Bulk electrochemical responses from EtDV (Figure 2A), ADV (Figure 2B), and MDV (Figure 2C) anolytes converged after exceeding 1 equiv of HBCD, while the response from an ABV anolyte (Figure 2D) showed no sign of change even with a high amount of HBCD added (4 equiv).…”

Section: ■ Results and Discussionsupporting

confidence: 74%

Supramolecular Viologen–Cyclodextrin Electrolytes for Aqueous Organic Redox Flow Batteries

Korshunov

Gibalova

Gruenebaum

et al. 2021

ACS Appl. Energy Mater.

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Along with a primary modification of redox active materials, an additional introduction of secondary noncovalent interactions can synergistically enhance bulk properties of electrolytes for redox flow batteries. Herein, we highlight the host–guest complex formation between tailored viologens and highly water soluble (2-hydroxypropyl)-β-cyclodextrin as a key electrolyte interaction to modulate relevant electrochemical properties of aqueous redox flow batteries (AORFBs). The cyclodextrin-modified AORFB anolytes demonstrated a complex interrelation of molecular structure and inherent binding activity as well as bulk electrochemical stability of the anolyte. The screening of different combinations of viologen substituents in the presence of cyclodextrin enabled an electrochemically stable AORFB performance for more than 500 cycles with a temporary capacity fade rate of 0.26%/day at high energy (>70%) and Coulombic (>99.7%) efficiencies. A selective interplay of supporting electrolytes and engineered redox active materials is a promising strategy for enhanced energy characteristics of AORFB electrolytes.

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Section: ■ Results and Discussionsupporting

confidence: 74%

Supramolecular Viologen–Cyclodextrin Electrolytes for Aqueous Organic Redox Flow Batteries

Korshunov

Gibalova

Gruenebaum

et al. 2021

ACS Appl. Energy Mater.

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“…The cell configuration and detailed assembly have been previously reported . All electrolytes were pumped into and out of the flow cell at a rate of 75 mL min –1 .…”

Section: Methodsmentioning

confidence: 99%

Isolation and Characterization of a Highly Reducing Aqueous Chromium(II) Complex

et al. 2022

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The highly reducing CrII-(1,3-propylenediaminetetraacetate) (CrPDTA) complex (−1.1 V vs SHE) has been isolated from aqueous solution and the solid-state structure is described. The reduced CrIIPDTA complex is characterized by single-crystal X-ray diffraction, elemental analysis, infrared spectroscopy, UV–vis spectroscopy, magnetic moment, and density functional theory calculations. The concentration profile, state of charge, and pH of CrPDTA electrolyte were monitored in a flow battery system in situ by absorption spectroscopy and a pH probe. The stability of CrIIPDTA in aqueous environments is demonstrated by the ability to isolate CaCrPDTA, despite the common misconception that water spontaneously evolves hydrogen at such potentials. The reduced CrIIPDTA prevents water from coordinating to the metal center by maintaining the same coordinatively saturated pseudo-octahedral structure as the oxidized CrIIIPDTA, despite experiencing an increased geometric strain from a Jahn–Teller distortion of the high-spin CrII ion. The important difference between solvent reactivity and solvent thermodynamic window is examined by comparing the electrochemical behavior of the reduced species of CrPDTA in various organic solvents to its behavior in aqueous solution. When examined in tetrahydrofuran (THF), the reduction potential of CrPDTA is observed to be −1.19 V vs cobaltocene (−2.52 V vs ferrocene). Reduced CrPDTA in aqueous solution is also exposed to atmospheric O2 without exhibiting any decomposition of the Cr(III) or Cr(II) species. The techniques detailed provide a higher standard method of characterization for flow battery electrolyte species.

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“…Prior studies of the techno-economic design space for AqRFBs have almost exclusively been limited to OCVs ≤1.5 V, ,, due, at least in part, to the idea that the ESW of aqueous electrolytes is 1.23 V (the equilibrium potential) or ∼1.5 V (if accounting for non-idealities). However, through careful consideration of electrolyte composition, cell design, and operating practices, AqRFBs with OCVs >1.5 V can exist with minimal and/or manageable solvent decomposition . For example, lead (Pb)-acid and vanadium RFBs operate above 1.5 V across the entirety or a portion of their accessible state-of-charge windows, respectively.…”

mentioning

confidence: 99%

“…However, through careful consideration of electrolyte composition, cell design, and operating practices, AqRFBs with OCVs >1.5 V can exist with minimal and/or manageable solvent decomposition. 17 For example, lead (Pb)-acid and vanadium RFBs operate above 1.5 V across the entirety or a portion of their accessible state-ofcharge windows, respectively. Development of high-voltage AqRFB chemistries increases the attractiveness of this technology platform and represents a promising pathway to low-cost energy storage.…”

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confidence: 99%

Untapped Potential: The Need and Opportunity for High-Voltage Aqueous Redox Flow Batteries

2022

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Redox flow batteries (RFBs) are attractive long-duration energy storage solutions, especially if system costs can be further reduced. One approach to lowering the system cost is to increase the energy and power densities through the use of higher voltage redox chemistries. To date, most techno-economic studies have considered the maximum open-circuit voltage (OCV) of aqueous RFBs to be ≤1.5 V. We provide a simple techno-economic analysis to illustrate the impact of cell voltage on capital cost and note the secondary benefits that arise from the operational flexibility enabled by aqueous RFBs with OCVs >1.5 V. We subsequently discuss potential pathways to achieving higher voltage chemistries. The goal of this Perspective is to inspire the research community to re-examine the perceived upper limits of aqueous RFB voltages and to explore options for achieving high-voltage systems, as well as identify the need for fundamental research on a variety of topics.

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Evaluating aqueous flow battery electrolytes: a coordinated approach

Abstract: 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...

Cited by 18 publications

References 68 publications

Supramolecular Viologen–Cyclodextrin Electrolytes for Aqueous Organic Redox Flow Batteries

Supramolecular Viologen–Cyclodextrin Electrolytes for Aqueous Organic Redox Flow Batteries

Isolation and Characterization of a Highly Reducing Aqueous Chromium(II) Complex

Untapped Potential: The Need and Opportunity for High-Voltage Aqueous Redox Flow Batteries

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