Strategies for Improving Solubility of Redox‐Active Organic Species in Aqueous Redox Flow Batteries: A Review

Wang, Xiao; Gautam, Rajeev K.; Jiang, Jianbing

doi:10.1002/batt.202200298

Cited by 17 publications

(13 citation statements)

References 135 publications

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“…Encouraged by these results, we proceeded to study the structure–property relationships for this class of anolytes in order to identify next-generation derivatives based on the indolo[2,3- b ]quinoxaline scaffold, with a focus on enhancing solubility and H-cell cycling stability. Previous studies have suggested the use of tetraalkylammonium groups and glycol ethers to enhance the solubility of ROMs . We first incorporated the solubilizing groups into the core through N -alkylation.…”

Section: Resultsmentioning

confidence: 99%

“…Previous studies have suggested the use of tetraalkylammonium groups and glycol ethers to enhance the solubility of ROMs. 57 We first incorporated the solubilizing groups into the core through Nalkylation. Ammonium salt (5b) and glycol ether derivatives 5c−e were synthesized through our convergent synthetic route in excellent yield (91−93%; see the SI).…”

Section: Study Of the Relationship Between The Structure Of Indolo[23...mentioning

confidence: 99%

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Indolo[2,3-b]quinoxaline as a Low Reduction Potential and High Stability Anolyte Scaffold for Nonaqueous Redox Flow Batteries

et al. 2023

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Redox flow batteries (RFBs) are a promising stationary energy storage technology for leveling power supply from intermittent renewable energy sources with demand. A central objective for the development of practical, scalable RFBs is to identify affordable and high-performance redox-active molecules as storage materials. Herein, we report the design, synthesis, and evaluation of a new organic scaffold, indolo[2,3-b]quinoxaline, for highly stable, low-reduction potential, and high-solubility anolytes for nonaqueous redox flow batteries (NARFBs). The mixture of 2-and 3-(tert-butyl)-6-(2-methoxyethyl)-6H-indolo [2,3-b]quinoxaline exhibits a low reduction potential (−2.01 V vs Fc/Fc + ), high solubility (>2.7 M in acetonitrile), and remarkable stability (99.86% capacity retention over 49.5 h (202 cycles) of H-cell cycling). This anolyte was paired with N-(2-(2-methoxyethoxy)-ethyl)phenothiazine (MEEPT) to achieve a 2.3 V all-organic NARFB exhibiting 95.8% capacity retention over 75.1 h (120 cycles) of cycling.

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Section: Resultsmentioning

confidence: 99%

Section: Study Of the Relationship Between The Structure Of Indolo[23...mentioning

confidence: 99%

Indolo[2,3-b]quinoxaline as a Low Reduction Potential and High Stability Anolyte Scaffold for Nonaqueous Redox Flow Batteries

et al. 2023

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“…Carboxylic acid groups tend to dissociate only above a pH of approximately 4.5, and so in acidic solutions their solubilisation effect is less dramatic. [45] Quaternary amine groups and sodium ions are isoelectronic, which may help explain the high solubilisation often seen for aminated ROMs. [44] A quaternary amine substituted TEMPO has a water solubility of 3.2 mol L À 1 , compared to 2.5 mol L À 1 for TEMPO with a sodium carboxylate substituent at the same position.…”

Section: Solubilitymentioning

confidence: 99%

Aqueous Redox Flow Batteries: Small Organic Molecules for the Positive Electrolyte Species

et al. 2023

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There are a number of critical requirements for electrolytes in aqueous redox flow batteries. This paper reviews organic molecules that have been used as the redox-active electrolyte for the positive cell reaction in aqueous redox flow batteries. These organic compounds are centred around different organic redox-active moieties such as the aminoxyl radical (TEMPO and N-hydroxyphthalimide), carbonyl (quinones and biphenols), amine (e. g., indigo carmine), ether and thioether (e. g., thianthrene) groups. We consider the key metrics that can be used to assess their performance: redox potential, operating pH, solubility, redox kinetics, diffusivity, stability, and cost. We develop a new figure of merit -the theoretical intrinsic power density -which combines the first four of the aforementioned metrics to allow ranking of different redox couples on just one side of the battery. The organic electrolytes show theoretical intrinsic power densities which are 2-100 times larger than that of the VO 2 + /VO 2 + couple, with TEMPO-derivatives showing the highest performance. Finally, we survey organic positive electrolytes in the literature on the basis of their redox-active moieties and the aforementioned figure of merit.

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“…This has been achieved through the development of "waterin-Li salt" and "water-in-ionic liquid" electrolyte systems. [108,117] "Water-in-ionic liquid" electrolytes involve the incorporation of ionic liquids into water to create stable electrolyte solutions with extended electrochemical stability windows. [118,119] Ionic liquids, which are organic salts with low volatility, can offer higher thermal stability and wider electrochemical stability ranges compared to traditional aqueous electrolytes.…”

Section: Wide Electrochemical Potential Windowmentioning

confidence: 99%

Quinones for Aqueous Organic Redox Flow Battery: A Prospective on Redox Potential, Solubility, and Stability

Hasan

Mahanta

Abdelazeez

2023

Adv Materials Inter

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In recent years, there has been considerable interest in the potential of quinones as a promising category of electroactive species for use in aqueous organic redox flow batteries. These materials offer tunable properties and the ability to function as both positive and negative electrolytes, making them highly versatile and suitable for a range of applications. Ongoing research has focused on improving the stability, solubility, and performance of quinones, with a particular emphasis on the creation of stable negolytes. The pairing of these advancements with alternate chemistries has created new prospects for commercial applications. However, challenges persist regarding the stability of quinones in high‐potential electrolytes and the limited number of viable quinones available. Despite these obstacles, significant strides have been made, and the potential for quinones to revolutionize energy storage technology is vast. This review article provides a comprehensive overview of recent progress in this area, with a specific focus on redox potential, solubility, and stability, and offers valuable insights into the future of quinone‐based aqueous organic redox flow batteries.

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Strategies for Improving Solubility of Redox‐Active Organic Species in Aqueous Redox Flow Batteries: A Review

Cited by 17 publications

References 135 publications

Indolo[2,3-b]quinoxaline as a Low Reduction Potential and High Stability Anolyte Scaffold for Nonaqueous Redox Flow Batteries

Indolo[2,3-b]quinoxaline as a Low Reduction Potential and High Stability Anolyte Scaffold for Nonaqueous Redox Flow Batteries

Aqueous Redox Flow Batteries: Small Organic Molecules for the Positive Electrolyte Species

Quinones for Aqueous Organic Redox Flow Battery: A Prospective on Redox Potential, Solubility, and Stability

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