A prototype of high-performance two-electron non-aqueous organic redox flow battery operated at −40 °C

Liang, Zhiming; Jha, Rahul Kant; Suduwella, T. Malsha; Attanayake, N. Harsha; Wang, Yangyang; Zhang, Wei; Cao, Chuntian; Kaur, Aman Preet; Landon, James; Odom, Susan A.

doi:10.1039/d2ta07876g

Cited by 9 publications

(13 citation statements)

References 69 publications

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“…25, [29][30][31] The assessed capacity of the cell may significantly decrease over cycles due to the reduced solubility of the radical form. 4,7,27 If this fact is ignored, researchers may not realize that the actual reason for low-capacity reten�on is the decreased solubility. In our study, we have synthesized a series of phenothiazine deriva�ves and conducted solubility measurements on both uncharged and isolated radical forms.…”

Section: Electrolytes Selec�onmentioning

confidence: 99%

“…2,18,25 Nevertheless, it is essen�al to highlight that for deriva�ves involving a two-electron transfer like B(MEEO)EPT, self-discharge is a significant challenge that demands aten�on. 2,7,[36][37] In Figure 7c, microelectrode cyclic voltammetry was used to characterize a 0.3 M B(MEEO)EPT symmetric cell. A�er comple�ng the charge or discharge cycles, two plateaus corresponding to the neutral or dica�on forms should be observed.…”

Section: Ensuring Chemical and Electrochemical Stabilitymentioning

confidence: 99%

“…These include two reservoirs func�oning as electrolyte containers, carbon fiber electrodes where electrochemical reac�ons take place, ion-selec�ve membranes that prevent cross-contamina�on of redox-ac�ve molecules, and a pump responsible for circula�ng the electrolyte solu�ons throughout the system. 1,7 Generally, RFBs can be classified into two types: aqueous redox flow bateries (ARFBs) and non-aqueous redox flow bateries (NAORFBs), depending on the solvents used. In the case of ARFBs, their widespread u�liza�on in real-life applica�ons is facilitated by the excellent solubility of redox species and the high selec�vity of the membranes.…”

Section: Introduc�onmentioning

confidence: 99%

“…Addi�onally, the high freezing point of water, around 0°C restricts their geographical and seasonal applica�ons. 7 As the next fron�er in RFB technology, NAORFBs offer a significantly wider size of electrochemical window and a lower freezing point (Table 1). 5,[12][13] These characteris�cs provide them with substan�al poten�al to enhance their energy density and prac�cal applica�ons.…”

Section: Introduc�onmentioning

confidence: 99%

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Molecular Tailoring of Phenothiazine Derivatives for High Performance Non-Aqueous Organic Redox Flow Batteries

Liang

2023

Preprint

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Non-aqueous organic redox flow batteries (NAORFBs) have gained significant attention as a promising electrochemical energy storage technology, offering numerous advantages such as grid-scale electricity production with variable intermittent delivery, decoupled energy and power density, and simplified manufacturing processes. However, despite their promising attributes, this system faces certain challenges including limited solubility, poor electrochemical stability of radicals, low redox potential, and inadequate ionic conductivity, hampering their widespread commercial utilization. In recent years, molecular engineering has emerged as a transformative tool for designing and synthesizing of high-performance redox-active molecules for NAORFBs. These molecules, such as quinone, nitroxyl radicals, dialkoxybenzenes, phenothiazine, phenazine, pyridiniums, and viologen derivatives, offer precise control over solubility, stability, and redox potential through the strategic introduction or removal of functional groups. Our team has focused extensively on molecular engineering, with a specific focus on the phenothiazine core. Through a concise synthesis process, we have successfully synthesized a series of finely tuned phenothiazine derivatives with adjustable redox potentials, solubility, and stability. These tailored derivatives have demonstrated remarkable longevity when applied in NAORFBs. The selection of appropriate supporting electrolytes and membranes plays a significant role in achieving high performance RFBs. In this account, we commence by summarizing the results of our comprehensive examination of various supporting electrolytes and commercially available membranes, assessing their effects to stability, electrochemical reversibility, and crossover rates of redox-active molecules such as N-[2-(2-methoxyethoxy)ethyl]phenothiazine (MEEPT). This comprehensive analysis provides a fundamental framework for evaluating the supporting materials for novel catholytes or anolytes. In efforts to fine-tune the solubility and redox potential of phenothiazines, we have employed molecular tailoring techniques. For instance, the introduction of alkyl or alkoxy groups on the nitrogen atom of phenothiazine has significantly improved solubility and electrochemical stability. These modifications have provided neutral molecules miscible with the commonly used organic solvents and allowed their radicals to reach concentrations of up to 0.5 M. However, monosubstituted phenothiazines still exhibit a relatively low usable oxidation potential, at 0.3 V vs. ferrocene/ferrocenium (Fc/Fc+). To address this limitation, we further modified the phenothiazine core by introducing substituents at positions 3 and 7. This alteration resulted in a notable increase in the stable oxidation potential. Notably, N-ethyl-3,7-bis(2-(2-methoxyethoxy)ethoxy)phenothiazine (B(MEEO)EPT) exhibited an oxidation potential of 0.65 V vs. Fc/Fc+. In pursuit of cost-effective NAORFBs, we developed a novel ionic compound named ethylpromethazine bis(trifluoromethanesulfonyl)imide (EPRT-TFSI). Through a concise three-step synthesis, EPRT-TFSI compound displayed a high redox potential of 1.12 V vs Fc/Fc+, a solubility of up to 1.3 M, and an ionic conductivity as high as 25 mS cm-1. The utilization of such ionic compounds eliminates the necessity for additional supporting salts in the electrolytes. Furthermore, we conducted investigations into the stability of radicals at various concentrations, employing different counter anions while maintaining controlled moisture levels in ambient environments. These stability tests provide valuable insights and guidelines for synthesizing other stable redox-active molecules. Our dedicated research efforts have been instrumental in advancing the development of high-performance NAORFBs, bringing us closer to realizing their potential as a prominent energy storage technology.

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Section: Electrolytes Selec�onmentioning

confidence: 99%

Section: Ensuring Chemical and Electrochemical Stabilitymentioning

confidence: 99%

Section: Introduc�onmentioning

confidence: 99%

Section: Introduc�onmentioning

confidence: 99%

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Molecular Tailoring of Phenothiazine Derivatives for High Performance Non-Aqueous Organic Redox Flow Batteries

Liang

2023

Preprint

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“…Studies at temperatures below the freezing point of water are often motivated by energy storage needs in colder regions. [29][30][31][32] Even fewer examples of elevated temperature cycling were found. 33,34 One example presented by Clegg is directly pertinent to our work, as it demonstrates capacity and performance decay of a NAqRFB cell employing a phenothiazine/viologen redox couple at 40 °C.…”

mentioning

confidence: 99%

Elucidating the Effects of Temperature on Nonaqueous Redox Flow Cell Cycling Performance

Quinn,

Ripley,

Matteucci

et al. 2023

J. Electrochem. Soc.

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The impact of cell temperature is a relatively underexplored area within the burgeoning field of nonaqueous redox flow batteries (NAqRFBs). Here, we investigate the effect of elevated temperature on the performance of nonaqueous redox electrolytes and associated flow cells. Using a model compound, N-(2-(2-methoxyethoxy)-ethyl)phenothiazine (MEEPT), in a propylene-carbonate-based electrolyte, we experimentally measure the temperature dependence of relevant physicochemical properties (i.e., electrolyte conductivity, viscosity, diffusivity) and electrochemical characteristics (i.e., chemical and electrochemical reversibility) across a temperature range of 30 °C to 70 °C. We then perform flow cell studies, finding that while ohmic and mass transport resistances decrease significantly with increases in temperature for the MEEPT/MEEPT+· redox couple, accessible electrolyte capacity gradually reduces at temperatures > 50 °C. Ex-situ, post-test characterization using microelectrode voltammetry suggests that this capacity fade is due to instability of the MEEPT radical cation. Finally, using MEEPT as a posolyte and a model viologen negolyte (bis(2-(2-methoxyethoxy)ethyl)viologen), we assemble a full cell and perform polarization analyses, observing a 2× increase in the peak power density when the operating temperature is increased from 30 °C to 70 °C. Broadly, this work highlights opportunities for systematic engineering of nonaqueous electrolytes and flow cells for higher power operation at elevated temperatures.

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Metal Coordination Compounds for Organic Redox Flow Batteries

Gao,

Xia,

et al. 2024

Batteries & Supercaps

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Along with the continuous optimization of the energy structure, more and more electricity come from intermittent renewable energy sources such as wind and solar energy. Redox flow batteries (RFBs) have the advantage that energy and power can be regulated independently, so they are widely used in large‐scale energy storage. Redox active materials are the important components of RFBs, which determine the performance of the battery and the cost of energy storage. Some metal coordination compounds (MCCs) and their derivatives have been considered redox active materials that can replace metal‐based redox flow batteries due to their properties such as tunability, high abundance and sustainability. MCCs can provide higher energy density because they are highly soluble both in the initial state and in any charged state during the battery cycling process. MCCs have also attracted a lot of attention from researchers because of their high economic value, low toxicity, and wide availability. This review provides an overview of the recent development of soluble metal coordination compounds, such as Ferrocene, and concludes with an in‐depth discussion of the prospects of metal coordination compounds for application in organic redox flow batteries.

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A prototype of high-performance two-electron non-aqueous organic redox flow battery operated at −40 °C

Abstract: Redox flow batteries (RFBs) which can be operated under subzero temperature is significant for applications in cold regions. However, very few of RFBs have been reported to use below -20...

Cited by 9 publications

References 69 publications

Molecular Tailoring of Phenothiazine Derivatives for High Performance Non-Aqueous Organic Redox Flow Batteries

Molecular Tailoring of Phenothiazine Derivatives for High Performance Non-Aqueous Organic Redox Flow Batteries

Elucidating the Effects of Temperature on Nonaqueous Redox Flow Cell Cycling Performance

Metal Coordination Compounds for Organic Redox Flow Batteries

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