Single‐Molecule Redox‐Targeting Reactions for a pH‐Neutral Aqueous Organic Redox Flow Battery

Zhou, Mingyue; Chen, Yan; Salla, Manohar; Zhang, Hang; Wang, Xun; Mothe, Srinivasa Reddy; Wang, Qing

doi:10.1002/anie.202004603

Cited by 55 publications

(68 citation statements)

References 49 publications

(64 reference statements)

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“…Pyridiniums, especially viologens, are outstanding electron acceptors [ 5 ] and have been used in the negative electrolyte of aqueous redox flow batteries (ARFBs). [ 6 ] Viologen can well work in neutral pH aqueous solution, [ 7 ] which makes it unique as compared with other organic compounds, such as quinone, [ 8 ] phenazine, [ 9 ] and phenothiazine. [ 10 ] As a result, the viologen‐based ARFBs can be operated under non‐corrosive conditions associated with low maintenance cost.…”

Section: Figurementioning

confidence: 99%

Phenylene‐Bridged Bispyridinium with High Capacity and Stability for Aqueous Flow Batteries

Huang

et al. 2021

Advanced Materials

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A rotating phenyl ring is introduced between the two pyridinium rings, namely, 1,1′‐bis[3‐(trimethylamonium)propyl]‐4,4′‐(1,4‐phenylene)bispyridinium tetrachloride ((APBPy)Cl4), to form a switchable conjugation. In this design, the conjugation is switched “off” in the oxidized state and the two pyridinium rings behave independently during the redox process, yielding a concomitant transfer of two electrons at the same potential and, thus, simplifying the battery management. The conjugation is switched “on” in the reduced state and the charge can be effectively delocalized, lowering the Lewis basicity and improving its chemical stability. By pairing 0.50 m (APBPy)Cl4 with a 2,2,6,6‐tetramethylpiperidin‐1‐yl oxyl derivative as the positive electrolyte, a flow battery delivers a high standard cell voltage of 1.730 V and a high specific capacity of 20.0 Ah L–1. The battery also shows an exceptionally high energy efficiency of 80.8% and a superior cycling stability at 80 mA cm–2. This strategy proves itself a great success in engineering viologen as a two‐electron storage mediator with high capacity and stability.

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Section: Figurementioning

confidence: 99%

Phenylene‐Bridged Bispyridinium with High Capacity and Stability for Aqueous Flow Batteries

Huang

et al. 2021

Advanced Materials

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“…During discharging process, the above process is reversed and S + will be first reduced to S at the current collector and transfers the electron to the delithiated LiFePO4. A pair of redox shuttle molecules with potentials sit astride the Fermi level of the targeted solid active material were often adopted for the charging and discharging process respectively in practical application [54][55][56][57][58][59][60] . The concept of redox-targeting RFB was first realized by using FcBr2 and Fc as redox shuttle molecules for the charging and discharging of LiFePO4 particles respectively 61,62 .…”

Section: Redox-targeting Approachmentioning

confidence: 99%

Strategies to Improve the Energy Density of Non-Aqueous Organic Redox Flow Batteries

Cong¹,

Lu²

2021

Acta Physico Chimica Sinica

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Redox flow batteries (RFBs) have been widely recognized as the primary choice for large-scale energy storage due to their high energy efficiency, low cost, and versatile design of decoupled energy storage and power output. However, the broad deployment of RFBs in the power grid has long been plagued by the high cost and low energy density of existing inorganic metal-based electrodes. Redox-active organic molecules (ROMs), on the other hand, have recently been extensively explored as the potentials electrodes in RFBs for their potential low cost, abundant resources, and highly tunable structure. The energy density of RFBs is proportional to the number of electrons transferred per unit reaction, the concentration of active materials, and the cell voltage. Therefore, strategies to improve the energy density of RFBs could be categorized into three classes: (1) expanding the cell voltage;(2) maximizing the practical concentration of active materials; (3) realizing multi-redox process. Benefited by the highly tunable structure and properties of ROMs, the cell voltage of RFBs could be realized by lowering the redox potentials of anolytes or/and increasing the redox potentials of catholytes. To fully exploit the low-potential anolytes and high-potential catholytes, non-aqueous electrolytes with wider electrochemical potential windows (EPWs) are preferred over the aqueous systems. However, the solubility of most ROMs in commonly used non-aqueous electrolytes is very limited. Several effective strategies to improve the practical concentrations of ROMs have been proposed: (1) the solubility of ROMs could be easily tailored by adjusting the intermolecular interactions between ROMs and the interactions between ROMs and electrolytes via molecular engineering; (2) the redox-active eutectic systems remain liquid at or near room temperature, allowing us to reduce or completely remove the inactive solvent used in the conventional electrolyte of RFBs, which leads to an enhanced practical concentration of the redox-active components; (3) the semi-solid suspension achieves a high practical concentration of ROMs by combining the advantages of solid ROMs with high energy density and liquid electrolytes with flowability; (4) the redox-targeting approach breaks the solubility limitation by realizing remote charge exchange between the solid active materials deposited in the tanks and the current collectors of the electrochemical stacks via ROMs dissolved in electrolytes. The first three strategies employ a homogeneous flowing redox-active fluid which suffers from deteriorated physical and electrochemical properties as the practical concentration of ROMs increase, e.g., high viscosity, phase separation, and salt precipitation. The redox-targeting approach uses a hybrid flowing liquid/static solid system, which avoids the aforementioned unfavorable changes in electrolyte properties, however, this design introduces additional chemical reactions between the ROMs and the solid active materials, which may reduce the power output. Another effici...

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“…Despite the great promise of solid redoxmediated flow batteries (also referred to as solid targeting or solid booster), only a couple of examples of aqueous full battery using solid materials in both compartments have been realized. [11,12] Herein, we report the fundamentals and proof of concept of a high-energy alkaline full redox-mediated flow battery based on the successful combination of two established battery technologies through the use of redox-mediating processes, i.e., static Ni-MH battery and aqueous organic redox flow battery (AORFB), into a new battery technology: the redox-mediated nickel-metal hydride (MH) flow battery. This novel flow battery combines the high energy density of Ni-MH solid materials with the easy recyclability and independent scalability of energy and power of flow configuration.…”

Section: Introductionmentioning

confidence: 99%

The Redox‐Mediated Nickel–Metal Hydride Flow Battery

Páez

Zhang

Muñoz

et al. 2021

Advanced Energy Materials

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market, and more are under development at lab scale to fulfill the growing requirements of applications. In general, battery technologies can be categorized into two main groups according to the location of the energy storing materials (active materials): redox flow batteries and static batteries. In the former, active materials are stored outside the electrochemical reactor, while in the latter, they are located inside the battery cell. Each group possesses intrinsic advantages and disadvantages. While redox flow batteries offer independent scalability of energy and power, and easy recyclability, static batteries usually have higher energy densities. As a result, static batteries are used in applications demanding higher energy densities, whereas redox flow batteries are more suitable for stationary energy storage.The development of a battery technology combining the best features of each category has been long desired. The use of solid electroactive materials stored in the external reservoirs of redox flow batteries is the most direct approach; however, challenging to be realized. The semisolid flow battery, in which dense but flowable slurries of solid materials are used, has demonstrated a drastic increase in energy density. [2,3] However, the practical application of this concept raised concerns as viscous slurries containing solid particles must be continuously flown through the system. This main concern is overcome by the confinement of the solid electroactive materials in the external reservoirs. In this case, the dissolved electroactive species act as Each battery technology possesses intrinsic advantages and disadvantages, e.g., nickel-metal hydride (MH) batteries offer relatively high specific energy and power as well as safety, making them the power of choice for hybrid electric vehicles, whereas aqueous organic flow batteries (AORFBs) offer sustainability, simple replacement of their active materials and independent scalability of energy and power, making them very attractive for stationary energy storage. Herein, a new battery technology that merges the above mentioned battery technologies through the use of redox-mediated reactions is proposed that intrinsically possesses the main features of each separate technology, e.g., high energy density of the solid active materials, easy recyclability, and independent scalability of energy and power. To achieve this, Ni(OH) 2 and MHs are confined in the positive and negative reservoirs of an AORFB that employs alkaline solutions of potassium ferrocyanide and a mixture of 2,6-dihydroxyanthraquinone and 7,8-dihydroxyphenazine-2-sulfonic acid as catholyte and anolyte, respectively. An energy density of 128 Wh L -1 is achieved based on the capacity of the reservoirs leaving ample room for improvement up to the theoretical limit of 378 Wh L -1 . This new battery technology opens up new market opportunities never before envisaged, for redox flow batteries, e.g., domestic energy storage and heavy-duty vehicle transportation.

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Single‐Molecule Redox‐Targeting Reactions for a pH‐Neutral Aqueous Organic Redox Flow Battery

Cited by 55 publications

References 49 publications

Phenylene‐Bridged Bispyridinium with High Capacity and Stability for Aqueous Flow Batteries

Phenylene‐Bridged Bispyridinium with High Capacity and Stability for Aqueous Flow Batteries

Strategies to Improve the Energy Density of Non-Aqueous Organic Redox Flow Batteries

The Redox‐Mediated Nickel–Metal Hydride Flow Battery

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