Sub-2-nm Channels within Covalent Triazine Framework Enable Fast Proton-Selective Transport in Flow Battery Membrane

Ion conductive membranes (ICMs) with robust sub-2-nm channels show high proton transport rate in flow battery, but it remains a great challenge to precisely control the ion sieving of the membranes. Herein, as a promising proton-selective carrier, sulfonated piperazine covalent triazine framework (s-pCTF) with the channel size of ≈1.5 nm and abundant fast proton hopping sites is introduced into sulfonated poly(ether ether ketone) (SPEEK) to fabricate advanced ICM for vanadium flow battery (VFB) application. The interior protoplasmic channels of s-pCTF demonstrate significant Donnan exclusion effect, resulting in a high proton/vanadium ion selectivity in theory (6.22 × 10⁵). Meanwhile, the nitrogen-rich sub-2-nm channels yield fast proton highway, and exterior-grafted sulfonic acid groups further facilitate the proton transfer. By regulating the ion sieving and proton conductivity, the optimal hybrid membrane exhibits synchronously improved battery performance with an enhanced energy efficiency (92.41% to 78.53% at 40–200 mA cm⁻²) and long-term stability for 900 cycles over 400 h (EE: 87.2–85% at 120 mA cm⁻²), outperforming pure SPEEK and Nafion212 membranes. This study validates the applicability of organic porous CTF with sub-2-nm channels and desired functionality in ICMs for high-performance VFB application.     

Solvent‐Induced Rearrangement of Ion‐Transport Channels: A Way to Create Advanced Porous Membranes for Vanadium Flow Batteries

Porous membranes with critically hydrophobic/hydrophilic phase‐separated‐like structures for use in vanadium flow battery application are first realized by solvent‐induced reassembly of a polymer blend system. Porous poly(ether sulfone) (PES)/sufonated poly(ether ether ketone) (SPEEK) blend membranes with tunable pore size are prepared via the phase inversion method. After solidification, isopropanol (IPA) is introduced to induce the reassembly of sulfonated groups and further form ion‐transport channels by using the interaction between IPA and functional groups in SPEEK. As a result, a highly phase separated membrane structure is created, composed of a highly stable hydrophobic porous PES matrix and hydrophilic interconnected small pores. The charged pore walls are highly beneficial to improving proton conductivity, while pores are simultaneously shrunk during the IPA treatment. Therefore, the resultant membranes show an excellent battery performance with a coulombic efficiency exceeding 99%, along with an energy efficiency over 91%, which is among the highest values ever reported. This article supplies an ease‐to‐operate and efficient method to create membranes with controlled ion‐transport channels.     

Enhancement of Proton Conduction at Low Humidity by Incorporating Imidazole Microcapsules into Polymer Electrolyte Membranes

Design and fabrication of hierarchically structured membranes with high proton conductivity is crucial to many energy‐relevant applications including proton exchange membrane fuel cell (PEMFC). Here, a series of imidazole microcapsules (IMCs) with tunable imidazole group loading, shell thickness, and lumen size are synthesized and incorporated into a sulfonated poly(ether ether ketone) (SPEEK) matrix to prepare composite membranes. The IMCs play two roles: i) Improving water retention properties of the membrane. The IMCs, similar to the vacuoles in plant cells, can render membrane a stable water environment. The lumen of the IMCs acts as a water reservoir and the shell of IMCs can manipulate water release. ii) They form anhydrous proton transfer pathways and low energy barrier pathways for proton hopping, imparting an enhanced proton transfer via either a vehicle mechanism or Grotthuss mechanism. In particular, at the relative humidity (RH) as low as 20%, the composite membrane exhibits an ultralow proton conductivity decline and the proton conductivity is one to two orders of magnitude higher than that of SPEEK control membrane. The enhanced proton conductivity affords the composite membrane an elevated peak power density from 69.5 to 104.5 mW cm^?2 in a single cell. Moreover, the application potential of the composite membrane for CO₂ capture is explored.     

Porous Proton Exchange Membrane with High Stability and Low Hydrogen Permeability Realized by Dense Double Skin Layers Constructed with Amino tris (methylene phosphonic acid)

Porous proton exchange membranes (PEMs) with abundant porous structures show enhanced phosphoric acid (PA) doping levels and proton transport capability. However, the high PA loss rate and serious hydrogen cross-over lead to poor membrane stability. Enhancing the stability of PA-doped porous PEMs is therefore crucial for obtaining high-performance proton exchange membrane fuel cells. Herein, a porous polybenzimidazole membrane with dense double skin layers is reported using amino tris (methylene phosphonic acid) (ATMP) constructed. This membrane effectively alleviates hydrogen permeation and PA loss in a water/anhydrous environment and exhibits enhanced stability. Surprisingly, as an organic proton conductor, ATMP has strong hydrogen bonding with PA, leading to the formation of more continuous proton transport channels. Due to the dense double skin layers protection and the synergistic mass transfer of ATMP and PA, the porous membrane shows excellent proton conductivity (0.112 S cm⁻¹) and a H₂-O₂ fuel cell peak power density of 0.98 W cm⁻² at 160 °C. Moreover, it presents excellent fuel cell stability, with a voltage decay rate of only 5.46 µV h⁻¹. In addition, the porous membrane surpasses the traditional working temperature range, operating in the range of 80–220 °C. This study provides new insight into developing high-performance porous PEMs.     

Cation Exchange Membranes with Bi-Functional Sites Induced Synergistic Hydrophilic Networks for Selective Proton Transport

Acid recycling via cation exchange membranes (CEMs) has attracted considerable attention from traditional industries and advanced manufacturing because of the economic and environmental advantages. However, current polymeric CEMs merely have constant ion channels by the fixed groups in the matrix and lack the synergy of bi-functional sites. Herein, a series of dibenzo-18-crown-6 (DB18C6) functionalized sulfonated poly(biphenyl alkylene) membranes is reported. The resultant membranes form phase separation and ordered ion channels by the electrostatic interaction between DB18C6-H⁺ complexes and the  SO₃⁻ anionic sites, constructing a low-swelling synergistic hydrophilic network. The prepared membranes have high proton permeation rates of 2.98-4.85 mol m⁻² h^-1 and extremely low ferrous ion permeabilities, leading to a high H⁺/Fe²⁺ selectivity of ≈3153 at the current density of 10 mA cm^-2, which is one order of magnitude higher than the commercial and previously reported membranes via the electrodialysis. These results provide strategies for designing bi-functional ion exchange membranes for selective ion transport via utilizing crown ether/cation complexes.     

N-CNTs-Based Composite Membrane Engineered By A Partially Embedded Strategy: A Facile Route To High-Performing Zinc-Based Flow Batteries

Zinc-based flow batteries are promising for distributed energy storage due to their low-cost and high-energy density advantages. One of the most critical issues for their practical application is the reliability that results from the heterogeneous zinc deposition and dead zinc from falling off the electrode. Herein, nitrogen-doped carbon nanotubes (N-CNTs)-based composite membrane through a facilely partially embedded method is reported to enable a dendrite-free alkaline zinc-based flow battery. The results indicate that the electrically conductive N-CNTs functional layer can enhance the transport dynamics of charge carriers and homogenize electric field distribution in membrane–electrode interface, which induces the initial nucleation of metallic zinc from the carbon felt electrode to N-CNTs functional layer and further achieve a uniform and dense plating of metallic zinc in alkaline media. Thus, the engineered membrane enables a stable alkaline zinc–iron flow battery performance for more than 350 h at a current density of 80 mA cm⁻². Moreover, an energy efficiency of over 80% can be afforded at a current density of 200 mA cm⁻². The scientific finding of this study provides a new strategy on composite membranes design and their capability to adjust the plating of metallic zinc in alkaline media.     

Rational Engineering CoxOy Nanosheets via Phosphorous and Sulfur Dual-Coupling for Enhancing Water Splitting and Zn–Air Battery

Herein, an efficient multifunctional catalyst based on phosphorus and sulfur dual-doped cobalt oxide nanosheets supported by Cu@CuS nanowires is developed for water splitting and Zn–air batteries. The formation of such a unique heterostructure not only enhances the number and type of electroactive sites, but also leads to modulated electronic structure, which produces reasonable adsorption energy toward the reactant, thereby improving electrocatalytic efficiency. The catalyst demonstrates small overpotentials of 116 and 280 mA cm⁻² to achieve 10 mA cm⁻² for hydrogen and oxygen evolution, respectively. As a result, a developed electrolyzer displays a cell voltage of 1.52 V at 10 mA cm⁻² and long-term stability with a current response of 92.3% after operating for 30 h. Moreover, using such a catalyst in the fabrication of a Zn–air battery also leads to a cell voltage of 1.383 V, along with a power density of 130 mW cm⁻² at 220 mA cm⁻².     

A Cost‐Effective Mixed Matrix Polyethylene Porous Membrane for Long‐Cycle High Power Density Alkaline Zinc‐Based Flow Batteries

Alkaline zinc‐based flow batteries (ZFBs) have received considerable interest for renewable energy storage due to their attractive features of low cost and high energy density. However, a membrane with high stability, high selectivity, and high ion conductivity is in urgent need. Herein, an economical mixed matrix membrane with highly anti‐alkali microporous hollow spheres (denoted as DM‐HM) is developed in this work. With excellent chemical and mechanical stability, DM‐HM can achieve a high area capacity of 100 mA h cm^?2 for carbon felt (CF)||Zn@CF symmetrical flow battery, and thereby exhibits 500 stable cycles with a coulombic efficiency of 98.6% and an energy efficiency of 88.3% at 80 mA cm^?2 for alkaline zinc–iron flow battery. Additionally, with 44 wt% of hollow spheres inside matrix, DM‐HM can dramatically shorten the ion transport pathway and results in a very high power density battery. A kilowatt stack assembled with DM‐HM shows a very impressive performance, further confirming the practicability of this scalable mixed matrix membrane for alkaline ZFBs.     

In Situ Defect-Free Vertically Aligned Layered Double Hydroxide Composite Membrane for High Areal Capacity and Long-Cycle Zinc-Based Flow Battery

Rechargeable aqueous zinc-based flow batteries (ZFBs) are promising candidates for large scale energy storage devices. However, the challenges from zinc dendrites and limited areal capacity considerably impede their wide application. Here, an in situ vertical growth of layered double hydroxide membrane (LDH-G) is constructed to enable long-life ZFBs. Owing to the high hydroxide ion conductivity and ion selectivity nature of LDH nanosheets, specifically, the precise control of directional ion transport in vertical arrangement LDHs, a superior battery performance can be realized. Moreover, the defect-free LDHs layer serves as a buffer layer to enable a uniform Zn deposition, which effectively enhances the areal capacity of the battery. As a result, the designed membrane endows an alkaline zinc-iron flow battery with excellent rate performance and cycling stability, maintaining an energy efficiency of 80% at 260 mA cm⁻² for 800 cycles, which is the highest performance ever reported. Most importantly, the LDHs layer enables the battery for 1200 h long-cycle stability with a uniform Zn deposition and high areal capacity of 240 mAh cm⁻². This work realizes an in situ growth of 3D LDHs arrays on the polymer substrate, which provides a strategy toward high areal capacity and dendrite-free Zn deposition for ZFBs.     

Subnanometer Nanowire-Reinforced Construction of COF-Based Membranes with Engineering Biomimetic Texture for Efficient and Stable Proton Conduction

Achieving rapid ion transport through nanochannels is essential for both biological and artificial membrane systems. Covalent organic frameworks (COFs) with well-defined nanostructures hold great promise for addressing the above challenge. However, due to the limited processability and inadequate interlamellar interaction of COF materials, it is extremely difficult to integrate them to prepare high-performance proton conductors. Herein, inspired by the ingenious bio-adhesion strategy in nature, ultrafast proton conduction is achieved by taking advantage of COF membranes where TP-COF nanosheets are linked by subnanometer nanowires/lignocellulosic nanofibrils composites (SNWs/LCNFs) through electrostatic and π-π interactions to form an ordered and robust structure. Notably, the synthesized SNWs exhibited impressive proton conductivity and adhesion capacity due to their inbuilt phosphotungstic acid (HPW) molecules and multidimensional interactions. Therefore, attributed to the synergistic contribution of TP-COFs and SNWs, the composite membrane achieves ultrahigh proton conductivity (0.395 S cm⁻¹ at 80 °C and 100% RH), superior mechanical property (109.8 MPa), exceptional fuel cell performance (71.6 mW cm⁻²), and superior operational stability (OCV decay rate is about 1.5 mV h⁻¹), demonstrating outstanding competitiveness. More importantly, the proposed design concept has the potential to be applied in membranes for various electrochemical devices and molecular separations.     

Highly Stable Anion Exchange Membranes with Internal Cross‐Linking Networks

Anion exchange membranes (AEMs) with excellent stability and high ion conductivity are fabricated via the formation of internal cross linking networks. The internal crosslinking networks are constructed by reacting 4,4′‐bipyridine with chloromethylated polysulfone. The bipyridine group simultaneously functions as ionic conductor and cross linker in this system. The performance of the membrane is tuned via controlling the 4,4′‐bipyridine content in the casting solution. The prepared membranes demonstrate excellent chemical stability and high ion conductivity under acidic conditions. As a consequence, the membranes show very promising performance for vanadium flow battery application, exhibiting a Coulombic efficiency of 99.2% and an energy efficiency of 81.8% at a current density of 140 mA cm^?2. The battery that is assembled with the prepared membrane shows a stable battery performance over more than 1600 cycles, which is by far the longest cycle life reported. These results indicate that the AEMs with internal crosslinking structures are promising candidates for battery systems and even for fuel cells.     

Advanced Charged Sponge‐Like Membrane with Ultrahigh Stability and Selectivity for Vanadium Flow Batteries

Advanced charged sponge‐like porous membranes with ultrahigh stability and selectivity are designed and fabricated for vanadium flow battery (VFB) applications. The designed porous membranes are fabricated via constructing positively charged cross‐linked networks on the pore walls of polysulfone membranes. The charge density of the pore walls can be tuned by changing the crosslinking time. The positively charged pore walls can effectively retain vanadium ions via Donnan exclusion, hence keeping extremely high selectivity, while the crosslinked network effectively increases the membrane stability. As a result, the designed membranes exhibit an outstanding performance, combining extremely high selectivity and stability. The single cell assembled with the prepared porous membrane shows a columbic efficiency of 99% and an energy efficiency of 86% at a current density of 80 mA cm^?2, which is much higher than Nafion 115 (93.5%; 82.3%). A battery assembled with the prepared membrane shows a stable battery performance over more than 6000 cycles, which is by far the longest record for porous membranes ever reported. These results indicate that advanced, charged, sponge‐like, porous membranes with a crosslinked pore‐wall structure are highly promising for VFB applications.     

Achieving over 1,000 mW cm−2 Power Density Based on Locally High-Density Cross-Linked Polybenzimidazole Membrane Containing Pillar[5]arene Bearing Multiple Alkyl Bromide as a Cross-Linker

Cross-linking is widely accepted as an effective method to improve the mechanical strength and durability of phosphoric acid (PA) doped polybenzimidazole (PBI) membranes. However, the cross-linked membranes generally exhibit compromised overall performance since their compact network structures decrease the free volumes of membranes, leading to poor proton conductivity. In this study, a locally high-density cross-linked polybenzimidazole network based on pillar[5]arene bearing multiple alkyl bromide is constructed for the first time to achieve high proton conductivity, desired mechanical properties, and excellent fuel cell performance. The pillar[5]arene-cross-linked network considerably enhances the mechanical strength of membrane (14.6 MPa), particularly with high PA uptake, and provides loose PBI chain segment packing to retain PA (315.9%). Surprisingly, the pillar[5]arene-cross-linked PBI membrane displays a high-power density of 1,084.1 mW cm⁻² at 180 °C and 0.6 mg cm⁻² Pt loading without backpressure and humidification, that is the highest value reported in cross-linked membranes for high-temperature proton exchange membrane fuel cells.     

Multifunctional Carbon Felt Electrode with N-Rich Defects Enables a Long-Cycle Zinc-Bromine Flow Battery with Ultrahigh Power Density

Zinc-bromine flow batteries (ZBFBs) are regarded as one of the most promising technologies for energy storage owing to high energy density and low cost. However, the sluggish reaction kinetics of Br₂/Br⁻ couples and zinc dendrite issue lead to low power density and poor cycle stability. Herein, a multifunctional carbon felt-based electrode (NTCF) with N-rich defects is fabricated for ZBFBs. The defects with abundant N-containing groups on carbon fibers of NTCF provide high catalytic activity on Br₂/Br⁻ reactions. Simultaneously, the lower energy barrier of N-rich defects to adsorb zinc atoms, and more deposition sites on NTCF induce more uniform zinc deposition. Thus, a ZBFB using NTCF as both the anode and cathode can stably operate at an unprecedentedly high current density of 180 mA cm⁻² with a coulombic efficiency of 97.25%. Moreover, a long cycle life of over 140 cycles with a coulombic efficiency of 98.93% for a Zn symmetric flow battery at 80 mA cm⁻² is achieved under a high areal capacity of 40 mAh cm⁻². This current density and areal capacity are by far the highest values ever reported for Zn symmetry flow batteries. Therefore, this work provides an available approach to improve the power density and cycle life of ZBFBs.     

High Ionic Conductivity Motivated by Multiple Ion-Transport Channels in 2D MOF-Based Lithium Solid State Battery

Metal-organic frameworks (MOFs) have been proposed as novel fillers for constructing polymer solid electrolytes based composite electrolytes. However, MOFs are generally used as passive fillers, in-depth revealing the binding mode between MOFs and polyethylene oxide (PEO), the critical role of MOFs in facilitating Li⁺ transport in solid electrolytes is full of challenges. Herein, inspired by density functional theory (DFT) the 2D-MOF with rich unsaturated metal coordination sites that can bind the O atom in PEO through the metal–oxygen bond,  anchor TFSI⁻ to release Li⁺, resulting in a remarkable Li⁺ transference number of 0.58, is reported according well with the experimental results and molecular dynamics (MD) simulation. Impressively, after the introduction of the 2D-MOF, the Li⁺ can rapidly hop along the benzene ring center within the 2D-MOF plane, and the interface between the benzene ring and PEO can also serve as a fast Li⁺ migration pathway, delivering multiple ion-transport channels, which present a high ion conductivity of 4.6 × 10⁻⁵ S cm⁻¹ (25 °C). The lithium symmetric battery is stable for 1300 h at 60 °C, 0.1 mA cm⁻². The assembled lithium metal solid state battery maintains high capacity of 162.8 mAh g⁻¹ after 500 cycles at 60 °C and 0.5 C. This multiple ion-transport channels approach brings new ideas for designing advanced solid electrolytes.     

Electrospinning Synthesis of Self-Standing Cobalt/Nanocarbon Hybrid Membrane for Long-Life Rechargeable Zinc–Air Batteries

Integrating high-efficiency oxygen electrocatalyst directly into air electrodes is vital for zinc–air batteries to achieve higher electrochemical performance. Herein, a self-standing membrane composed of hierarchical cobalt/nanocarbon nanofibers is fabricated by the electrospinning technique. This hybrid membrane can be directly employed as the bifunctional air electrode in zinc–air batteries and can achieve a high peak power density of 304 mW cm⁻² with a long service life of 1500 h at 5 mA cm⁻². Its assembled solid-state zinc–air battery also delivers a promising power density of 176 mW cm⁻² with decent flexibility. The impressive rechargeable battery performance would be attributed to the self-standing membrane architecture integrated by oxygen electrocatalysts with abundant cobalt–nitrogen–carbon active species in the hierarchical electrode. This study may provide effective electrospinning solutions in integrating efficient electrocatalyst and electrode for energy storage and conversion technologies.     

High-performance Poly(biphenyl piperidinium) Type Anion Exchange Membranes with Interconnected Ion Transfer Channels: Cooperativity of Dual Cations and Fluorinated Side Chains

The performance of alkaline fuel cells is severely limited by substandard anion exchange membranes (AEMs) due to the lower ionic conductivity compared to the proton exchange membranes. The ionic conductivity of AEMs can be effectively improved by regulating the microphase structure, but it still cannot meet the practical use requirements. Here, enhanced microphase-separated structures are constructed by the cooperativity of highly hydrophilic dual cations and highly hydrophobic fluorinated side chains. Meanwhile, the introduction of  O enhances the flexibility of side chains and facilitates the formation of ion transport channels. The dual piperidinium cation functionalized membrane (PB2Pip-5C8F) which is grafted with the ultra-hydrophobic fluorocarbon chain exhibits a high conductivity of 74.4 mS cm⁻¹ at 30 °C and 168.46 mS cm⁻¹ at 80 °C. Furthermore, the PB2Pip-5C8F membrane achieves the highest peak power density of 718 mW cm⁻² at 80 °C under a current density of 1197 mA cm⁻² without back pressure. A long-term life cell test of this AEM shows a low voltage decay rate of 1.68 mV h⁻¹ over 70 h of operation at 80 °C.     

A Prussian-Blue Bifunctional Interface Membrane for Enhanced Flexible Al–Air Batteries

Flexible Al–air batteries have attracted widespread attention in the field of wearable power due to the high theoretical energy density of Al metal. However, the efficiency degradation and anodizing retardation caused by Al parasitic corrosion severely limit the performance breakthrough of the batteries. Herein, a Prussian-blue bifunctional interface membrane is proposed to improving the discharge performance of hydrogel-based Al–air battery. When a rational 12 mg·cm⁻² membrane is loaded, the effect of anticorrosion and activation is optimal thanks to the formation of a stable and breathable interface. The results demonstrate that a flexible Al–air battery using the membrane can output a high power density of 65.76 mW·cm⁻². Besides, the battery can achieve a high capacity of 2377.43 mAh·g⁻¹, anode efficiency of 79.78%, and energy density of 3176.39 Wh·kg⁻¹ at 10 mA·cm⁻². Density functional theory calculations uncover the anticorrosion-activation mechanism that Fe³⁺ with a large number of empty orbitals can accelerate electrons transfer, and nucleophilic reactant [Fe^II(CN)₆]⁴⁻ promotes the Al³⁺ diffusion. These findings are beneficial to the inhibition of interfacial parasitic corrosion and weakening of discharge hysteresis for flexible Al–air batteries.     

Ultra-Stable,Highly Proton Conductive,and Self-Healing Proton Exchange Membranes Based On Molecule Intercalation Technique and Noncovalent Assembly Nanostructure

Proton exchange membranes (PEMs) that can heal mechanical damage to restore original functions are imperative for fabricating reliable and durable proton exchange membrane fuel cells (PEMFCs). Here, an ultra-stable, highly proton conductive self-healing PEM via hydrogen-bonding complexation between Nafion and poly(vinyl alcohol) (PVA) followed by incorporation of sodium lignosulfonate (SLS) intercalation-modified graphene oxide (GO) and post-modification with 4-formylbenzoic acid (FBA) is presented. Notably, the introduction of GO complexes and post-modification of FBA molecules effectively improves the stability of composite membranes and also participate in the establishment of proton-conducting nanochannels. Compared with recast Nafion, the FBA-Nafion/PVA@SLS/GO composite membranes exhibit enhanced mechanical properties (36.2 MPa at 104.8% strain) and higher proton conductivity (0.219 S cm⁻¹ at 80 °C-100% RH and 23.861 mS cm⁻¹ at 80 °C-33% RH, respectively). More importantly, the incorporated PVA gives the FBA-Nafion/PVA@SLS/GO composite membranes superior self-healing capabilities that can heal mechanical damage of several tens of micrometers in size and restore their original proton conductivity under the operating conditions of the PEMFCs. This study opens an avenue toward the development of reliable and durable PEM for PEMFCs.     

An Extremely Stable,Highly Soluble Monosubstituted Anthraquinone for Aqueous Redox Flow Batteries

An extremely stable, energy-dense (53.6 Ah L⁻¹, 2 m transferrable electrons), low crossover (permeability of <1 × 10⁻¹³ cm² s⁻¹ using Nafion 212 (Nafion is a trademark polymer from DuPont)), and potentially inexpensive anthraquinone with 2-2-propionate ether anthraquinone structure (abbreviated 2-2PEAQ) is synthesized and extensively evaluated under practically relevant conditions for use in the negolyte of an aqueous redox flow battery. 2-2PEAQ shows a high stability with a fade rate of 0.03–0.05% per day at different applied current densities, cut-off voltage windows, and concentrations (0.1 and 1.0 m ) in both a full cell paired with a ferro/ferricyanide posolyte as well as a symmetric cell. 2-2PEAQ is further shown to have extreme long-term stability, losing only ≈0.01% per day when an electrochemical rejuvenation strategy is employed. From post-mortem analysis (nuclear magnetic resonance (NMR), liquid chromatography–mass spectrometry (LC-MS), and cyclic voltammetry (CV)) two degradation mechanisms are deduced: side chain loss and anthrone formation. 2-2PEAQ with the ether linkages attached on carbons non-adjacent to the central ring is found to have three times lower fade rate compared to its isomer with ether linkages on the carbon adjacent to the central quinone ring. The present study introduces a viable negolyte candidate for grid-scale aqueous organic redox flow batteries.