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Secondary batteries, or rechargeable batteries, have revolutionized various industries by offering the ability to be reused after depletion. Membranes in secondary batteries act as separators, preventing direct contact between electrodes while facilitating ion transport, crucial for energy storage and preventing short circuits. Despite their theoretical ability to be used infinitely, real-time applications face challenges, including the inefficiency of available membranes. This review focuses on the use of chitosan, a biopolymer derived from chitin, in three promising secondary batteries: vanadium redox flow batteries, Aq. zinc batteries, and lithium-ion batteries due to their wide range of applications and promising future scope. For lithium-ion batteries, N-succinyl chitosan-chitosan and chitosan–lithium membranes offer potential improvements in ionic conductivity and mechanical strength, while in Aq. zinc battery chitosan-based carbon membrane and phosphorylcholine zwitterionic protective layer reduces the dendrite formation and alleviates side reactions and for vanadium redox flow battery chitosan modified batteries aim to reduce vanadium ion crossover. Using a chitosan-based membrane increases the energy efficiency of the vanadium redox flow battery to 88.6% from 60% and sustains an Aq. zinc ion battery for up to 2000 cycles. Comprehensively, this review also imparts a roadmap leading to the future prospects of chitosan biopolymer-based secondary batteries to ameliorate the energy density, and overall electrochemical performance of chitosan-derived batteries by modifying the electrode material, for heading toward a green, and sustainable energy storage system. [ABSTRACT FROM AUTHOR]

Overcoming the trade‐off between the graphitization of the carbon substrate and enhanced electronic metal–support interaction (EMSI) and intrinsic activity of Pt‐C catalysts remains a major challenge for ensuring the durable operation of energy conversion devices. This article presents a hybrid catalyst consisting of PtFe nanoparticles and single Pt and Fe atoms supported on N‐doped carbon (PtFeNPs@PtFeSAs‐N‐C), which exhibits improved activities in hydrogen evolution and oxygen reduction reactions (HER and ORR, respectively) and has excellent durability owing to the high graphitization, rich edge defects, and porosity of the carbon in PtFeNPs@PtFeSAs‐N‐C, as well as strong EMSI between the PtFe nanoparticles and edge‐defective carbon embedded with Pt and Fe atoms. According to theoretical calculations, the strong EMSI optimizes the H* adsorption–desorption and facilitates the adsorption OOH*, accelerating the HER and ORR processes. A novel flow seawater‐Al/acid hybrid fuel cell using the PtFeNPs@PtFeSAs‐N‐C cathode can serve as a high‐efficiency energy conversion device that delivers a high power density of 109.5 mW cm−2 while producing H2 at a significantly high rate of 271.6 L m−2 h−1. Moreover, PtFeNPs@PtFeSAs‐N‐C exhibits a remarkable performance (high power density of 298.0 mW cm−2 and long‐term durability of 1000 h) in a flow Zn–air battery. [ABSTRACT FROM AUTHOR]

Electrodes, which offer sites for mass transfer and redox reactions, play a crucial role in determining the energy efficiencies and power densities of redox flow batteries. This review focuses on various approaches to enhancing electrode performance, particularly the methods of surface etching and catalyst deposition, as well as some other advanced strategies for regulating electrode surface properties. These approaches aim to increase active sites and enhance kinetics for the redox reactions, which are crucial for elevating power density and electrolyte utilization, eventually determining the performance of the flow battery. Highlighting the need for interdisciplinary research, this mini‐review suggests that future advancements in electrode design will significantly impact the commercial viability and adoption of redox flow batteries in sustainable energy storage solutions. [ABSTRACT FROM AUTHOR]

[Display omitted] Zinc-based flow batteries hold potential promise for extensive energy storage on a large scale owing to their high energy density and low cost. However, their widespread implementation is impeded by challenges associated with zinc (Zn) dendrites and side reactions like the hydrogen evolution reaction on the anode. Theoretical calculations have confirmed that glycine (Gly) has the ability to coordinate with Zn2+, displacing H 2 O molecules in the solvation shell, thereby restoring the solvation structure of Zn2+ and promoting the release of reactive Zn2+ during plating/stripping processes. As a result, the incorporation of Gly into the anolyte of a neutral zinc-ferricyanide (Zn/Fe) flow battery (ZIFB) effectively inhibits the formation of Zn dendrites and impedes side reactions, leading to highly reversible and stable Zn plating/stripping reactions. A Zn||Zn symmetric flow battery utilizing Gly in the anolyte demonstrated extended cycling durability, lasting over 550 h at a current density of 30 mA cm−2, in contrast to the failure of a Gly-free anolyte system after 150 h. Notably, this approach facilitates a neutral ZIFB achieving an impressive energy efficiency exceeding 70 %, even at a high current density of 70 mA cm−2, with a cycle lifespan exceeding 800 h (33 days) at a current density of 30 mA cm−2. Conversely, the neutral ZIFB lacking Gly showed a significantly shorter cycle life of only 260 h under identical operational conditions (30 mA cm−2). Due to the economic benefits of Gly and the proposed user-friendly route, this strategy demonstrates great potential for promoting the widespread adoption of zinc-based flow batteries with improved performance for practical use. [ABSTRACT FROM AUTHOR]

Aqueous organic redox flow batteries (AORFBs) have pioneered new routes for large-scale energy storage. The tunable nature of redox-active organic molecules provides a robust foundation for creating innovative AORFBs with exceptional performance. Molecular engineering endows various organic molecules with considerable advantages in solubility, stability, and redox potential. Advanced characterizations have enabled a comprehensive understanding of the redox reaction and degradation mechanisms of these organic molecules. Computational chemistry and machine learning have guided the development of new organic molecules. The practical application of AORFBs will depend on the complementary efforts of multiple parties. This paper consolidates the current design principles of molecular engineering, degradation mechanisms, characterization techniques, and the utilization of computational chemistry. It also offers perspectives and forecasts the necessary attributes and strategic efforts for the next-generation AORFBs, aiming to provide the research community with a deeper understanding. [ABSTRACT FROM AUTHOR]

Biredox deep‐eutectic solvents (DESs)‐based electrolytes have shown unique features in non‐aqueous asymmetrical redox flow batteries (RFBs) that can potentially mitigate the crossover issue. However, strong intermolecular interactions among the electrolyte constituents in DESs bring in practical challenges such as limited mass transfer rates, slow redox kinetics, and degraded cyclability. Here, by using a novel biredox‐type DES based on 4‐methoxy‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy (4‐MeO‐TEMPO) and 3,3′‐dimethylazobenzene (3,3′‐Azo) as a model electrolyte system, the intermolecular interaction involving in the biredox DESs is unlocked by first‐principles calculations, and their influence on the electrochemical performance of biredox DESs couples is systematically investigated in comprehensive consideration of the solvents and the supporting salts. It demonstrates that employing tetrabutylammonium bis‐trifluoromethane sulfonimidate‐acetonitrile as the supporting electrolyte synergistically weakens the intermolecular interactions within the DESs, thereby significantly promoting the redox kinetics and electrochemical reversibility in non‐aqueous symmetrical RBFs. With such an optimized electrolyte, a prototype symmetrical cell under static mode is capable of delivering a high output voltage of ∼2.15 V, a decent cyclability, and the exceptional rate capability with a current density of 25 mA cm−2. This study provides a simple yet effective way to develop advanced RFBs with dependable electrolyte regulation. [ABSTRACT FROM AUTHOR]

Manganese (Mn), possessing ample reserves on the earth, exhibits various oxidation states and garners significant attentions within the realm of battery technology. Mn-based flow batteries (MFBs) are recognized as viable contenders for energy storage owing to their environmentally sustainable nature, economic feasibility, and enhanced safety features. Nevertheless, the advancement of MFBs is hindered by contentious reaction mechanisms, suboptimal energy density, and inadequate cycling stability. This review offers a comprehensive analysis of various MFBs based on the specific redox couples utilized in the catholyte, including Mn3+/Mn2+, MnO2/Mn2+, and MnO4−/MnO42−. Moreover, recent advancements and concerns encountered by each type of MFBs are subsequently addressed and discussed in detail. Additionally, the current understanding of the mechanisms for different Mn-based pairs and their potentials for energy storage applications are introduced. Finally, challenges for the future development of MFBs, along with suggested improvement strategies are outlined. [ABSTRACT FROM AUTHOR]

Zinc–bromine flow batteries (ZBFBs) have received widespread attention as a transformative energy storage technology with a high theoretical energy density (430 Wh kg−1). However, its efficiency and stability have been long threatened as the positive active species of polybromide anions (Br2n+1−) are subject to severe crossover across the membrane at a high concentration. Herein, a novel highly hydrophilic complexing agent, N‐methyl‐N, N‐bis(2‐hydroxyethyl)‐1‐propanaminium bromide (PMDA), is developed to effectively manage bromine in a homogeneous posolyte, which realizes a low bromine crossover at a high operating concentration in ZBFBs. Both theoretical and experimental results suggest that the PMDA interacts with Br2n+1− and forms a larger‐size complex PMDABr2n+1. When adding 0.40 m PMDA, the bromine stays homogeneous at a high concentration up to 1.20 m, and its permeability is remarkably decreased by 74%. For demonstration, the ZBFB achieves a operating capacity record of 57.2 Ah L−1 in a homogeneous bromine posolyte with a high Coulombic efficiency of ≈90.0% and superior cycling stability (capacity retention rate of 100.0% per cycle). This work provides one innovative bromine management strategy to realize a high capacity and superior stability in ZBFBs. [ABSTRACT FROM AUTHOR]

Iron redox flow batteries (Fe‐RFBs) hold significant promise for achieving cost‐effectiveness and utilizing abundant materials for stationary energy storage applications. Here, a design of a novel Fe complex utilizing a nitrogenous phosphonate/carboxylate mixed ligand, N,N‐Bis(phosphonomethyl)glycine (BMPG), is presented to achieve high performance Fe anolyte. Compared to its all‐phosphonate form, nitrilotri(methylphosphonic acid) (NTMPA), the new complex Fe(BPMG)2 demonstrates a negatively shifted redox potential, resulting in ≈0.07 V (≈10%) increase in battery output voltage. Full battery testing paired with ferrocyanide catholyte demonstrates stable cycling (capacity degradation <0.0001%/cycle) over 730 consecutive charge/discharge cycles with Coulombic Efficiency of 100% at a current density of 20 mA cm−2 under near neutral pH (≈8). Of particular interest, density functional theory (DFT) studies and operando Raman measurements provide strong evidence supporting a molecular structure in BPMG, which reveals the mixed phosphonate/carboxylate groups in BPMG maintain the octahedral coordination of the Fe ion center with phosphonates exclusively, while leaving the carboxylate unbound for both Fe(II) and Fe(III) complexes. This structural similarity between BPMG‐based Fe(II) and Fe(III) complexes effectively mitigates the slow redox reaction kinetics observed in Fe(NTMPA)2 anolyte, where significant ligand reorientation occurs between Fe(II) and Fe(III) complexes. [ABSTRACT FROM AUTHOR]

Salt cavern flow batteries (SCFBs) are an energy storage technology that utilize salt caverns to store electrolytes of flow batteries with a saturated NaCl solution as the supporting electrolyte. However, the geological characteristics of salt caverns differ significantly from above-ground storage tanks, leading to complex issues in storing electrolytes within salt caverns. Therefore, investigating and summarizing these issues is crucial for the advancement of SCFB technology. This paper's innovation lies in its comprehensive review of the current state and development trends in SCFBs both domestically and internationally. First, the current development status of SCFB energy storage technology both domestically and internationally is summarized. Then, eight main issues are proposed from the perspectives of salt cavern geological characteristics (tightness, conductivity, ions, and temperature) and electrolyte properties (selection, permeability, corrosion, and concentration). Finally, a novel SCFB system is proposed to address the most critical issue, which is the low concentration and uneven distribution of active materials in the current SCFB system. The review in this paper not only comprehensively summarizes the development status of SCFBs both domestically and internationally, but also points out the direction for the future research focussing on SCFBs. [ABSTRACT FROM AUTHOR]

This paper contains the results of numerical investigations into two cooling system types for cells of three types. The galvanic cell geometries which were considered were pouches, cylinders and prisms. By design, the cooling system for a vehicle is specialised to prevent an uncontrolled temperature increase at higher discharge rates. Consideration was given to the question of which cooling method would be sufficient to reduce the temperature rise of battery cells. The first cooling method investigated is one that uses direct contact with the air flow to cool the cells, a method that is very commonly used in automotive engineering, as it is less complicated. This study employs a method that uses a fan to induce forced convection, increasing the airflow over cells housed within a thermoplastic composite container. Another method, fluid cooling, is notable for its greater efficiency due to the use of a non-conducting coolant, which has also better energy absorption properties. In this study, immersion cooling was employed, utilising oil circulation through cells contained within a thermoplastic composite container, which was facilitated by a pump system. This publication shows the influence of the cell's geometry and the type of cooling system on the temperature rise of cells when they are discharging at the appropriate power rate. The results of this study highlight the differences in cooling performance between the two methods, providing a clear basis for selecting the most suitable solution for specific applications. [ABSTRACT FROM AUTHOR]

Alkaline all‐iron flow batteries possess intrinsic safety and low cost, demonstrating great potential for large‐scale and long‐duration energy storage. However, their commercial application is hindered by the issue of capacity decay resulting from the decomposition of iron complexes and ligand crossovers. In this paper, an robust anolyte Fe(TEA‐2S) is reported, which is formed by chelating iron ions with the sulfonate‐enriched ligand (TEA‐2S) in alkaline environment. By skillfully designing the ligands, the binding energy of the iron complexes increases and ligand crossovers are suppressed, making the iron complexes highly stable in the charge–discharge cycles. Alkaline all‐iron flow batteries coupling with Fe(TEA‐2S) and the typical iron‐cyanide catholyte perform a minimal capacity decay rate (0.17% per day and 0.0014% per cycle), maintaining an average coulombic efficiency of close to 99.93% over 2000 cycles along with a high energy efficiency of 83.5% at a current density of 80 mA cm−2. In addition, Fe(TEA‐2S) exhibits high solubility of up to 1.85 м (with a theoretical capacity of up to 49.58 Ah L−1), even at low temperatures as extreme as −30 °C. This work demonstrates a promising pathway toward achieving long‐duration and large‐scale energy storage. [ABSTRACT FROM AUTHOR]

The rising energy demand driven by human activity has posed pressing challenges in embracing renewable energy, necessitating advances in energy storage technologies to maximize their utilization efficiency. Recent studies in aqueous organic redox flow batteries have focused primarily on the development of organic negative electrolytes, while the progress in organic positive electrolytes remains constrained by limitations in their redox potentials and effective electron concentrations. Herein, we report a spatially twisted chlorinated spirobifluorene ammonium salts (CSFAs), created through an unexpected green chlorination‐protection pathway during the initial cycling in the flow battery cell, utilizing chloride ions from counterions in aqueous solution. The chlorinated, nonplanar spiral structure of CSFAs possesses a one‐step four‐electron transfer electrochemical property and offers exceptional resistance to nucleophilic attacks, exhibiting an unprecedented redox potential as high as 1.05 V (vs. SHE). A full redox flow battery based on CSFA‐Cl (chloride ions as the counter ions) with 1.4 M electron concentration achieved an average coulombic efficiency exceeding 99.4 % and a capacity utilization reaching 95 % of the four‐electron capacity for a stable cycling over 250 cycles (~22 days). The present work exemplifies the use of side reactions to develop new redox species, which can be extended to create more structurally versatile energy storage materials. [ABSTRACT FROM AUTHOR]

Redox flow batteries (RFBs) are an attractive choice for stationary energy storage of renewables such as solar and wind. Non‐aqueous redox flow batteries (NARFBs) have garnered broad interest due to their high voltage operation compared to their aqueous counterparts. Further, the utilization of bipolar redox‐active molecules (BRMs) is a practical way to alleviate crossover faced by asymmetric RFBs. In this work, ferrocene (Fc) and phthalimide (PI) are covalently linked with various tethering groups which vary in structure and length. The compiled results suggest that the length and steric shielding ability of the linker group can greatly influence the stability and overall performance of Fc‐n‐PI BRM‐based NARFBs. Primary sources of capacity loss are found to be BRM degradation for straight chain spacers <6 carbons and membrane (Nafion) fouling. Fc‐hexyl‐PI provided the most stable battery cycling and coulombic efficiencies of >98 % over 100 cycles (~13 days). NARFB using Fc‐hexyl‐PI as an active material exhibited high working voltage (1.93 V) and maximum capacity (1.28 Ah L−1). Additionally, this work highlights rational strategies to improve cycling stability and optimize NARFB performance. [ABSTRACT FROM AUTHOR]

ABSTRACT A new 1,2,3‐triazole functionalized ferrocene (1,2,3‐TAFc) produced by Cu(I)‐catalyzed click reaction was investigated as positive electrolyte for aqueous organic flow batteries (AOFBs). The molecule is highly soluble in 1 M hydrochloric acid and displays high electrochemical reversibility. 1,2,3‐TAFc demonstrated good stability during cycling with a low capacity decay (0.011%/cyc, 3.0%/day) and high Coulombic efficiency (99.4%) over 280 cycles when tested in a flow battery at low concentration. This low capacity decay was attributed to the instability of ferrocene. These findings indicate that a stable and water‐soluble catholyte for AOFBs can be obtained with structural modifications of 1,2,3‐TAFc. [ABSTRACT FROM AUTHOR]

Quality control in a production plant shows its maximum potential in the form of inline measurements. Defects and imperfections can be detected early and directly, and waste and costs can be reduced. Nuclear Magnetic Resonance offers a wide range of applications but requires dedicated adaptation to the respective process and material conditions. A V-shaped low-field NMR sensor was developed for non-invasive inline measurements on anode slurries in a battery production plant. In battery production, inline monitoring of the quality of anode slurries is demanded, offering the possibility of predictive control of the following process steps. Methods of low-field NMR to determine flow properties were adapted to the desired application. Further, magnetic resonance imaging measurements were made to determine the flow properties of model substances and anode slurries, thus providing verification. The sensor measurements show the ability to measure the flow behavior of, amongst other fluids, anode slurries in a form suitable for inline quality control in a battery production plant. [ABSTRACT FROM AUTHOR]

Fluorenones are suitable candidates for negolytes in flow batteries, as they demonstrate the ability to store 2 electrons, and can achieve reversibility, solubility, and stability with appropriate molecular design. However, limitations persist such as the use of alkaline media, high redox potentials, and a limited scope for optimization. Herein, azoniafluorenones is reported as a novel class of negolytes. They can be readily accessed in a highly modular fashion from inexpensive commercially available materials (e.g., boronic acids). Variations in the substitution patterns reveal the 3‐substituted N‐alkylated AZON3, which demonstrates excellent solubility at neutral pH (1.64 m) with two low reversible redox potentials (−0.31 and −0.58 V vs Ag/AgCl). AZON3 exhibits high stability when evaluated at high concentration in a neutral supporting electrolyte (1 m in 3 m KCl), paired with BTMAP‐Fc on the positive side. Capacity retentions of 99.95% and 99.91% per cycle (99.35% and 99.21% per day) are achieved when cycling with 1 and 2 electrons, respectively, coupled with high volumetric capacity of 46.4 Ah L−1 (87% of capacity utilization). [ABSTRACT FROM AUTHOR]

Viologens are ideal anolytes for organic redox flow batteries due to their stable redox behaviour, but they face the challenge of poor solubility of mono-cation radical dimers formed during the oxidation/reduction process. In our study, we prepared four viologen derivatives: sulfonic acid (SV), carboxylic acid (VAV), quaternized ammonium salt (QV), and imidazole (IV). IV exhibited the most stable mono-cation radical dimer, followed by QV, VAV, and SV. The stability was assessed by recording EPR spectra during the battery operation and confirmed by 1H NMR after the battery operation. Intriguingly, the most stable dimer led to poor battery performance. With the least stable dimer, SV performed best using 0.5 M [Fe(CN)6]3−/4− catholyte in a 1 M NH4Cl solution with a polyethylene/styrene interpolymer cation exchange membrane. The battery achieved an impressive 99% Coulombic efficiency (CE) and 60.3% energy efficiency (EE) at an applied current density of 100 mA cm−2. Over 200 stable charge and discharge cycles, it reached 11.25 Ah L−1 capacity at 20 mA cm−2 current density. This study highlights the need to address the stability and solubility of mono-cation radical dimers and emphasizes intelligent molecular engineering to optimize viologen derivatives in organic redox flow batteries. [ABSTRACT FROM AUTHOR]

The iron–chromium redox flow battery (ICRFB) has a wide range of applications in the field of new energy storage due to its low cost and environmental protection. Graphite felt (GF) is often used as the electrode. However, the hydrophilicity and electrochemical activity of GF are poor, and its reaction reversibility to Cr3+/Cr2+ is worse than Fe2+/Fe3+, which leads to the hydrogen evolution side reaction of the negative electrode and affects the efficiency of the battery. In this study, the optimal composite modified GF (Bi-Bio-GF-O) electrode was prepared by using the optimal pomelo peel powder modified GF (Bio-GF-O) as the matrix and further introducing Bi3+. The electrochemical performance and material characterization of the modified electrode were analyzed. In addition, using Bio-GF-O as the positive electrode and Bi-Bio-GF-O as the negative electrode, the high efficiency of ICRFB is realized, and the capacity attenuation is minimal. When the current density is 100 mA·cm−2, after 100 cycles, the coulomb efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) were 97.83%, 85.21%, and 83.36%, respectively. In this paper, the use of pomelo peel powder and Bi3+ composite modified GF not only promotes the electrochemical performance and reaction reversibility of the negative electrode but also improves the performance of ICRFB. Moreover, the cost of the method is controllable, and the process is simple. [ABSTRACT FROM AUTHOR]

A water‐soluble anthraquinone derived from alizarin, 3HAAQ, is introduced as the redox‐active material in a negative potential electrolyte (anolyte) for aqueous redox flow batteries operating at pH 14. The synthesis of 3HAAQ is carried out using the Mannich reaction, which significantly improves the solubility of the new compound, an important factor for its use in RFB. Pairing with potassium ferri/ferrocyanide positive electrolyte, this flow battery exhibits an open‐circuit voltage of 1.24 V and maintains nearly 80% of the theoretical capacity at 40 mA cm−2 current density. [ABSTRACT FROM AUTHOR]

Recent advances in 3D printing have enabled the manufacture of porous electrodes which cannot be machined using traditional methods. With micron-scale precision, the pore structure of an electrode can now be designed for optimal energy efficiency, and a 3D printed electrode is not limited to a single uniform porosity. As these electrodes scale in size, however, the total number of possible pore designs can be intractable; choosing an appropriate pore distribution manually can be a complex task. To address this challenge, we adopt an inverse design approach. Using physics-based models, the electrode structure is optimized to minimize power losses in a flow reactor. The computer-generated structure is then printed and benchmarked against homogeneous porosity electrodes. We show how an optimized electrode decreases the power requirements by 16% compared to the best-case homogeneous porosity. Future work could apply this approach to flow batteries, electrolyzers, and fuel cells to accelerate their design and implementation. [ABSTRACT FROM AUTHOR]

Soluble lead redox flow battery (SLRFB) is an emergent energy storage technology appropriate for integrating solar and wind energy into the primary grid. It is an allied technology of conventional lead‐acid batteries. This appraisal compares lead‐acid batteries and SLRFB apropos their general characteristics. SLRFBs can overcome the inadequate cycle‐life of Lead‐Acid batteries as the electrodes of SLRFB do not participate in the reaction, which helps extending its durability. However, SLRFB has challenges of dendrite formation, oxygen evolution reaction, passivation of PbO2 and shunt current. These problems need to be resolved before SLRFBs can be projected for large‐scale energy storage applications. In this technical update, we have reviewed the recent studies pertinent to dendrite formation, mechanism of the lead electrode, and reversibility of the PbO2 electrode in the state‐of‐art of SLRFB along with progress in advances while developing a 12 V – 250 Wh 8‐cell SLRFB stack. [ABSTRACT FROM AUTHOR]

Mediated processes using a solid material, often called "solid booster", have been proposed to increase the energy density in redox flow batteries (RFB). The strategy alters the energy storage in the dissolved redox species to a solid active material placed in a compartment of the device. Understanding the reaction kinetics of the dissolved redox mediator and the solid booster is crucial for proposing feasible pairs of solid boosters and dissolved redox mediators. We demonstrate a nanoelectrochemical methodology to monitor the reaction between the dissolved species in solution and the solid active material electrodeposited in recessed carbon nanoelectrodes. Our strategy overcomes issues inherent to standard methodologies, such as mass transport limitation, and evaluation of the intrinsic reactivity of the solid material. As a proof of concept, Prussian blue was electrodeposited in a recessed carbon nanoelectrode and used as a confined‐solid material platform to evaluate the reaction between the reduced form of Prussian blue and triiodide, I3- ${{{\rm I}}_{3}^{-}}$. A high conversion rate of the solid booster was observed in the presence of μM concentrations of the dissolved redox species. The proposed nanoelectrode was successfully employed as a potentiometric sensor to monitor the evolution of the reaction with the dissolved active species. [ABSTRACT FROM AUTHOR]

As one of the latest research directions, membraneless batteries provide an economical solution to redox flow batteries. Advances in electrolyte and device design have promoted membraneless batteries from microfluidic demonstration to systems with stimulated modes and considerable electrochemical properties. However, the achieved cycling volumetric capacity is typically limited. Herein, a biphasic membraneless zinc‐iodine battery (Z|T‐I) is proposed, through optimized Zn growth, the Z|T‐I battery achieved a volumetric capacity of 8.93 Ah L−1 for 100 cycles with an average Coulombic efficiency (CE) of 98.49% (2300 h), the deep cycling exhibited a volumetric capacity of 21.7 Ah L−1 (50.43 Wh L−1 based on typical membraneless battery calculation, 1200 h); both values are the highest among single/biphasic membraneless batteries using liquid active materials with/out stimulations (<6.6 Ah L−1) reported so far based on the total electrolyte volume. A thorough analysis of Zn growth in Zn‐Br2/I2 electrolytes with various testing conditions provided direct evidence of the contrasting Zn electrodeposition morphologies at both macro and micro scales. The biphasic ZnI2 battery design strategy gives insights into optimizing material crossover/spatial utilization and electrolyte interfacial stability to realize a scalable membraneless energy storage system with a reduced cost. [ABSTRACT FROM AUTHOR]

Redox flow batteries (RFBs) with high energy densities are essential for efficient and sustainable long‐term energy storage on a grid scale. To advance the development of nonaqueous RFBs with high energy densities, a new organic RFB system employing a molecularly engineered tetrathiafulvalene derivative ((PEG3/PerF)‐TTF) as a high energy density catholyte was developed. A synergistic approach to the molecular design of tetrathiafulvalene (TTF) was applied, with the incorporation of polyethylene glycol (PEG) chains, which enhance its solubility in organic carbonate electrolytes, and a perfluoro (PerF) group to increase its redox potential. When paired with a lithium metal anode, the two‐electron‐active (PEG3/PerF)‐TTF catholyte produced a cell voltage of 3.56 V for the first redox process and 3.92 V for the second redox process. In cyclic voltammetry and flow cell tests, the redox chemistry exhibited excellent cycling stability. The Li|(PEG3/PerF)‐TTF batteries, with concentrations of 0.1 M and 0.5 M, demonstrated capacity retention rates of ~94 % (99.87 % per cycle, 97.52 % per day) and 90 % (99.93 % per cycle, 99.16 % per day), and the average Coulombic efficiencies of 99.38 % and 98.35 %, respectively. The flow cell achieved a high power density of 129 mW/cm2. Furthermore, owing to the high redox potential and solubility of (PEG3/PerF)‐TTF, the flow cell attained a high operational energy density of 72 Wh/L (100 Wh/L theoretical). A 0.75 M flow cell exhibited an even higher operational energy density of 96 Wh/L (150 Wh/L theoretical). [ABSTRACT FROM AUTHOR]

Ion exchange membranes (IEMs) play a critical role in aqueous organic redox flow batteries (AORFBs). Traditional IEMs that feature microphase‐separated microstructures are well‐developed and easily available but suffer from the conductivity/selectivity tradeoff. The emerging charged microporous polymer membranes show the potential to overcome this tradeoff, yet their commercialization is still hindered by tedious syntheses and demanding conditions. We herein combine the advantages of these two types of membrane materials via simple in situ hypercrosslinking of conventional IEMs into microporous ones. Such a concept is exemplified by the very cheap commercial quaternized polyphenylene oxide membrane. The hypercrosslinking treatment turns poor‐performance membranes into high‐performance ones, as demonstrated by the above 10‐fold selectivity enhancement and much‐improved conductivities that more than doubled. This turn is also confirmed by the effective and stable pH‐neutral AORFB with decreased membrane resistance and at least an order of magnitude lower capacity loss rate. This battery shows advantages over other reported AORFBs in terms of a low capacity loss rate (0.0017 % per cycle) at high current density. This work provides an economically feasible method for designing AORFB‐oriented membranes with microporosity. [ABSTRACT FROM AUTHOR]

Fabrication of ion‐conducting membranes with continuous sub‐nanometer channels holds fundamental importance for flow batteries in achieving safe integration of renewable energy into grids. Self‐standing covalent organic polymer (COP) membranes provide feasibility due to their rapid and selective ion transport. However, the development of a scale‐up possible, mechanically robust and chemically stable membranes remains a significant challenge. Herein, using irreversible strong secondary amine linkage, we propose a self‐standing COP membrane with sub‐nanometer pores ranging from 4.5 to 6.4 Å, by a simple and efficient in situ polymerization approach. This membrane exhibits enhanced selectivity for proton and vanadium ions, especially excellent electrochemical stability, delivering an energy efficiency of over 80 % at the current density of 200 mA cm−2 over 1000 cycles for an all‐vanadium redox flow battery (VFB). This study provides novel insights for COP‐based ion‐sieving membranes in sustainable energy fields. [ABSTRACT FROM AUTHOR]

Hybrid flow chemical power source (Pt–C)H2|Nafion|VO2+(C) in which the membrane–electrode assembly combines gas-diffusion anode of hydrogen–air fuel cell and cathode of vanadium redox flow battery is studied. Concept of such a hydrogen–vanadium flow battery had been proposed earlier (2013) as an alternative to the vanadium redox flow battery, also designed for large-scale electrical energy storage but its practical implementation has so far been limited to single cells having the active area within several tens of cm2. The goal of this work is the establishing of the factors limiting the discharge power density of such hybrid. hydrogen–vanadium flow battery cells which is inferior to both hydrogen–air fuel cell and vanadium redox flow batteries, even though the hydrogen–vanadium flow battery cell represents a combination of their more reversible half-cells. The object of the study is a cell with a 2 × 2 cm membrane–electrode assembly equipped with Luggin capillary on the vanadium electrolyte side. Measurements of the current–voltage characteristics of the entire cell, as well as the polarization characteristics of its half-cells, are performed using a six-electrode scheme of the cell connection with varied vanadium electrolyte circulation rate and different cathode materials (carbon felts, 4.6 or 2.5 mm thick, as well as carbon paper). The contribution of the hydrogen gas diffusion electrode to the total dc resistance of the hydrogen–vanadium flow battery cell is shown being twice that of the flow-through vanadium cathode. A record high discharge power density has been achieved: 0.75 W cm–2, for the cell based on the commercially available material, Sigracell GFD 2.5 EA-TA carbon felt as the cathode material, without its special surface modification. [ABSTRACT FROM AUTHOR]

For proton exchange membranes (PEM) used in vanadium redox batteries (VRBs), doping metal-organic framework (MOF) materials to enhance the proton permeability and vanadium ion barrier property of PEM has become a research focus. In synthesizing MOFs, conventional hydrothermal method is hindered by prolonged reaction time and suboptimal material structures. This study utilizes microwave assisted heating for the preparation of UIO-66-NH2 crystals, which are then combined with Nafion to fabricate composite membranes. The results indicate that microwave heating enables a more efficient and rapid synthesis of MOF crystals (MU-NH2), with enhanced uniformity and higher yield than the conventional hydrothermal process (CU-NH2). Compared to MU-NH2/Nf-0(vanadium ion permeability: 4.4 × 10−7 cm2·min−1; ion selectivity: 5 × 104 S·min·cm−3), the vanadium ion permeability of MU-NH2/Nf-3 and CU-NH2/Nf-3 membranes exhibits a similar level of reduction, approximately 82%. Additionally, the former demonstrates an enhanced ion selectivity by 33.3%, while the latter shows an increase of 30.9%. VRBs equipped with MU-NH2/Nf membranes exhibit higher energy efficiency (83.8% at 100 mA·cm−2) and better capacity retention than those with CU-NH2/Nf membranes (82.7% at 100 mA·cm−2). Therefore, UIO-66-NH2 synthesized via the microwave method can effectively enhance the comprehensive properties of proton exchange membranes and shows promising prospects in optimizing the performance of VRBs. [ABSTRACT FROM AUTHOR]

This work presents the first proof‐of‐concept of a membraneless micro redox flow battery with an automated closed‐loop control. Using micro actuators and micro sensors, charge and discharge is achieved in continuous operation in recirculation. A maximum value of 60 % State of Charge with commercial Vanadium electrolyte, monitored via online spectrometry, is delivered, with a maximum discharge current density of 60 mA/cm2, and a discharge volumetric capacity of 21.5 Ah/L. Next, cycling tests show a decrease in coulombic efficiency of 0.5 % per cycle, and capacity loss. To overcome some drawbacks encountered with Vanadium, an alkaline quinone electrolyte is used instead in the membraneless micro redox flow battery. Using this new electrolyte, sixty continuous cycles are performed showing a decrease in coulombic efficiency of 0.6 % per cycle, and a capacity loss of only 1.2 % per cycle. The performances obtained outshine previous literature results. The highest energy efficiency ever obtained for a membraneless micro redox flow battery is presented here with alkaline quinone having an efficiency of 28.9 %. The cycling of a membraneless micro redox flow battery is successfully performed for the first time. This work also includes performance improvement suggestions for future work, with this landmark opening a promising path towards achieving the metrics of conventional redox flow batteries. [ABSTRACT FROM AUTHOR]

This study examines the need for bismuth as a catalyst for the Cr2+/Cr3+ redox couple in an iron–chrome redox flow battery (ICRFB) using 1) open‐circuit voltage (OCV) periods to understand the impact of bismuth and the mechanism of hydrogen production with and without electrolyte flow, and 2) charge/discharge cycles to evaluate how bismuth influences ICRFB performance. The OCV study finds that the capacity decay in the ICRFB cycling is not solely due to the hydrogen evolution reaction, suggesting an alternative oxidation reaction is involved, likely catalyzed by metallic carbides like bismuth carbide. Both the OCV and the ICRFB confirm that the presence of bismuth negatively influences the battery performance due to increased H2 production. Further research is ongoing to validate the decay mechanism and confirm these results on a larger scale. [ABSTRACT FROM AUTHOR]

Solar redox flow batteries (SRFB) have attracted increasing interest for simultaneous capture and storage of solar energy by integrating a photoelectrochemical cell with a redox flow battery. Herein, a scalable, nanostructured α‐Fe2O3 photoanode exhibiting a high photovoltage of 0.68 V in a fully integrated Na4Fe(CN)6/AQDS SRFB is demonstrated. Thanks to its optimal band alignment, it uniquely enables stable, unassisted photocharging of the SRFB up to a state‐of‐charge (SOC) higher than 50%. Concurrently, its improved charge transfer results in a record unbiased photocurrent density of 0.22 mA cm−2, with a sixfold increase at zero SOC compared to α‐Fe2O3 film. Through an in‐depth optical and photoelectrochemical characterization of different α‐Fe2O3 morphologies, the impact of nanostructuring on charge transfer is quantified. Most interestingly, an increase in unbiased photocurrent is observed at 10% SOC (0.31 mA cm−2) and attributed to adsorption of ferricyanide, which enhances charge transfer. Importantly, it is demonstrated that the superior performance is retained after device scale‐up to 5.72 cm2. Overall, the demonstrated unassisted device is on par with previously reported dye‐sensitized solar cell‐assisted hematite‐based SRFBs. More broadly, this work contributes to the real‐world deployment of cost‐effective SRFBs based on Earth‐abundant materials. [ABSTRACT FROM AUTHOR]

At present, the energy consumption and carbon emissions of maritime transportation have raised concerns about environmental issues. A potential way to reduce carbon emissions from vessels is the use of chemical-based carbon capture and storage (CCS) technology. However, this technology faces challenges such as high energy consumption, large space occupation, and high processing costs. Therefore, the development of a technology with low energy consumption and compact CO2 storage is crucial to promote the advancement of CCS technology. This paper introduces a magnesium CO2 battery system that converts CO2 into new energy, in the form of hydrogen, while storing CO2. By preparing highly efficient catalytic electrodes and testing the electrolyte and CO2 flow rate on the battery performance, the optimal process parameters were determined to be Pd/CeO2-oct for the electrodes, a 0.5 mol/L NaOH solution for the electrolyte, and a CO2 flow rate of 1 L/h. The battery system demonstrated high cycling stability and conversion efficiency at a current density of 8 mA·cm−2, with a stable cycling time of 600 min (20 cycles), a cathode hydrogen production of 10.135 mL, and a Faraday efficiency of 97.03%. [ABSTRACT FROM AUTHOR]

The integration of energy storage batteries into renewable energy stations is a crucial development in the quest for sustainable and reliable energy solutions. This review provides a comprehensive analysis of this integration, detailing the types of energy storage batteries, including lithium-ion, lead-acid, and flow batteries, as well as their respective benefits and limitations. The study addresses significant challenges such as the intermittency of renewable energy sources, battery degradation and lifetime, cost and efficiency issues, and technical challenges. It also explores potential solutions to these challenges. Additionally, future directions are discussed, focusing on emerging battery technologies and smart grid system integration. This paper highlights the essential role of energy storage batteries in overcoming the intermittency of renewable sources and ensuring a stable and efficient energy supply. [ABSTRACT FROM AUTHOR]

Nonaqueous flow batteries hold promise given their high cell voltage and energy density, but their performance is often plagued by the crossover of redox compounds. In this study, we used permselective lithium superionic conducting (LiSICON) ceramic membranes to enable reliable long-term use of organic redox molecules in nonaqueous flow cells. With different solvents on each side, enhanced cell voltages were obtained for a flow battery using viologen-based negolyte and TEMPO-based posolyte molecules. The thermoplastic assembly of the LiSICON membrane realized leakless cell sealing, thus overcoming the mechanical brittleness challenge. As a result, stable cycling was achieved in the flow cells, which showed good capacity retention over an extended test time. [ABSTRACT FROM AUTHOR]

Abstract Recent advances in 3D printing have enabled the manufacture of porous electrodes which cannot be machined using traditional methods. With micron-scale precision, the pore structure of an electrode can now be designed for optimal energy efficiency, and a 3D printed electrode is not limited to a single uniform porosity. As these electrodes scale in size, however, the total number of possible pore designs can be intractable; choosing an appropriate pore distribution manually can be a complex task. To address this challenge, we adopt an inverse design approach. Using physics-based models, the electrode structure is optimized to minimize power losses in a flow reactor. The computer-generated structure is then printed and benchmarked against homogeneous porosity electrodes. We show how an optimized electrode decreases the power requirements by 16% compared to the best-case homogeneous porosity. Future work could apply this approach to flow batteries, electrolyzers, and fuel cells to accelerate their design and implementation.

[Display omitted] Flow battery is a safe and scalable energy storage technology in effectively utilizing clean power and mitigating carbon emissions from fossil fuel consumption. In the present work, we demonstrate an aqueous colloid flow battery (ACFB) with well-dispersed colloids based on nano-sized Prussian blue (PB) cubes, aiming at expanding the chosen area of various nano redox materials and lowering the cost of chemicals. Taking advantage of the two redox pairs of PB, the developed all-PB cell employing a low-cost dialysis membrane with the synthesized PB on both sides displays an open-circuit voltage (OCV) of 0.74 V. Moreover, when paired with an organic tetra pyridine macrocycle the cell with PB as positive electrolyte exhibits an OCV of 1.33 V and a capacity fade rate of 0.039 %/cycle (0.8 %/day). Redox-active colloids exhibit enduring physicochemical stability, with no evident structural or morphological changes after extensive cycling, highlighting their potential for cost-effective and reliable ACFB energy storage. [ABSTRACT FROM AUTHOR]

In the pursuit of sustainable energy solutions, zinc‐based flow batteries stand out for their potential in large‐scale energy storage, offering a blend of cost efficiency and safety. Although the porous electrode provides an increased specific surface area for reaction, the non‐uniform deposition of zinc, attributed to uneven concentration distribution within the porous electrode, has been a pivotal issue in accelerating the formation of zinc dendrites, which hinders the enhancement of energy density. A composite electrode with a strategic hierarchical pore structure has been developed with aligned nitrogen‐doped carbon fibers and traditional carbon felt. This structure takes advantage of the large pores of the carbon felt for efficient through‐flow paths, ensuring higher flow rates, while the dual‐scale pores within the electrospun film enhance mass transfer and increase the specific surface area. At 320 mA cm−2, it achieved an ≈11.4% improvement in the battery's energy efficiency. Moreover, the nitrogen doping and the optimized reaction uniformity within the composite electrode have been instrumental in reducing the generation of zinc dendrites. The battery, integrated with the innovative composite electrode, maintained an energy efficiency of 59.2% at 320 mA cm−2 after 300 cycles, which is a substantial improvement in operational longevity. [ABSTRACT FROM AUTHOR]

Development and application of large‐scale energy storage systems are surging due to the increasing proportion of intermittent renewable energy sources in the global energy mix. Redox flow batteries are prime candidates for large‐scale energy storage due to their modular design and scalability, flexible operation, and ability to decouple energy and power. To date, several different redox couples are exploited in redox‐flow batteries; some are already commercialized. This battery technology is facing a lot of challenges in the science, engineering, and economic front. Issues plaguing flow batteries are low energy density, high overall cost, poor stability of electrolytes, shifting of solvent from anolyte to catholyte while using cation exchange membrane, reverse flow with anion exchange membrane, and corrosion of graphite felt in the catholyte side. Significant research efforts are ongoing to address these challenges. This comprehensive and critical review summarizes the recent progress in electrolyte technologies, including electrochemical performance and stability, strategies to enhance the energy and power densities and, in the end, the levelized and life‐cycle cost of these batteries analyzed. A comprehensive outlook on this technology with respect to practical energy storage applications is also provided. [ABSTRACT FROM AUTHOR]

Among multivalent redox flow batteries, the Zn‐based redox flow battery (RFB) has the advantages of high energy density, nontoxicity, and low cost. However, the severe dendrite issue hinders its deployment. Therefore, the Sn‐based RFB is reported as a prospective alternative, particularly in alkaline systems, due to its lower redox potential and four electrons transfer in redox reactions. However, the continuous growth of Sn during charge forms large Sn bulk, which increases the risk of “dead Sn” formation. By combining experiments and theoretical calculations, urea is proposed as an electrolyte additive to regulate Sn deposition on graphite felt. This is achieved through the enhanced adsorption and robust reaction of Sn(OH)62− with graphite felt. Consequently, a more uniform morphology ensues, reducing “dead Sn” formation and thus improving the average discharge voltage and areal capacity. Moreover, the Columbic efficiency becomes more stable, extending the cycle life to over 420 h (>200 cycles) without deep discharge during cycling. This study demonstrates the role of urea in achieving high‐performance Sn‐I flow battery with long cycle life, paving the way for further development of metal‐based hybrid RFBs. [ABSTRACT FROM AUTHOR]

This research investigates the interactions between Carbopol® and zinc microparticles and their role in the stabilization of zinc within the framework of zinc slurry–air redox flow batteries (Zn-air RFBs). The study explores the potential of yield stress fluids, particularly PAA (Carbopol®) microgels, as stabilizers for zinc particles during battery operation, and regarding sedimentation in particular. Two effects that can limit the effectiveness of PAA yield stress in stabilizing the suspension are examined in this study. First is the ionic strength and pH that can evolve during the slurry formulation. The second effect is associated to zinc polymer interactions that can develop during the suspension preparation. Using methodologies based on rheometry and UV–Vis spectroscopy, the research identifies that the primary stabilization challenge is the adsorption of Carbopol® microgels onto zinc surfaces, which significantly influences the gel's yield stress. These insights contribute to an enhanced understanding of the physical chemistry of the suspending fluid, facilitating the development of more efficient and stable Zn-Air RFBs. [ABSTRACT FROM AUTHOR]

When considering the frequency stability issues brought on by load shifts in a microgrid (μ G) due to a significant integration of fluctuating renewable energy source-based generators and an inherent low inertia, energy storage units (ESUs) are unavoidable. The ESUs can immediately charge or discharge to make up for any shifts in load in the μ G since they react more quickly. This research investigates how a redox flow battery unit (RFBU) impacts the dynamic responses of a standalone μ G (S μ G) in this respect. As the secondary controller, an optimal intelligent model predictive control (iMPC) approach is presented. The cyclical parthenogenesis algorithm is implemented to improve the tuning parameter ( τ w ) in the iMPC cost function to demonstrate an optimal performance of the recommended control approach. The effectiveness of the iMPC approach is contrasted with that of other well-known control approaches. The simulation findings clearly demonstrate the impact of RFBU integration in the S μ G and the capability of the recommended iMPC approach in terms of improved dynamic responses and their transient characteristics. As a consequence, the peak value of the S μ G dynamic response improves by 70.53%, and the settling time improves by 82.26%. The suggested control approach's sensitivity to the S μ G parametric uncertainties is also justified. The closed-loop stability of the suggested approach is also established. The effectiveness of the proposed iMPC approach and the impact of the RFBU integration are then confirmed by statistical analysis. [ABSTRACT FROM AUTHOR]

This review exploits the crucial role of computational methods in discovering and optimizing materials for redox flow batteries (RFBs). Integration of high‐throughput computational screening (HTCS) and machine learning (ML) accelerates materials discovery, guided by algorithms categorizing RFBs. A collaborative exploration, spanning macroscopic to mesoscopic scales, combines quantum machine learning with reinforcement learning, transfer learning, time series analysis, Bayesian optimization, active learning and various generative models. The collaborative integration of ML with computational techniques and experimental methods, anchored in experimentally validated Density Functional Theory (DFT) calculations and molecular dynamics (MD) simulations, proves indispensable for cost‐effective RFBs. Data collection and feature engineering are explored, emphasizing the integration of optimization goals and precise data collection within the ML framework. Feature analysis importance is highlighted, utilizing methods such as the filter, embedded, wrapper and deep learning methods for efficient energy materials exploration. Computational perspectives on materials features and operating conditions encompass membrane characteristics, fluid dynamics, temperature dependence and pressure sensitivity. Time‐dependent features and ML‐generated insights are crucial for understanding cycling performance intricacies, providing a comprehensive understanding of RFB materials. [ABSTRACT FROM AUTHOR]

Aqueous Organic Redox Flow Batteries are a family of promising energy storage systems. However, they face various challenges related to their lifetime, such as the Faradaic imbalance due to the occurrence of parasitic reaction leading to the fading of its energy storage capacity. Herein, automatization of a rebalancing system to reverse the detrimental effects of Faradaic imbalance due to the unavoidable presence of small quantities of oxygen in the negative reservoir or hydrogen evolution reaction is developed and implemented in an alkaline flow battery. A membrane‐free rebalancing cell is proposed to promote the oxygen evolution reaction and reverse the accumulated charge in the catholyte showing a 100 % coulombic efficiency. The programmable logic controller monitors the open circuit voltage to calculate the charge stored in each charge/discharge step and closes a circuit so a fixed voltage is applied to the rebalancing cell when the battery needs to be rebalanced. The system is tested using an alkaline flow battery consisting of ferrocyanide and 2,6‐dihydroxyanthraquinone, improving the energy capacity retention from 0.27 % cycle‐1 and 0.47 % h‐1 without rebalancing system to 100 % retention after >850 cycles and >24 days (without Ar‐filled glovebox), demonstrating the feasibility of this proposed system to address the Faradaic imbalance. [ABSTRACT FROM AUTHOR]

To address the problem of suboptimal performance in deep eutectic solvents displayed by traditional TiO2 photoelectrodes and Cu2O photoelectrodes that have undergone simplistic modifications that result in a mismatch with battery discharge capacity, a method combining hydrothermal and dip-coating techniques was developed to create a Fe2O3-CuO heterojunction structure on the FTO surface. Then, the impact of the heterojunction structure on the performance of solar flow batteries was investigate in this study. The experimental findings reveal that the formation of the heterojunction structure effectively mitigates the recombination rate of photogenerated carriers within the photoelectrode. Furthermore, by meticulously adjusting the CuO loading, the harmonious balance between charging and discharging currents was achieved, thereby enhancing the overall performance of the solar redox flow batteries. In comparison to standalone Fe2O3 photoelectrodes, this innovative approach significantly broadens the spectrum of sunlight utilization. Notably, the fabricated Fe2O3/CuO-2 photoelectrode demonstrates a remarkable photocharging performance, far surpassing both Fe2O3 photoelectrodes and commercial TiO2 photoelectrodes. Specifically, the Fe2O3/CuO-2 photoelectrode boosts an average current density of 598.68 μA∙cm−2, with its charging current density being 2.74 and 5.15 larger, respectively, than that of the Fe2O3 and commercial TiO2 photoelectrodes. [ABSTRACT FROM AUTHOR]

As a promising large‐scale energy storage technology, all‐vanadium redox flow battery has garnered considerable attention. However, the issue of capacity decay significantly hinders its further development, and thus the problem remains to be systematically sorted out and further explored. This review provides comprehensive insights into the multiple factors contributing to capacity decay, encompassing vanadium cross‐over, self‐discharge reactions, water molecules migration, gas evolution reactions, and vanadium precipitation. Subsequently, it analyzes the impact of various battery parameters on capacity. Based on this foundation, the article expounds upon the significance of battery internal state estimation technology. Additionally, the review also summarizes domestic and international mathematical models utilized for simulating capacity decay, serving as a valuable reference for future research endeavors. Finally, through the comparison of traditional experimental methods and mathematical modeling methods, this article offers effective guidance for the future development direction of battery state monitoring. This review generally overview the problems related to the capacity attenuation of all‐vanadium flow batteries, which is of great significance for understanding the mechanism behind capacity decay and state monitoring technology of all‐vanadium redox flow battery. [ABSTRACT FROM AUTHOR]

Redox flow batteries (RFBs) are considered as promising candidates for large‐scale energy storage. However, traditional RFBs based on toxic metal ions have deficiencies in resource utilization and environmental protection. Considering the corrosiveness of acidic and alkaline electrolytes and sustainability of energy storage devices, neutral aqueous organic redox flow batteries (AORFBs) have more development prospects. Herein, an AORFB is reported, using 9,10‐anthraquinone‐2,7‐disulfonic salt (2,7‐AQDS) and 1,4‐dihydroxyphenylsulfonate potassium (HQS) as negative and positive electroactive materials, respectively. It is found that the anions in the neutral solution further affected the solubility and kinetics of the electroactive materials by affecting the hydrogen bond in the solution, and the Na2SO4 solution showed the optimal comprehensive performance. Therefore, an all‐quinone AORFB employing neutral Na2SO4 electrolytes with a cell voltage of 0.9 V is constructed, which presented a capacity utilization of 70.1% and delivered stable cycling performance at 60 mA cm−2. This work designs an innovative neutral all‐quinone AORFB and points out how anions affect the properties of the electrolyte by affecting hydrogen bonds within the solution. These findings open a new avenue for the design and application of neutral all‐organic aqueous RFBs. [ABSTRACT FROM AUTHOR]

Ion conducting membranes play a crucial role in redox flow batteries, separating anolyte and catholyte while allowing proton transport to complete the circuit. However, most membranes are trapped in a trade‐off relation and show either low conductivity or high vanadium crossover. This study investigates the use of dense sulfonated para‐polybenzimidazole membranes for vanadium redox flow batteries (VRFBs), and analyzes the effects of membrane preparation process, membrane thickness and operating temperature on the VRFB performance. The results demonstrate superior performance of VRFBs utilizing fluorine‐free sulfonated para‐polybenzimidazole membranes compared to other types. Under optimal conditions, the VRFB exhibits high coulombic efficiency (>99%) and high energy efficiency (EE, 92.2% at a current density of 80 mA cm−2), and durability. The achieved EE represents one of the highest reported in the literature for VRFBs. In addition, it is shown that operation at 35 °C has benefits at high current densities (EE at 300 mA cm−2 is over 80% at 35 °C but 72% at 25 °C), while the operation at 80 mA cm−2 only shows a small temperature effect (91.8 and 92.2%, respectively). [ABSTRACT FROM AUTHOR]

Electrochemical energy conversion and storage are playing an increasingly important role in shaping the sustainable future. Differential electrochemical mass spectrometry (DEMS) offers an operando and cost-effective tool to monitor the evolution of gaseous/volatile intermediates and products during these processes. It can deliver potential-, time-, mass- and space-resolved signals which facilitate the understanding of reaction kinetics. In this review, we show the latest developments and applications of DEMS in various energy-related electrochemical reactions from three distinct perspectives. (I) What is DEMS addresses the working principles and key components of DEMS, highlighting the new and distinct instrumental configurations for different applications. (II) How to use DEMS tackles practical matters including the electrochemical test protocols, quantification of both potential and mass signals, and error analysis. (III) Where to apply DEMS is the focus of this review, dealing with concrete examples and unique values of DEMS studies in both energy conversion applications (CO2 reduction, water electrolysis, carbon corrosion, N-related catalysis, electrosynthesis, fuel cells, photo-electrocatalysis and beyond) and energy storage applications (Li-ion batteries and beyond, metal–air batteries, supercapacitors and flow batteries). The recent development of DEMS-hyphenated techniques and the outlook of the DEMS technique are discussed at the end. As DEMS celebrates its 40th anniversary in 2024, we hope this review can offer electrochemistry researchers a comprehensive understanding of the latest developments of DEMS and will inspire them to tackle emerging scientific questions using DEMS. [ABSTRACT FROM AUTHOR]

Alkaline zinc‐ferricyanide flow batteries are efficiency and economical as energy storage solutions. However, they suffer from low energy density and short calendar life. The strongly alkaline conditions (3 mol L−1 OH−) reduce the solubility of ferri/ferro‐cyanide (normally only 0.4 mol L−1 at 25 °C) and induce the formation of zinc dendrites at the anode. Here, we report a new zinc‐ferricyanide flow battery based on a mild alkalescent (pH 12) electrolyte. Using a chelating agent to rearrange ferri/ferro‐cyanide ion‐solvent interactions and improve salt dissociation, we increased the solubility of ferri/ferro‐cyanide to 1.7 mol L−1 and prevented zinc dendrites. Our battery has an energy density of ~74 Wh L−1catholyte at 60 °C and remains stable for 1800 cycles (1800 hours) at 0 °C and for >1400 cycles (2300 hours) at 25 °C. An alkalescent zinc‐ferricyanide cell stack built using this alkalescent electrolyte stably delivers 608 W of power for ~40 days. [ABSTRACT FROM AUTHOR]