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All-vanadium redox flow batteries (VRFBs) are one of the potential energy storage systems for renewable energy storage. The high cost of vanadium electrolytes is one of the barriers to VRFB commercialization. To reduce the cost of the battery, the aqueous negative electrolyte is replaced with gaseous hydrogen, whereas the positive electrolyte retains vanadium ions as a hydrogen–vanadium redox flow battery (HVRFB). Hydrogen can be supplied using renewable energy sources, which enhances the kinetics of the reaction. The HVRFB is investigated in this study by examining the effects of negative electrode configuration, Pt loading, humidity conditions, and electrolyte flow rate. Pt loading and positive electrolyte flow rate are discovered to have a significant effect on electrolyte utilization. The highest battery performance is obtained when the catalyst loading is set at 0.3 mg Pt cm−2 and the positive electrolyte flow rate is around 2 L h−1. The HVRFB operates continuously for 200 cycles and demonstrates an energy efficiency of around 88% when operated at a current density of 80 mA cm−2. [ABSTRACT FROM AUTHOR]

Summary: An all‐iron aqueous redox flow battery using iron (Fe) 2,2‐bis(hydroxymethyl)‐2,2′,2′‐nitrilotriethanol (BIS‐TRIS) complex (Fe(BIS‐TRIS)) and Ferrocyanide (Fe[CN]6) as redox couple is newly suggested. The redox potential of Fe(BIS‐TRIS) is −1.11 V (vs Ag/AgCl) and this makes Fe(BIS‐TRIS) appropriate as active material for anolyte, while Fe(CN)6 is proper for catholyte due to its excellent redox reactivity, redox potential, and cheap cost. According to quantitative evaluations, Fe(BIS‐TRIS) does not produce any side reactions and is more stable than Fe triethanolamine (TEA) (Fe(TEA)) complex that is conventionally considered for the purpose. This fact is confirmed by computational analysis using density functional theory. In the calculation, energy barrier of Fe(BIS‐TRIS) suppressing the occurrence of undesirable side reactions is higher than that of other Fe‐ligand complexes, indicating that desirable redox reaction of Fe(BIS‐TRIS) occurs more stably. In redox flow battery (RFB) tests, RFBs using Fe(BIS‐TRIS) do not show any side reactions even after 250 cycles with excellent performances, such as capacity of 11.7 Ah L−1 and coulombic efficiency and capacity retention rate of 99.8 and 99.9%, respectively. This corroborates that RFBs using Fe(BIS‐TRIS) have excellency in both performance and stability, while the cheap cost of BIS‐TRIS and Fe(CN)6 enhances the economic benefit of RFBs. [ABSTRACT FROM AUTHOR]

Summary: Iodide and triiodide ions (I− and I3− ions) are interesting active redox materials for aqueous redox flow batteries (ARFBs) due to high solubility in various supporting electrolytes. However, under alkaline and neutral electrolytes, the redox reaction of I− and I3− ions is unstable due to undesirable potassium iodate produced during the reaction, whereas the reaction is stably operated under an acidic electrolyte state. As a redox couple, anthraquinone‐2,7‐disulfonic acid (AQDS) is considered due to excellent stability and high solubility, and perchloric acid is determined as an electrolyte because this suppresses another undesirable water‐splitting reaction. For providing abundant I− and I3− ions, hydroiodic acid (HI) is used because hydrogen ions contained in HI can act as a proton donor, increasing the conductivity in the solution leading to better kinetics of the redox reaction of I− and I3−. When asymmetric ARFB using this redox couple is operated, gradual decay in both capacity and efficiencies is observed. This is due to the crossover of I− ions to the AQDS side. To overcome the problem, symmetric ARFB using the mixture of HI and AQDS in both electrolytes is adopted, and with that, the crossover issue is solved because the ionic balance of electrolyte is well maintained by the use of symmetric electrolyte, while its energy efficiency and discharging capacity are excellent as 67.6% and 26.6 Ah L−1, respectively, with capacity retention of 99.99% for 100 cycles. [ABSTRACT FROM AUTHOR]

Summary: Aiming to improve electrolyte distribution in flow batteries at lower pumping cost, a sinusoidal wave‐type serpentine (SWS) flow pattern was designed and fabricated on graphite plate. The performance of the channel with graphite felt electrode, employing in vanadium redox flow battery, was analyzed by polarization curves and electrochemical impedance spectroscopy (EIS) measurements, obtained by varying flow rates of electrolyte. The pressure drop of the half‐cell assembly was measured by varying water flow rates. Results show that increasing flow rate reduces potential loss. Mass transfer overpotential is low even at 30 mL/min, and at 120 mL/min, the overpotential is negligible even at very high current density of 500 mA/cm2. The iR‐free power density monotonically increases with current density. The EIS measurements show that charge transfer resistance decreases with increasing flow rates and is lower than that for conventional serpentine flow pattern. The pressure drop across the cell is also lower. These results clearly indicate that better electrolyte distribution is achieved using SWS channels at lower pumping cost. [ABSTRACT FROM AUTHOR]

Growing numbers of electric vehicles (EVs) as well as controversial discussions on cost, scarcity and the environmental and social sustainability of primary raw materials that are needed for battery production together emphasize the necessity for battery recycling in the future. Nonetheless, the market for battery recycling is not fully understood and captured in data today. The underlying reasons are found in both market size and various parameters such as the battery-technology mix, the resulting material demand and expected battery lifetime. In consequence, the question of when secondary-material availability from battery recycling is sufficient to satisfy the global cobalt demand for EV applications has not yet been clarified. To address this question, this study estimates the global battery raw-material demand together with the expected amount of the recycled materials by 2035, taking into account a number of parameters affecting future battery material flows. While focusing on cobalt, nickel, lithium, and manganese, the results indicate that the global cobalt demand can be satisfied from secondary sources by the early 2030s in three out of four different technology forecast scenarios. Furthermore, a sensitivity analysis highlights the amount of waste occurring during battery production and battery lifetime as the main drivers for secondary-material availability by 2035. [ABSTRACT FROM AUTHOR]

Benefiting from the advantageous features of high safety, abundant reserves, low cost, and high energy density, aqueous Zn‐based rechargeable batteries (AZBs) have received extensive attention as promising candidates for energy storage. To achieve high‐performance AZBs with high reversibility and energy density, great efforts have been devoted to overcoming their drawbacks by focusing on the modification of electrode materials and electrolytes. Based on different cathode materials and aqueous electrolytes, the development of aqueous AZBs with different redox mechanisms are discussed in this review, including insertion/extraction chemistries (e.g., Zn2+, alkali metal ion, H+, NH4+, and so forth) dissolution/deposition reactions (e.g., MnO2/Mn2+), redox couples in flow batteries (e.g., I3−/3I−, Br2/Br−, and so forth), oxygen electrochemistry (e.g., O2/OH−, O2/O22−), and carbon dioxide electrochemistry (e.g., CO2/CO, CO2/HCOOH). In particular, the basic reaction mechanisms, issues with the Zn electrode, aqueous electrolytes, and cathode materials as well as their design strategies are systematically reviewed. Finally, the remaining challenges faced by AZBs are summarized, and perspectives for further investigations are proposed. [ABSTRACT FROM AUTHOR]

With the rapid development of renewable energy harvesting technologies, there is a significant demand for long-duration energy storage technologies that can be deployed at grid scale. In this regard, polysulfide-air redox flow batteries demonstrated great potential. However, the crossover of polysulfide is one significant challenge. Here, we report a stable and cost-effective alkaline-based hybrid polysulfide-air redox flow battery where a dual-membrane-structured flow cell design mitigates the sulfur crossover issue. Moreover, combining manganese/carbon catalysed air electrodes with sulfidised Ni foam polysulfide electrodes, the redox flow battery achieves a maximum power density of 5.8 mW cm−2 at 50% state of charge and 55 °C. An average round-trip energy efficiency of 40% is also achieved over 80 cycles at 1 mA cm−2. Based on the performance reported, techno-economic analyses suggested that energy and power costs of about 2.5 US$/kWh and 1600 US$/kW, respectively, has be achieved for this type of alkaline polysulfide-air redox flow battery, with significant scope for further reduction. Polysulfide-air redox flow batteries are an appealing energy storage technology but suffer from polysulfide crossover and the use of costly catalysts. Here, the authors report a cell structure that enables battery operation using a cost-effective catalyst while mitigating polysulfide crossover. [ABSTRACT FROM AUTHOR]

Zinc-air batteries (ZABs), known for their high energy density and environmental friendliness, are emerging as promising solutions for sustainable energy storage. However, the irregular deposition of zinc on electrodes hinders the widespread utilization of rechargeable ZABs due to limited durability and stability. This study investigates the role of electrolyte flow in enhancing zinc electrodeposition and overall performance in zinc-air flow batteries (ZAFBs) at high current densities. We explore the interplay between current density, flow rate, and their influence on electrode surface morphology and the removal of the passivating zinc oxide layer to improve battery efficiency and lifespan. Using advanced in-situ synchrotron radiation x-ray tomography, we found that incorporating flowing electrolyte at specific current densities results in rounded dendrite tips, thinner and more uniform deposition layers, and improved zinc adhesion. Imaging and electrochemical analyses further reveal that flowing electrolyte enhances zinc morphology, reduces charge transfer resistance, diminishes passivation, and lowers galvanostatic charge/discharge polarization across various current densities, thereby improving battery cycling performance. Notably, the impact of flowing electrolyte is more pronounced at a moderate current density of 50 mA/cm2 compared to lower or higher currents. Our findings underscore the importance of electrolyte flow and current density management in developing high-performance ZAFBs, providing valuable insights for their future commercialization. [Display omitted] • Optimize current density for improved zinc structure and longevity. • Control electrolyte flow to reduce resistance and increase efficiency. • Employ synchrotron tomography for zinc behavior insights. • Balance flow and density for better battery stability and efficiency. • Offer zinc-air battery guidelines focusing on flow and density balance. [ABSTRACT FROM AUTHOR]

• First-principles DFT modeling of nitrobenzene adsorption on the Ag(111) surface. • Nitrobenzene preferentially adsorbs to HCP sites on the Ag(111) surface. • Hybridization of O (p) and Ag (d) orbitals enhances adsorption. • Nitrobenzene adsorption weakens at higher states of electronic charge. This study explores the potential of nitrobenzene as an anolyte material for nonaqueous redox flow batteries (RFBs) by theoretically examining its low-coverage adsorption behavior on neutral and charged Ag(111) model electrode surfaces. At the low coverage limit, DFT calculations show a preference for nitrobenzene to adsorb parallel to the surface, with the benzene ring and nitro group centered over HCP sites. Interactions between nitrobenzene and the surface were analyzed using induced charge density analysis, Bader charge analysis, and projected density of states (PDOS). It was found that nitrobenzene adsorbs primarily through van der Waals interactions with the surface. As nitrobenzene accumulates negative charge, the strength of adsorption diminishes. Understanding the electrode-electrolyte interface is crucial for enhancing RFB electrochemical performance, and this study sheds light on nitrobenzene's interaction with a model Ag electrode. [Display omitted] [ABSTRACT FROM AUTHOR]

Capacity is a key factor in assessing battery health. Traditional capacity estimation methods assume by default the battery is in a normal state. When there is a latent short-circuit fault, the measured current deviates from the actual current flowing into or out of the battery unit, leading to errors in capacity estimation. To address this challenge, we have constructed an end-cloud collaborative framework to accurately estimate the module's capacity considering the latent short-circuit faults. The core scheme is to estimate the module's charging capacity and discharging capacity simultaneously, obtain the module's operating mode based on the historical relationship between the two, conduct quantitative diagnosis for the short-circuit fault, and feedback the accurate capacity value. This framework addresses the coupled issue of erroneous capacity estimation in the presence of latent short-circuit faults, and the inability to diagnose module external short-circuit faults due to the lack of a comparison. This has profound significance for achieving more reliable battery safety management. • Different from traditional algorithms, the core algorithm in this paper can accurately estimate module capacity considering the latent SC faults; • Utilizing capacity estimation results, this paper has achieved the diagnosis of module ESC faults, overcoming the challenge posed by the lack of a comparison; • We have proposed an end-cloud collaborative framework that effectively combines the advantages of both the vehicle end and the cloud, achieving accurate module capacity estimation and quantitative diagnosis of SC faults. [ABSTRACT FROM AUTHOR]

In recent decades, flow batteries have been rapidly developing for large-scale, low-cost energy storage, yet with concerns about the corrosivity and cost of metal-based electrolytes, such as vanadium. Recent research has shown great interest in seeking alternative redox couples for aqueous organic flow batteries (AOFB) due to their potentially improved safety, relatively lower cost and a wide diversity of tailored molecular structures. While most literature emphasises microscale or cell-scale experiments and modelling for AOFB, very little literature has reported on a detailed stack-level model. To this end, this work proposes an electrochemical stack model for the MV/TEMPTMA system, one of the MV/TEMPO derivatives, which claims high capacity and power density when maintaining excellent stability. The electrochemical stack model is based on the equivalent circuit method, which determines the flow battery's resistances, currents, voltages, efficiencies and capacity fade over multiple cycles, considering shunt currents, ion diffusion, self-discharge and degradation side reactions. The results show that ion diffusion and degradation play a predominant role in the capacity fade of the MV/TEMPTMA AOFB when the accumulation of diffused ions across the membrane suppresses the ion crossover and stabilises the coulombic capacity in the long run. The model uses MV/TEMPTMA as a demonstration but can also be adapted to other non-mixing AOFBs to predict and optimise battery performance. • An electrochemical stack model for the MV/TEMPTMA aqueous organic flow battery is developed. • The stack model is based on the equivalent circuit method to predict the battery performance over multiple cycles. • The effect of current density, ion diffusion across the membrane and degradation on the stack performance is revealed. • The ion diffusion and degradation play a predominant role in the capacity fade of the battery stack. • Diffused ions across the membrane suppress ion crossover and stabilise the capacity but may lead to cell voltage fluctuation. [ABSTRACT FROM AUTHOR]

• The performance of an all-rare earth flow battery is reported for the first time. • The europium-cerium flow battery has a battery voltage of 1.9 V. • Europium ions can coexist with hydrogen ions in the electrolyte. • The average coulombic efficiency, voltage efficiency and energy efficiency of ECFB are 90.9 %, 91.0 % and 82.7 %, respectively. We report the performance of an all-rare earth redox flow battery with Eu2+/Eu3+ as anolyte and Ce3+/Ce4+ as catholyte for the first time, which can be used for large-scale energy storage application. The cell reaction of Eu/Ce flow battery gives a standard voltage of 1.90 V, which is about 1.5 times that of the all-vanadium flow battery (1.26 V). Large standard voltage is conducive to the improvement of battery energy density and power density. The Eu2+/Eu3+electrode reaction in a NaCl solution on platinum electrode was investigated detailedly using cyclic voltammetry, linear sweep voltammetry, tafel plot and chronoamperometry. Unlike zinc-cerium flow battery, the active species of Eu/Ce flow battery are always present in the electrolyte, and no liquid-solid phase transition occurs. Thus, Eu/Ce flow battery is free of the problems associated with dendrite growth and theoretically have a longer cycle lifetime. The negative electrolyte is very sensitive to oxygen and can directly cause battery failure if exposed to air. The average energy efficiency of Eu/Ce flow battery exposed to air is only 22.0 %. However, the average energy efficiency of Eu/Ce flow battery stripped of oxygen reaches 82.7 % at 25 mA/cm2. Preliminary experimental studies have shown that Eu/Ce flow batteries are a promising method for large-scale energy storage. [ABSTRACT FROM AUTHOR]

Zinc-bromine (Zn–Br) flow battery is a promising option for large scale energy storage due to its scalability and cost-effectiveness. However, the sluggish reaction kinetics of Br 2 /Br− have hindered further advances. In this study, we report that a nitrogen-doped carbon felt electrode derived from a metal-organic framework can facilitate the adsorption of N-methyl N-ethyl pyrrolidinium polybromide (MEP-pBr) complex droplet dispersed in aqueous electrolyte. Density functional theory (DFT) calculation and Zeta potential measurement suggest that the adsorption is primarily due to the positively charged surface induced by graphitic nitrogen defects. Electrochemical analysis indicates that the enhanced adsorption of MEP-pBr droplet significantly boosts the redox kinetics and decreases the crossover of bromine-bearing species. Consequently, the cell performance improves, achieving an energy efficiency of over 79 % during 900 cycles at a current density of 100 mA cm−2. Our work underscores the importance of providing access of MEP-pBr droplet to the electrode surface in augmenting the energy efficiency of Zn–Br flow battery. [Display omitted] • A nitrogen-doped carbon felt cathode derived from a metal-organic framework (ZIF-8). • A positively charged surface on cathode induced by graphitic nitrogen defects. • A positively charged cathode surface facilitates the anchoring of MEP-pBr droplet to boost the redox kinetics. • Optimized nitrogen-doped carbon felt cathode exhibits superior performance and durability. [ABSTRACT FROM AUTHOR]

Zinc-based flow batteries hold great promise for grid-scale energy storage. However, the formation of zinc dendrites challenges their lifespan and safety. In this work, we devise a bimetallic organic framework material on carbon cloth (CuZn@MOF-CC) using a one-step dip coating method to address the dendrite issue. The prepared CuZn@MOF-CC promotes the creation of zincophilic sites on the electrode surface, facilitating smooth and uniform zinc deposition. Electrochemical csharacterizations and density functional theory (DFT) calculations reveal much stronger electronic interactions between CuZn@MOF and the zinc atoms compared to the commonly used anode material through an obvious electron interaction between the Zn atom and the Cu sites linked in the CuZn@MOF chain. By mitigating the zinc dendrite problem, this approach effectively improves the coulombic efficiency, cycle life, and safety of zinc-based flow batteries. The battery incorporating the prepared material demonstrates impressive stability, exceeding 450 cycles without dendrites at a high current density of 320 mA cm−2, paving the way for efficient and reliable energy storage solutions and a sustainable future. CuZn@MOF interfacial layer can improve the nucleation uniformity of zinc, inhibit dendrite formation and form a flat and uniform zinc coating. [Display omitted] [ABSTRACT FROM AUTHOR]

• Water optimizes deep eutectic solvent electrolyte viscosity and conductivity. • 75 % water in deep eutectic electrolyte boosts peak current up to 9.5-fold. • Tuned deep eutectic electrolyte matches all-vanadium battery performance. • Water-tuning enables cost-effective, efficient iron-vanadium flow batteries. Deep eutectic solvents (DES) are being recognized as a highly promising electrolyte option for redox flow batteries. This study examines the impact of modifying the molar ratio of water to a DES consisting of urea and choline chloride on important measures of electrolyte performance, such as viscosity, cyclic voltammetry, and impedance spectroscopy. According to the findings, when the molar ratio of water to DES is 1:3, the viscosity of the electrolyte falls by 75 %, the peak current density increases by 5–9.5 times, the ionic conductivity increases by 5–10 times, and the ohmic resistance decreases by 60–90 %. This approach greatly enhances the conductivity and diffusion coefficient of the electrolyte, resulting in a novel, cost-effective, and highly efficient electrolyte for iron-vanadium redox flow battery applications. This study enhances the efficiency of DESs at the molecular level, establishing the foundation for future extensive implementations. [ABSTRACT FROM AUTHOR]

The exceptional advantages of vanadium redox flow batteries (VRFBs) have garnered significant attention, establishing them as the preferred choice for large-scale and long-term energy storage solutions. However, side reactions such as hydrogen evolution reaction (HER) lead to suboptimal performance of VRFB parameters, resulting in an overall decrease in VRFB performance. Therefore, it is imperative to investigate the mechanism by which HER affects VRFB performance and identify effective methods to mitigate its impact. In light of this, critical parameters such as charge-discharge curve, internal resistance, pressure-drop, pump power consumption, efficiency, and capacity retention rate are selected to evaluate the impact of HER on VRFB performance. Experimental results demonstrate that HER causes an increases in voltage during charging and a decrease during discharging stages leading to voltage loss; additionally, bubble generation significantly increases pressure drop and pump power consumption; furthermore, blockage of flow channels and electrodes due to bubbles leads to an increase in ohmic resistance. Finally, HER has a substantial impact on efficiency and capacity with an average energy efficiency of 2.92 %. After 60 cycles, the capacity retention rate decreased by nearly 7.69 %. [ABSTRACT FROM AUTHOR]

[Display omitted] • The cysteine groups grafted onto Cys-COF resulted in a narrowed particle channel size and altered electrical properties. • The Cys-COF exhibited increased resistance to vanadium ion conduction while maintaining high proton conductivity. • The optimal hybrid membrane exhibited superior ion selectivity of 4.11 × 105 S min cm−3 and enhanced VFB performance. Flow batteries demand for ion conductive membranes (ICMs) with high ion selectivity to achieve efficient energy conversion. Herein, we engineered a cysteine-modified covalent organic framework (Cys-COF) by a Thiol-ene click reaction. As a promising proton carrier, the incorporation of the Cys-COF with sulfonated poly(ether ketone) (SPEEK) yields advanced ICMs for vanadium flow batteries (VFBs). The zwitterionic cysteine groups anchored on the nanochannel walls simultaneously narrowed the pore size and ameliorated the protophilicity of Cys-COF, resulting in improved vanadium permeating resistance and proton conductivity. As a result, the optimal membrane demonstrated synchronized improvements in coulombic efficiency (95.01 %–98.84 %), voltage efficiency (95.15 %–77.84 %) and energy efficiency (90.41 %–76.94 %) with the current densities ranging from 40 to 200 mA cm−2. Regarding stability test, it achieved exceptional energy efficiency (∼84.3 %) over 1100 cycles and 550 h at the constant current density of 120 mA cm−2, outperforming pure polymer membrane and Nafion 212. [ABSTRACT FROM AUTHOR]

[Display omitted] • Experimental and modelling investigation on one method to reduce parasitic currents; • Proposed design to reduce ionic shortcut currents using manifold reducers; • Pressure losses were quantified with and without the presence of manifold reducers; • The model was able to calculate parasitic currents and how they varied in the stack; • The design was found to improve the performance of Acid-Base Flow Battery systems. The Acid-Base Flow Battery is an innovative and sustainable electrochemical storage system storing energy in the form of salinity and pH gradients. However, parasitic currents via manifolds dramatically affect system by reducing its Round-Trip Efficiency (RTE). This work experimentally studies this phenomenon using a purposely designed methodology involving sticks placed in the manifold ducts. Various figures of merit were calculated to evaluate battery performance in the charge and discharge phases. A mathematical model was validated and applied to investigate the ionic parasitic currents. The results highlighted the importance of studying this phenomenon, as achieving a reduction in the parasitic currents caused a 25% increase in the net power and more than tripled the RTE compared to the reference configuration without sticks. Although reducing manifold diameter increases pumping losses, it was found to be anyway really beneficial for the process performance and paves the way for future, more suitable, battery designs. [ABSTRACT FROM AUTHOR]

Neutral aqueous organic redox flow battery (NAORFB) represents a highly promising energy storage device. However, one of its challenges is the need for high Cl− conductivity, highly stable ion-selective membranes. In this work, N-methylpiperidine-modified carbazole-based long side chain anion exchange membranes (QPCEP-x) were designed and prepared. The rigidity and hydrophobicity provided by the carbazole on the main chain, in conjunction with the flexibility and hydrophilicity provided by the alkyl-piperidine groups on the side chains, resulted in the observed excellent microphase separation properties of the prepared membranes. The prepared membranes exhibited excellent overall performance, with QPCEP-1 achieving a Cl− conductivity of 20.33 mS cm−1 at 25 °C. In NAORFB, the energy efficiency of QPCEP-1 ranges from 91.7 % to 62.4 % at 20–160 mA cm−2, far exceeding the 89.1 %–38.4 % of commercial AMVN. Furthermore, long-term cell cycling tests demonstrate that the energy efficiency of QPCEP-1 remains unchanged at 82.7 % at 60 mA cm−2 after 10,000 complete charge and discharge cycles, exceeding the majority of cycles reported in literatures. These findings suggest that QPCEP-x has significant potential for use in NAORFB. [Display omitted] • A systematic approach was developed to prepare rigid carbazole-based anion exchange membranes containing flexible alkyl piperidine side chains. • The planar conjugated non-rotating carbazole structure is a key factor in ensuring the long-term battery cycling. • The incorporation of flexible alkyl-piperidine side chains resulted in enhanced microphase separation, which in turn led to an improvement in the Cl− conductivity and energy efficiency of the NAORFB. • The prepared membranes demonstrated the capacity for full charge/discharge at 200 mA cm−2 and retained 82 % of energy efficiency after 10,000 cycles at 60 mA cm−2. [ABSTRACT FROM AUTHOR]

Membraneless micro redox flow batteries operate within the laminar flow regime to mitigate the convective mixing between catholyte and anolyte. The absence of an ion-exchange membrane reduces manufacturing costs and overall cell resistance, thereby enhancing battery performance. However, it also poses a new challenge: the precise control of the thin mixing layer established between the two co-flowing electrolytes. Undesired displacements of the mixing region lead to increased crossover losses and significant liquid transfer between tanks. This work addresses the deflection of the mixing region under varying flow conditions, considering electrolyte viscosity variations due to the changes in the local state of charge arising during battery operation. This is achieved through a combination of mathematical analysis, numerical simulations, and experimental results. The conservation equations and non-dimensional parameters governing the problem are first written and discussed. The model is then integrated numerically incorporating different inlet and outlet boundary conditions to simulate the effect of various flow control strategies. Next, the numerical results are validated against experimental realizations of the flow. Finally, three case studies are presented and discussed. This work highlights the relevance of variable viscosity in the operation of co-laminar membraneless micro redox flow batteries, and proposes for the first time feasible control methods to mitigate undesired disturbances in the hydraulic circuit, thereby minimizing crossover losses. • A new model for a membraneless X-shaped micro RFB is validated experimentally. • The effect of variable viscosity and ion dependent diffusivities is considered. • Physical and operational parameters affect electrolyte separation to a large extent. • Various control strategies are used to reduce ion crossover and net electrolyte transfer. • The best strategy for symmetric SoC involves symmetric inlet and outlet flow rates. • Strong performance loss is observed under uncontrolled/asymmetric conditions. [ABSTRACT FROM AUTHOR]

Perfluorosulfonic acid (PFSA) is the most widely used membrane material for all-vanadium redox flow batteries (VRFB). However, severe vanadium ion permeation of PFSA membranes remains to be solved. In this work, a series of PFSA-based composite membranes are prepared by introducing two-dimensional continuous covalent organic framework (COF) to achieve enhanced performance. Two dimensional continuous Schiff base network-type COFs (GO/SNW) are synthesized by using the two-dimensional multi-functionalized surface of graphene oxide (GO) as a reaction site. Compared to the original form of agglomerated particles, two-dimensional continuous structure obtained a larger vanadium resistance area. Comparing to conventional PFSA membranes, the special pores of COF have a size sieving mechanism for selectively proton transfer, leading to simultaneously enhancement of proton conductivity and vanadium barrier property. VRFB assembled with PFSA-GO/SNW-7 showed high Coulombic efficiency (CE: 97.47%–98.18 % VS PFSA: 80.73%–91.92 %) and energy efficiency (EE: 93.04%–85.71 % VS PFSA: 77.53%–81.78 %) at 40–120 mA cm−2. In addition, there is no significant decrease in the efficiency of battery assembled with PFSA-GO/SNW-7 after 800 cycle (than 650 h) tests. This work provides a new direction in the design of fillers for mixed matrix membranes. • Fast proton selective conduction due to pore size sieving. • The continuous COF sheets provide enhanced vanadium resistance. • Effectively solves the problem of GO and COF agglomeration. [ABSTRACT FROM AUTHOR]

• The N and S heteroatom doping can adjust the O vacancy percentage of Ti-WO 3 and Nb-h-WO 3. • Doped transition metal oxides greatly enhance the actual electrochemical activity of graphite felt. • Doped transition metal oxides are advantageous in reducing the capacity decay of AORFBs. In this study, a graphite felt (GF) electrode was modified with N and S heteroatoms before being loaded with Ti-doped or Nb-doped WO 3 to produce Ti-WO 3 /GF-N-S and Nb-WO 3 /GF-N-S electrodes. X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy were used to analyze the crystal structure, morphology, and elemental state of the modified GF electrodes and investigate the impact of nonmetallic and metallic element doping. The influence of metal doping on the electronic distribution of the oxide was determined using first-principle calculations. The electrochemical properties of the modified GF were studied using cyclic voltammetry, electrochemical impedance spectroscopy, and single-cell tests. The results showed that Ti or Nb doping changed the energy band structure, bond length, and bond angle in the WO 3 crystal and formed O vacancies. The chemical properties of Ti and Nb resulted in different numbers of O vacancies for the two doped-WO 3.The doping of N and S heteroatoms on the carbon fibres altered the O vacancy concentration of WO 3. The synergism between the two doping methods accelerated electron transfer in the anthraquinone redox reaction. In addition, the N-containing functional groups provide lone-pair electrons, which accelerate electron transfer and anthraquinone adsorption. Therefore, compared to the pristine GF, the discharge capacities of the Ti-WO 3 /GF-N-S and Nb-h-WO 3 /GF-N-S graphite GF electrodes increased by 58 % and 41 %, respectively, and the Nb-h-WO 3 /GF-N-S graphite GF electrodes exhibited a good capacity retention rate. This study broadens the practical applications of aqueous anthraquinone redox flow batteries. [ABSTRACT FROM AUTHOR]

The Front Cover highlights how the direct functionalization of quinones has always fascinated research communities due to their biological and redox activities and subsequent application. In their Review (DOI: 10.1002/ejoc.202400535), R. Kumar Jha and S. Kumar have brought together the historical importance of and the recent advancements made towards the direct functionalization of quinones for the construction valuable functionalized quinones. Most of the synthesized quinone derivatives have applications in biological activities, flow batteries and catalysis...By Raushan Kumar Jha and Sangit KumarReported by Author; Author [Extracted from the article]

Due to their almost unlimited scalability, redox flow batteries can make versatile and affordable energy storage systems. Redox active materials (redoxmers) in these batteries largely define their electrochemical performance, including the life span of the battery that depends on the stability of charged redoxmers. In this study, we examine the effects of expanding the π-system in the arene rings on the chemical stability of dialkoxyarene redoxmers that are used to store positive charge in RFBs. When 1,4-dimethoxybenzene is π-extended to 1,4-dimethoxynaphthalene, a lower redox potential, improved kinetic stability, and longer cycling life are observed. However, when an additional ring is fused to make 9,10-dimethoxyanthracene, the radical cation undergoes rapid O -dealkylation possibly due to increased steric strain that drives methoxy out of the arene plane thus breaking the π-conjugation with O 2p orbitals. On the other hand, the planar structure of 1,4-dimethoxynaphthalene may facilitate second-order reactions of radical cations leading to their neutralization in the bulk. Our study suggests that extending the π-system changes reactivity in multiple (sometimes, opposite) ways, so lowering the oxidation potential through π-conjugation to improve redoxmer stability should be pursued with caution. [Display omitted] • Ring fusion has competing effects on the stability of dimethoxyarene radical cations. • Steric stress can modulate molecular conformation and compromise stability. • Second-order neutralization of radical cations can occur for planar molecules. • Electrochemical titration can decouple charge and discharge capacities. [ABSTRACT FROM AUTHOR]

In this study, we develop a membrane-free Zn hybrid redox flow battery (RFB) using an unconventional water-in-salt aqueous biphasic system (WIS-ABS). This membrane-free Zn hybrid battery employs soluble ferrocene (Fc) derivative and Zn salt as the active species in the immiscible catholyte and anolyte, respectively. Initially, we demonstrate the potential of using WIS-ABS for a totally aqueous membrane-free Zn battery under static conditions. This static battery operates at a cell voltage of 1.01 V and effectively eradicates the detrimental self-discharge observed in membrane-free batteries, achieving excellent coulombic efficiency (CE) consistently around 100 % over 2000 cycles. However, due to transport limitations in the static configuration, the battery exhibits a low capacity utilization of 17.4 % for the catholyte, ultimately restricting the energy density of the battery. Further improvements in the battery performance are achieved by employing a specially designed RFB cell reactor to operate under real flowing conditions. Impressively, the developed membrane-free Zn hybrid RFB cell significantly shows an improved catholyte utilization, reaching up to 95 %. Furthermore, the membrane-free RFB consistently maintains CE higher than 95 % throughout the cycling process, ultimately achieving a capacity retention as high as 96.5 % after 30 cycles at 100 % depth of discharge. This work highlights the potential of utilizing a water-in-salt aqueous biphasic system to develop a membrane-free Zn hybrid RFB with excellent electrochemical performance, effectively avoiding the undesired self-discharge phenomena. • New Zn hybrid membrane-free battery with two immiscible aqueous electrolytes. • First example of Zn hybrid membrane-free battery under real flowing conditions. • Effective suppression of self-discharge in membrane-free batteries. • Flow operation increases the material utilization and allows stable performance over cycling. [ABSTRACT FROM AUTHOR]

• A numerical model coupling mass transfer and electrochemical reaction is built for the battery. • The discharge performance and thermo-electric conversion efficiency are studied in detail. • The initial reactant concentration under various discharge conditions is determined. • The Carnot-relative efficiency is up to 80.48 %. This paper established a numerical model of mass transport and electrochemical reaction coupling in porous media of thermally regenerative ammonia-based flow battery with foam copper electrode (TRAFB-FCE) for the first time. The effects of the structural parameters of the foam copper electrode on the power density, energy density, discharge capacity, and active species distribution of the battery were comprehensively studied based on the coupled numerical model. Special attention was paid to the selection strategy of the initial reactant concentration for the battery under different discharge conditions. The results suggest that increasing the porosity or thickness of the foam copper electrode causes the voltage and power density of the battery to first increase and then decrease, while the discharge capacity and energy density monotonically increase. Moreover, the battery should avoid discharging at current densities exceeding 720 A·m−2. When the discharge current density is less than 200 A·m−2, it is preferable to set the initial concentration of Cu2+ to 0.4 mol/L, while the discharge current density is in the range of 200–720 A·m−2, the initial concentration of Cu2+ is preferable to be 0.3 mol/L. When it discharges at about 5 % of its maximum power density, the Carnot-relative efficiency of this battery is comparable to the highest value currently reported in the field of liquid-based thermo-electric conversion achieved by the Thermal Regenerative Electrochemical Cycle (TREC) technology, and the power density of the former is 8.87 times that of the latter. [ABSTRACT FROM AUTHOR]

• Low-cost, highly reversible eutectic-based positive electrolyte was developed. • Eutectic-based negative electrolyte shows superior electroplating/stripping. • Low-cost deep eutectic-based all-iron hybrid RFBs were assembled. • Battery delivered over 98% average coulombic efficiency in 360-hour cycle. Redox flow batteries (RFBs) emerge as highly promising candidates for grid-scale energy storage, demonstrating exceptional scalability and effectively decoupling energy and power attributes. Nevertheless, the high cost of vanadium metal hinders the continued commercialization of vanadium redox flow batteries (VRFBs), prompting the exploration of low-cost all-iron RFBs as a viable alternative. In this context, we propose an innovative deep eutectic-based all-iron hybrid RFBs. By synthesizing a deep eutectic solvent through the mixture of choline chloride, ethylene glycol, and an appropriate amount of deionized water, the deficiencies in mass transport performance of the deep eutectic electrolyte have been successfully addressed, while enhancing its conductivity. The deep eutectic solvents facilitate the restructuring of the solvent shell surrounding the negative electrolyte Fe2+, effectively suppressing its hydrolysis. Additionally, the synergistic interaction between the restructured solvation structure and the chelating ring structure formed between Fe2+ and glycine improves the deposition morphology of iron. Simultaneously, utilizing a eutectic-based positive electrolyte improves the solubility of active substances while maintaining excellent cycling stability and mass transport performance. The entire battery system exhibits an average coulombic efficiency exceeding 98 % in a 360-hour charge–discharge cycle at 10 mA/cm2. In the first 66 cycles, the coulombic efficiency remains at 100 %, and the energy efficiency approaches 54 %. This indicates that the battery system developed using deep eutectic solvents demonstrates promising applications within the same category of eutectic-based batteries. [ABSTRACT FROM AUTHOR]

Aqueous organic redox flow batteries (AORFBs) have become a promising electrochemical energy storage technology due to their low cost, high safety, and sustainability. As key components of emerging AORFBs, membranes face challenges such as scarcity of available membranes and high prices. Moreover, currently available membranes have low battery performance because these membranes are not optimized for specific AORFBs. In this work, a new cation exchange membrane sulfonated anthrone-containing poly(aryl ether ketone) (SAnPEK) membrane was prepared for the first time and achieved significantly improved performance in (SPr) 2 V/K 4 [Fe(CN) 6 ] AORFBs. SAnPEK membrane has excellent selectivity and high mechanical strength (>50 MPa). SAnPEK membranes exhibit high conductivity in 1 M NH 4 Cl solution. For example, SAnPEK-4 membranes exhibit low surface resistance (0.176 Ωcm2) in 1 M NH 4 Cl solution, which is significantly better than Nafion117 (1.02 Ωcm2) and Nafion212 membranes (0.276 Ωcm2). SAnPEK membrane exhibtis impressive performance in (SPr) 2 V/K 4 [Fe(CN) 6 ] AORFB. The SAnPEK-4 membrane exhibits high coulombic efficiency (CE) and excellent energy efficiency (EE) (CE = 99.1 %, EE = 83.4 % at 100 mAcm−2), and the EE for SAnPEK-4 membrane is significantly better than that for the Nafion117 membrane (CE = 99.3 %, EE = 62.4 %) and Nafion212 membrane (CE = 99.1 %, EE = 80.8 %, 100 mAcm−2). In addition, the SAnPEK-4 membrane exhibits excellent cycle stability over 3000 cycles in AORFB. As a high-performance, easy-to-prepare, low-cost cation exchange membrane, SAnPEK membranes have good application potential in AORFBs. [Display omitted] • New sulfonated anthrone-containing poly(aryl ether ketone) membranes are prepared. • SAnPEK membranes are first applied in AORFBs. • SAnPEK membranes exhibit low area resistance and high membrane selectivity. • SAnPEK membranes exhibit an impressive energy efficiency of 83.4 % at 100 mAcm−2. [ABSTRACT FROM AUTHOR]

The efficient operation of vanadium redox flow batteries requires the half cell specific monitoring of the state of charge (SOC). Monitoring of the SOC is affected by temperature fluctuations, which need to be distinguished from the SOC signal. Several SOC monitoring approaches have been proposed in the literature and either been evaluated individually or compared to one other approach. The aim of this study is to contribute to SOC sensor development for VRFB by providing a first correlated assessment of several established and new SOC monitoring methods. We perform multi observable measurements of: half cell electrolyte potentials, electrolyte densities, electrolyte volumes, electrolyte viscosity related pressure drops, pH related potentials and UV/Vis absorbances. We determine SOC correlations of these observables in full charge/discharge cycles at constant temperature and derive temperature corrections in additional measurements over a range of 12 °C to 32 °C at 25 %, 50 % and 75 % SOC. We compare the SOC and temperature sensitivity as well as the accuracy of these monitoring methods at constant and varied temperature. We find that the established half cell electrolyte potentials and UV/Vis absorbances can estimate the SOC at constant temperature with measurement errors of 1.7% and 4%, respectively and with slightly higher errors at varying temperatures. The viscosity related pressure drop and electrolyte density are both suitable for SOC estimation if temperature corrections are included. The pH related potentials for the positive half cell and both half cell electrolyte volumes could be used for a rough SOC estimate, but need accurate temperature corrections and further long term stability evaluation. [ABSTRACT FROM AUTHOR]

A recent article in the journal Angewandte Chemie International Edition discusses the development of a hydrothermal method for synthesizing naphthalene diimide anolytes for neutral flow batteries. This method improves the solubility and stability of the anolytes, leading to higher capacity and power density. The authors, Gang He et al., suggest that this cost-effective approach could contribute to the commercialization of advanced energy storage technologies by providing a competitive advantage over traditional methods. The article is authored by Xu Liu, Heng Zhang, Chenjing Liu, Zengrong Wang, Xuri Zhang, Haiyan Yu, Yujie Zhao, Ming-Jia Li, Yinshi Li, Ya-Ling He, and Gang He. [Extracted from the article]

A recent article in Angewandte Chemie discusses the development of a hydrothermal method for synthesizing naphthalene diimide anolytes for neutral flow batteries. This method improves the solubility and stability of the anolytes, resulting in higher capacity and power density. The authors, Gang He et al., suggest that this cost-effective approach could contribute to the commercialization of advanced energy storage technologies by providing a competitive advantage over traditional methods. The article is authored by Xu Liu, Heng Zhang, Chenjing Liu, Zengrong Wang, Xuri Zhang, Haiyan Yu, Yujie Zhao, Ming-Jia Li, Yinshi Li, Ya-Ling He, and Gang He. [Extracted from the article]

This article, published in Angewandte Chemie, discusses the discovery of the largest organic-ligand-protected Pt nanoclusters with atomic precision. The researchers found that these Pt23 nanoclusters exhibited superior catalytic activity for the oxygen reduction reaction under acidic conditions compared to commercial Pt/C catalysts, without the need for additional treatments. Additionally, the nanoclusters demonstrated excellent photothermal conversion efficiency, suggesting potential applications in various fields. The article also briefly mentions other research topics, including the synthesis of sulfur-containing polymers and the development of naphthalene diimide anolytes for neutral flow batteries. [Extracted from the article]

[Display omitted] • A self-healing electrocatalyst was proposed for the first time. • The self- healing catalyst was self-growth on the electrode surface by introducing transition metal ions. • The improved TMFB operates well with a volume capacity of 45 Ah L−1 (over 42 days). Manganese-based flow battery has attracted wide attention due to its nontoxicity, low cost, and high theoretical capacity. However, the increasing polarization at the end of the charging process greatly limits the battery capacity. Here we found that the introduction of specific transition metal ions could induce the formation of uniform MnO 2 layer on the cathode of titanium-manganese flow batteries. Excitingly, the uniform MnO 2 layer can catalyze the electrochemical reaction of Mn2+ to Mn3+, and then obviously enhance the charge capacity. Herein, the MnO 2 layer formation mechanism and catalysis effect of the MnO 2 layer have been analyzed in detail. More interestingly, the MnO 2 layer would be consumed at the end of the discharge process and regenerated again after the next charge process. Different from the conventional catalysts, the MnO 2 layer could self-heal in every cycle, which could mitigate the fall-off and deactivation risk of the catalyst and prolong the cycle life of the battery. As a result, the TMFB achieves a volume capacity of 45 Ah L−1 and runs over 400 charge–discharge cycles (42 days). Besides, the design route of a self-healing catalyst was summarized in the work, which is expected to be applied widely in the electrochemical systems. [ABSTRACT FROM AUTHOR]

• Electroactive FeRB can be rapidly enriched by electrochemical methods. • FeRB improved output performance and electrochemical properties in half-battery. • The specific capacity prominently increased in RFB by FeRB before 0.3 M, 12 mA/cm2. • Use electrocatalysis to accelerate bacteria-mediated iron reduction process. At present, the all-iron redox flow batteries (RFBs) have greater application potential due to high accessibility of electrolytes compared to traditional RFBs. Meanwhile, although electroactive bacteria can accelerate the electrons transfer, their potential to improve the performance of RFBs has been overlooked. Previously, we had confirmed that ferrous-oxidizing bacteria (FeOB) could enhance the performance of an all-iron RFB, therefore we conducted several batch experiments and chronopotentiometry experiments by using the ferric-reducing bacteria (FeRB) or mixed culture (FeOB and FeRB) to demonstrate whether they have the same or stronger effects on Fe3+-DTPA/Na 4 [Fe(CN) 6 ] RFB. The results showed that the experimental reactors could achieve higher charging current density and initial cathodic potential during constant voltage charging process. The electrochemical impedance spectroscopy data and cyclic voltammetry curves demonstrated that the polarization impedance increased slower and reduction peak potential of experimental groups also emerged a positive shift compared to CK. According to chronopotentiometry experiments results, the microbes could function at maximum 0.3 M, 12 mA/cm2, and also improved the charging specific capacity. Combined the SEM pictures and microbial composition analysis, the main functional electroactive FeRB were Alcaligenes , Corynebacterium and Bacillus , which indicated to have important potential in improving the performance of RFBs. [ABSTRACT FROM AUTHOR]

• A simple and highly actionable method to design electrode's pore structure. • Flow field and combination of large and small pores are considered simultaneously. • The power density was increased by 2.4 times compared to that with the pristine felt. • For VRFB, perforate under the rib near the outlet channel is optimal. To further enhance the efficiency of redox flow batteries, there is a vital need to decouple the conflict between specific surface area and hydraulic permeability in porous electrodes. In this work, we propose a facile and highly productive method to devise porous electrode's pore structure in conjunction with the flow field topology based on the infrared laser perforation to reconcile the combination of large and small pores. We find experimentally that the method of perforation under the center of the rib yields a significant improvement on the overall performance, with an increase in the maximum power density by approximately 2.4 times compared to that without the perforation. We also devise a pore-network model, by using which we explore the effects of large pores formed by the laser perforation on the distributions with respect to the local velocity, active species concentration and reaction rate, as well as the effects of the perforation location and diverse operating conditions on flow cell's overall performance. The results show that under the general operating conditions of the VRFB, we recommend to produce large pores in the region under the rib close to the outlet channel to enable substantial performance gains. [ABSTRACT FROM AUTHOR]

This paper presents a nonlinear observer to estimate the active species concentrations in vanadium flow batteries. To conduct the estimation, the observer relies only on current, flow rate and two half-cell voltage measurements. In contrast to previous works in the field, the proposed observer is capable to deal simultaneously with two significant and challenging conditions: (1) a not necessarily high flow rate, which results in different concentrations for tanks and cells, and (2) presence of crossover and oxidation side reactions, that result in imbalance between the electrolytes on the positive and negative sides of the system. The stability and convergence of the observer are formally demonstrated using a Lyapunov analysis and subsequently validated through comprehensive computer simulations. Finally, utilising the information provided by the observer, a strategy to independently regulate the flow rate of each electrolyte based on their individual state of charge is developed. • Nonlinear observer for active species concentrations in vanadium flow batteries. • Online algorithm relying on flow rates, current and half-cell voltage measurements. • Consideration of electrolyte imbalance and tanks-cells concentration differences. • Formal proof of stability and convergence; no prior information required. • Application for SoC and SoH monitoring, and battery performance optimisation. [ABSTRACT FROM AUTHOR]

Zinc-based flow batteries (ZFBs) have attracted considerable attention due to their high energy density, high safety, and low cost. However, the notorious dendrite problem is universally recognized as a bottleneck limiting the commercial application of ZFBs. This work proposes a zincophobic interface engineering strategy based on electrostatic repulsion to achieve uniform distribution of zincate ions along the membrane-electrode interface, where the carboxymethyl cellulose (CMC) is introduced for customized optimization of membrane surface charge. Such interface engineering successfully realizes crystal-facet manipulation that contributes to a 33.76% increase in the exposure of preferential crystallographic orientation ((002) plane), as evidenced by molecular scale characterization techniques, in-situ dynamic observation and density functional theory study. Moreover, the good wettability of hydrophilic CMC and the positive impact of its abundant –OH functional groups on the transport dynamics of charge carrier (OH−) synergistically enable the prepared membrane delivering high ion conductivity. Consequently, the battery employing the as-prepared membrane achieves stable operation for over 3000 cycles at 80 mA cm−2 with an average energy efficiency of ∼80%. This study provides a new solution for metal dendrite problem by crystal-facet manipulation, and so as to facilitate the commercialization of ZFBs in long-term energy storage. The –COOH groups of carboxymethyl cellulose (CMC) was aimed to regulate the microenvironment charge properties of membrane-electrode interface to realize crystal-facet manipulation based on electrostatic repulsion. Meanwhile, the hydrophilic of CMC and its abundant –OH groups jointly provided fast transport channels for OH−. The battery with the composite membrane demonstrated outstanding battery performance over 3000 cycles. [Display omitted] • This work achieved dendrite-free ZFBs by regulating the microenvironment charge. • Such interface engineering realized crystal-facet manipulation for even deposition. • Various characterization methods were used to verify the uniform plating process. • The hydrophilic CMC and its abundant –OH groups contributed to ion conductivity. • The battery finally achieved stable operation for over 3000 cycles with ∼80% EE. [ABSTRACT FROM AUTHOR]

• A phase-field model is constructed to simulate dynamic zinc dendrites growth. • Dendrite morphologies depend on ion transport and electrochemical reaction. • Flowing electrolyte uniformizes the concentration gradient on Zn anode surface. • Flowing electrolyte induces inhomogeneous deposition along the flow direction. The growth of zinc dendrites poses a major challenge in developing stable aqueous zinc batteries. It is crucial to understand the mechanism underlying dendrite growth and the influences of various factors on the process of dendrite growth. In this study, a phase field model is constructed to simulate the growth of zinc dendrite and investigate the temporal and spatial distributions of ions and electric potential in both static and flowing electrolytes. The influences of various critical factors, including overpotential, anisotropic strength and electrolyte flow rate, on the morphology evolution of electrodeposit are investigated. Results reveal that the surface morphology evolution is intimately dependent on the competition between ion transport and the electrochemical reaction, and it can be modulated by various parameters. In particular, flowing electrolyte not only enhances the convective ion transport but also suppresses the dendrite bifurcation on the surface, resulting in a uniform distribution of the concentration gradient and a compact deposit. However, nonuniformity induced by the flowing electrolyte from the inlet to outlet may impede the stable cycling of zinc anodes in the flow batteries. Therefore, further design and optimization of the flow field are desired for zinc-based flow batteries. This work provides insights into the growth process of zinc dendrites and the influences of several critical parameters, which could inform the design of stable aqueous zinc batteries. [Display omitted] [ABSTRACT FROM AUTHOR]

Derived from N-(ferrocenylmethyl)-N-(butylphthalimide)-N,N-dimethylammonium bis(trifluoromethane-sulfonyl)imide (FcPI-TFSI), ferrocene/naphthalimide (FcNI-TFSI) based ionic bipolar redox-active organic molecule is constructed via nucleophilic substitution between amines and halogenated hydrocarbons. Due to the elevated delocalized negative charge density in the radical anion, the FcNI-TFSI based nonaqueous redox flow batteries (NARFBs) exhibits substantially improved cycling stability; 764 and 233 cycles are successfully performed before 50% of the initial discharge capacity is lost at 0.01 M and 0.1 M, respectively, whereas 82 cycles for FcPI-TFSI at 0.01 M. Similar to capacity diving phenomenon in lithium-ion batteries, sudden accelerated capacity loss is observed in the high-concentration battery. The possible degradation mechanism is discussed, involving crossover issue and parasitic reactions. [Display omitted] • A strategy is applied to construct ionic bipolar ROMs based on nucleophilic substitution. • The FcNI-TFSI based NARFBs exhibit improved cycling stability with N 50 of 233 at 0.1 M. • Capacity diving phenomenon is observed in the high-concentration battery. • The reasons for sudden accelerated capacity are explored. [ABSTRACT FROM AUTHOR]

Porous composites with 50 wt% LiFePO 4 (LFP) and a poly(vinylidene fluoride) binder (PVDF) have been prepared by an industrially-scalable melt-extrusion technique. A third water-soluble component, i.e. poly(ethylene oxide) (PEO), was used to create open porous structures by water leaching. PEO was fully and selectively removed during leaching due to the formation of co-continuous morphologies in extruded blends. The porosity of LFP-PEO composites was precisely tuned up to 67 % by the initial PEO content and, beyond this limit, granules disintegrated during leaching due to phase inversion. Importantly, no LFP loss was detected during leaching indicating that LFP was fully trapped by PVDF. This selective localization of LFP could be linked to its the carbon coating. As expected, porous LFP-PVDF granules were found to be more electrochemically reactive (LiFePO 4 → FePO 4) than non-porous ones when reacted with Fe(CN) 6 3− aqueous solutions. The extent and kinetics of this oxidation reaction were found to be improved when 1) the Fe(CN) 6 3−/LFP ratio is increased, 2) when the porosity of the blend is raised, and 3) when flow is applied to the solution. Finally, a full LFP oxidation was observed for 65 % porous granules under flow mode within 5 h and with a 3–5 fold molar excess of Fe(CN) 6 3−. • Polymer extrusion is used to prepare porous granules containing insertion materials. • The insertion material is LiFePO 4 (LFP), the redox mediator is Fe(CN) 6 3-. • Porous LFP-PVDF composite granules are made using extrusion with PEO as porogen agent. • With 65 % porous granules, full capacity of LFP is accessible. [ABSTRACT FROM AUTHOR]

This paper presents a techno-economic model based on experimental and market data able to evaluate the profitability of vanadium flow batteries, which are emerging as a promising technology for specific stationary energy services. Models like this are very informative on the present and perspective competitivity of industrial flow batteries in operating specific services, but they have not yet been developed to an accurate grade. This model uses technical parameters which are taken from large-area multi-cell stacks, rather than from small single cell experiments, to better characterize the behavior of real industrial reactors, and from real financial market and economic patterns of some major manufacturers. The model yields economic performance indicators as the capital cost, the operative cost, the levelized cost of storage and the net present value. A prudential present-state and a perspective analysis are elaborated to show where the economic indicators are heading, and which parameters affect more the investment profitability, thus tracking a possible roadmap for system optimization. Perspective estimations indicate that technological and market evolutions are heading to much more competitive systems, with capital costs down to 260 € kWh−1 at a energy/power duration of 10 h, to be compared with a break-even point in the net present value of 400 € kWh−1, which suggests that flow batteries may play a major role in some expanding markets, notably the long duration energy storage. [Display omitted] • A techno-economic model for vanadium redox flow battery is presented. • The method uses experimental data from a kW-kWh-class pilot plant. • A market analysis is developed to determine economic parameters. • Capital cost and profitability of different battery sizes are assessed. • The results of prudential and perspective analyses are presented. [ABSTRACT FROM AUTHOR]

• A multistep electrode treatment is developed to form defects on carbon fibers. • Carbon defects facilitate electrode kinetics of Fe/Fe2+ redox reaction at Fe anode. • Uniform Fe deposition is achieved on carbon defect induced carbon felts. • The all-iron flow battery exhibits both enhanced stability and cycling efficiency. Low-cost all-iron flow batteries recently promise a great alternative to conventional flow battery technologies for large-scale energy storage. However, inferior Fe deposition/dissolution reversibility at anode largely impedes further advance of all-iron flow battery in application. Here, we report a surface engineered carbon felt with abundant carbon defects, which realizes highly reversible Fe deposition/dissolution for all-iron flow batteries. By introducing nano-scale pores on carbon fibers via a multistep electrode treatment approach, the modified carbon felt features a high degree of defects and proves effective in promoting Fe/Fe2+ kinetics and improving Fe nucleation and growth morphology, which is beneficial for both uniform Fe deposition and complete Fe dissolution rendering a substantially enhanced reversibility for Fe anode. Theoretical calculations further ascribe the enhanced Fe/Fe2+ reversibility to strong adsorption and intensified hybridization between Fe2+ and carbon defects, while all-iron flow cell tests adopting the modified carbon felt finally demonstrates a high power density of 80 mW cm−2 as well as stable charge–discharge operation over 250 cycles with a Coulombic efficiency of 99 %, which highlights the importance of electrode design in developing stable Fe anode for use in high-performance all-iron flow batteries. [ABSTRACT FROM AUTHOR]

• Capacity attenuation mechanism of alkaline all-iron ion RFBs has been systematically analyzed. • Indirect chemical reduction of Fe(CN) 6 3− by the free ligands leads to the capacity imbalance. • Chemical reaction between Fe(CN) 6 3− and free ligands is intermediated by the hydroxyl radical (•OH). • The capacity decay can be completely restored by rebalancing capacity through an oxygen exposure process. Alkaline all-iron ion redox flow batteries (RFBs) based on iron (III/II) complexes as redox pairs are considered promising devices for low-cost and large-scale energy storage. However, present alkaline all-iron ion RFBs suffer from the issue of capacity decay, and the deeper mechanisms are elusive. Here, the attenuation mechanism of alkaline all-iron ion flow batteries is investigated by the capacity-unbalance cells combining iron (III/II)-cyanide complexes (Fe(CN) 6) in positive electrolyte and iron (III/II)-sulfonated triethanolamine complexes (Fe(DIPSO)) in negative electrolyte. It is found that the Fe(CN) 6 3− shows strong oxidizing power in the alkaline medium and can oxidize the free ligands migrated from the negative electrolyte. Further studies reveal that the chemical reaction between Fe(CN) 6 3− and free ligands is intermediated by the hydroxyl radical (•OH). This side reaction leads to the capacity imbalance, which is the root cause of capacity decay. Thanks to without irreversible decomposition and deposition of redox species, the capacity decay can be completely restored by rebalancing capacity through an oxygen exposure process, indicating a great potential for long-duration energy storage. This work clarifies the attenuation mechanism and offers insights for the subsequent optimization of alkaline all-iron ion RFBs. [ABSTRACT FROM AUTHOR]

Zinc-bromine flow batteries (ZBFBs) are considered as one of the most promising energy storage technologies, owing to the high energy density and low cost. However, the sluggish electrochemical kinetics and severe self-discharge lead to the limited power density and service life, hindering the practical application of ZBFBs. Herein, Prussian blue modified nitrogen-doped carbon (PB@NC) is synthesized as an auxiliary redox-targeting catalyst for the bromine cathode. The excellent conductivity and adsorption capability of nitrogen-doped carbon (NC) ensure the smooth electron transfer and the enriched bromine species at the reaction interface. Under the assistance of NC, Prussian blue (PB) could rapidly lose or gain electrons, then transform into the oxidized or reduced states that subsequently engages in the targeted redox reactions with the contacted Br ‐ or Br 2. It offers an alternative reaction pathway for the bromine redox, promoting the electrochemical kinetics significantly, which demonstrates a reversible redox-targeting catalytic effect. Therefore, a ZBFB modified with PB@NC achieves an energy efficiency of 85.9% at a current density of 80 mA cm−2, and ultra-high energy efficiency of 71.1% even at current density of 160 mA cm−2. This work offers a promising strategy for advancing the development of ZBFBs by the efficient cathode material design. PB is combined on NC to get a floral-like PB@NC composite, employing BG/PB redox couple as the targeting-redox catalyst. NC endows BG/PB with excellent conductivity, and enrich reactants Br 2 /Br− at the reaction interface. BG/PB could rapidly gain or lose electrons, and then undergo a direct redox reaction with the bromine species, providing an additional reaction path for Br 2 /Br− redox. Consequently, the electrochemical kinetics of ZBFB is significantly improved. [Display omitted] • Berlin-green/Prussian-blue is employed as the targeting-redox catalyst for Br 2 / Br ‐. • BG/PB redox couple provides alternative reaction path for bromine electrode. • Combination of PB and NC gains a synergistic catalytic effect. • An ultra-high energy efficiency of 71.1% is achieve at 160 mA cm−2 for ZBFB. [ABSTRACT FROM AUTHOR]

The aqueous redox flow battery (ARFB), a promising large-scale energy storage technology, has been widely researched and developed in both academic and industry over the past decades owing to its intrinsic safety and modular designability. However, compared to other technologies (e.g. Li-ion batteries), the relatively low energy density, inferior efficiency, and high investment cost of the ARFB limit its further applications. Although tremendous efforts have been made to improve the performance as well as the cost-effectiveness of ARFB by various approaches, it is still a challenge to recognize a united and general roadmap for the next commercial-available ARFB. Here we review the evaluation criteria for the performance of flow batteries and the development status of different types of flow batteries. The factors affecting the performance of flow batteries are analyzed and discussed, along with the feasible means of improvement and the cost of different types of flow batteries, which is expected to provide useful references for the further development of high-efficiency and low-cost flow batteries. • Performance/cost balance is the key to low cost flow batteries • The characteristics of various aqueous redox flow batteries are discussed • Challenges include low energy density, slow kinetics, and instability • Future trends favor aqueous organic and iron-based chemistries [ABSTRACT FROM AUTHOR]

• Carbon paper electrode shows poor mechanical stability, affecting the AORFB performance. • The mechanical robustness of carbon cloth electrode contributes to a reliable and durable AORFB performance. • Carbon cloth electrode showed high stability when used on quinone oxidation–reduction cycles. • Electrochemical active sites on the carbon cloth increase current densities and AORFB power density. • Carbon cloth electrode provides higher AORFB power density at high electrolyte flow rate. Aqueous organic redox flow batteries (AORFBs) are emerging as promising candidates for efficient energy storage in grid-scale applications. In this study, we present a comprehensive analysis comparing the performance of thermally treated carbon paper and chemically oxidized carbon cloth electrodes, which have been extensively examined for their potential suitability in AORFBs. Results indicate that carbon cloth electrodes exhibit a higher concentration of oxygenated functional groups, contributing to enhanced electrochemical kinetics and improved electrochemical stability. These attributes translate to an AORFB with 62 times higher power density when compared to paper-based electrodes used. Through repeated charge-discharge cycles utilizing the BQDS║AQS model as a representative AORFB prototype, superior performance in the carbon cloth electrodes is consistently observed. Our findings even suggest the potential for optimizing the flow rate of the electrolyte to further enhance performance. [ABSTRACT FROM AUTHOR]

Zinc-based redox flow batteries (ZRFBs) have been considered as ones of the most promising large-scale energy storage technologies owing to their low cost, high safety, and environmental friendliness. However, their commercial application is still hindered by a few key problems. First, the hydrogen evolution and zinc dendrite formation cause poor cycling life, of which needs to ameliorated or overcome by finding suitable anolytes. Second, the stability and energy density of catholytes are unsatisfactory due to oxidation, corrosion, and low electrolyte concentration. Meanwhile, highly catalytic electrode materials remain to be explored and the ion selectivity and cost efficiency of membrane materials demands further improvement. In this review, we summarize different types of ZRFBs according to their electrolyte environments including ZRFBs using neutral, acidic, and alkaline electrolytes, then highlight the advances of key materials including electrode and membrane materials for ZRFBs, and finally discuss the challenges and perspectives for the future development of high-performance ZRFBs. [ABSTRACT FROM AUTHOR]

Stable and soluble redox‐active nitroxyl radicals are highly desired for high‐capacity and long‐life aqueous zinc hybrid flow batteries (AZHFBs). Here we report a "π–π" conjugated imidazolium and "p–π" conjugated acetylamino co‐functionalized 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (MIAcNH‐TEMPO) as stable catholyte for AZHFBs. The incorporation of double‐conjugate substituents could delocalize the electron density of the N−O head and thus remarkably stabilize the radical and oxoammonium forms of TEMPO, avoiding the side reaction of ring‐opening. Consequently, the applied MIAcNH‐TEMPO/Zn AZHFB demonstrates the hardly time‐dependent stability with a constant capacity retention of 99.95 % per day over 16.7 days at a high concentration catholyte of 1.5 M and high current density of 50 mA cm−2. This proposed molecular engineering strategy based on electron density regulation of redox‐active structures displays an attractive efficacy and thus represents a remarkable advance in high‐performance AZHFBs. [ABSTRACT FROM AUTHOR]