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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]

Zinc‐bromine flow batteries (ZBFBs) offer the potential for large‐scale, low‐cost energy storage; however, zinc dendrite formation on the electrodes presents challenges such as short‐circuiting and diminished performance. Herein, an indium nanoparticle‐decorated graphite felt composite electrode for ZBFBs is proposed to mitigate zinc dendrite formation, improve performance, and prolong operational longevity. Using a facile in situ electrodeposition method, indium nanoparticles are uniformly and densely distributed on the carbon fiber surface, demonstrating exceptional efficacy in regulating zinc deposition. Thus, a higher prevalence of Zn (002) crystal planes and a smoother and more compact surface morphology are obtained, compared with those of thermally treated graphite felt. Furthermore, integration of the composite electrode into the negative side of a ZBFB yielded substantial improvements in cell performance, achieving an energy efficiency of 66.83% ± 0.45% at 120 mA cm−2, significantly surpassing the performance of batteries utilizing thermally treated graphite felt (52.64% ± 1.50%). Notably, the cycle life of the battery is extended by more than five‐fold with the composite electrode, underscoring the remarkable zinc deposition‐regulating capabilities of the indium nanoparticles. [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]

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]

ObjectivesUnder the background of the “dual carbon” target, the safety and economic problems of peak shaving caused by the construction of high wind power penetration system are urgent to be solved.MethodsBy using the solution of peak shaving and valley filling of battery energy storage system, a peak shaving optimization control method for zinc-bromine flow battery (ZBB) energy storage taking into account both technology and economy was proposed. According to the actual battery device, the structure analysis and the mathematical model construction of ZBB energy storage were carried out. Considering the technical effects of peak shaving, and taking the minimum standard deviation of load curve after peak shaving as the objective function, a bidirectional optimization control strategy for energy storage considering peak shaving effects was proposed. On this basis, according to the time of use (TOU) policy of the power grid, taking the technical and economic optimization as the objective function, an economic model of energy storage peak shaving based on the TOU price mechanism was proposed, and the optimal power timing results for energy storage were obtained. Finally, taking the load and wind power data of a certain area in Northeast China as an example, the effectiveness of the proposed strategy was verified by comparison.ResultsCompared with the original load, the proposed strategy reduces the daily average load peak-valley difference and peak-valley difference rate by 35.973% and 34.205%, respectively, and improves the peak shaving economic optimization by 5.582%. In addition, the problem of wind curtailment in the power grid is alleviated.ConclusionsThe proposed strategy achieves a certain peak shaving effect while maintaining a good peak shaving economy throughout its life cycle.

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]

Carbon nanotubes (CNTs) are applied as catalysts to improve redox reaction of iron and 2,2-bis(hydroxymethyl)-2,2',2''-nitrilotriethanol (Fe(BIS–TRIS)) complex as negolyte of iron-based flow batteries (FBs). Especially, multi-walled CNT (MWCNT) and carboxylic acid-functionalized MWCNT (CACNT) are adopted as the catalysts. Effects of the catalysts are electrochemically analyzed. CACNT is expected to have a better performance than MWCNT due to its abundant hydrophilic functional groups. However, MWCNT is more effective catalyst than CACNT for improving redox reactivity of Fe(BIS–TRIS). This is because carboxylic acid groups of CACNT are deprotonated to form COO− ions in aqueous electrolytes. FB single cell tests show that energy efficiency (EE) is 80.2% without catalyst at 80 mA cm−2, but the EE increases when catalyst is doped at negative electrode. When MWCNT and CACNT are doped, EE is 84.0 and 83.5%. The lower performance of CACNT is because of electrostatic repulsion occurring between anionic Fe(BIS–TRIS) molecules and COO− ions. Therefore, a larger overpotential is formed in the case of CACNT than MWCNT. This means when electrode is treated by catalyst, interaction of active material and catalyst should be considered. [ABSTRACT FROM AUTHOR]

Copyright of Iron Steel Vanadium Titanium is the property of Iron Steel Vanadium Titanium Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Neutral aqueous organic redox flow batteries (AORFBs) hold the potential to facilitate the transition of renewable energy sources from auxiliary to primary energy, the commercial production of anolyte materials still suffers from insufficient performance of high‐concentration and the high cost of the preparation problem. To overcome these challenges, this study provides a hydrothermal synthesis methodology and introduces the charged functional groups into hydrophobic naphthalene diimide cores, and prepares a series of high‐performance naphthalene diimide anolytes. Under the synergistic effect of π–π stacking and H‐bonding networks, the naphthalene diimide exhibits excellent structural stability and the highest water solubility (1.85 M for dex‐NDI) reported to date. By employing the hydrothermal method, low‐cost naphthalene diimides are successfully synthesized on a hundred‐gram scale of $0.16 g−1 ($2.43 Ah−1), which is also the lowest price reported to date. The constructed full battery achieves a high electron concentration of 2.4 M, a high capacity of 54.4 Ah L−1, and a power density of 318 mW cm−2 with no significant capacity decay observed during long‐duration cycling. These findings provide crucial support for the commercialization of AORFBs and pave the way for revolutionary developments in neutral AORFBs. [ABSTRACT FROM AUTHOR]

To offset the intermittent nature, renewable energy sources must be paired with energy storage systems (ESS) to cater to the demand for clean energy solutions. The performance characteristics requirements of these ESS are application‐specific, say batteries are characterized by their high energy capacity while supercapacitors offer greater power density. Currently, the research concentration in this domain is on improving the performance parameters of proven energy storage chemistries. Two‐dimensional (2D) materials characterized by high specific surface area, and tunable physical and electrical properties are explored extensively to enhance ESS performance. This review comprehends the progress made by two typical 2D materials, Graphene and Molybdenum disulfide, to enhance the energy/ power capacity, and life span of a few chosen rechargeable storage chemistries, lithium‐ion, lithium‐sulfur batteries, supercapacitors, and flow batteries. Further the review presents the current state of ESS, the challenges identified so far which restrict their capacity and life span, and the solutions employed to date. Finally, the challenges associated with these solutions are critically analyzed to suggest future directions and research perspectives in this domain. [ABSTRACT FROM AUTHOR]

Copyright of Power Generation Technology is the property of Power Generation Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This work reports the preparation and characterization of composite membranes with potential applications in flow battery devices. A polymer solution of polyvinylidene fluoride (PVDF), sulfonated polyether ether sulfone (SPEES), and polyether sulfone (PES) was used to prepare proton exchange membranes with low permeation of cationic species, which is a desirable feature in energy conversion devices, such as vanadium flow batteries (VRFB). Vanadyl ion (VO2+) acidic solution was selected as a model to reveal the permeation capacity through the membranes as an affordable alternative to the Nafion® 117 commercial membrane. The effects of the chemical composition and the thickness of the membranes on the morphology and proton exchange properties were evaluated. Characterization of the membranes was performed using physicochemical techniques including water uptake, swelling ratio, thermogravimetric analysis, scanning electron microscopy, Fourier transform infrared, surface charge density, atomic force microscopy, dynamic mechanical analysis, electrochemical impedance spectroscopy for proton conductivity, proton exchange rate, and the permeability of VO2+ ions. With VO2+ ion permeability of the order of 0.62 mM and H+ exchange rates of up to 498.5 × 1018 H+ cm−2*µm−1*min−1, the PVDF/PES/SPEES composite membranes emerge as an option with potential application for VRFB compared to the Nafion® 117 membrane, which presented a VO2+ ion permeation value of 2.72 mM and H+ exchange rates of 445.2 × 1018 H+ cm−2*µm−1*min−1. [ABSTRACT FROM AUTHOR]

Vanadium redox flow batteries are promising energy storage devices and are already ahead of lead–acid batteries in terms of installed capacity in energy systems due to their long service life and possibility of recycling. One of the crucial tasks today is the development of models for assessing battery performance and its residual resource based on the battery's present state. A promising method for estimating battery capacity is based on analyzing present voltage and current values under various load conditions. This paper analyzes the discharge characteristics of a 10 kW all-vanadium redox flow battery at fixed load powers from 6 to 12 kW. A linear dependence of operating voltage and initial discharge voltage on load power is established. It is also determined that the slope of the discharge curve linear section does not increase linearly in absolute value, and the Box–Lucas model can be used to describe it. Models for predicting current VRFB capacity based on different curve fitting functions are proposed. These models can be used to roughly estimate battery capacity at different load powers. [ABSTRACT FROM AUTHOR]

Abstract 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 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.

[Display omitted] The mounting global energy demand urges surplus electricity generation. Due to dwindling fossil resources and environmental concerns, shifting from carbon-based fuels to renewables is vital. Though renewables are affordable, their intermittent nature poses supply challenges. In these contexts, aqueous flow batteries (AFBs), are a viable energy storage solution. This study tackles AFBs' energy density and efficiency challenges. Conventional strategies focus on altering molecule's solubility but overlook interface's transport kinetics. We show that triggering electrostatic forces at the interface can significantly enhance the mass transport kinetics of redox active molecules by introducing a powerful electrostatic flux over the diffusional flux, thereby exerting a precise directionality on the molecular transport. This approach of controlling the directionality of molecular flux in an all iron redox flow battery amplifies the current and power rating with approximately 140 % enhancement in the energy density. [ABSTRACT FROM AUTHOR]

Fast proton conduction plays an essential role in ion conductive membranes (ICMs) for energy conversion and storage technologies, but the demand for low reactive species permeation always limits further enhancement in proton transport rate. Herein, an ICM incorporating ZSM‐5 zeolite with optimized physicochemical property of pore channels was developed to achieve highly conductive ion transport via regulating the silicon‐aluminum atomic (Si/Al) ratio of ZSM‐5. Benefiting from the regulation of pore channels of zeolites, the proton conductivity of the pristine membrane was remarkably improved to 1.7‐fold. As expected, the optimized membrane exhibited outstanding voltage efficiency (VE) of 85.7% and energy efficiency (EE) of 85.1% at 120 mA/cm2, which is considerably better than pure polymer membrane (VE of 80.5% and EE of 79.4%) and commercial Nafion 212 (VE of 81.3% and EE of 77.4%) membrane, respectively. [ABSTRACT FROM AUTHOR]

There has been an increase in wind power penetration into the utility grid. The wind speed variations exhibit undesirable oscillations that influence power quality and system reliability. Therefore, the grid operation is challenging in this scenario. Battery energy storage system (BESS) smooths out wind power production and reduces fluctuations. However BESSs low power density and high capacity requirements to compensate for fluctuation limit its implementation for high-power applications. This paper introduces a wind energy conversion system (WECS) based on a doubly fed induction generator (DFIG) incorporating a vanadium redox flow battery (VRFB) in the DC-link, which supports grid power smoothing and power balance even under varying wind speed. Real-site wind data was used to develop a technique for designing the VRFB. The rotor side converter (RSC) employs an off-maximum power point tracking to keep the VRFB operation within the limit and deliver consistent power to the grid. An improved phase lock loop control is designed for DFIG that suppresses DC offset at the input and allows RSC and grid side converter (GSC) to perform appropriately even under grid disturbances. The GSC control is designed with an improved DC-link voltage control by adopting an anti-windup fractional-order proportional-integral (AWFOPI) controller, which can improve transient response. A sparrow search algorithm is adopted to tune the AWFOPI controller. Matlab Simulink is used to simulate the system. Test results show that the system performs well under various operating conditions and is satisfactory. It has also been tested on the OPAL-RT real-time simulator test bench. [ABSTRACT FROM AUTHOR]

Zinc-air batteries are widely considered as the next-generation rechargeable batteries due to their high energy density, low cost, and high safety. However, internal short circuits caused by zinc dendrite growth and bubble generation by side reaction during high-speed charging can deteriorate battery performance. To address this issue, a zinc-air flow battery with an electrolyte flow has been proposed for high-speed charging, and previous studies have shown improved cycle performance. Optimization of operating conditions for practical use requires elucidation of the behavior of the zinc electrode and bubble with electrolyte flow during battery operation, but this remains unclear. This study utilized operando X-ray imaging to investigate the zinc electrode and bubble behavior of a zinc-air flow battery during charging. The results revealed that when charging without electrolyte flow, zinc was deposited in a dendrite structure, and the dendrite growth rate increased with the charging speed. In contrast, it was observed that dendrite growth was suppressed, and dense zinc deposition was achieved even under high current density conditions when charged with a flowing electrolyte. Furthermore, the voltage fluctuation due to a decrease in the reaction area caused by the bubbles generated by water reduction was successfully suppressed when the flow was present. This was achieved by removing the bubbles through convection, which prevented the increase in overvoltage. Overall, it can be said that the flow of electrolytes has a positive effect on battery performance, as it helps to achieve a more uniform deposition of zinc and to prevent voltage fluctuation.

Flow battery is an ideal choice for long-term and large-scale energy storage due to its advantages of numerous charge-discharge cycles, high capacity and long lifespan. However, the flow battery's complex structure poses high demands on battery control system, and traditional development methods are challenging to meet the flow battery system's diverse control requirements. To address this problem, a method for developing a flow battery control system based on event-driven technology is proposed, which aims to improve control precision and real-time performance. The proposed approach firstly presents a main-auxiliary stack synergistic architecture to address issues such as high stability requirements and large internal losses of flow batteries, and the architecture is modeled and analyzed. Then, the control system is designed by modularization based on event-driven technology, including the modules of flexible charging-discharging control, black start-up control strategy with auxiliary stacks, and state of charge (SOC) estimation based on Kalman filtering. Finally, a semi-physical simulation platform is built to validate the proposed architecture and strategies, which demonstrates that the proposed architecture and strategies can improve the energy conversion efficiency and stability of the system.

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.

Aqueous all‐iron flow batteries (AIFBs) are attractive for large‐scale and long‐term energy storage due to their extremely low cost and safety features. To accelerate commercial application, a long cyclable and reversible iron anolyte is expected to address the critical barriers, namely iron dendrite growth and hydrogen evolution reaction (HER). Herein, we report a robust iron complex with triethanolamine (TEA) and 2‐methylimidazole (MM) double ligands. By introducing two ligands into one iron center, the binding energy of the complex increases, making it more stable in the charge‐discharge reactions. The Fe(TEA)MM complex achieves reversible and stable redox between Fe3+ and Fe2+, without metallic iron growth and HER. AIFBs based on this anolyte perform a high energy efficiency of 80.5 % at 80 mA cm−2 and exhibit a record durability among reported AIFBs. The efficiency and capacity retain nearly 100 % after 1,400 cycles. The capital cost of this AIFB is $ 33.2 kWh−1 (e.g. 20 h duration), cheaper than Li‐ion battery and vanadium flow battery. This double‐ligand chelating strategy not only solves the current problems faced by AIFBs, but also provides an insight for further improving the cycling stability of other flow batteries. [ABSTRACT FROM AUTHOR]

In recent years, energy challenges such as grid congestion and imbalances have emerged from conventional electric grids. Furthermore, the unpredictable nature of these systems poses many challenges in meeting various users' demands. The Battery Energy Storage System is a potential key for grid instability with improved power quality. The present study investigates the global trend towards integrating battery technology as an energy storage system with renewable energy production and utility grid systems. An extensive review of battery systems such as Lithium-Ion, Lead–Acid, Zinc–Bromide, Nickel–Cadmium, Sodium–Sulphur, and the Vanadium redox flow battery is conducted. Furthermore, a comparative analysis of their working principles, control strategies, optimizations, and technical characteristics is presented. The review findings show that Lead–Acid, Lithium-Ion, Sodium-based, and flow redox batteries have seen increased breakthroughs in the energy storage market. Furthermore, the use of the BESS as an ancillary service and control technique enhances the performance of microgrids and utility grid systems. These control techniques provide potential solutions such as peak load shaving, the smoothing of photovoltaic ramp rates, voltage fluctuation reduction, a large grid, power supply backup, microgrids, renewable energy sources time shift, spinning reserve for industrial consumers, and frequency regulation. Conclusively, a cost summary of the various battery technologies is presented. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Engineering Technology is the property of Editorial Department of Electric Power Engineering Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Covalent organic frameworks (COFs) display great potential to be assembled into proton conductive membranes for their uniform and controllable pore structure, yet constructing self‐standing COF membrane with high crystallinity to fully exploit their ordered crystalline channels for efficient ionic conduction remains a great challenge. Here, a macromolecular‐mediated crystallization strategy is designed to manipulate the crystallization of self‐standing COF membrane, where the −SO3H groups in introduced sulfonated macromolecule chains function as the sites to interact with the precursors of COF and thus offer long‐range ordered template for membrane crystallization. The optimized self‐standing COF membrane composed of highly‐ordered nanopores exhibits high proton conductivity (75 mS cm−1 at 100 % relative humidity and 20 °C) and excellent flow battery performance, outperforming Nafion 212 and reported membranes. Meanwhile, the long‐term run of membrane is achieved with the help of the anchoring effect of flexible macromolecule chains. Our work provides inspiration to design self‐standing COF membranes with ordered channels for permselective application. [ABSTRACT FROM AUTHOR]

Zinc‐bromine flow batteries (ZBFBs) are promising candidates for the large‐scale stationary energy storage application due to their inherent scalability and flexibility, low cost, green, and environmentally friendly characteristics. ZBFBs have been commercially available for several years in both grid scale and residential energy storage applications. Nevertheless, their continued development still presents challenges associated with electrodes, separators, electrolyte, as well as their operational chemistry. Therefore, rational design of these components in ZBFBs is of utmost importance to further improve the overall device performance. In this review, the focus is on the scientific understanding of the fundamental electrochemistry and functional components of ZBFBs, with an emphasis on the technical challenges of reaction chemistry, development of functional materials, and their application in ZBFBs. Current limitations of ZBFBs with future research directions in the development of high performance ZBFBs are suggested. [ABSTRACT FROM AUTHOR]

Ion conductive membranes (ICMs) with highly conductive proton selectivity are of significant importance and greatly desired for energy storage devices. However, it is extremely challenging to construct fast proton-selective transport channels in ICMs. Herein, a membrane with highly conductive proton selectivity was fabricated by incorporating porous carbon sieving nanospheres with a hollow structure (HCSNs) in a polymer matrix. Due to the precise ion sieving ability of the microporous carbon shells and the fast proton transport through their accessible internal cavities, this advanced membrane presented a proton conductivity (0.084 S·cm−1) superior to those of a commercial Nafion 212 (N212) membrane (0.033 S·cm−1) and a pure polymer membrane (0.049 S·cm−1). The corresponding proton selectivity of the membrane (6.68 × 105 S·min·cm−3) was found to be enhanced by about 5.9-fold and 4.3-fold, respectively, compared with those of the N212 membrane (1.13 × 105 S·min·cm−3) and the pure membrane (1.56 × 105 S·min·cm−3). Low-field nuclear magnetic resonance (LF-NMR) clearly revealed the fast proton-selective transport channels enabled by the HCSNs in the polymeric membrane. The proposed membrane exhibited an outstanding energy efficiency (EE) of 84% and long-term stability over 1400 cycles with a 0.065% capacity decay per cycle at 120 mA·cm−2 in a typical vanadium flow battery (VFB) system.

Abstract Zinc‐bromine flow batteries (ZBFBs) are promising candidates for the large‐scale stationary energy storage application due to their inherent scalability and flexibility, low cost, green, and environmentally friendly characteristics. ZBFBs have been commercially available for several years in both grid scale and residential energy storage applications. Nevertheless, their continued development still presents challenges associated with electrodes, separators, electrolyte, as well as their operational chemistry. Therefore, rational design of these components in ZBFBs is of utmost importance to further improve the overall device performance. In this review, the focus is on the scientific understanding of the fundamental electrochemistry and functional components of ZBFBs, with an emphasis on the technical challenges of reaction chemistry, development of functional materials, and their application in ZBFBs. Current limitations of ZBFBs with future research directions in the development of high performance ZBFBs are suggested.

The hydrogen‐iron (HyFe) flow cell has great potential for long‐duration energy storage by capitalizing on the advantages of both electrolyzers and flow batteries. However, its operation at high current density (high power) and over continuous cycling testing has yet to be demonstrated. In this paper, we discuss our design and demonstration of a water management strategy that supports high current and long cycling performance of a HyFe flow cell. Water molecules associated with the movement of protons from the iron electrode to the hydrogen electrode are sufficient to hydrate the membrane and electrode at a low current density of 100 mA cm−2 during the charge process. At higher charge current density, more aggressive measures must be taken to counter back‐diffusion driven by the acid concentration gradient between the iron and hydrogen electrodes. Our water management approach is based on water vapor feeding in the hydrogen electrode, and water evaporation in the iron electrode, thus enabling the high current density operation of 300 mA cm−2. [ABSTRACT FROM AUTHOR]

Flow batteries (FBs) are characterized by relatively high round trip efficiencies and benefit from high scalability. The storable energy and the power of charging and discharging the battery can be increased by increasing the size of the electrolyte storage tanks and the electrodes. Charge and discharge cycles covering many hours may be designed with flow batteries. This makes flow batteries a better choice than lithium‐ion batteries for large‐scale energy storage systems, particularly for non‐dispatchable renewable energy systems such as wind and solar, where the energy generated is highly variable and requires effective energy storage solutions. However, flow batteries also have some disadvantages, including a higher cost per unit of energy stored compared with other batteries, as well as the use of materials that in some cases are toxic, expensive, or scarce. Additionally, flow batteries cannot solve the energy storage issues over long times of a grid only supplied by non‐dispatchable electricity such as wind or solar, namely intermittency and summer to winter variability of solar, or low wind days of wind. Despite these limitations, the potential benefits of flow batteries in terms of their scalability and long cycle life, and cost‐effectiveness in case their design could be improved, making them one of the key contributors progressing towards net zero. Specifically in New Zealand, in the progress toward net‐zero the total energy supply (TES) cannot be covered by only expanding wind energy production and pumped hydro energy storage (PHES). Solar photovoltaic and likely nuclear energy supply will have to be introduced. Not all of the TES will be electrified, part of the TES will need coverage by green hydrogen fuel. Hydrogen energy storage (HES) will have to grow much more than PHES, energy storage by FBs as well as lithium‐ion batteries (LIBs) will also have to be included, given their complementarity to the other energy storage systems. [ABSTRACT FROM AUTHOR]

Vanadium redox flow batteries are gaining great popularity in the world due to their long service life, simple (from a technological point of view) capacity increase and overload resistance, which hardly affects the service life. However, these batteries have technical problems, namely in balancing stacks with each other in terms of volumetric flow rate of electrolyte. Stack power depends on the speed of the electrolyte flow through the stack. Stacks are connected in parallel by electrolytes to increase battery power. If one of the stacks has a lower hydrodynamic resistance, the volume of electrolytes passing through it increases, which leads to a decrease in the efficiency of the remaining stacks in the system. This experimental study was conducted on a 10 kW uninterruptible power supply system based on two 5 kW stacks of all-vanadium redox flow batteries. It was demonstrated that forced flow attenuation in a circuit with low hydrodynamic resistance leads to an overall improvement in the system operation. [ABSTRACT FROM AUTHOR]

Vanadium redox flow batteries are promising energy storage devices and are already ahead of lead–acid batteries in terms of installed capacity in energy systems due to their long service life and possibility of recycling. One of the crucial tasks today is the development of models for assessing battery performance and its residual resource based on the battery’s present state. A promising method for estimating battery capacity is based on analyzing present voltage and current values under various load conditions. This paper analyzes the discharge characteristics of a 10 kW all-vanadium redox flow battery at fixed load powers from 6 to 12 kW. A linear dependence of operating voltage and initial discharge voltage on load power is established. It is also determined that the slope of the discharge curve linear section does not increase linearly in absolute value, and the Box–Lucas model can be used to describe it. Models for predicting current VRFB capacity based on different curve fitting functions are proposed. These models can be used to roughly estimate battery capacity at different load powers.

The development of a rechargeable battery that can produce valuable chemicals in both electricity storage and generation processes holds great promise for increasing the electron economy and economic value. However, this battery has yet to be explored. Herein, we report a biomass flow battery that generates electricity while producing furoic acid, and store electricity while yielding furfuryl alcohol. The battery is composed of a rhodium‐copper (Rh1Cu) single‐atom alloy as anode, a cobalt‐doped nickel hydroxide (Co0.2Ni0.8(OH)2) as cathode, and furfural‐containing anolyte. In a full battery evaluation, this battery displays an open circuit voltage (OCV) of 1.29 V and a peak power density up to 107 mW cm−2, surpassing most catalysis‐battery hybrid systems. As a proof‐of‐concept, we demonstrate that this battery produces 1 kg furoic acid with 0.78 kWh electricity output, and yields 0.62 kg furfuryl alcohol when 1 kWh electricity is stored. This work may shed light on the design of rechargeable batteries with value‐added functionality such as chemicals production. [ABSTRACT FROM AUTHOR]

The objective of this work is to carry out a bibliographic review, leading to the evaluation and comparison of alternatives for internal components of a vanadium redox flow battery, which can improve efficient and economically viable energy storage. This review leads to the design of a theoretical BRFV on a laboratory scale (100 Wh and 12 V.), handling the following parameters: electrolyte 3.0 M in V2O5 and 6.0 M HCl and 3.0 M H2SO4, felt electrodes of graphite treated with polyacrylonitrile and NafionTM 117 membrane. In parallel, it is suggested to use 9 cells, 2 liters of electrolyte, flow rate of 373 mL/min and charging time of 13.69 hours. Finally, an Excel file is generated with the operating parameters for the proposed battery. [ABSTRACT FROM AUTHOR]

Manganese dioxide（MnO2） is widely used in aqueous zinc-manganese batteries due to its high abundance and low cost. Flow batteries can realize the decoupling of energy component and power component, thus they have been paid more attention in the field of long-term large-scale energy storage. In this study, semi-solid electrodes were designed with MnO2 as the active substance, and a high volumetric specific capacity flow battery was designed. Firstly, semi-solid electrodes were prepared using Xanthan gum as suspension matrix and Ketjen Black as conductive agent, and the optimal ratio of MnO2 semi-solid electrodes was determined by characterizing the electrochemical properties and rheological properties of the electrodes. The critical concentration for conductivity percolation of Ketjen Black is 9 g/L, and the semi-solid electrodes prepared with this concentration show good rate performance and cycling stability. The volumetric specific capacity of the semi-solid electrodes can reach 32.5 Ah/L with 300 g/L MnO2. Semi-solid electrodes exhibit non-Newtonian rheology with a yield stress of approximately 2 Pa which can maintain the mechanical stability of the suspensions while the pumping energy loss is low. The volumetric specific capacity of zinc-manganese flow battery with semi-solid electrodes can reach 22.3 Ah/L, showing promising prospects for development. [ABSTRACT FROM AUTHOR]

In the wake of increasing the share of renewable energy-based generation systems in the power mix and reducing the risk of global environmental harm caused by fossil-based generation systems, energy storage system application has become a crucial player to offset the intermittence and instability associated with renewable energy systems. Due to the capability to store large amounts of energy in an efficient way, redox flow batteries (RFBs) are becoming the energy storage of choice for large-scale applications. Vanadium-based RFBs (V-RFBs) are one of the upcoming energy storage technologies that are being considered for large-scale implementations because of their several advantages such as zero cross-contamination, scalability, flexibility, long life cycle, and non-toxic operating condition. This review presents the current state of the V-RFB technology for power system applications. The basic working operation of the V-RFB system with the principle of operation of its major components, the design considerations, and the limitations of each component are discussed. It presents technical information to improve the overall performance of the V-RFB by considering the materials of the cell components, modeling methods, stack design, flow rate optimization, and shunt current reduction.

The intervention of renewable energy for curbing the supply demand mismatch in power grids has projected the added advantage of having lower greenhouse gas (GHG) emissions. Non-depleting sources are characterised by variability and unpredictability. This necessitates the adequate design and sizing of Energy Storage Devices (ESD). This study focusses on life cycle study of three different types of storage devices, Valve Regulated Lead Acid Battery (LAB), Lithium Iron Phosphate (LFP-G) Battery and Polysulphide Bromine Flow Battery (PSB). It has been concluded that the PV-VRLA system has an Energy Pay Back Time (EPBT) of 4.3 years, PV-LFP-G system having 4.56 years and PV-PSB system with a value of 8.2 years. The environmental impact of the systems is measured by the GHG emission factor expressed in kgCO2eq/kWh of energy generated. The PV-PSB system has the highest value owing to the material production and operating energy component, the values being 0.321, 0.343 and 0.70 kgCO2eq/kWh for the LAB, LFP-G and PSB, respectively. The impact of the generation mix for the present, Business as Usual (BAU) and a future Renewable Energy Intensive has also been studied. It has been concluded that emission metrics of the PSB system is more sensitive to generation mix characteristics. [ABSTRACT FROM AUTHOR]

Redox flow batteries (RFBs) have been widely recognized in the domain of large-scale energy storage due to their simple structure, long lifetime, quick response, decoupling of capacity and power, and structural simplicity. Because of the limited open circuit voltage (OCV) by hydrogen and oxygen evolution reactions, together with the relatively low solubility of active species, RFBs with aqueous electrolytes are challenging to reach high energy densities. Researchers have been trying to develop new solvent systems without water to remove the electrochemical window limitation of water and pursue higher cell potential. However, non-aqueous solvents are also hindered by some key problems, such as high viscosity and poor safety. Meeting these challenges require a comprehensive understanding of relevant structural design parameters and multi-variable operation in the non-aqueous flow battery (NAFB) system. Modeling and simulation are not only an effective way to understand the basic mechanism of flow batteries at different scales of size and time but also an ideal tool for optimizing the reaction process, battery assembly, and the whole flow battery installation. This review paper introduces the development of the non-aqueous flow battery, the challenges it faces, and the research progress of related modeling and simulation for verification or optimization. Finally, the future development prospects of the non-aqueous flow battery model are pointed out, especially for those systems and fields that have not yet been explored. [ABSTRACT FROM AUTHOR]

In recent years, energy challenges such as grid congestion and imbalances have emerged from conventional electric grids. Furthermore, the unpredictable nature of these systems poses many challenges in meeting various users’ demands. The Battery Energy Storage System is a potential key for grid instability with improved power quality. The present study investigates the global trend towards integrating battery technology as an energy storage system with renewable energy production and utility grid systems. An extensive review of battery systems such as Lithium-Ion, Lead–Acid, Zinc–Bromide, Nickel–Cadmium, Sodium–Sulphur, and the Vanadium redox flow battery is conducted. Furthermore, a comparative analysis of their working principles, control strategies, optimizations, and technical characteristics is presented. The review findings show that Lead–Acid, Lithium-Ion, Sodium-based, and flow redox batteries have seen increased breakthroughs in the energy storage market. Furthermore, the use of the BESS as an ancillary service and control technique enhances the performance of microgrids and utility grid systems. These control techniques provide potential solutions such as peak load shaving, the smoothing of photovoltaic ramp rates, voltage fluctuation reduction, a large grid, power supply backup, microgrids, renewable energy sources time shift, spinning reserve for industrial consumers, and frequency regulation. Conclusively, a cost summary of the various battery technologies is presented.

In this paper, we propose a sophisticated battery model for vanadium redox flow batteries (VRFBs), which are a promising energy storage technology due to their design flexibility, low manufacturing costs on a large scale, indefinite lifetime, and recyclable electrolytes. Primarily, fluid distribution is analysed using computational fluid dynamics (CFD) considering only half-cells. Based on the analysis results, a novel model is developed in the MATLAB Simulink environment which is capable of identifying both the steady-state and dynamic characteristics of VRFBs. Unlike the majority of published studies, the inherent characteristics of the flow battery, such as shunt current, ion diffusion, and pumping energy consumption, are considered. Furthermore, simplified charge transfer resistance (CTR) is taken into account based on electrochemical impedance spectroscopy (EIS) measurement results. The accuracy of the model was determined by comparing the simulation results generated by the equivalent circuit battery model developed in this study with real datasets. The obtained results indicate that the developed model has an accuracy of 3% under the sample operating conditions selected. This study can also be used to fill the gap left by the absence of the VRFB battery model in commonly used programs for renewable energy systems, such as TRNSYS. [ABSTRACT FROM AUTHOR]

Flow batteries are a promising energy storage solution. However, the footprint and capital cost need further reduction for flow batteries to be commercially viable. The flow cell, where electron exchange takes place, is a central component of flow batteries. Improving the volumetric power density of the flow cell (W/Lcell) can reduce the size and cost of flow batteries. While significant progress has been made on flow battery redox, electrode, and membrane materials to improve energy density and durability, conventional flow batteries based on the planar cell configuration exhibit a large cell size with multiple bulky accessories such as flow distributors, resulting in low volumetric power density. Here, we introduce a submillimeter bundled microtubular (SBMT) flow battery cell configuration that significantly improves volumetric power density by reducing the membrane-to-membrane distance by almost 100 times and eliminating the bulky flow distributors completely. Using zinc–iodide chemistry as a demonstration, our SBMT cell shows peak charge and discharge power densities of 1,322 W/Lcell and 306.1 W/Lcell, respectively, compared with average charge and discharge power densities of <60 W/Lcell and 45 W/Lcell, respectively, of conventional planar flow battery cells. The battery cycled for more than 220 h corresponding to >2,500 cycles at off-peak conditions. Furthermore, the SBMT cell has been demonstrated to be compatible with zinc–bromide, quinone–bromide, and all-vanadium chemistries. The SBMT flow cell represents a device-level innovation to enhance the volumetric power of flow batteries and potentially reduce the size and cost of the cells and the entire flow battery. [ABSTRACT FROM AUTHOR]

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Thermally regenerative electrochemical cycle (TREC) is an efficient, clean and feasible low-temperature thermoelectric conversion technology. Coupling it with flow battery (FB) can not only achieve continuous operation, but also can be used to realize the heat energy recovery of the photovoltaic/thermal (PV/T) system. In this paper, a continuous TREC-FB system including two charging-free cells is proposed for outputting power at both high and low temperatures. An electrochemical-thermodynamic coupling algebraic model is established to explore the effects of electrolyte flow rate, temperature difference and design parameters of heat exchanger on the power density (P TREC) and thermoelectric efficiency (η ele,TREC) of the TREC-FB. Experimental study on TREC-FB is carried out for model validation. The results show that P TREC is determined by the temperature difference and the electrolyte flow rate, which contribute to enhanced voltage and mass transfer, respectively. For specific heat source scenarios, the η ele,TREC is mainly affected by the flow rate, followed by the heat transfer area A H , and finally is the flow channel height and the thermal conductivity of the heat exchanger. Moreover, for the continuous TREC-FB-PV/T coupled system, the energy conversion efficiency reaches an average of 11 % within one day by optimizing the designed temperature difference. [Display omitted] • Flow battery is combined with charging-free TREC for operating continuously. • An algebraic model of continuously operated TREC-FB is established. • Effects of operating parameters on system performance are analyzed. • Experimental study of continuous TREC-FB is conducted for model validation. • The continuous TREC-FB is coupled with PV/T system to realize waste heat recovery. [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-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]

[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]

• Cs+ and Gdm+ are added to I−/I 3 −//Fe(CN) 6 3−/4− pairs to form concentration gradient. • The charging-free TREC achieves record high temperature coefficient of −3.6 mV/K. • The power density of charging-free TREC increases from 0.7 W/m2 to 1.4 W/m2. • The modified membrane is used to inhibit the migration of I− and I 3 − ions. • The charging-free flow TREC with modified membrane realizes 36 h continuous operation. Low-temperature thermal energy widely exists in nature and is sustainable. The thermally regenerative electrochemical cycle (TREC) based on the Seebeck effect has attracted widespread attention due to its high thermoelectric efficiency and good cycle stability. However, it has a low power density and cannot sustain continuous operation for extended periods. This work proposes a continuous charging-free thermally regenerative electrochemically cycled flow battery (TREC-FB) system, which can discharge continuously at both high and low temperatures without the assistance of external power source. By adding guanidine hydrochloride (GdmCl) and inorganic salt ions (Cs+, Ca2+, Mg2+, etc.) to the K 3 Fe(CN) 6 /K 4 Fe(CN) 6 and I 2 /KI electrolytes respectively, precipitates are formed in the electrolytes at low temperature and dissolve at high temperature, which creates the concentration gradient of ions. As a result, the temperature coefficient of the full cell increases from −2.24 mV/K to −3.6 mV/K, and both voltage and power density are doubled. Theoretical analysis of the temperature coefficient enhancement is conducted based on the Nernst equation, and the mechanism of the temperature coefficient enhancement is verified using UV–vis spectra. The discharging capacity and energy of the charging-free TREC-FB with high temperature coefficient reach 5 Ah/L and 1.9 kJ/L, respectively, and the thermoelectric efficiency reaches 8.9 % under sufficient heat recuperation. Two TREC-FBs at high and low temperatures are connected to carry out continuous operation experiments of the charging-free TREC-FB system. The use of charge-reinforced ion-selective membrane can effectively inhibit the migration of I− and I 3 − ions, achieving about 36 h of continuous operation, and the average power density achieves 0.6 W/m2. [ABSTRACT FROM AUTHOR]