Flow Battery Research Articles

Physiochemical and Electrochemical Properties of a Heat-Treated Electrode for All-Iron Redox Flow Batteries

Physiochemical and Electrochemical Properties of a Heat-Treated Electrode for All-Iron Redox Flow Batteries

Dual-Function Electrolyte Additive Design for Long Life Alkaline Zinc Flow Batteries.

Alkaline zinc-based flow batteries (AZFBs) have emerged as a promising electrochemical energy storage technology owing to Zn abundance, high safety, and low cost. However, zinc dendrite growth and the formation of dead zinc greatly impede the development of AZFBs. Herein, a dual-function electrolyte additive strategy is proposed to regulate zinc nucleation and mitigate the hydroxide corrosion of zinc depositions for stable AZFBs. This strategy, as exemplified by urea, introduces an electrolyte additive to coordinate with Zn2+/Zn with proper strength, slowing zinc deposition kinetics to induce uniform nucleation and protecting the deposited zinc surface from attack by hydroxide ions through preferable adsorption. The zincate complexes with urea are identified to be Zn(OH)2(urea)(H2O)2 and Zn2(OH)4(H2O)4(urea), which exhibit slow zinc deposition kinetics, allowing instantaneous nucleation. Calculation results reveal an additional energy barrier of 1.29eV for the subsequent adsorption of an OH- group when a urea molecule absorbs on the zinc cluster, significantly mitigating the formation of dead zinc. Consequently, prolonged cell cycling of the prototype alkaline zinc-iron flow battery demonstrates stable operation for over 130 h and an average coulombic efficiency of 98.5%. It is anticipated that this electrolyte additive strategy will pave the way for developing highly stable AZFBs.

In situ growth of CoO on MXene sheets for modification of all‑vanadium redox flow battery electrodes

In order to greatly improve the energy efficiency and electrolyte utilization efficiency of vanadium redox flow batteries (VRFBs) and to enable them to operate at high current densities, MXene/CoO composites were used for the first time in this research as electrocatalysts for the V3+/V2+ reaction. The catalytic effect of the materials was characterized by cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) tests. Then battery performance of MXene/CoO composite modified plasma-treated graphite felt (GF) negative electrodes (MXene/CoO/GF) were tested in a VRFB. The results show that MXene/CoO composites can improve the catalytic activity. There is a 22.93 % increase in energy efficiency and 124.94 % increase in electrolyte utilization efficiency when MXene/CoO/GF is applied as VRFB negative electrode at a current density of 200 mA cm−2 compared to GF. At a current density of 250 mA cm−2, the energy efficiency of MXene/CoO/GF is maintained at 75.55 %. The excellent performance is attributed to the addition of MXene/CoO, which increases the active sites for redox reactions and thus improves the kinetics of the V3+/V2+ reaction.

O vacancy-rich doped WO3/GF as a novel electrode for an aqueous DHAQ/ K4Fe(CN)6 redox flow battery

O vacancy-rich doped WO3/GF as a novel electrode for an aqueous DHAQ/ K4Fe(CN)6 redox flow battery

Porous Graphite Felt Modified with Carbon Nanoparticles for an MV/4-HO-TEMPO Flow Battery

Porous Graphite Felt Modified with Carbon Nanoparticles for an MV/4-HO-TEMPO Flow Battery

A low-cost all-iron hybrid redox flow batteries enabled by deep eutectic solvents

A low-cost all-iron hybrid redox flow batteries enabled by deep eutectic solvents

A sulfonated polyimide containing imidazole ring with a low vanadium ion permeable for vanadium redox flow battery

A new type of sulfonated polyimide membrane (6f-abSPI) containing benzimidazole group and trifluoromethyl group (-CF3) is synthesized by one-step copolymerization. The 6f-abSPI-60 membrane with the highest ion selectivity is selected and applied to all vanadium redox flow battery (VRFB). Compared with Nafion 212 (N212) membrane and 6f-SPI-60 membrane, the vanadium ion permeability of 6f-abSPI-60 membrane (1.78×10-7cm2 min-1) is 1/13 lower than that of N212 membrane (2.33×10-6 cm2 min-1) and 1/2 lower than 6f-SPI-60 membrane (3.60×10-7 cm2 min-1). At the same time, the 6f-abSPI-60 membrane (2.69 × 105 S min cm−3) has significant selectivity, which is 5.6 times higher than N212 membrane (0.48 × 105 S min cm−3). In VRFB tests, the coulombic efficiency (CE) of 6f-abSPI-60 membrane (98.88%) is significantly higher than that of N212 membrane (92.99%) and 6f-SPI-60 membrane (97.65%) at 100 mA cm-2, and the energy efficiency (EE) also reaches a higher value (77.29%). Additionally, the VRFB equipped with the 6f-abSPI-60 membrane exhibits consistent and reliable performance throughout the 100 cycles of charging and discharging at the current densities of 100 mA cm−2. The good stability of 6f-abSPI membranes is explained by calculating C atoms’ natural bond orbital (NBO) charges on different polyimide (PI) rings.

Crossover analysis in a commercial 6 kW/43kAh vanadium redox flow battery utilizing anion exchange membrane

Crossover analysis in a commercial 6 kW/43kAh vanadium redox flow battery utilizing anion exchange membrane

Vanadium redox flow battery: Characteristics and application

Renewable energy such as solar energy and wind energy will enter a new period of development. However, the output power of photovoltaic power generation has great randomness. In order to ensure the normal operation of the whole photovoltaic power generation system, it is particularly important to introduce smooth power dynamics of energy storage system (ESS) to ensure electrical stability. As an energy storage device, flow batteries will develop in the direction of large-scale and modularization in the future. The flow battery system can easily realize computer automatic control and is an ideal smart battery. In addition, the combination of flow batteries with photovoltaic cells, wind power stations, tidal power stations, biogas power stations and other renewable energy systems is an important category and content in developing the application fields of flow batteries. As a new type of green battery, Vanadium Redox Flow Battery (VRFB) has the advantages of flexible scale, good charge and discharge performance and long life. It is suitable for large-scale electric energy storage and has attracted wide attention in recent years. In this paper, the characteristics and applications of liquid flow battery and VRFB are summarized. This paper starts from introducing ESS, analyzing several types of flow batteries, and finally focusing on VRFB to analyze its technical characteristics and application market.

Amino–Functionalized Multi–walled Carbon Nanotube/SPEEK Hybrid Proton Exchange Membrane for Iron–chromium Redox Flow Battery**

AbstractIn the field of iron–chromium redox flow battery (ICRFB), the optimal doping ratio of the amino–functionalized multi–walled carbon nanotube (MWCNT−NH2) blended with SPEEK as hybrid proton exchange membrane (PEM) is determined to be 2 wt % by series tests. The ICRFB single–cell containing the S/MWCNT−NH2−2 PEM was tested and compared with the Nafion 212 and original SPEEK PEMs. It is worth noting that the single–cell containing S/MWCNT−NH2–2 exhibits significantly higher coulombic efficiency (CE : 96.06 %) and energy efficiency (EE : 88.68 %) under 40 mA cm−2 than that of the Nafion 212 (EE : 82.83 %, CE : 88.9 %). Differing from the original SPEEK PEM, it also exhibits higher EE (82.04 %) than the Nafion 212 (81.09 %) at 100 mA cm−2. During the self–discharge test, the lower permeability of iron/chromium ions through S/MWCNT−NH2–2 PEM also allows for a longer self–discharge time than the other two single–cells. Additionally, the single–cell containing S/MWCNT−NH2–2 showed a smaller decay range of EE (from 82.67 % to 77.36 %) and more discharge capacity retention (48 %) than that of the Nafion 212 (EE : from 82.64 % to 75.01 %, discharge capacity retention: 18 %) after 100 cycles, which suggests that the hybrid SPEEK PEM with optimal content of MWCNT−NH2 has a great potential to replace Nafion PEMs in the large‐scale commercialization of ICRFB.

Controlled Construction of a N-Doped Carbon Nanotube Network Endows Carbon Felt with Superior Performances for High-Rate Vanadium Flow Batteries

Controlled Construction of a N-Doped Carbon Nanotube Network Endows Carbon Felt with Superior Performances for High-Rate Vanadium Flow Batteries

Long term performance evaluation of a commercial vanadium flow battery system

This paper describes the results of a performance review of a 10 kW/100 kWh commercial VFB system that has been commissioned and in operation for more than a decade. The evaluation focused on the system efficiencies, useable capacity, electrolyte stability and stack degradation. The analysis shows that the system has stable performance and very little capacity loss for over a decade since commissioning. Only very recently, a slight decrease in system discharge capacity (approximately 5 %) was observed and indicated by changes in the electrolyte valence state. The capacity was restored to the original level after conducting a rebalancing procedure. This demonstrates the advantage that the flow batteries employing vanadium chemistry have a very long cycle life. Furthermore, electrochemical impedance spectroscopy analysis was conducted on two of the battery stacks. Some degradation was observed in one of the stacks reflected by the increased charge transfer resistance. To further investigate the ageing of the stacks, reverse polarity tests were carried out. It is found that reversing the polarity both hydraulically and electrically can restore the stack performance. The study shows that the VFB is a reliable technology for large-scale energy storage applications.

Frequency regulation in a hybrid renewable power grid: an effective strategy utilizing load frequency control and redox flow batteries

Renewable energy sources (RESs) have become integral components of power grids, yet their integration presents challenges such as system inertia losses and mismatches between load demand and generation capacity. These issues jeopardize grid stability. To address this, an effective approach is proposed, combining enhanced load frequency control (LFC) (i.e., fuzzy PID- T IλDμ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${I}^{\\lambda }{D}^{\\mu }$$\\end{document}) with controlled energy storage systems, specifically controlled redox flow batteries (CRFBs), to mitigate uncertainties arising from RES integration. The optimization of this strategy's parameters is achieved using the crayfish optimization algorithm (COA), known for its global optimization capabilities and balance between exploration and exploitation. Performance evaluation against conventional controllers (PID, FO-PID, FO-(PD-PI)) confirms the superiority of the proposed approach in LFC. Extensive testing under various load disturbances, high renewables penetration, and communication delays ensures its effectiveness in minimizing disruptions. Validation using a standardized IEEE 39-bus system further demonstrates its efficiency in power networks grappling with significant renewables penetration. In summary, this integrated strategy presents a robust solution for modern power systems adapting to increasing renewable energy utilization.

An Aqueous All‐Quinone‐Based Redox Flow Battery Employing Neutral Electrolyte

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

Binder-Free CNT-Modified Excellent Electrodes for All-Vanadium Redox Flow Batteries

Electrodes are one of the key components that influence the performance of all-vanadium redox flow batteries (VRFBs). A porous graphite felt with modified fiber surfaces that can provide a high specific activation surface is preferred as the electrode of a VRFB. In this study, a simple binder-free approach is developed for preparing stable carbon nanotube modified graphite felt electrodes (CNT-GFs). Heat-treated graphite felt electrodes (H-GFs) are dip-coated using CNT homogeneous solution. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) results conclude that CNT-GFs have less resistance, better reaction currents, and reversibility as compared to H-GF. Cell performances showed that CNT-GFs significantly improve the performance of a VRFB, especially for the CNT-GF served in the positive side of the VRFB. CNT presence increases the electrochemical properties of the graphite electrode; as a result, reaction kinetics for both VO2+/VO2+ and V3+/V2+ are improved. Positive CNT-GF (P-CNT-GF) configured VRFB exhibits voltage efficiency, coulombic efficiency, and energy efficiency of 85%, 97%, and 82%, respectively, at the operating current density of 100 mA cm−2. At high current density of 200 mA cm−2, the VRFB with P-CNT-GF shows 73%, 98%, and 72% of the voltage, coulombic, and energy efficiencies, respectively. The energy efficiency of the CNT-GF is 6% higher when compared with that of B-H-GF. The VRFB with CNT-GF can provide stable performance for 300 cycles at 200 mA cm−2.

Lithium‐Free Redox Flow Batteries: Challenges and Future Prospective for Safe and Efficient Energy Storage

AbstractConsidering the costs, waste, and impact on the environment of current energy consumption, accurate, cost‐effective, and safely deployed energy storage systems are required. Lithium (Li)‐free redox flow batteries (RFBs) are a feasible solution. RFBs can store enormous amounts of energy effectively and are increasingly used for large‐scale applications. The use of RFBs has significantly enhanced the performance of energy storage systems and effectively reduced the costs and wastage of energy storage operations. Vanadium‐based RFBs are an emerging energy‐storage technology being explored for large‐scale deployment owing to their numerous benefits, including zero cross‐contamination, scalability, flexibility, extended life cycle, and nontoxic working state. This study describes the fundamental operating principles of redox flow battery‐based systems as well as the design considerations and constraints placed on each component. It discusses recent progress in the design and deployment of RFBs for energy‐related applications and the remaining obstacles and prospects. Finally, this study highlights the enormous potential of RFBs and suggests some solutions to scale up the use of RFBs in the near future.

Redox Behaviour and Redox Potentials of Dyes in Aqueous Buffers and Protic Ionic Liquids.

Organic dyes hold promise as inexpensive electrochemically-active building blocks for new renewable energy technologies such as redox-flow batteries and dye-sensitised solar cells, especially if they display high oxidation and/or low reduction potentials in cheap, non-flammable solvents such as water or protic ionic liquids. Systematic computational and experimental characterisation of a representative selection of acidic and basic dyes in buffered aqueous solutions and propylammonium formate confirm that quinoid-type mechanisms impart electrochemical reversibility for the majority of systems investigated, including quinones, fused tricyclic heteroaromatics, indigo carmine and some aromatic nitrogenous species. Conversely, systems that generate long-lived radical intermediates -- arylmethanes, hydroquinones at high pH, azocyclic systems -- tend to display irreversible electrochemistry, likely undergoing ring-opening, dimerisation and/or disproportionation reactions.

Simultaneously improved H+ conductivity and H+/V4+ selectivity for all vanadium flow battery by ZIF-8 induced physical cross-linking

One of the major challenges in all vanadium redox flow battery (VRFB) is the trade-off between proton conductivity and vanadium ion cross-mixing. Here, we simultaneously enhanced proton conductivity and sharply reduced the vanadium crossover by introducing ZIF-8 into a sulfonated polyimide (6FTMA-100) to prepared a high performance VRFB membrane. Compared with the pristine membrane, the proton conductivity increased from 34.6 to 47.4 mS cm−1, and the vanadium ion permeation rates decreased from 3.56 × 10−7 to 0.82–1.88 × 10−7 cm2 min−1 with different ZIF-8 doping concentrations. The ZIF-8 doped membranes also showed increased viscosity, reduced membrane swelling ratio and increased Young's modulus. We propose this is due to the strong hydrogen bonding (−106.68 Kcal/mol) between the N in imidazole group and H in -SO3H. Battery performance confirmed that the optimized MMM-2 (2 % ZIF-8 loading) displayed the energy efficiency of 80 % at 160 mA cm−2 that much higher than its pristine 6FTMA-100, N117, and most of the reported sulfonated polyimides. This idea of creating physical crosslinked network provided an efficient way for achieving highly efficient VRFB membranes.

Transient Mechanism Analysis of Three-Dimensional Zinc-Nickel Single Flow Battery Based on Different Negative Electrode Structures

Abstract On the basis of the mass, momentum, charge conservation equations, in addition to coupled with the global reaction kinetic equations, a transient three-dimensional mechanistic analytical model of zinc-nickel single flow batteries (ZNBs), which comprehensively takes into account the hydrogen and oxygen evolution side reactions, the polarization distribution, as well as the structural effects of the pole lugs, is developed in this paper. After grid independence validation and experimental verification, the polarization distribution, side-reaction current density, and battery efficiency of ZNBs at high current density and multiple cycles of charging and discharging were comparatively analyzed based on this model with different anode materials of nickel sheet (NS) and porous nickel foam (NF). Subsequently, the effects of changes in negative electrode porous nickel foam thickness and porosity on battery polarization, side-reaction current density and battery efficiency were further investigated. Finally, the performance of the battery under the optimal battery state was studied. The results showed that the NF negative electrode effectively reduced the battery polarization, suppressed the battery side reactions as well as improved the battery efficiency under high current density and multiple cycles of charging and discharging, which improved the efficiency and stability of the battery.

Accelerating Computation of Acidity Constants and Redox Potentials for Aqueous Organic Redox Flow Batteries by Machine Learning Potential-Based Molecular Dynamics.

Due to the increased concern about energy and environmental issues, significant attention has been paid to the development of large-scale energy storage devices to facilitate the utilization of clean energy sources. The redox flow battery (RFB) is one of the most promising systems. Recently, the high cost of transition-metal complex-based RFB has promoted the development of aqueous RFBs with redox-active organic molecules. To expand the working voltage, computational chemistry has been applied to search for organic molecules with lower or higher redox potentials. However, redox potential computation based on implicit solvation models would be challenging due to difficulty in parametrization when considering the complex solvation of supporting electrolytes. Besides, although ab initio molecular dynamics (AIMD) describes the supporting electrolytes with the same level of electronic structure theory as the redox couple, the application is impeded by the high computation costs. Recently, machine learning molecular dynamics (MLMD) has been illustrated to accelerate AIMD by several orders of magnitude without sacrificing the accuracy. It has been established that redox potentials can be computed by MLMD with two separated machine learning potentials (MLPs) for reactant and product states, which is redundant and inefficient. In this work, an automated workflow is developed to construct a universal MLP for both states, which can compute the redox potentials or acidity constants of redox-active organic molecules more efficiently. Furthermore, the predicted redox potentials can be evaluated at the hybrid functional level with much lower costs, which would facilitate the design of aqueous organic RFBs.