Performance Of Vanadium Redox Flow Battery Research Articles

Enhanced Vanadium Redox Flow Battery Performance with New Amphoteric Ion Exchange Membranes.

Vanadium redox flow batteries (VRFBs) depend on the separator membrane for their efficiency and cycle life. Herein, two amphoteric ion exchange membranes are synthesized, based on sulfonic acid group-grafted poly(p-terphenyl piperidinium), for VRFBs. Using ether-free poly(p-terphenyl piperidine) (PTP) as the polymer matrix, and sodium 2-bromoethanesulphonate (ES) and 1,4-butane sultone (BS) as grafting agents, We achieve quaternization of PTP through an environmentally friendly process without alkaline catalysts. PTP-ES and PTP-BS membranes exhibit low area resistance, high H+ permeability, and significantly reduced vanadium ion permeability, leading to exceptional ion selectivity, which is 3.06×106Smincm-3 and 4.34×106Smincm-3, respectively,three orders of magnitude higher than that of Nafion115 (0.27×104Smincm-3). The VRFB with PTP-BS achieves a self-discharge duration of 190h, compared to 86h for Nafion 115. Additionally, under current densities of 40-160mAcm-2, PTP-BS shows coulombic efficiencies of 98.1-99.1% and energy efficiencies of 92.0-82.1%, outperforming Nafion 115. The VRFB with PTP-BS also demonstrates excellent cycle stability and discharge capacity retention over 300 cycles at 100mAcm-2. Therefore, the amphoteric PTP-BS membrane shows remarkable performance, offering significant potential for VRFB applications.

A comprehensive study in experiments combined with simulations for vanadium redox flow batteries at different temperatures

Ensuring the appropriate operation of Vanadium Redox Flow Batteries (VRFB) within a specific temperature range can enhance their efficiency, fully exploiting the advantages of renewable energy. This study employs a comprehensive approach combining experimentation and simulation to systematically investigate the impact of temperature on VRFB performance. Experimental evaluations of VRFB performance across various temperatures were conducted through charge and discharge experiments, electrochemical impedance spectroscopy, hydraulic pressure drop testing, and cycling charge and discharge trials. Additionally, a three-dimensional multi-field coupled model was developed to provide a theoretical analysis and elucidate VRFB performance under varying temperature conditions, incorporating temperature-dependent variations in the physical parameters of different components. The results suggest that in VRFB systems, an increase in temperature leads to a reduction in overpotential and pressure drop, resulting in improved system efficiency, albeit accompanied by a slight decrease in Coulombic efficiency. Furthermore, compared to ohmic overpotential and electrochemical overpotential, the impact of temperature on concentration overpotential appears to be relatively insignificant. Increasing the flow rate or temperature could contribute to a more stable degradation rate of capacity and Coulombic efficiency during the battery cycling process. Higher flow rates enhance the voltage efficiency of the battery, with the degree of improvement decreasing as temperature increases.

Electrolyte Gradients and Capacity Drop in Large Flow Battery Tanks: From Experiments to Fluid-Dynamic Investigations

A study of the effects of electrolyte flow inside the tanks on electrical performance of an industrial-size Vanadium Redox Flow Battery (VRFB) is presented. The concentration of electrolytes feeding the stacks of VRFBs is crucial in determining the device voltage and overall power performance. Usually, the assumption of perfect mixing in the tanks is assumed, but the hydraulic behavior of large VRFB can deviate significantly from this assumption depending on the electrolyte flow rate, stochiometric factor and geometry of the tanks. In this study, the State of Charge (SoC) measurements have been analyzed, starting from the signal produced by an Open Circuit Voltage (OCV) cell. An experimental campaign has been conducted during charge/discharge roundtrip cycles at different current levels and constant stoichiometric factor. Building on the delay in the voltage response of the battery, a fluid-dynamic model was developed to study how the hydraulic behavior of electrolytes inside tanks influences the electrolyte concentration and, consequently, the SoC of the electrolyte that feeds the stack and the electrical time response of the battery. The model indicated that a stratification of charged electrolyte is responsible for this delay resulting in an initial voltage plateau. A different hydraulic behavior was found in each tank and in each charge/discharge phase. These results highlight the tank role in the industrial-scale VRFB performance. References Sanchez-Diez, E. Ventosa, M. Guarnieri, A. Trovò, C. Flox, R. Marcilla, F. Soavi, P. Mazur, E. Aranzabe, R. Ferret, “Redox flow batteries: status and perspective towards sustainable stationary energy storage”, J. Power Sources, 481, (2021) 228804.Kurilovich, A. Trovò, M. Pugach, K. J. Stevenson, M. Guarnieri. Prospect of Modeling Industrial Scale Flow Batteries – from Experimental Data to Accurate Overpotential Identification, Renew. Sust. Energ. Rev. 167, (2022) 112559.Trovò, V. Di Noto, J. E. Mengou, C. Gambaro, M. Guarnieri. Fast Response of kW-Class Vanadium Redox Flow Batteries, IEEE Trans. Sustain. Energy 12, (2021) 2413–2422.Trovò, M. Rugna, N. Poli, M. Guarnieri. Prospects for industrial vanadium flow batteries, Ceram. Int., 49 (14), (2023) 24487-24498.Maggiolo, A. Trovò, M. Guarnieri, “Reactant Flow in Flow Batteries”, in L. Cabeza (ed.), Encyclopedia of Energy Storage, vol. 4, pp. 231-242. Oxford: Elsevier. March 2022.A. Prieto-Díaz, S. E. Ibáñez, M. Vera. Fluid dynamics of mixing in the tanks of small vanadium redox flow batteries: Insights from order-of-magnitude estimates and transient two-dimensional simulations, Int. J. Heat Mass Transf. 216, (2023) 124567.Trovò, N. Poli, M. Guarnieri. New strategies for the evaluation of Vanadium Flow Batteries: testing prototypes, Cur. Opin. Chem. Eng. 37, (2022) 100853. Figure 1

Evaluation of the effect of hydrogen evolution reaction on the performance of all-vanadium redox flow batteries

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 %.

Highly active nitrogen-phosphorus co-doped carbon fiber@graphite felt electrode for high-performance vanadium redox flow battery

Heteroatom-doped electrodes offer promising applications for enhancing the longevity and efficiency of vanadium redox flow battery (VRFB). Herein, we controllably synthesized N, P co-doped graphite fiber electrodes with conductive network structure by introducing protonic acid and combining electrodeposition and high temperature carbonization. H2SO4 and H3PO4 act as auxiliary and dopant, respectively. The synergistic effect between N and P introduces additional defect structures and active sites on the electrodes, thereby enhancing the reaction rate, as confirmed by density functional theory calculations. Furthermore, the conductive network structure of carbon fibers improves electrode-to-electrode connectivity and reduces internal battery resistance. The optimized integration of these strategies enhances VRFB performance significantly. Consequently, the N, P co-doped carbon fiber modified graphite felt electrodes demonstrate remarkably high energy efficiency at 200 mA cm−2, surpassing that of the blank battery by 7.9 %. This integrated approach to in-situ controllable synthesis provides innovative insights for developing high-performance, stable electrodes, thereby contributing to advancements in the field of energy storage.

Carbon nanofibers embedded in nanopores decorated graphite felt electrodes for enhanced vanadium redox flow batteries performance

This study introduces a novel electrode design, incorporating carbon nanofibers (CNFs) embedded in nanopores on graphite felt, achieved through a simplified one-step chemical vapor deposition process. The electrodes exhibit a uniform distribution of carbon nanofibers and nanopores, significantly enhancing active sites for vanadium redox reactions. Comprehensive characterization, including X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) surface area analysis, confirmed a significant increase in surface area and catalytic activity. When tested at a current density of 200 mA cm−2, the modified electrodes demonstrated a notable improvement in electrochemical performance, achieving over 75 % energy efficiency and maintaining this efficiency over 300 cycles. The cyclic voltammograms (CV) and electrochemical impedance spectroscopy (EIS) results indicated enhanced kinetics and reduced charge transfer resistance. Post-mortem SEM images confirmed the structural integrity of the nanofibers after extensive cycling tests.

2-Acrylamido-2-methylpropane sulfonic acid (AMPS) grafted poly(vinylidene fluoride) (PVDF) membrane for improved vanadium redox flow battery (VRFB) performance

Polymer modification techniques are crucial for customizing material properties to suit specific applications, particularly in energy storage systems. This study investigates the modification of poly(vinylidene fluoride) (PVDF) membranes via atom transfer radical polymerization (ATRP) to graft 2-acrylamido-2-methylpropane sulfonic acid (AMPS) onto the fluorinated backbone. The successful grafting was confirmed via nuclear magnetic resonance (NMR) spectroscopy, while the membrane structure was evaluated using infrared (IR) and X-ray photoelectron spectroscopies (XPS). Thermogravimetric analysis (TGA) and universal testing machine (UTM) tests verified the thermal and mechanical stability of the membranes. Electrochemical analysis showed sustained performance over 300 cycles. The FluorCat-25 membrane demonstrated high coulombic efficiency (>98 %), voltage efficiency (83 %), and energy efficiency (81 %) at a current density of 100 mA cm−2. Notably, FluorCat-25 achieved a peak power density of 353 mW cm⁻², surpassing that of Nafion-117 (304 mW cm⁻²), with >85 % capacity retention, indicating its superior performance and suitability for VRFB applications. These findings position FluorCat-25 as a promising candidate for efficient and durable energy storage solutions in VRFB technology.

Investigation of the impact of the flow mode in all-vanadium-redox-flow battery using macroporous and mesoporous carbon electrodes

Energy storage in vanadium redox flow batteries (VRFBs) is significantly impacted by both the cell design and the kinetics of electron transfer at the electrode/electrolyte interfaces. In this work, a novel VRFB flow field was designed and evaluated, allowing a portion of the flow to go through the porous electrodes in the direction of current flow. It was found that, when using standard carbon paper electrodes with moderate hydrophilicity, as compared to flow-by or only flow-through, concurrent 50 % flow-through and 50 % flow-by mode decreased the voltage loss by 46 % and increased the voltage efficiency from 74 % to 80 % compared to flow-by only (flow rate of 60 ml s−1). The voltage efficiency and energy efficiency were also enhanced to 82 % and 68 %, respectively, in the flow-through mode. This was likely due to enhanced mass transfer and increased utilization of the internal electrode surface area, in turn lowering the overpotential during both charging and discharging. To further determine the benefits of flow-through conditions, the effect of a binder-free, hydrophilic, and mesoporous carbon scaffold electrode (NCS85) was also investigated under flow-through mode and compared with the standard carbon paper electrodes with moderate hydrophilicity. NCS 85 has monodisperse, 3-D interconnected 85 nm pore diameters and thus a much higher surface area, resulting in a further increase in voltage and energy efficiency to 86 and 65 %, respectively. Heat treatment of the NCS85 to graphitize it and thus lower its resistance showed further improvements when using the flow-through mode, giving a voltage efficiency of 94 % and energy efficiency of 72 %. These improvements show the benefits that can be realized by optimizing both flow mode and carbon electrode porosity and permeability on VRFB performance.

In Situ Growth of Amorphous MnO2 on Graphite Felt via Mild Etching Engineering as a Powerful Catalyst for Advanced Vanadium Redox Flow Batteries.

Owing to the advantages of low cost, high safety, and a desirable cycling lifetime, vanadium redox flow batteries (VRFBs) have attracted great attention in the large-scale energy storage field. However, graphite felts (GFs), widely used as electrode materials, usually possess an inferior catalytic activity for the redox reaction of vanadium ions, largely limiting the energy efficiency and rate performance of VRFBs. Here, an in situ growth of amorphous MnO2 on graphite felt (AMO@GF) was designed for application in VRFBs via mild and rapid etching engineering (5 min). After the etching process, the graphite felt fibers showed a porous and defective surface, contributing to abundant active sites toward the redox reaction. In addition, formed amorphous MnO2 can also serve as a powerful catalyst to facilitate the redox couples of VO2+/VO2+ based on density functional theoretical (DFT) calculations. As a result, the VRFB using AMO@GF displayed an elevated energy efficiency and superior stability after 2400 cycles at 200 mA cm-2, and the maximum current density can reach 300 mA cm-2. Such a high-efficiency and convenient design strategy for the electrode material will drive the further development and industrial application of VRFBs and other flow battery systems.

Coupled Experimental-Theoretical Characterization of a Carbon Electrode in Vanadium Redox Flow Batteries using X-ray Absorption Spectroscopy.

Vanadium redox flow batteries (VRFBs) have emerged as promising solutions for stationary grid energy storage due to their high efficiency, scalability, safety, near room-temperature operation conditions, and the ability to independently size power and energy capacities. The performance of VRFBs heavily relies on the redox couple reactions of V2+/V3+ and VO2+/VO2+ on carbon electrodes. Therefore, a thorough understanding of the surface functionality of carbon electrodes and their propensity for degradation during electrochemical cycles is crucial for designing VRFBs with extended lifespans. In this study, we present a coupled experimental-theoretical approach based on carbon K edge X-ray absorption spectroscopy (XAS) to characterize carbon electrodes prepared under different conditions and identify relevant functional groups that contribute to unique spectroscopic features. Atomic models were created to represent functional groups, such as hydroxyl, carboxyl, methyl, and aldehyde, bonded to carbon atoms in either sp2 or sp3 environments. The interactions between functionalized carbon and various solvated vanadium complexes were modeled using density functional theory. A library of carbon K-edge XAS spectra was generated for distinct carbon atoms in different functional groups, both before and after interacting with solvated vanadium complexes. We demonstrate how these simulated spectra can be used to deconvolve ex situ experimental spectra measured from carbon electrodes and to track changes in the electrode composition following immersion in different electrolytes or extended cycling within a functional VRFB. By doing so, we identify the active species present on the carbon electrodes, which play a crucial role in determining their electrochemical performance.

Ammonium Bifluoride‐Etched MXene Modified Electrode for the All−Vanadium Redox Flow Battery

AbstractThe development of electrodes with high performance and long‐term stability is crucial for commercial application of vanadium redox flow batteries (VRFBs). This study compared the performance of VRFB with thermal‐treated and MXene‐modified carbon paper. To prepare the MXene, a modified‐etching process with ammonium−bifluoride (NH4HF2) led to a mild and efficient conversion of the MAX‐phase to MXene compared to etching process with hydrofluoric‐acid (HF). Electron microscopy and X‐ray diffraction studies revealed that the etching process with NH4HF2 led to MXene nanostructures with a large interlayer spacing. The results show that at a current density of 60 mA cm−2, the energy efficiency increased by 25.5 % when using a NH4HF2 ‐etched MXene‐modified negative electrode, by 12.5 % with a thermal‐treated MXene‐modified electrode, and by 4 % with an HF‐etched MXene‐modified electrode, in comparison to the pristine electrode. The maximum power density of the battery was increased by more than 40 %. In long‐term cycling experiments the MXene modified electrode exhibited excellent stability over 1000 cycles of charge‐discharge, with 0.05 % discharge capacity decay per cycle, amongst the lowest values reported to date and four times lower than for thermally‐treated electrode. The superior performance was linked to the improved electrical conductivity and wettability, higher interlayer spacing, and lower charge transfer resistance for the V2+/V3+ redox reaction.

Carbon cloth modified by direct growth of nitrogen-doped carbon nanofibers and its utilization as electrode for zero gap flow batteries

The synthetic procedure and characterization of carbon nanofibers (CNFs) grown on carbon cloth (CC) are explored in this study, with a focus on their potential application as electrodes in vanadium redox flow batteries (VRFBs). CC offers an attractive platform for surface modification owing to its conductive properties and three-dimensional architecture, while the N-doped CNFs formed by nitrogen (N) rich composition of melamine precursor enhance wettability of electrolyte and redox reactivity of vanadium ions. Electrochemical assessments reveal that NCC electrodes significantly increase voltage efficiency (VE) and capacity retention in VRFBs compared to bare CC (BCC) electrodes. Notably, NCC demonstrates a VE of 65.9%, surpassing the 55.9% of BCC electrodes. Additionally, NCC maintains superior capacity retention under varying current densities, a crucial factor for VRFBs. Long-term stability tests over 1000 cycles highlight the NCC electrode's durability, with only a minimal decrease in VE. Post-experiment analysis confirms the structural integrity of the CNFs on the CC electrodes, validating their resilience in VRFB operations. In summary, the study introduces a novel approach for fabricating N-doped CNFs on CC, resulting in electrodes that significantly boost VRFB performance in terms of efficiency, capacity retention, and stability, marking a notable advancement in flow battery technology.

Quinone convertible sulfated ion conductive side chain for highly selective vanadium redox flow batteries

In this work, the concept of a quinone convertible sulfated ion conductive side chain is first proposed with tunable Donnan effect and strong proton conducting ability to achieve high vanadium redox flow battery performance.

A poly(2-ethylaniline) blend membrane for vanadium redox flow batteries

Processable E-PANI polymer blend SPES membrane for enhancement of vanadium redox flow battery performance.

Investigation of Polarization in Vanadium Redox Flow Batteries with a Fluctuating Supply of Electrolyte Solution

The rapid development of renewable energy has led to increasing demand for energy storage equipment. The vanadium redox flow battery (VRFB) has attracted more attention due to its advantages such as good safety, long service life, and flexible design [1].In the VRFB, the electrolyte flow characteristics are important for the concentration overpotential as it significantly affects the supply of vanadium ions [2]. Therefore, many studies are focusing on the influence of flow rates and electrolyte distribution on VRFB performance [3-4]. However, few studies have focused on the effects of fluctuations in electrolyte flow rates on battery polarization and overpotential, which often occurs in practical situations and affects the mass transfer of ions. In this study, we focused on the effect of fluctuations in electrolyte supply induced by the peristaltic pump on the polarization behavior of the VRFB.The electrodes of the experimental VRFB are Sigracet® GDL 38AA, the membrane is Nafion® 211, and the vanadium ion concentration of the electrolyte is 1.7 mol/L. Before the formal experiment, the cell was charged to 50% state of charge. To determine the fluctuation effect on battery polarization, a peristaltic pump was used on one electrode side and a smooth pump on the other.Fig. 1 (a) and (b) show the charging and discharging voltage variation with a current of 200 mA/cm2 at different flow rates. The average voltages during charging decrease with increasing flow rates, while the average voltages during discharging increase with increasing flow rates, and all voltages fluctuate up and down.It can be known that the voltage variation is attributed to the fluctuating supply of electrolyte affecting the mass transfer. At higher flow rates, the vanadium ion transport speed is faster, and the concentration gradient of the reaction surface is smaller, resulting in lower overpotential and polarization. Under fluctuating conditions, the changing electrolyte flow rates also lead to changes in vanadium ion supply speed, resulting in the voltage fluctuation periodically.AcknowledgementThis work was supported by JSPS KAKENHI Grant Number 21H04540. The first author was supported by the China Scholarship Council.

Adaptation of a Vanadium Redox Flow Battery for Thermal Applications Using a Solid Capacity Booster

In this work a novel approach for the use of the Vanadium Redox Flow Batteries (VRFB) is made by viewing it as a dual system with the ability to store both electrical and thermal energy. Electrical energy is thanks to the electrochemical reactions of the vanadium ions dissolved in the electrolyte, while thermal energy will use the sensible heat of the electrolyte mass.The performance of VRFB has been widely studied over the last 40 years and there is an extensive bibliography on the subject regarding the electrochemical performance attending only to the conventional energy storage requirements, but the hybrid electrical-thermal function is a novel subject that has been scarcely explored. One of the most critical aspects is the narrow operating temperature range of these batteries (15-40°C) that strongly limits their thermal energy storage capacity.Practical vanadium electrolytes operate with electrolytes containing a vanadium concentration between 1.6 and 2.0 M, and usually also employ cooling and heating systems to maintain the temperature between 15 and 40ºC. In particular, at temperatures below 15ºC the slower reaction kinetics, high viscosity and reduced conductivity of the concentrated electrolytes introduce remarkable energy losses in the battery. On the other hand, at temperatures over 35ºC the positive electrolyte is not stable due to the limited solubility of VO2 + species. High temperatures also boost the kinetics of parasitic reactions such as hydrogen and oxygen evolution, thus increasing energy losses.In this study, we address these limitations aiming to open up new possibilities of a successful integration of vanadium redox flow batteries into thermal applications. For this, the functionality and stability limits of a diluted vanadium electrolyte are analyzed for an extended operational temperature window from 5ºC to 50ºC and compared to commercial electrolyte formulations. In a second step, the use of a solid capacity booster is investigated to compensate the loss of energy density due to electrolyte dilution.[1] S. Berling, S. Mavrikis, N. Patil, E. García – Quismondo, J. Palma, C. Ponce de León “Lignin as redox-targeted catalyst for the positive vanadium electrolyte”, Electrochemistry Communications 142 (2022) 107339.[2] S. Berling, J. M. Hidalgo, N. Patil, E. García - Quismondo, J. Palma, C.Ponce de León, “A mediated vanadium flow battery: Lignin as redox-targeting active material in the vanadium catholyte”. Submitted

Improved Vanadium Redox Flow Battery Performance through a Pulsating Electrolyte Flow Regime

The increase in emissions of greenhouse gases and their environmental impact lead to a transition from primarily fossil fuel-based energy sources to renewable and eco-friendly ones, such as solar panels and wind turbines. However, these sources are intermittent, resulting in fluctuating energy production levels that require buffering, which poses significant challenges in matching production-consumption profiles. [1,2] In order to stabilise the grid and reduce dependency on fossil fuels, integrating electrical energy carriers into a smart grid to store excess energy produced during peak periods and employ it during periods of low production is a potential solution. Redox flow batteries hold promise in this regard, as the storage capacity can be decoupled from the battery size, enabling capacity to be scaled independently of power output by increasing the volume of the electrolyte. [3] In contrast to conventional secondary battery types, such as lead-acid or lithium-ion batteries, the electrolyte in a redox flow battery is non-stationary, inducing convective mass transport effects that are critical for achieving a high power output.In this work we introduced pulsations to the electrolyte flow of an all-vanadium redox flow battery, leading to a reduced stagnant boundary layer attributed to shear forces. Previously, Pérez-Gallent et al. demonstrated that the conversion can be increased by a factor of two while selectivity gains of 15-20% can be made in a electrolyser by introducing a pulsating flow. [4] Furthermore, Vranckaert et al. studied a pulsating flow combined with pillar field electrodes, using the well-known ferri-ferrocyanide redox couple, and concluded that the average limiting current density can be increased fourfold compared to working with a conventional steady state flow regime. [5] Overall, a pulsating flow behaviour yields an enhanced mass transfer of electroactive species by increasing the local velocity through pulsations. The net residence time of the reactants remains unchanged since the pulsating flow has no influence on the overall flow velocity. However, the resulting improvement of mass transfer leads to an increase in conversion. As it is clear that mass transfer enhancement strategies open the door for more efficient systems, our work will for the first time focus on the influence of a pulsating electrolyte flow on the redox flow battery performance. The results show a significant improvement: the discharge capacity at 100 mA/cm2 increased by 38.7% when applying a pulse with pulse amplitude (PA) 0.4ml and pulse frequency (PF) 2.4 Hz at a flow rate of 5 ml/min (Figure 1 A). Furthermore, this 38.7% increase in discharge capacity surpassed the performance achieved at a constant steady-state flow of 25 ml/min. Therefore, a fivefold reduction of the net flow rate is possible without performance losses, decreasing necessary pumping costs. When regarding the stability of an all-vanadium redox flow battery operated with a pulsating electrolyte flow initial fluctuations of the current efficiency (CE), voltage efficiency (VE) and energy efficiency (EE) were recorded. However, the efficiencies became stable at 98.4%, 70.5% and 69.4% respectively, showing no decline over time (Figure 1 B). This novel and improved redox flow battery system allows to take the next step towards integrating electrical energy carriers into a smart grid suitable for renewable and green energy sources.[1] P. D. Lund, J. Lindgren, J. Mikkola, J. Salpakari, Renew. Sustain. Energy Rev. 2015, 45, 785–807.[2] H. Kondziella, T. Bruckner, Renew. Sustain. Energy Rev. 2016, 53, 10–22.[3] E. Sánchez-Díez, E. Ventosa, M. Guarnieri, A. Trovò, C. Flox, R. Marcilla, F. Soavi, P. Mazur, E. Aranzabe, R. Ferret, J. Power Sources 2021, 481, 228804.[4] E. Pérez-Gallent, C. Sánchez-Martínez, L. F. G. Geers, S. Turk, R. Latsuzbaia, E. L. V. Goetheer, Ind. Eng. Chem. Res. 2020, 59, 5648–5656.[5] M. Vranckaert, H. P. L. Gemoets, R. Dangreau, K. Van Aken, T. Breugelmans, J. Hereijgers, Electrochim. Acta 2022, 436, 141435. Figure 1

Proton conducting zeolite composite membrane boosts the performance of vanadium redox flow battery

In a vanadium redox flow battery (VRFB), the selectivity of protons over vanadium ions for an ion-conducting separator is crucial to achieving capacity retention in charge/discharge cycles. Conventionally used perfluorinated or hydrocarbon-based membranes are not able to resolve cross-contamination of vanadium during VRFB operation. Engineered inorganic materials like zeolites have inherent selectivity towards specific ions based on the size and charge of the ions. In this work, ZSM-5 zeolites with different Si/Al ratios were modified by a facile ion-exchange process to obtain proton rich zeolites, followed by successful infiltration into the SPEEK matrix. The composite membranes demonstrated excellent oxidative stability in 2 M H2SO4 containing 1.5 M VO2+ ions as well as favourable electrochemical properties. In a single-cell VRFB, the membrane with the highest proton conductivity i.e., SPEEK-ZSM 5 (25) 2H+ was able to achieve an average Coulombic efficiency of 97.0% and average energy efficiency of 78.0% over 300 charge/discharge cycles at 80 mA cm−2 current density. The polarization curve and self-discharge experiment results illustrated 21.7% higher peak power density and 2.5 times slower self-discharge compared to state-of-the-art Nafion-117 in identical operating conditions indicating zeolite-composite membranes as a potential candidate to enhance the durability and performance of VRFBs.

Large-scale all-climate vanadium batteries

The vanadium redox flow battery (VRFB) is a highly promising technology for large-scale energy storage applications due to its exceptional longevity and virtually unlimited capacity. However, for this technology to be widely applicable across different geographical locations, a thorough understanding of its all-climate properties is essential. In recent years, VRFBs have been improved by optimising vanadium electrolytes, exchange membranes, carbon fabric electrodes, and casings. However, most research activities have been limited to batteries operating in moderate temperature conditions, and all-climate vanadium batteries are rarely considered. Therefore, this research work focuses on the effect of temperature on the performance of VRFBs. Existing models that deal with the thermal-hydraulic-chemical modelling of VRFBs either ignore the coupling between the governing physical processes or the variation of key material properties with temperature. In this study, we consider both the coupling of the multi-physics processes that influence the behaviour of VRFBs and the variation of their underpinning properties with temperature.

Enhancing Vanadium redox flow batteries performance through local compression ratio adjustment using stiffness gradient carbon felt electrodes

Vanadium redox flow batteries (VRFBs) are assembled by compressing the electrodes to reduce the contact resistance between electrodes and bipolar plates and prevent liquid electrolyte leakage. However, an excessive compression ratio can impede the mass transfer and cause high-pressure drops in the electrolyte, ultimately reducing energy and system efficiencies. Accordingly, conventional stacks require a compromised compression ratio of 20 to 30%, resulting in substantial contact resistance and lower cell performance. To address this issue, we proposed a new approach to adjust the local compression ratio of carbon felt electrodes by creating a gradient in compressive stiffness along the through-thickness direction. We achieved this by selectively treating the carbon felt electrode to increase the interaction of carbon fibers in a treated region. This approach deforms the electrode non-uniformly, increasing the electrical contact point between the electrode and bipolar plate in regions with higher deformation and improving the convection and diffusion of ions at the interface between the electrode and membrane in regions with lower deformation, where porosity is relatively high. In a VRFB single-cell test, the electrode with the stiffness gradient demonstrated the highest energy efficiency (86.5%) under a current density of 100 mA∙cm−2, 10% higher than that of neat CF.