Performance Of Redox Flow Battery Research Articles

Impact of Bromine Complexing Agents and Battery Construction on Hydrogen–Bromine Redox Flow Battery Performance

Impact of Bromine Complexing Agents and Battery Construction on Hydrogen–Bromine Redox Flow Battery Performance

Capacity fade-aware parameter identification of zero-dimensional model for vanadium redox flow batteries

This study proposes a framework for evaluating the electrochemical performance of a vanadium redox flow battery (VRFB) system. First, a numerical solver for redox flow battery is constructed to represent the multi-physics system through systems of ordinary differential equations, which describe the mass conservation of existing vanadium ions. The present numerical model is validated regarding the voltage by comparing its results with the experimental results of previous studies. Second, we identify the parameters in the governing equations using a genetic algorithm with the present numerical model. We select seven parameters by considering the physical meaning of each parameter related to the electrochemical performance. The voltage for the first charging/discharging cycle and capacity fade data are used to identify the selected parameters. The voltage and capacity fade estimated by the parameters identified using the numerical model align with the previous studies. Finally, we analyze the global sensitivity of the identified parameters in terms of the voltage and capacity fade using the total Sobol’ indices because the high sensitivity confirms that the identified parameters have reliable values. As expected, voltage- and capacity-related parameters show high total Sobol’ indices for the voltage and discharging capacity, respectively. Furthermore, we predict the performance of the VRFBs using the identified parameter set and numerical model during 30-cycle operations. Additionally, the performance is compared according to the current density and vanadium concentration in the electrolyte. The proposed framework can be used to evaluate the electrochemical characteristics of developed VRFBs by identifying parameters related to physical performance, such as voltage and capacity fade. Moreover, the identified parameters can be utilized to predict voltage and capacity performance, enabling the optimization of operating conditions and configurations of VRFBs.

Pre-magnetization smashing hydrated vanadium ions to improve redox flow batteries performance

The vanadium redox flow battery (VRFB) has received extensive attention due to its intrinsic safety and high scalability. Currently, there are still deficiencies of low energy efficiency and higher unit capacity cost in VRFB energy storage. Continuously optimizing the battery performance through reducing electrode polarization losses is a necessary way to achieve efficient VRFB energy storage technology. In this study, a method of pre-magnetizing the electrolyte to improve the performance of the battery was proposed. A permanent magnet with an intensity of 0.9 T was used to pre-magnetize the vanadium-ion aqueous electrolyte before feed into the battery stack and working-on, it was found that the diffusion capacity of vanadium ions increased by 133.6 % after pre-magnetized even if the external magnetic field was removed. Meanwhile, both of the charge transfer and concentration polarization resistance of the electrode were reduced. The energy efficiency (EE) of the battery was increased by 6.4 % in the charge–discharge test at current density of 300 mA cm−2. The power density increased by 6.19 % with current density 400 mA cm−2 at most, and it prefers to continuously increase as current larger. The electrolyte pre-magnetization showed significant positive improvements on the electrode reaction kinetics and battery charge–discharge cycle.

Designer Fluorescent Redoxmer Self‐Reports Side Reactions in Nonaqueous Redox Flow Batteries

The state of health (SOH) is a critical measure for evaluating and predicting performance of redox flow batteries (RFBs). However, diagnosing SOH of RFBs is often challenging due to the overwhelming complexity of the electrolytes and associated electrochemical reactions. Designing active molecules or redoxmers that can autonomously exhibit property changes upon specific stimuli may provide a viable way for early diagnosis of SOH. Herein, a dimerized redoxmer, DGL‐N‐CH3, was designed and synthesized by linking blue‐green fluorescent monomers through a diglycolamide linker. While DGL‐N‐CH3 still maintains similar electrochemical behavior and strong fluorescence, we observe a unique side reaction when cycling DGL‐N‐CH3 in H‐cells, which leads to a side product, NHCH3‐BzNSN via linker cleavage. Interestingly, NHCH3‐BzNSN also emits fluorescence but at a longer wavelength. By taking advantage of this unique fluorescent change that corresponds to the growth of NHCH3‐BzNSN, we successfully established the capacity decay of DGL‐N‐CH3 H‐cell cycling, exemplifying a proof‐of‐concept self‐reporting redoxmer design towards in situ SOH monitoring.

Study on the effects of electrode fiber and flow channel arrangements on mass transfer and electrochemical performance of vanadium redox flow batteries

Study on the effects of electrode fiber and flow channel arrangements on mass transfer and electrochemical performance of vanadium redox flow batteries

A convection-enhanced flow field with height-changing ribs for redox flow batteries

Serpentine flow fields with flat ribs can effectively improve the performance of redox flow batteries. However, the marginal pressure difference between adjacent channels near the end side of ribs in conventional designs leads to weak convection in the regions, increasing the local concentration overpotential. This problem will be exacerbated in scaled-up redox flow battery stacks due to enlarged under-rib regions near the end side of ribs. In this work, two modified serpentine flow fields with height-changing ribs are proposed to adjust the electrode compression ratio at the under-rib region, thereby enhancing the convection in the electrode near the end side of ribs. Therefore, the active species are distributed more uniformly, resulting in an improved battery performance. Specifically, the uniformity of V2+, the energy efficiency and the system efficiency of the vanadium redox flow batteries with the ramp ribs are improved by 21 %, 2.7 %, and 2.7 % respectively compared with that of the conventional flat ribs, at the current density of 200 mA cm−2, the flow rate of 3.4 mL min−1 cm−2, and the active area of 117 cm2.

Enhancing Vanadium Redox Flow Battery Performance with ZIF-67-Derived Cobalt-Based Electrode Materials.

Vanadium redox flow batteries (VRFBs) have emerged as a promising energy storage solution for stabilizing power grids integrated with renewable energy sources. In this study, we synthesized and evaluated a series of zeolitic imidazolate framework-67 (ZIF-67) derivatives as electrode materials for VRFBs, aiming to enhance electrochemical performance. Four materials-Co/NC-700, Co/NC-800, Co3O4-350, and Co3O4-450-were prepared through thermal decomposition under different conditions and coated onto graphite felt (GF) electrodes. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analyses confirmed the structural integrity and distribution of the active materials. Electrochemical evaluations revealed that electrodes with ZIF-67-derived coatings exhibited significantly lower charge transfer resistance (Rct) and higher energy efficiency (EE) compared to uncoated GF electrodes. Co/NC-800//GF delivered the highest energy efficiency and discharge capacity among the tested configurations, maintaining stable performance over 100 charge-discharge cycles. These results indicate that Co/NC-800 holds great potential for use in VRFBs due to its superior electrochemical activity, stability, and scalability.

Enhancement in the performance of a vanadium-manganese redox flow battery using electrospun carbon metal-based electrode catalysts

This study investigates the performance of both a vanadium/manganese redox flow battery (V/Mn RFB) and an all-vanadium redox flow battery (VRFB), employing carbon metal fabrics (CMFs) prepared through electrospinning followed by carbonization. Noteworthy advancements are observed in both systems upon coupling CMFs with thermally treated graphite felt (GF) electrodes. Nearly doubled peak power density and 50 % higher capacity utilization over 150 charge/discharge cycles at 75 mA cm−2 are achieved for the V/Mn RFB with the incorporation of CMFs alongside graphite felt as catalysts. The VRFB demonstrates notable enhancements too, achieving approximately 200 cycles at a current density of 80 mA cm−2, with high efficiencies (85 %) and electrolyte utilization (79 %) when CMFs are used in combination with graphite felts. These advancements may facilitate pilot-scale testing and integration of the V/Mn RFB for the employment in the renewable energy storage sector and grid-balancing studies.

State of Charge (SoC) of the Vanadium and Other Redox Flow Batteries: Identification of the Electrode and Bipolar Plate Contributions

In this paper attention is directed toward one of the key measures of performance, State of Charge (SoC) for vanadium and other battery chemistries. Explored are its simple definition, as well as a more complete examination of just what is meant by this terminology. Developed is a more sophisticated exposition of how to calculate it properly, including spatial distributions, and what consequences arise from various simplifications. Open Circuit voltage through the Nernst equation, is related to the SoC. Non-equilibrium overpotential is also related to the concentrations when treated as averaged field variables. Other chemistries examined include iron-chromium, all-iron, and hydrogen-bromine. For the first time, a rigorous decomposition of the spatial variation of the electrode and bipolar plate contributions is identified, allowing new formulas to be obtained. This may allow optimization of redox flow battery performance. Finally, an expression is found for the open circuit voltage cost going between no bipolar plates and their incorporation into the redox flow battery.

High-performance composite electrode based on polyaniline/graphene oxide carbon network for vanadium redox flow batteries

In this study, an electrode wrapped in a carbon network is fabricated using a straightforward hydrothermal technique. Conducting polymers such as polyaniline (PANi) have been used to form carbon networks on the surfaces of carbon fibers. However, the cycling instability of PANi, which is a consequence of structural modifications, is a significant obstacle to its commercial application. This study presents an innovative and effective approach for synthesizing carbon networks using PANi/reduced graphene oxide (PANi-rGO-CF) composites to enhance the performance of vanadium redox flow battery (VRFB) electrodes. PANi-rGO was deposited on carbon felt using a hydrothermal method, followed by calcination under an argon atmosphere. The presence of graphene oxide facilitated the uniform distribution of PANi and enhanced its stability. PANi-rGO-CF demonstrated superior electrocatalysis toward vanadium redox couples owing to the abundant heteroatom active sites, affording VRFBs with extraordinary stability and outstanding energy efficiency after 100 cycles at 100 mA/cm2.

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.

Numerical and experimental study on fractal flow field for improving the performance of non-aqueous redox flow battery

The flow field design of the non-aqueous redox flow battery (RFB) decides the electrolyte flow and mass transfer of active species inside porous electrode, which has a significant influence on the operation of RFB. In this work, a fractal tree-like flow channel is proposed to enhance the electrolyte convection and optimize the concentration distribution of active species inside the graphite felt electrode, thus boosting the overall battery performance. Using the finite element simulation method, a three-dimensional numerical model of single cell is established to comparatively study the steady-state discharge process characteristics of deep eutectic solvent (DES) electrolyte-based vanadium‑iron RFBs with fractal and serpentine flow fields, respectively. Moreover, by assembling the single cell of this RFB and building the full cell test system, an experimental study is conducted to compare the discharging output voltage and power of the RFBs with serpentine flow field and fractal flow fields of different fractal dimensions. The numerical results show that the fractal tree-like flow field can improve the discharging power of RFB as well as reduce the pumping loss compared with the conventional serpentine flow field. That is mainly attributed to that fractal flow field is conducive to reducing the polarization loss and strengthening the convection in porous electrode simultaneously. What's more, the role of fractal dimension of flow field is also investigated numerically, thus knowing that large fractal dimension promotes lower pumping loss while small fractal dimension is in favor of higher output voltage. In addition, the experimental results also demonstrate that the fractal flow field could improve the output voltage and maximum discharging power of RFB compared to serpentine flow field. This work provides an optimization method for the flow field design of DES electrolyte-based vanadium‑iron RFB, and is expected to be employed in the other non-aqueous RFBs.

Hierarchical interconnected polyaniline nanocomposite with hydrothermally synthesized pyrite structure for improved electrochemical properties in a vanadium redox flow battery

In this study, FeS2 (FS) was synthesized via the hydrothermal technique. The various percentages of FS were subsequently incorporated into polyaniline (PANI) through an in-situ chemical process, aiming to improve the performance of the vanadium redox flow battery (VRFB). The synthesized nanocomposites (NPFS) were characterized using various techniques such as spectroscopy, microscopy, chemical, thermal study and electrochemical analysis (CV, EIS and Tafel) and charge discharge cycles study to understand their structure and performance. Morphological, chemical and structural analyses revealed the successful integration of FS into the PANI matrix, forming a hierarchical with highly porous nanocomposite structure. The results of the electrochemical analysis significantly improved the redox behavior and charge transfer kinetics compared to PANI. Based on the characterization and electrochemical characterizations, the best performing composition (NPFS15) sample (3 mg/cm2) was coated on 132 cm2 graphite felt (GF) and inserted in VRFB to examine the charge–discharge cycles. At a current density 70 mA/cm2, the selected nanocomposite with the specified loading on GF exhibited superior electrochemical performance due to the sufficient availability of active sites. Besides, the integration of NPFS nanocomposite materials in VRFB technology may pave the way for more efficient and sustainable energy storage solutions in the future.

Mitigation of Negative-Electrode Degradation in Vanadium Redox Flow Batteries

Electrode overpotentials are among the major factors that impact the performance of redox flow batteries (RFBs). However, even though the all-vanadium redox flow battery (VRFB) is the most mature flow-battery chemistry, a recent review article has pointed out that “there is poor agreement between the reported values of kinetic parameters” [1]. Major contributors to this disagreement are the wide variety of carbon materials that are used as electrodes and because the kinetics of both the V(II)/V(III) and V(IV)/V(V) reactions on carbon depend on the electrode pretreatments. The role of surface functional groups and the mechanisms of electron transfer for these reactions is not well understood [1]. There is general agreement that the V(IV)/V(V) kinetics are more facile than the V(II)/V(III) kinetics [2, 3]. Multiple researcher groups have reported electrode overpotential increases with time, and “there is evidence that it occurs mainly on the negative electrode” [1]. Additionally, “reversing the polarity of the VRFB has been suggested as one strategy to recover lost performance but not all investigators have found this strategy effective” [1]. Exposing the V(II)/V(III) electrode to V(IV)/V(V) electrolyte may increase the roughness and oxidize the electrode, which can both improve the activity. It has also been suggested that reversing the polarity may remove impurities, such as copper metal from the negative electrode [4]. More recently, it has been proposed that surface activity may be improved by oxidizing adsorbed V(II) [5]. We hypothesize that V(II)/V(III) electrode degradation on graphitic carbon-fiber electrodes is primarily due to the adsorption of a contaminate that is oxidized when exposed to V(IV)/V(V) electrolyte. We will describe what we suspect is the relevant contaminate species, and we will show the stability of the V(II)/V(III) electrode can be substantially improved by simply removing certain electrolyte-wetted components from the VRFB test apparatus. References A. Bourke, D. N. Buckley, et.al., “JES, 170 (2020). 10.1149/1945-7111/acbc99 D. Aaron, T. A. Zawodzinski, et. al., ECS Electrochem. Letters, 2 (2013) 10.1149/2.001303eel N. Pour, Y. Shao-Horn, et.al., J. of Physical Chemistry C, 119 (2015).10.1021/jp5116806 D. Reynard, H. Girault, et.al., ChemSusChem, 12 (2019). 10.1002/cssc201802895T. Greese and G. Reichennauer, J. Power Sources, 500 (2021). 10.1016/j/jpowsour.2021.229958

A Stable Polymer-Blended Anion-Exchange Membrane for Enhanced Performance in Redox Flow Batteries

Redox flow batteries (RFBs) operate with a membrane, responsible for the separation of cationic active species and allowing the passage of counter-ions, to preserve electroneutrality on each side of RFBs. Commercial cation-exchange membranes (CEMs), such as Nafion®, possess excellent ionic conductivity and chemical stability. However, they face challenges in blocking cationic active species common in RFBs, leading to significant capacity loss over time. Anion-exchange membranes (AEMs) efficiently block active species with the assistance of the Donnan effect. Nevertheless, commercial AEMs lack acid stability and conductivity compared to their cationic counterparts.Polytetrafluoroethylene (PTFE)-reinforced quaternary ammonium cardo poly(ether)ketone (QPEK-C)-based membranes with Al2O3 additives (PQPAM), a heterogeneous AEM developed in our lab1, possess excellent ionic conductivity with low permeability of active species and good mechanical properties. PQPAM has demonstrated better acid stability than commercial AEMs. However, its acidic and oxidative stability require improvement, as evidenced by degradation after 250 hours of in-situ harsh RFB cycling due to the heterogeneous nature of PQPAM and the exposure of the susceptible QPEK-C-rich side to the electrolytes2. To address this issue, we propose a strategy to enhance the chemical stability of QPEK-C-based membranes by inhibiting the exposure of QPEK-C to oxidation agents through blending with a hydrophobic engineering thermoplastic like polybenzimidazole (PBI)3,4. Furthermore, PBI's known ability to protonate in acidic media will reinforce ionic conductivity and the separation of active species, thus improving the Donnan effect, in addition to enhancing chemical and mechanical stability.Elemental analyses and microscopy images confirm a homogeneous blending of PBI and QPEK-C, promising stability improvement. The results of ex-situ tests on ionic conductivity, cation permeability, and chemical stability align with the mentioned hypotheses, showcasing that blend of PBI/QPEK-C outperforms pure PBI and QPEK-C AEMs. Additionally, the mechanical properties of the PBI/QPEK-C blended AEMs are improved compared to pure QPEK-C AEMs and PBI/QPEK-C blended AEMs outperform pure PBI and QPEK-C AEMs in in-situ cycling tests with our patented titanium-cerium RFBs5. Moreover, this work will explore other strategies to improve the blended AEM properties, such as utilizing inorganic fillers or PTFE reinforcement.

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

Operando Visualization of Redox Flow Batteries Using Fluorescence Spectroscopy with Alizarin Red S Electrolyte

Redox flow batteries (RFBs) charge and discharge by transferring electrons between two pairs of redox species separated by a proton exchange membrane. Unlike traditional batteries that store energy in redox-active materials within an enclosed cell, RFBs store energy in liquid electrolytes housed in external reservoirs1. These electrolytes are pumped through the cell, enabling redox reactions on the surface of electrodes. The energy storage capacity of RFBs is determined by the concentration of the active species and the size of the reservoirs, making them a promising technology for large-scale energy storage applications2. While RFBs possess advantages such as long lifetime, flexible design for battery capacity and power, and rapid response, they suffer from drawbacks like low energy density, power density, and energy efficiency3. Efforts to address these issues have primarily focused on modifications to the electrode materials or the flow field4 , 5. However, evidence supporting performance enhancements often relies on global parameters such as energy efficiency, energy density, and voltage drop, lacking detailed mechanistic and microscopic studies. Real-time observation of the electrode-electrolyte interface during redox reactions and the transport of redox species in the flow field holds the potential to significantly contribute to understanding the electrode structure and mass transport phenomena in RFBs6. This understanding, in turn, facilitates prediction and purposeful enhancement of battery performance by developing desirable structures for both electrode and flow fields. Microscopy, particularly confocal microscopy, serves as a powerful tool for observing microscopic structures. Confocal microscopes yield sharper images with higher resolution than widefield microscopy, enabling rapid acquisition of high-resolution images.In this study, we employed a confocal laser scanning microscope for operando visualization of RFBs. We designed a transparent framework for the battery, allowing light to pass through, and covered its surface with a glass cover to visualize the porous carbon electrode. We selected a fluorescent redox-active species, Alizarin Red S to enable visualization using fluorescence spectroscopy. Leveraging its unique fluorescence properties, we established a correlation between fluorescence intensity and the state of charge. This innovative approach enables us to observe the distribution of electrolytes, the dynamics of redox reactions on the electrode surface (with fast speed of imaging ＜0.2s), the mass transfer behavior of the electrolyte on the electrode surface, and the uniformity of electrolyte flow in the flow field, including areas of stagnation or recirculation. Zhang, J. et al. An all-aqueous redox flow battery with unprecedented energy density. Energy Environ. Sci. 11, 2010–2015 (2018).Rubio-Garcia, J., Kucernak, A. & Charleson, A. Direct visualization of reactant transport in forced convection electrochemical cells and its application to redox flow batteries. Electrochem. commun. 93, 128–132 (2018).Tolmachev, Y. V. Flow Batteries From 1879 To 2022 And Beyond. Qeios 1–79 (2023).Wang, R. et al. Gradient-distributed NiCo2O4 nanorod electrode for redox flow batteries: Establishing the ordered reaction interface to meet the anisotropic mass transport. Appl. Catal. B Environ. 332, 122773 (2023).Kumar, S. & Jayanti, S. Effect of flow field on the performance of an all-vanadium redox flow battery. J. Power Sources 307, 782–787 (2016).Wong, A. A., Rubinstein, S. M. & Aziz, M. J. Direct visualization of electrochemical reactions and heterogeneous transport within porous electrodes in operando by fluorescence microscopy. Cell Reports Phys. Sci. 2, 100388 (2021).

(Invited) Operando Visualization of the Electrolyte Distribution in Vanadium Redox Flow Electrodes

Electrolyte transport losses are among the main factors that limit the performance of Vanadium Redox Flow Batteries (VRFBs)1. The electrolyte must percolate into the electrode and reach the reaction sites with minimum resistance to reduce such losses. The optimized electrolyte flow ensures that the reactants and products are transported to and away from the reaction sites freely and decreases the pumping losses of the electrochemical cell, increasing the overall efficiency of the battery system.The electrolyte distribution in a porous electrode is crucial for the stability and performance of the electrode. The presence of gas bubbles in the electrode reduces the electrochemically active surface, resulting in cell potential fluctuations. In addition, the gas bubbles cause poor contact between the electrolyte and the electrode, and the ionic conductivity could be locally blocked2. These effects lead to inhomogeneous potential distribution (spikes), accelerating the electrode material's corrosion. Gas bubbles are very common in VRFBs, and they result from parasitic side reactions, such as carbon corrosion, hydrogen evolution (HER), or incomplete electrode wetting3.Synchrotron X-ray imaging is a powerful tool for tracking these bubbles in porous carbon materials. We have designed an experimental setup resembling an operating VRFB cell to image the flow through the porous carbon electrode. With its modular structure, the setup offers excellent flexibility to evaluate different designs and operational aspects of VRFBs4, 5. The findings of our investigations over the years will be discussed in this presentation. References J. Kim and H. Park, Journal of Power Sources, 2022, 545, 231904. K. Krause, C. Lee, J. K. Lee, K. F. Fahy, H. W. Shafaque, P. J. Kim, P. Shrestha and A. Bazylak, ACS Sustainable Chemistry & Engineering, 2021, 9, 5570-5579. M.-A. Goulet, M. Skyllas-Kazacos and E. Kjeang, Carbon, 2016, 101, 390-398. L. Eifert, N. Bevilacqua, K. Köble, K. Fahy, L. Xiao, M. Li, K. Duan, A. Bazylak, P.-C. Sui and R. Zeis, ChemSusChem, 2020, 13, 3154-3165. K. Köble, L. Eifert, N. Bevilacqua, K. F. Fahy, A. Bazylak and R. Zeis, Journal of Power Sources, 2021, 492, 229660. Figure 1

Pegylated Viologen Derivatives to Improve Performance of Aqueous Organic Redox Flow Battery

Renewable energy sources like wind and solar power are great alternatives for a clean way to produce electricity but have the inconvenience to fluctuate1. To address this issue and promote the implementation of renewables sources, scientists are developing new ways to store energy while production is at a maximum for a subsequent release when there is demand. Redox flow batteries (RFBs) are the most appropriate solution and are increasingly gaining attention for stationary, large scale electrochemical energy storage2,3. One variation of RFBs are aqueous organic redox flow batteries (AORFBs), where water-soluble organic molecules are use as the redox couple. Viologen type molecules are particularly well-suited as a negative potential species to develop cheaper and better AORFBs with great scalability, reversibility and long-term stability4.In this study, viologen derivatives were synthesized with various N-functional groups to explore the impact of the substituent on their solubility, viscosity and redox potential. We showed that the use of short chains of poly(ethylene glycol) improved the solubility of the viologens derivatives which could lead to batteries with higher capacity. The symmetric viologen (with two identical substituents) provided a great solubility in water and the formal potential was unaffected by the chemical nature of the substituents. We demonstrated that the 1,1’-(bisethylene glycol)-4,4’-bipyridium (PEG2-V-PEG2) showed the most promising properties with a high solubility (2.3 M in 1M KCl) and low viscosity (3.01 mPa*s at 1M). As such, this derivative was selected for further evaluation in an asymmetrical labs-scale RFB prototype cell versus bis(trimethylamoniumpropyl)ferrocene (BTMAP-Fc). The compound was studied at various concentrations to assess the maximum energy density that can be reached and the effect of concentration on cycling life by achieving a comparison to the symmetrical 1,1’-bis(3-sulfonatopropyl)-4,4’-bipyridium (SPr-V-SPr) at 0.5 M. Figure 1: Redox flow battery scheme using Viologen derivative as the negolyte and BTMAP-Fc as the posolyte Reference Shi, X., Qian, Y. and Yang, S. Fluctuation analysis of a complementary wind–solar energy system and integration for large scale hydrogen production. ACS Sustainable Chemistry & Engineering, 8(18), pp.7097-7110. (2020)Sánchez-Díez, E.; Ventosa, E.; Guarnieri, M.; Trovò, A.; Flox, C.; Marcilla, R.; Soavi, F.;Mazur, P.; Aranzabe, E.; Ferret, R., Redox flow batteries: Status and perspective towards sustainable stationary energy storage. Journal of Power Sources, 481, 1-23. (2021)Poullikkas, A., A comparative overview of large-scale battery systems for electricity storage. Renewable and Sustainable energy reviews, 27, pp.778-788. (2013)Gentil, S., Reynard, D. and Girault, H.H. Aqueous organic and redox-mediated redox flow batteries: a review. Current Opinion in Electrochemistry, 21, pp.7-13. (2020) Figure 1

Synergetic Functionalization of the ZnS@ASCs Biocomposite: For Enhanced Electrochemical Performance of Redox Flow Batteries and Supercapacitors

Synergetic Functionalization of the ZnS@ASCs Biocomposite: For Enhanced Electrochemical Performance of Redox Flow Batteries and Supercapacitors