Vanadium Redox Flow Battery Cell Research Articles

Investigating the Role of Temperature on the Performance of Vanadium Redox Flow Batteries Using a Steady Validated Unit-Cell Model

Redox Flow Batteries (RFBs) are an evolved electrochemical energy storage technology crucial for the transition into a renewable energy future. Mainstream adoption of RFBs is subject to reduction of the capital and operation costs. In that sense, of particular importance is the optimization of the electrochemical stack, which affects the overall efficiency of the battery. Several studies have investigated the importance of thermal effects on the performance of vanadium redox flow batteries through transient non-isothermal models [1-2]. However, due to the simplified assumptions made by these authors some important temperature-dependent features are not included. Therefore, reliable and validated continuum models are also crucial to study the impact of the system temperature on all the fundamental physics in the electrochemical cells as well as to find the key aspects to optimize the stack.In this work, we present a 2D stationary model of a vanadium redox flow battery cell with a comprehensive and updated multiphysics description. The model was validated at a constant temperature of 25 ºC by polarization, conductivity, and open circuit voltage measurements. In a second step, the temperature was also included as a key operating variable in the model. Electrolyte properties, electrochemical rate constants, and H2SO4 dissociation equilibrium were described as a function of temperature as well as the state of charge (SoC) and the total vanadium concentration. The model is currently being validated through a second experimental campaign (see Fig. 1) conducted inside a climatic chamber imitating different environmental scenarios. The model can be used to explore the relevance of each phenomenon or element in the electrochemical stack and the influence of the operating conditions on them, e.g. temperature, state of charge and volumetric flow rate. By using the proposed model, we can elucidate the best temperature strategy to increase the performance of vanadium redox flow batteries in diverse operating scenarios.Figure 1. Open circuit voltage – SoC relation at different operating temperatures. References Al-Fetlawi, A.A. Shah, F.C. Walsh, Electrochimica Acta, 55, 78-89 (2009).Tang, S. Ting, J. Bao, M. Skyllas-Kazacos, Journal of Power Sources, 203, 165-176 (2012). Acknowledgments This work has been partially funded by the Agencia Estatal de Investigación (PID2019-106740RB-I00 and RTC-2017-5955-3/AEI/10.13039/501100011033). Figure 1

A coupled-layer ion-conducting membrane using composite ionomer and porous substrate for application to vanadium redox flow battery

A thin ionomer layer composed of perfluorosulfonic acid (PFSA) polymer in composite with functionalized alkoxysilane (FAS) is prepared and coated onto one side of a porous polyethylene (PE) substrate for vanadium redox flow battery (VRFB) to produce a coupled-layer membrane. The approaches are: (1) suppression of permeation through membrane using additive component, (2) the use of thin ionomer layer for lowering the amount of costly PFSA, and (3) strengthening the thin ionomer layer by coating onto an inexpensive PE substrate. The membrane is easily prepared using automatic control coater. The observation of morphology and infrared spectroscopy at both sides of the coupled-layer membrane confirm the thin ionomer layer on only one side of the PE substrate, plus the addition of FAS helps achieve lower diffusion coefficient. After the unit cell cycling, the coupled-layer membrane shows the good cycling performance closing to Nafion 212 membrane level. Additionally, the morphology after cycling of the coupled layers between PFSA ionomer and PE substrate can remain the same as in initial state, indicating a stable combination from both layers. Based on the easy production and the good performance, the developed membrane can be readily adapted by membrane manufacturer for the wide application in VRFB. • A thin ionomer layer is coated on one side of porous polyethylene substrate. • The thin layer reduces amount of costly perfluorinated sulfonic acid ionomer. • VRFB cell performance was good by closing to that of Nafion 212 membrane. • Unchanged morphology between two layer was found after VRFB unit cell operation.

Thermally cross-linked sulfonated poly(ether ether ketone) membranes containing a basic polymer-grafted graphene oxide for vanadium redox flow battery application

Sulfonated poly(ether ether ketone) (SPEEK) with a very high degree of sulfonation (DS) and poly(2,5-benzimidazole)-grafted graphene oxide (ABPBI-GO) are prepared and used as a polymer matrix and a filler, respectively, to prepare thermally cross-linked membranes for vanadium redox flow battery (VRFB) application. The thermally cross-linked SPEEK membranes containing ABPBI-GO exhibit significantly enhanced physicochemical stabilities due to the formation of the well-developed cross-linked structures by the chemical bonds formed through the solvothermal process and the acid–base interactions between the benzimidazole groups in filler and sulfonic acid groups in polymer chain. In addition, ABPBI-GO in the polymer matrix is found to be effective in decreasing the vanadium ion permeability while retaining high proton conductivity producing a high-performance VRFB membrane. The ionic selectivity of the thermally cross-linked SPEEK membrane containing 0.5 wt% of ABPBI-GO (TC-SPEEK/0.5) is 13.15 × 107 mS min cm−3, which is approximately 8 times larger than that of Nafion 212 (1.57 × 107 mS min cm−3). Accordingly, the VRFB cell fabricated using TC-SPEEK/0.5 membrane exhibits higher coulombic efficiencies (CE: 98.1–99.4%), voltage efficiencies (VE: 92.5–85.2%), and energy efficiencies (EE: 90.7–84.7%) than that using Nafion 212 (CE: 89.2–93.3%, VE: 90.7–81.2%, EE: 80.9–75.7%) at current density of 40–100 mA cm−2. Furthermore, the long-term stability of the VRFB cell using TC-SPEEK/0.5 membrane evaluated by the cycle test under realistic VRFB operation conditions is also found to be much better than that using Nafion 212.

An all-extruded tubular vanadium redox flow cell - Characterization and model-based evaluation

The vanadium redox flow battery (VRFB) as one of the most promising electrochemical storage systems for stationary applications still needs further cost reductions. Tubular cell designs might reduce production costs by extrusion production of cell components and small sealing lengths. Based on a first study of the authors [1], this work demonstrates the feasibility of extruded tubular VRFB cells with high power density in the flow-by electrode configuration. Extruded cell components are the perfluorosulfonic acid cation exchange membrane with a diameter of 5.0 mm and carbon composite current collectors. The cell performance is experimentally characterized by polarization curve, ohmic resistance and galvanostatic cycling measurements. A maximum volumetric power density of 407 kW/m 3 and a maximum current density of 500 mA/cm 2 can be achieved. A non linear E cell / i -model is used to evaluate exchange and limiting current densities while in-situ half cell SoC monitoring is applied to evaluate the extruded membrane.

Functionalized carbon black modified sulfonated polyether ether ketone membrane for highly stable vanadium redox flow battery

Sulfonated polyether ether ketone (SPEEK) membranes have attracted much attention as ion exchange membranes for vanadium redox flow batteries (VRFBs) owing to their affordability and low vanadium permeability. It's noted that they suffer from poor proton conductivity at low degree of sulfonation (DS) while poor mechanical stability at high DS. Therefore, it is a challenge to balance their performance and DS. In this work, functionalized carbon black (FCB) particles with sulfonic acid substituents were prepared and used as fillers to obtain advanced SPEEK composite membranes. This kind of SPEEK/FCB composite membranes show outstanding ion selectivity, low vanadium permeability, high proton conductivity and excellent stability. The VRFB cell with the optimized SPEEK/FCB composite membrane shows high energy efficiency (94.26%, at 50 mA cm−2), low-capacity fade rate (0.052% per cycle, at 120 mA cm−2) and long cycle life.

Surface‐engineered Nafion/CNTs nanocomposite membrane with improved voltage efficiency for vanadium redox flow battery

AbstractA carbon nanotubes (CNTs) reinforced Nafion membrane (CNT/N) with reduced interfacial resistance was prepared and served as a promising ion exchange membrane for vanadium redox flow batteries (VRFBs). The reinforcement of CNT effectively enhanced the tensile properties of Nafion membranes. The electrochemical properties of CNT/N membrane were analyzed by electrochemical impedance spectroscopy (EIS) and fitted with an analytical model to investigate the ionic and interfacial resistances. The EIS measurement reveals that the exposed CNT on the composite membrane surface significantly reduced the interfacial resistance of the membrane. The VRFB single cell performance of the CNT/N shows higher voltage efficiency (93% vs 89%) and energy efficiency (86% vs 83%) than recast Nafion at a current density of 40 mA cm−2. The cycling stability measurement showed that the discharge capacity retention of the VRFB cell equipped with CNT/N was greatly enhanced. The results suggest that the incorporation of CNT in ion exchange membrane is an effective approach for achieving lower membrane bulky and interfacial resistance, and thus, improving capacity retention, voltage, and energy efficiency.

Parameter identification of thermal model of vanadium redox batteries by metaheuristic algorithms

Typically, the battery stack temperature assumes constant in electrochemical or equivalent circuit models of the battery. However, experiments on a Vanadium Redox Flow Battery (VRFB) unit show that the temperature varies significantly during charge and discharge processes and considerably affects the value of the State of Charge (SoC) and other battery internal parameters. Therefore, monitoring and modeling the battery temperature is essential. An electrochemical based thermal model of VRFBs is adapted to the experimental data of a nine-cell VRFB unit in this study to find the optimal values of the coefficients and parameters of the VRFB's electrochemical and thermal models. The electrochemical model of VRFB and its thermal model include many unknown parameters and coefficients that need to be estimated. The objective of the current study is to determine the optimal value of all of these unknown parameters. According to the literature, the empirical methods are not sufficient to accurately determine the model's coefficients and parameters. An Optimization framework is defined to identify these coefficients by minimizing the mean square error between the measured experimental data of VRFB and the electrochemical model-based terminal voltage and electrolyte temperature. Moreover, a VRFB cell's electrochemical and thermal models are highly nonlinear; thus, excellent optimization techniques are needed to find these coefficients and parameters. A few metaheuristic optimizers are tested on the proposed optimization framework, where three of these algorithms have shown consistent and able to converge to reliable solutions. These algorithms are Genetic Algorithm (GA), Particle Swarm Optimizer (PSO), and Ant Lion Optimizer (ALO). The low RMS errors of the estimations by the metaheuristic-based algorithms compared to the measured data, show the accuracy of the proposed parameter identification approaches of VRFB's electrochemical and thermal model.

Advanced hybrid membrane for vanadium redox flow battery created by polytetrafluoroethylene layer and functionalized silicon carbide nanowires

As a key component of vanadium redox flow battery (VRFB), ion exchange membrane determines the performance of VRFB, wherein commercial membrane (such as Nafion) exacerbate problems including high permeability of vanadium ions and poor cyclic stability. In this study, a low vanadium ion permeation hybrid membrane is developed by dispersing functionalized silicon carbide nanowires in perfluorinated sulfonic acid (PFSA) matrix and sandwiching an ultrathin porous polytetrafluoroethylene (PTFE) layer. This hybrid membrane greatly improves the performance of VRFB cell exhibiting good Coulombic efficiency (up to 96.2%) and high energy efficiency (up to 87.1%) at 120 mA cm−2, contrasted with the Nafion 212 membrane (91.3% and 79.8%). Furthermore, a single cell with the hybrid membrane possesses ultra-stable cyclicity (1000 cycles, over 233.4 h). This can be assigned to the unique structure of the membrane in which the functionalized nanowires are uniformly dispersed in PFSA matrix to sandwich an ultra-thin PTFE layer to block or lengthen the diffusion paths of vanadium ions, while the functionalized groups on the surface of the rigid nanowires facilitate protons transportation. This strategy of reshaping membrane may serve in relative fields including proton exchange membrane fuel cells and water treatment.

Fluoropolymer impregnated graphite foil as a bipolar plates of vanadium flow battery

Renewable energy in recent years plays an increasingly important role in the energy industry. Therefore, the problem of inventing efficient and affordable energy storage devices is of current importance. Vanadium redox flow battery stands out between a wide range of various chemical sources of electric energy. Discovering the way for optimizing the price of energy storage is one of the most important questions of the mentioned battery. New graphite-polymer composite materials study shows that they may become a replacement for commonly used brittle graphite. The current article presents the study of graphite foil (or flexible graphite) filling with a copolymer of tetrafluoroethylene and vinylidene fluoride F-42 properties. The article uses an implementation approach of putting the fluoropolymer into the pores of graphite foil, which shows a slight decrease in electrical conductivity, while a significant increase in its electrochemical stability in comparison with untreated graphite foil. Testing results of such material as current collectors (or bipolar plates) in a single membrane-electrode assembly of vanadium redox flow battery cell show peak value of discharge power density of 843 mW/cm2, energy efficiency of 78%-79% during cycling at 200 mA/cm2 allowing us to assume the possibility of its successful application in redox flow battery stacks.

A feasible strategy to enhance mass transfer property of carbon nanofibers electrode in vanadium redox flow battery

Carbon nanofibers (ECNFs) electrode possess good electrochemcial reactivity towards the V3+/V2+ and VO2+/VO2+ redox couples in vanadium redox flow battery (VRFB), while its inferior mass transfer property limits the cell power density seriously due to the lower porosity and poorer permeability. In order to improve the mass transfer property, starch based carbon microsphere (SCMS) of a few micrometers is synthesized by a green hydrothermal method and introduced into the electrospun precursor solution. Subsequently, a novel spherical-filament binary carbon nanofibers electrode (ECNFs-SCMS) is constructed by the controllable electrospining technique along with the subsequent heat treatment processes. The novel binary carbon nanofibers exhibits more loose structure, improved hydrophilia, increased oxygen contents and more defects, which result in the simultaneous improvement of electrochemical reaction area, electrocatalytic activity and mass transfer kinetics. The single VRFB cell with ECNFs-SCMS as electrodes shows higher energy efficiency and maximun power density as compared to the one with pure ECNFs electrodes. The results in this work suggest that improving permeability is a feasible strategy to enhance the mass transfer property of carbon nanofibers electrode.

Facile preparation of an oxygen-functionalized carbon felt electrode to improve VO2+/VO2+ redox chemistry in vanadium redox flow batteries

Herein, a new method for the facile introduction of oxygen-containing functional groups on a carbon felt electrode in a short treatment time has been proposed for application in a vanadium redox flow batteries (VRFBs). Benzoyl peroxide (BPO) can produce free radicals by attacking the CC bonds or CH bonds of the carbon felt. The generated unstable free radicals allow further reactions with oxygen to yield oxygen-containing functional groups on the surface of the carbon felt electrode. The electrochemical performance of the BPO-treated carbon felt electrode toward the VO2+/VO2+ redox reaction was superior to that of the pristine carbon felt electrode. Therefore, the VRFB cell employing the BPO-treated carbon felt electrode showed an outstanding energy efficiency of 75% at a current density of 100mAcm−2. This improvement is attributed to the well-known electrocatalytic effects of the oxygen-functionalized surface properties of the BPO-treated carbon felt electrode.

Planar orientation of hydrophilic channels by biaxial deformation of perfluorinated sulfonic acid membranes for vanadium redox flow batteries

Commercially available perfluorosulfonic acid (PFSA) membranes are used as cation exchange membranes for vanadium redox flow batteries (VRFBs) due to their outstanding chemical stability and proton conductivity. However, high vanadium crossover, and expensive production cost of PFSA membranes are considered as limitations for the further commercialization of VRFBs. Here, in order to overcome the issues, PFSA membranes are biaxially stretched for planar orientation of hydrophilic channels with the expanded membrane area over 800%. The area stretching ratio (γ) of PFSA membranes is controlled by water bath temperature, and by the degree of biaxial stretching. As γ increases, vanadium permeability and proton conductivity, known as thickness independent material properties, decrease, and then reach constant values over γ ~1.25. Thus, both of the hydrophilic channel orientation and the membrane thickness matter for the VRFB cell performance. With thick PFSA membranes, a VRFB cell is not operated at high current density, but with the biaxially 827% area expanded Nafion 117, a VRFB cell shows stable efficiencies even at high current density and better capacity retention (82.9%) than a thin Nafion 211 (57.8%) during the long-term cycling. This planarly oriented morphology by biaxial stretching offers an efficient way to utilize the expansive PFSA membranes.

Boron-functionalized carbon felt electrode for enhancing the electrochemical performance of vanadium redox flow batteries

Herein, boron-doped carbon felt (B-CF) was proposed as a promising electrode for ensuring the outstanding electrochemical performance of vanadium redox flow batteries (VRFBs). Boron-functional groups can be successfully introduced onto carbon felt (CF) via NH4BF4 treatment. The hydrophobic nature of CF is changed to hydrophilicity via the incorporation of boron-functional groups, resulting in excellent affinity with the electrolytes of VRFBs. A VRFB cell containing B-CF exhibits higher energy efficiency (80.56%) than that of CF (63.40%) at 100 mA cm−2 current density. This improvement is attributed to the enhanced electrocatalytic properties of B-CF toward VO2+/VO2+ and V2+/V3+ redox reactions.

Vanadium Redox Flow Battery State of Charge Estimation Using a Concentration Model and a Sliding Mode Observer

Vanadium redox flow batteries are very promising technologies for large-scale, inter-seasonal energy storage. Tuning models from experimental data and estimating the state of charge is an important challenge for this type of devices. This work proposes a non-linear lumped parameter concentration model to describe the state of charge that differentiates the species concentrations in the different system components and allows to compute the effect of the most relevant over-potentials. Additionally, a scheme, based on the particle swarm global optimization methodology, to tune the model taking into account real experiments is proposed and validated. Finally, a novel state of charge estimation algorithm is proposed and validated. This algorithm uses a simplified version of previous models and a sliding mode control feedback law. All developments are analytically formulated and formally validated. Additionally, they have been experimentally validated in a home-made single vanadium redox flow battery cell. Proposed methods offer a constructive methodology to improve previous results in this field.

Vanadium Redox Flow Batteries: A Review Oriented to Fluid-Dynamic Optimization

Large-scale energy storage systems (ESS) are nowadays growing in popularity due to the increase in the energy production by renewable energy sources, which in general have a random intermittent nature. Currently, several redox flow batteries have been presented as an alternative of the classical ESS; the scalability, design flexibility and long life cycle of the vanadium redox flow battery (VRFB) have made it to stand out. In a VRFB cell, which consists of two electrodes and an ion exchange membrane, the electrolyte flows through the electrodes where the electrochemical reactions take place. Computational Fluid Dynamics (CFD) simulations are a very powerful tool to develop feasible numerical models to enhance the performance and lifetime of VRFBs. This review aims to present and discuss the numerical models developed in this field and, particularly, to analyze different types of flow fields and patterns that can be found in the literature. The numerical studies presented in this review are a helpful tool to evaluate several key parameters important to optimize the energy systems based on redox flow technologies.

Vanadium Flow Battery Electrochemistry and Fluid Dynamics Model with in-Situ Current Distribution Validation

It has been estimated that the high penetration of renewable electricity generation (68%-73% from solar and wind) could be possible in the United States by 2050. To achieve this goal, large-scale energy storage technologies will play important role. Energy storage technologies can help to improve electricity stability, flexibility, reliability and resilience on the grid. Among different energy storage methods vanadium redox flow batteries (VRFBs) have been a recent focus of interest due to distinct advantages, i.e., flexibility and scalability, high columbic efficiency, and long cycle life. However, high system cost is a main challenge for widespread commercialization of VRFBs. Although the component costs (membrane cost and chemical cost) tend to dominate the overall system costs, it is possible to decrease costs by improving electrolyte utilization and system efficiency. This can be achieved through increasing vanadium solubility in the solvent, modifying membrane and minimizing crossover, facilitating electrochemical kinetics, improving mass transport and reducing parasitic pump losses. However, VRFB is a complex system with multiple interrelated parameters (mass transport and electrochemical reactions) affecting electrochemical cell performance; these interrelated parameters are difficult to disentangle experimentally. A comprehensive and suitably validated mathematical simulations can both help to understand complex phenomena inside the VRFB cell and provide practical knowledge for controlling and optimizing VRFB systems. In this study, three dimensional, steady-state multi-physics model is developed for VRFB strip cell architecture under the dilute solution theory assumption. The simulation domain includes membrane, electrodes, flow plates and current collectors. Continuum equations: conservation of mass, momentum, species and charge coupled with Butler-Volmer kinetics are employed. Polarization curve analysis and fully segmented, printed circuit board (PCB)-based, localized current distribution measurements are employed to validate the mathematical model. Good agreement is achieved between the model predictions and the experimental measurements. The model successfully predicts not only the charge-discharge polarization curve but also the current distribution along the channel. Figure 1

Highly Energy-Efficient Vanadium Redox Flow Batteries with Thermo-Chemically Activated Graphite Felt Electrodes

The Vanadium Redox Flow Battery (VRFB) is a promising energy storage technology for large scale stationary applications that require a long cycle life of over 10 years. The specific feature of VRFB is the slower kinetics of redox reactions (V2+/V3+) on the negative electrode (NE) as compared to the kinetics of the redox reaction (VO2 + /VO2+) on the positive electrode (PE) and poor kinetic reversibility.. The commonly used electrodes for VRFBs are graphite felt electrodes (GFE). One of the main challenges facing these GFEs is their activation that enhances a rate of redox reactions due to the increase of GFE wettability and surface area. Another challenge is capability to maintain GFE activation over cycling.In this work, we report on thermal and thermo-chemical activation of GFEs which leads to the formation of functional groups (carboxyl C=O, phenolic C-O, and adsorbed O or H2O for the enhancement of the electrode wettability and active surface area. The physicochemical characterization of the activated GFEs was performed using X-ray photoelectron spectroscopy (XPS) and contact angle measurements. The electrochemical study was conducted by cyclic voltammetry (CV) measurements in 0.2M VOSO4/2M H2SO4 at 1 mV/s and cycling tests (50 cycles, three tests for every GFE) in a commercial 9cm2 VRFB ( Standard Energy Corp.) using a charge/discharge current density of 80 mA/cm2 at 20oC and a commercial vanadium electrolyte 1.6M [V]/2M H2SO4. The increase of temperature of GFE heat treatment of GFEs from 400 to 500oC resulted in the growth of the energy efficiency (EE) of VRFBs with such electrodes from 81.3 to 87.2%, respectively, due to the increase of adsorbed oxygen or water from 1.6 to 8.72% and C-O (C-OH) groups from 0.49 to 2.09%, respectively and wettability (contact angle (CA) decreases from 78.7 to 65.1o). Analysis of CVs of the redox reaction VO2 + /VO2+ shows the decrease of the peak of potential separation ΔEp (Epa-Epc) from 0.357 to 0.345 V and the peak of current ratio (Jpa/Jpc) from 1.406 to 1.26, indicating lower polarization due to the increase of the electrode surface area, acceleration and reversibility of these redox reaction, respectively (Table 1). The proposed additional treatment of the heat treated GFE at 400oC (GFE400) in strong oxidants H2O2, H2SO4 and HNO3 for the decomposition of C=O and the enhancement of the content C-O groups and GFE wettability didnt result in the performance improvement (VRFB with GFE400+10%H2O2 - energy efficiency of 78%).The thermal treatment of GFE at 500oC demonstrated improvement of VRFB cell performance, namely growth of energy efficiency to 87.2% and VE to 90.1%, % due to the increase of wettability and active surface area of GFEs. Figure 1

Polypyrrole thin film composite membrane prepared via interfacial polymerization with high selectivity for vanadium redox flow battery

In order to improve the selectivity of porous membrane for vanadium redox flow battery (VRB). A polypyrrole (PPy) thin film composite (TFC) membrane was prepared via interfacial polymerization (IP) method and investigated for VRB application. The optimized PPy TFC membrane has shown both low VO2+ permeability and low area resistance compared to that of commercial Nafion 115 membrane. The VRB cell assembled with PPy TFC membrane shows a coulombic efficiency (CE) of 98.1% and energy efficiency of 81.0% at 80 mA cm−2, which is 2.0% and 6.3% higher than that of Nafion 115 membrane, respectively. Furthermore, 93 cycles charge-discharge test proves that the PPy TFC membrane is very stable and the CE decrease rate is only 0.4% for per-cycle on average. Considering the high selectivity, facile preparation procedure and high stability of PPy TFC membrane, it is thus an ideal system for VRB application to overcome the trade-off between vanadium ions permeability and proton conductivity.

Influence of electrode design parameters on the performance of vanadium redox flow battery cells at low temperatures

Performance of electrochemical batteries suffers at cold temperatures. In this paper, we report on an experimental investigation of sensitivity of the vanadium redox flow battery (VRFB) to the cell operating temperature. Experiments have been carried out on a VRFB cell with an active area of 426 cm2 at cell temperatures of 25, +10 and −10 °C. Measured parameters include cycle efficiency and discharge capacity at three current densities and two flow rates, peak power and cell impedance obtained through electrochemical impedance spectroscopy (EIS) studies. The influence of electrode compression and electrode thickness has also been studied through comparative experimental protocols. Results indicate significant loss of discharge capacity and cell efficiency at low temperatures; this can be attributed to substantial increase in ohmic resistance and even higher increase in charge transfer resistance of the cell. Two methods known to reduce cell resistance, namely, increasing compression ratio of the electrode and using thinner electrode, have led to restoring much of the lost discharge capacity and energy efficiency. Optimizing the electrode parameters such as its compression, permeability and thickness for industrial scale cells, together with possible use of electrocatalysts, seems to be a promising way of improving low temperature performance of VRFB cells.

Numerical study on serpentine design flow channel configurations for vanadium redox flow batteries

Abstract A flow channel is a significant factor determining the performance of vanadium redox flow batteries (VRFBs). In this study, we use a three-dimensional numerical model to investigate the complexities of the fluid dynamics and electrochemical reactions of VRFBs considering a number of serpentine design flow channels. The results show that cell voltage increases with the reduction in the number of flow channels and increase in the electrolyte flow rate during the discharging process. The higher electrolyte flow rate significantly improves the uniformity of vanadium concentration at both electrodes. We observe that the pressure drop in the VRFB cell decreases with increasing number of flow channels. Moreover, the electrolyte disturbance and flow resistance reduces when the number of flow channels increases, which lead to a smaller pressure drop. As a result, the pumping power derived from the pressure drop decreases with the increase in the number of flow channels. The maximum power-based efficiency calculated for the quadruple serpentine design flow channel at an electrolyte flow rate of 60 ml/min is 97.18%. This serpentine design shows the lowest pumping power and achieves the optimum power-based efficiency. The proposed numerical approach provides comprehensive insights into serpentine design flow channel configurations for VRFBs.