All-vanadium Redox Flow Battery Research Articles

Numerical simulation of all-vanadium redox flow battery performance optimization based on flow channel cross-sectional shape design

This paper numerically investigates optimizing trapezoidal flow channel cross-sectional shapes to improve all‑vanadium redox flow battery performance. A 3D steady-state multiphysics model coupling fluid dynamics, mass transfer, and electrochemistry was developed in COMSOL. Eight trapezoidal and one rectangular cross-section serpentine flow fields were simulated at varied flow rates. Results showed the TCS-T06 design reduced pressure drop by 12 % and pump power by 12 % versus the RCS. The concentration distribution of VO2+ was also improved, enhancing mass transfer. At 60 mA/cm2, TCS-T06 achieved 0.9 % higher pump power-based voltage efficiency. The optimized trapezoidal cross-section was proven to minimize losses, improve electrolyte distribution, and enhance VRFB performance. This work provides guidance for optimizing trapezoidal flow channel cross-sections to improve VRFB performance via enhanced mass transfer and reduced pressure drop.

Study of 10 kW Vanadium Flow Battery Discharge Characteristics at Different Load Powers

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

In situ growth of covalent organic framework on graphene oxide nanosheet enable proton-selective transport in flow battery membrane

Perfluorosulfonic acid (PFSA) is the most widely used membrane material for all-vanadium redox flow batteries (VRFB). However, severe vanadium ion permeation of PFSA membranes remains to be solved. In this work, a series of PFSA-based composite membranes are prepared by introducing two-dimensional continuous covalent organic framework (COF) to achieve enhanced performance. Two dimensional continuous Schiff base network-type COFs (GO/SNW) are synthesized by using the two-dimensional multi-functionalized surface of graphene oxide (GO) as a reaction site. Compared to the original form of agglomerated particles, two-dimensional continuous structure obtained a larger vanadium resistance area. Comparing to conventional PFSA membranes, the special pores of COF have a size sieving mechanism for selectively proton transfer, leading to simultaneously enhancement of proton conductivity and vanadium barrier property. VRFB assembled with PFSA-GO/SNW-7 showed high Coulombic efficiency (CE: 97.47%–98.18 % VS PFSA: 80.73%–91.92 %) and energy efficiency (EE: 93.04%–85.71 % VS PFSA: 77.53%–81.78 %) at 40–120 mA cm−2. In addition, there is no significant decrease in the efficiency of battery assembled with PFSA-GO/SNW-7 after 800 cycle (than 650 h) tests. This work provides a new direction in the design of fillers for mixed matrix membranes.

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

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

A Review of Capacity Decay Studies of All-vanadium Redox Flow Batteries: Mechanism and State Estimation.

As a promising large-scale energy storage technology, all-vanadium redox flow battery has garnered considerable attention. However, the issue of capacity decay significantly hinders its further development, and thus the problem remains to be systematically sorted out and further explored. This review provides comprehensive insights into the multiple factors contributing to capacity decay, encompassing vanadium cross-over, self-discharge reactions, water molecules migration, gas evolution reactions, and vanadium precipitation. Subsequently, it analyzes the impact of various battery parameters on capacity. Based on this foundation, the article expounds upon the significance of battery internal state estimation technology. Additionally, the review also summarizes domestic and international mathematical models utilized for simulating capacity decay, serving as a valuable reference for future research endeavors. Finally, through the comparison of traditional experimental methods and mathematical modeling methods, this article offers effective guidance for the future development direction of battery state monitoring. This review generally overview the problems related to the capacity attenuation of all-vanadium flow batteries, which is of great significance for understanding the mechanism behind capacity decay and state monitoring technology of all-vanadium redox flow battery.

Highly ion-selective sulfonated poly (4,4′-diphenylether-5,5′-bibenzimidazole) membranes for vanadium redox flow battery

Renewable energy requires long-duration energy storage technologies, of which vanadium flow battery is regarded as the ­most suitable candidate for safe and long-duration energy storage ­applications. However, vanadium flow batteries still suffer from capacity decay and low power density, which arise from membrane degradation and high resistance. Herein, a sulfonated poly (4,4′-diphenylether-5,5′-bibenzimidazole) (SOPBI) membrane is reported for use in vanadium redox flow batteries. The prepared SOPBI membranes show an area resistance of 0.63 Ω cm2 at room temperature after doped with 3 M H2SO4. Moreover, membranes with 3 M H2SO4 doping exhibit tensile stress at break of 15.1 MPa. Benefiting from the SOPBI membrane, the all-vanadium redox flow battery delivers a superior energy efficiency of 77.7% at 140 mA cm−2 while operating stably at a current density of 120 mA cm−2 for 200 cycles.

Revealing the Effects of Impurities among Phosphoric Acid Electrolytes for the Stability of All-Vanadium Redox Flow Batteries

Revealing the Effects of Impurities among Phosphoric Acid Electrolytes for the Stability of All-Vanadium Redox Flow Batteries

Robust Polyaniline-silica@polypropylene for High-Performance, High-Capacity Retention All-Vanadium Redox Flow Battery

Robust Polyaniline-silica@polypropylene for High-Performance, High-Capacity Retention All-Vanadium Redox Flow Battery

Synchronized dual-modified graphite felt electrodes for all-vanadium redox flow batteries with high power density and ultra-long lifespan

All-vanadium redox flow battery (VRFB) with high safety and long lifespan is recognized as promising large-scale energy storage system for intermittent renewable energy sources. However, the large-scale development of VRFBs is still hindered by untreated graphite felt electrodes with poor electrocatalytic performance. In this work, we report a modified GF electrode with synchronous etching of the electrode surface and loading of nitrogen-rich biomass carbon, which allows the formation of pores on the GF electrode surface while introducing enriched nitrogen as active sites. The obtained electrode N-EGF exhibits superior wettability, and the structural modification also contributes to the catalytic activity and reversibility of the vanadium redox reaction. The voltage efficiency (VE), energy efficiency (EE) and discharge capacity of the VRFB single cell with N-EGF are improved at current densities from 80 to 280 mA cm−2. Significantly, the power density of the VRFB achieves a peak value of 804.6 mW cm−2. In addition, the N-EGF exhibits excellent stability and ultra-low EE decay rate (0.0018 %) after long-term cycling operation (1285 cycles) at a current density of 200 mA cm−2.

Experimental Validation of Side Reaction on Capacity Fade of Vanadium Redox Flow Battery

The all-vanadium redox flow battery (VRFB) is widely regarded as the most effective solution for mitigating the intermittent nature of renewable energy sources and simultaneously achieving “carbon neutrality goals.” Nevertheless, the battery’s overall performance is adversely affected by capacity loss resulting from side reactions, hence constraining its viability for usage in large-scale energy storage systems. This study proposes a novel approach that aims to minimize side reactions and mitigate capacity fade by employing an appropriate charge cut-off voltage mechanism. The experiment centers around the examination of performance indicators, including battery charge/discharge capabilities, internal resistance, capacity retention rate, and efficiency, for analytical purposes. The findings indicate that by setting the charge cut-off reference voltage at 1.65 V, the battery’s capacity can be sustained at 61.76% after 60 cycles. When the charge cut-off voltage is raised by increments of 0.1 V and 0.15 V, the corresponding reductions in battery capacity amount to 1.74% and 5.16% respectively. The aforementioned findings emphasize the significance of considering the effect of side reactions on battery capacity and implement that mechanism can significantly enhance the battery’s overall performance.

Hydropower-Centric Renewable Integration: Advancements in Sustainable VRFB Technology for Energy Storage Solutions

The urgent need to address climate change has prompted a shift from fossil fuels towards green energy sources, such as hydropower for reducing greenhouse gas emissions. All-vanadium redox flow battery (VRFB) is suitable for large-scale energy storage, aimed at stabilizing the renewable energy output. However, VRFB faces challenges in terms of membrane design, electrode performance, and environmental impact. This article provides a comprehensive review of key components in VRFB technology, namely electrodes, membranes, and bipolar plates, discussing their working principles, designs, and recent research findings. The critical role of Nafion® membranes is explored, as they impact both performance and environmental implications. Several strategies are discussed to mitigate the environmental impact, such as alternative membrane materials and protective coatings. The article emphasizes the potential development of VRFB systems as an adaptable and effective energy storage solution for hydropower applications while acknowledging the necessity of sustainable practices for their broader adoption.

Tungsten oxide nanostructures for all-vanadium redox flow battery: Enhancing the V(II)/(VIII) reaction and inhibiting H2 evolution

Vanadium redox flow batteries (VRFBs) offer remarkable performance capabilities for renewable energy power plants. However, the kinetics of the VRFBs' redox reactions are slow and the efficiency is low due to parasitic reactions such as the hydrogen evolution reaction (HER). In this work, to overcome these limitations, the effect of modifying the carbon cloth electrode with tungsten oxide nanowires, nanoflakes, and nanospheres prepared was elucidated for the negative half-cell reaction V(II)/V(III). The physical and chemical properties of those nanostructures were characterized using FESEM, XPS, XRD, FTIR, and contact angle measurements. The effect of the catalyst loading and structure, pH and composition of the synthesis solution, and the presence of binder on catalytic activity was evaluated using CV and EIS. The results showed that the effective loading of all three structures is ~2 mg/cm2, with all of the structures showing a significant enhancement of the V(II)/(VIII) reaction kinetics in comparison to the untreated carbon cloth and greater stability than the thermally treated carbon cloth. The tungsten oxide nanostructures prepared at pH 2 showed the best catalytic activity, with the suppression of hydrogen evolution reaction (HER) being inversely proportional to the number of defects. Tungsten oxide nanoflakes prepared at pH 2 using water as a solvent exhibited the optimum balance between promoting the V(II)/(VIII) reaction kinetics and suppressing the HER. The performance evaluation in a two-electrodes setup of all‑vanadium RFB revealed that the WNFs structure have the highest charge/discharge capacity and energy efficiency at a relatively high current density of 60 mA/cm2 due to its improved kinetics.

Effect of Parasitic Gas Evolution Reactions on the All-Vanadium Redox Flow Battery Performance

All-vanadium redox flow batteries (VRFB) as the most promising candidates for large-scale energy storage can overcome the inherent defect of natural energy, such as intermittent and fluctuating, et al. During the operation of VRFB, the parasitic gas evolution reactions (GERs) are unavoidable due to thermodynamic limitation, which yet will cause a series of issues, such as imbalance of state of charge (SOC), graphite electrode degradation, security risk, etc. To have a deeper understanding of the parasitic GERs in VRFB, the present work developed a transient, multidimensional, multiphysics VRFB model coupling the multiphase species transport and electrochemical reactions. The model was validated with in-house experimental data and published literature, which showed great consistency. Following, the temporal-spatial characteristics of GERs and their competition with main cell reactions were analyzed in detail under different charging current densities and electrolyte flowrate. The results showed that the rate of hydrogen evolution reaction (HER) at the negative electrode is several magnitudes higher than that of the oxygen evolution reaction (OER) at the positive electrode. Besides, the HER happens during the whole charge-discharge process since the activation overpotential remains negative while the OER occurs only at the end of the charging process under high charging current density. It is notable that the HER mainly occurs in the region near the bipolar plate and increases with increasing charging current density. Since HER is favored thermodynamically over the reduction reaction of trivalent vanadium ions, the activation overpotential of the HER remains much higher than that of the main cell reaction during the whole charge-discharge process, albeit the volumetric current density for hydrogen evolution accounts for only part of the overall current due to the limitation of the reaction kinetics. The HER increases with the SOC and causes a SOC imbalance of 0.54% within 10 charge-discharge cycles, thereby accounting for an 11.0% degradation in the VRFB’s capacity. A high current density decreases the amount of hydrogen generated during a charge-discharge cycle yet also causes hydrogen accumulation in the porous electrode due to faster hydrogen generation. The present work takes a comprehensive and detailed discussion about the characteristics of parasitic gas evolution reactions and their effect on the VRFB performance, which gives a deeper understanding of the energy loss mechanism of VRFB for its development and optimization. Figure 1

Manufacturing Strategies for Engineering Carbon Electrodes Via Non-Solvent Induced Phase Separation

Porous electrodes are at the core of emerging electrochemical systems and tuning the electrode properties is critical to overcome system-specific limitations. To meet the stringent performance and cost requirements, there is a need for tailored microstructures generated through inexpensive and scalable synthesis methods with precursors originating from reliably-sourced, globally-abundant feedstocks. To this end, we recently introduced a manufacturing route using non-solvent induced phase separation (NIPS), yielding porous carbon electrodes with multimodal and interconnected porosity. The synthesized NIPS electrodes demonstrated a beneficial trade-off between transport properties (permeability, mass transfer) and electrochemically active surface area (ECSA) resulting in high performance in iron and all-vanadium redox flow batteries (RFBs)[1,2]. Moreover, NIPS manufacturing offered control over electrode characteristics (pore size, surface area) which are critical parameters for broader electrochemical devices. Besides its use for RFB application, we hypothesize that the electrode morphologies resulting from NIPS could be applied to a broader range of electrochemical systems employing porous electrodes. Consequently, here we focus on extending the library of electrode microstructures achievable via NIPS through the alteration of simple process parameters.In this presentation, I will discuss our latest advances on the bottom-up manufacturing of porous electrodes using NIPS targeting porosity gradients and high ECSA materials. For the former, we introduce the use of a control layer, casted on top of the NIPS polymer solution at the interface with the coagulation bath, thereby altering the rate of the phase separation process. We investigate various process parameters such as the composition, viscosity, and thickness of the control layer and assess their effect onto the resulting microstructures. The NIPS method assisted by a control layer generates porosity gradients, resulting in a slight increase of the electrode ECSA at the cost of a higher pressure drop. To further increase the ECSA of the prepared electrodes, we also propose nano-patterning approaches to significantly enhance ECSA through addition of nano-scale porosity without compromising the pressure drop through the porous structure. Finally, both porosity gradient and nano-patterned NIPS electrodes are tested in a all-vanadium redox flow cell to extract microstructure-performance relationships. Despite being in its early technological stage, this work illustrates the versatility of NIPS to manufacture porous electrodes through a very broad microstructural design space.

Electrode Imbibition and Surfactant Interactions with Vanadium Flow Battery Electrolytes

Redox flow batteries (RFB) are a critical technology for stationary grid-scale energy storage, with potential usage with intermittent power sources, such as wind and solar. RFBs are attractive for long-duration energy storage because the anolyte and catholyte are stored separately external to the electrochemical reactor. Separating the electrolytes and the electrochemical cell decouples energy and power densities, unlike batteries that store charge in the solid-state, such as Li-ion, Pb-acid, or Ni-Cd. A standard RFB chemistry is the all-vanadium redox flow battery (VRFB), which utilizes the four oxidation states of vanadium, with V2+, V3+, V4+, and V5+. Recently our group found that adding small amounts of sodium dodecyl sulfate (SDS) to a VFRB increased the kinetics of the V2+ to V3+oxidation.Furthermore, surfactants play essential roles in battery manufacturing and operation. Surfactants can change metal oxide crystal structure, inhibit dendrite growth, limit corrosion, and prevent nanoparticle agglomeration. Surfactants are never wholly removed during manufacturing and can be present during battery operation. Therefore, it is crucial to understand how surfactants impact battery performance and their effect on the materials.This talk describes SDS's equilibrium surface properties and adsorption characteristics at the liquid−air and liquid-solid interfaces, thus providing insights into the interactions of SDS with a VFRB electrolyte. Experiments focusing on the effects of sulfuric acid and vanadium ions on SDS's equilibrium surface tension and critical micelle concentration (CMC) were completed. The Szyszkowski equation is used to calculate SDS's adsorption parameters, such as interfacial surface excess, Γsz [mol/m2], the surface excess at the saturated interface, Γ∞ [mol/m2], the minimum molecular area in the adsorption layer at the saturated interface, Amin [nm2], and the Gibbs free energy of adsorption, ΔGads [kJ/mol]. Furthermore, an examination of the spontaneous imbibition of the VFRB electrolyte with SDS into a porous carbon electrode is presented. The microstructure of porous systems, interfacial tension, and fluid−solid interactions controls the capillary-driven flow and is vital in multiphase flow in porous media. Therefore, understanding SDS's effects on the VFRB electrolyte in an electrode is critical to understanding the electrochemical reactions and molecular interactions occurring.This work was supported as part of the Breakthrough Electrolytes for Energy Storage and Systems (BEES2), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0019409.

Effect of Anionic, Cationic, and Non-Ionic Surfactants on the Structural Stability and Morphology of Perfluorinated Sulfonic Acid Membranes

Redox flow batteries (RFB) are a critical technology for stationary grid-scale energy storage, with potential usage with intermittent power sources, such as wind and solar. RFBs are attractive for long-duration energy storage because the anolyte and catholyte are stored separately external to the electrochemical reactor, which allows the RFBs to be modular and stationary. Separating the electrolytes and the electrochemical cell decouples energy and power densities, unlike batteries that store charge in the solid-state, such as Li-ion, Pb-acid, or Ni-Cd. A standard RFB chemistry is the all-vanadium redox flow battery (VRFB), which utilizes the four oxidation states of vanadium, with V2+, V3+, V4+, and V5+. Recently, new electrolytes are being studied in energy storage devices. Such as the first redox flow battery to utilize microemulsions as the electrolyte.Microemulsions are a breakthrough electrolyte for energy storage (BEES) that is emerging as an alternative to traditional RFB electrolytes because they produce thermodynamically stable, homogeneous solutions of polar and non-polar molecules. The stabilization of oil and water solutions allows microemulsion electrolytes to accommodate organic redox species with fast electron transfer rates that are not soluble in the aqueous phase while still offering the high conductivity of an aqueous salt electrolyte. Microemulsions consist of two immiscible phases stabilized by a surfactant, a non-polar "oil" phase, solubilizing the redox material, and the polar phase, which typically consists of an aqueous brine that provides charge balance and conductivity. Additionally, if the redox molecule was a non-polar liquid, it could serve as the entire oil phase, maximizing the energy density. An attractive property of a microemulsion electrolyte is that each component can be environmentally and biologically safe. For example, the aqueous phase only contains salt and water, and surfactants are found in many household, personal, and food products. Furthermore, some redox materials investigated in our lab are vitamins such as menadione (vitamin K3) and tocopherol (vitamin E).This talk describes the structural, mechanical, and morphological studies of surfactants' effects on perfluorinated sulfonic acid membranes. Small-angle X-ray scattering monitored the morphological changes as a function of surfactant concentration and soaking time, revealing how the surfactant penetrated and altered the polymer membrane. FTIR and NMR spectroscopy are also employed, providing insight into any polymer membrane degradation or dissolution. We demonstrate that surfactant choice is not only crucial to the stability of the microemulsion used as an electrolyte but can ultimately destroy the separator in a redox flow battery.This work was supported as part of the Breakthrough Electrolytes for Energy Storage and Systems (BEES2), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0019409.

Scaling up Electrode Manufacturing with Non-Solvent Induced Phase Separation Technology

Grid-scale energy storage technologies must be deployed at a massive scale to balance the mismatch between energy generation using renewable technologies and demand. Redox flow batteries are an emerging technological option for large-scale and multi-hour electrochemical energy storage thanks to their ability to decouple energy and power1. Despite their intrinsic advantages, the current elevated costs of this technology hinders commercialization2. To improve cost competitiveness, research efforts have focused on developing novel electrolyte chemistries and optimized reactor concepts. To the latter, optimizing the porous electrode microstructure and surface chemistry offers a promising pathway to increase the performance of flow batteries. However, porous electrodes design is challenging as they must fulfil contradictory requirements such as providing high surface area for electrochemical reactions, facilitating mass transport of reactive species, and maintaining low operational pressure drop. Furthermore, state-of-the-art porous electrodes have been repurposed from other mature electrochemical technologies but have not been tailored for the unique requirements of redox flow batteries3.Non-solvent induced phase separation (NIPS) has been recently introduced as a versatile method to synthesize porous structures suitable for RFBs with unique properties, which are unattainable with current fibrous materials4,5. Drawing inspiration from membrane fabrication techniques, we reengineered the method for the synthesis of porous electrodes for use in redox flow batteries. The porous electrodes synthesized with NIPS were tested in a single-electrolyte cell configuration and then in an all-vanadium redox flow battery, showing promising electrochemical performance in comparison with existing commercial fibrous carbon materials. In this presentation, I will discuss our current efforts to scale up the NIPS method to manufacture electrodes at industrial scale. We believe that non-solvent induced phase separation is a cost-effective alternative to traditional carbon fibrous materials thanks to the few simpler steps required for the electrode preparation. Based on technoeconomic modeling, we estimate that the production cost of the NIPS electrodes can be less than half of the production costs of traditional carbon fibrous electrodes6. Moreover, the phase separated electrodes do not require post-manufacturing heat treatment to increase the surface area and wettability, which further translates into savings on energy costs. In this project, we aspire to scale-up the NIPS materials to a final size, after carbonization, of 30·30 cm2 while retaining similar microstructural and electrochemical performance properties as in laboratory scale. We perform a suite of microscopy, spectroscopic and flow cell diagnostics to correlate the electrode microstructure, surface chemistry and device performance. In this presentation, I will discuss the scalability of the method, reproducibility based on statistical analysis of sample properties and performance, and finally electrochemical performance on two flow battery chemistries.References Markard, J. (2018). The next phase of the energy transition and its implications for research and policy. Nature Energy, 3(8), 628-633.Darling, R. M. (2022). Techno-economic analyses of several redox flow batteries using levelized cost of energy storage. Current Opinion in Chemical Engineering, 37, 100855.Forner-Cuenca, A., and Brushett, F. R. (2019). Engineering porous electrodes for next-generation redox flow batteries: recent progress and opportunities. Current Opinion in Electrochemistry, 18, 113-122.Wan, C. T. C., Jacquemond, R. R., Chiang, Y. M., Nijmeijer, K., Brushett, F. R., & Forner‐Cuenca, A. (2021). Non‐Solvent Induced Phase Separation Enables Designer Redox Flow Battery Electrodes. Advanced Materials, 33(16), 2006716.Jacquemond, R. R., Wan, C. T. C., Chiang, Y. M., Borneman, Z., Brushett, F. R., Nijmeijer, K., & Forner-Cuenca, A. (2022). Microstructural engineering of high-power redox flow battery electrodes via non-solvent induced phase separation. Cell Reports Physical Science, 3(7), 100943.Minke, Christine, Ulrich Kunz, and Thomas Turek. "Carbon felt and carbon fiber-A techno-economic assessment of felt electrodes for redox flow battery applications." Journal of Power Sources342 (2017): 116-124.

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

Harnessing redox flow batteries for industrial applications: Opportunities and future directions

This paper provides a brief introduction to flow battery technology as an energy storage device, with a particular focus on the all-vanadium redox flow battery (VRFB). These rechargeable batteries are well suited for reducing greenhouse gas (GHG) emissions for small commercial or multi-family residential dwellings. This paper will explore, in greater depth, the specific industrial and marketing mechanisms by which a storage battery, that does not generate electricity, is able to actually reduce CO2 gas emissions, while at the same time benefiting all stakeholders. The startup company, Ashlawn Energy, is discussed by way of example of the process being followed to push this technology into the mass market, and thus realize this technology's full potential.

Heteroatom co-doped biomass carbon modified electrodes for all-vanadium redox flow batteries with ultra-low decay rate of energy efficiency

The intermittent nature of renewable energy calls for advanced energy storage systems, of which all-vanadium redox flow batteries (VRFBs) are recognized as the most promising long-duration energy storage devices. The most common electrode for VRFBs is graphite felt (GF), however with poor hydrophilicity and weak electrochemical activity, making it difficult to be a perfect electrode. In this work, we report a nitrogen-phosphorus co-doped biomass carbon modified GF (NP-GF), in which the introduction of cross-linking agents enhances the linkage between the carbon material and the GF. With excellent electrolyte wettability and electrochemical catalytic activity, the NP-GF electrode exhibits enhanced electrochemical activity and reversibility for VO2+/VO2+ and V2+/V3+ in electrochemical tests. The coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) are all boosted at current densities of 80–280 mA cm−2 in VRFB single cell tests assembled with NP-GF. The power density of the VRFB reaches a peak of 757.0 mW cm−2. Furthermore, the VRFB has an extremely low EE decay rate per cycle (0.0018 %), demonstrating superior electrochemical performance stability.