Bromine Redox 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

Function regionalized catalyst promoted bromine redox kinetics for bromine-based flow battery

Bromine-based flow batteries are considered as ideal large-scale energy storage devices, due to their attractive high energy density and low cost. However, the inferior redox activity of the Br3−/Br− couple leads to limited power density, which cannot meet the practical application requirements. Herein, a flexible catalytic electrode is constructed by interweaving a nitrogen-doped porous carbon (NPC) coated TiO2 (TiO2@NPC) nanofiber, via electrospinning technique. In the electrode, the NPC component with superior affinity to the reactant Br−, could assistant rapid charge transfer, and facilitate the conversion from Br− to Br3−, which plays an excellent catalytic function. With a stronger adsorption for the oxidation product Br3− than NPC, the TiO2 component can transfer Br3− from NPC, releasing the catalytic active sites on NPC timely and enabling the reaction smoothly proceeded. Consequently, the regional differentiation strategy of the catalysis and adsorption functions significantly boosts the redox kinetic of the bromine chemistry. The Zinc-bromine flow batteries equipped with TiO2@NPC can run 200 cycles stably at 80 mA cm−2, with the voltage efficiency and energy efficiency of 82.8 % and 81.6 %, respectively. This design provides a brand-new improvement strategy for bromine cathode from the perspective of accelerating the reaction rate-determining step.

Bifunctionally Electrocatalytic Bromine Redox Reaction by Single-Atom Catalysts for High-Performance Zinc Batteries.

Aqueous zinc-bromine (Zn||Br2) batteries are regarded as one of the most promising energy storage devices due to their high safety, theoretical energy density, and low cost. However, the sluggish bromine redox kinetics and the formation of a soluble tribromide (Br3 -) hinder their practical applications. Here, it is proposed dispersed single iron atom coordinated with nitrogen atoms (FeN5) in a mesoporous carbon framework (FeSAC-CMK) as a conductive catalytic bromine host, which possesses porous structure and electrocatalytic functionality of FeN5 species for enhanced confinement and electrocatalytic effect. The active FeN5 species can fix the bromine (Br0) species to suppress the formation of Br3 - effectively and bifunctionally catalyze the bromide (Br-)/Br° conversion. These free up 1/3 Br- locked by Br3 - complexing agent for enhanced bromine utilization efficiency and conversion reversibility. Accordingly, the Zn||Br2 battery with FeSAC-CMK delivers an impressive specific capacity of 344 mAh g-1 at 0.2 A g-1 and superior rate capability with 164 mAh g-1 achieved even at 20 A g-1, much higher than that of inactive CMK (262 mAh g-1 at 0.2 A g-1; 6 mAh g-1 at only 8 A g-1). Furthermore, the battery demonstrates excellent cycling performance of 88% capacity retention after 2000 cycles.

Effect of Hydrogen Pressure on The Mass Transfer Characteristics of Hydrogen-Bromine Flow Battery Electrodes

The mass transfer characteristics of porous carbon electrodes in the liquid side of a hydrogen bromine redox flow battery (H2-Br2 RFB) were investigated under compressive deformation caused by operation at elevated hydrogen pressure. Here, flow cell measurements of permeability and micro-particle image velocimetry (μPIV), alongside electrochemical measurements of capacitance and battery discharge were used to characterize changes in the liquid side electrode compression, in-plane liquid flow, accessible surface area, polarization, and mass transfer scaling brought by hydrogen pressure. We studied two electrode types with different structures, carbon paper and carbon cloth, in untreated well as heat-treated forms in the pressure range 0–8 bar H2. It was found that pressure-induced compression of the liquid side electrode increases the accessible area of untreated electrodes, with little effect on heat-treated electrodes, but decreases the electrochemical performance of the battery in all cases by increasing the ohmic resistance of the cell and decreasing the mass transfer coefficient of the porous electrode. Overall, heat treatment is shown to affect the rigidity, saturation behavior, and generalized mass transfer of paper electrodes but not of cloth electrodes. Our findings will guide the selection of electrode materials and operation parameters for the H2-Br2 RFB.

Development of Bromine Adsorbing Carbon Felt Electrode by Coating of Nitrogen-Doped Mesoporous Carbon Layer for Highly Stable Flowless Zinc-Bromine Battery

Renewable energy is well known for the extreme volatility of power production, and secondary battery-based energy storage systems (BESS) are the key to the novel and safe energy industry to expand the supply of renewable energy. Currently, lithium-ion battery-based ESS is commonly used, but the frequent ignition accidents from these ESSs rather become an obstacle to the growth of the renewable energy field. Among the redox batteries, the flowless zinc-bromine battery (FLZBB) is studied as the alternative since it uses a non-flammable and cost-effective aqueous Zn- Br2 electrolyte. However, its main challenges are that bromine (Br2) and polybromide anions (), formed at the positive electrode during the charging process, cross over to the negative electrode due to the difference in chemical potential between the electrodes. The diffused Br2 oxidizes the zinc metal, electrodeposited on the negative electrode, and causes a self-discharge reaction that consumes the charging active material and Br2 the battery performance and life. Herein, we present a nitrogen-doped mesoporous carbon coated on the pristine graphite felt fibers (NMC/GF). By uniformly forming a nitrogen-doped porous carbon material on the GF fibers through the evaporation-induced self-assembly (EISA) method, it is a simple and cost-effective method to develop the structural and properties of the GF positive electrode to increase the ability of adsorption and storing the active materials, Br2 and polybromide anions (,, and ) generated during the charging process. In addition, it also improved the bromine redox reaction kinetics by having a strong affinity with the aqueous Zn-Br2 electrolyte. This facilitates long-term charge/discharge cycles, enabling high performance and improved durability for Coulombic efficiency over 95% for 5000 cycles in the FLZBB single-cell platform at a current density of 20 mA cm-2 and a high-rate areal capacity of 2 mAh cm-2.

Tungsten oxide embedded graphene oxide doped with SPEEK composite membrane for zinc–bromine redox flow batteries

Zinc-bromine redox flow batteries (Zn/Br2 RFBs) are fingerprint candidates for large-scale energy storage applications owing to their low cost, flexibility, high energy density, and astonishing round-trip efficiency. However, during the charging and discharging process, the diffusion of bromine through the porous membrane creates significant capacity decay and reduces the membrane efficiency of Zn/Br2 RFBs. In this respect, we developed various amounts of tungsten trioxide (WO3) nanoparticle-decorated graphene oxide (WO3@GO)-loaded sulfonated poly (ether ether ketone) (SPEEK) membranes and investigated their Zn/Br2 redox flow battery performance. The optimum amount of WO3@GO-loaded WO3@GO/SPEEK-3 membrane exhibits higher mechanical stability and ionic conductivity, significantly restricting the bromine crossover through the membrane. Due to their higher hydrophilic ability and uniform dispersion, WO3-loaded GO nanosheets provide strong interaction between the sulfonic acid group of the SPEEK membrane, which acts as an effective barrier for bromine crossover and significantly alters the Zn/Br2 battery performance. As a result, at a current density of 40 mA cm−2, the Zn/Br2 single cell of the WO3@GO/SPEEK-3 demonstrated higher coulombic efficiency (96.6 %), voltage efficiency (89.6 %), and energy efficiency (86.6 %), better than the WO3@GO/SPEEK-5 and pristine SPEEK membranes. These performances indicate that the proposed low-cost WO3@GO/SPEEK membrane can be highly applicable to other energy-related fields, including fuel cells and water treatment.

Urchin-Like Mesoporous TiN Hollow Sphere Enabling Promoted Electrochemical Kinetics of Bromine-Based Flow Batteries.

Bromine-based flow batteries (BFB) have always suffered from poor kinetics due to the sluggish Br3 -/Br- redox, hindering their practical applications. Developing cathode materials with high catalytic activity is critical to address this challenge. Herein, the in-depth investigation for the free energy of the bromine redox electrode is conducted initially through DFT calculations, establishing the posterior desorption during oxidation as the rate-determining step. An urchin-like titanium nitride hollow sphere (TNHS) composite is designed and synthesized as the catalyst for bromine redox. The large difference in Br- and Br3 - adsorption capability of TNHS promotes rapid desorption of generated Br3 - during the oxidation process, liberating active sites timely to enable smooth ongoing reactions. Besides, the urchin-like microporous/mesoporous structure of TNHS provides abundant active surface for bromine redox reactions, and ample cavities for the bromine accommodation. The inherently high conductivity of TNHS enables facile electron transfer through multiple channels. Consequently, zinc-bromide flow batteries with TNHS catalyst exhibit significantly enhanced kinetics, stably operating at 80mAcm-2 with 82.78% energy efficiency. Overall, this study offers a solving strategy and catalyst design approach to the sluggish kinetics that has plagued bromine-based flow batteries.

Achieving unprecedented cyclability of flowless zinc-bromine battery by nitrogen-doped mesoporous carbon on thick graphite felt electrode

The flowless zinc-bromine battery (FLZBB) is non-flammable as it is based on an aqueous electrolyte and is considered an alternative to redox flow batteries because of its cost-effectiveness using a simple cell platform. However, it faces challenges related to self-discharge caused by the crossover of bromine (Br2) and polybromide anions (Brn+2-) formed at the positive electrode during the charging process. The self-discharge reaction consumes the charging active materials, thereby decreasing battery performance and lifespan. To address the critical issues, this study introduces the development of a revolutionary positive electrode: a nitrogen-doped mesoporous carbon-coated thick graphite felt (NMC/GF). This positive electrode effectively suppresses the crossover of active materials and prevents the self-discharge reaction. The mesopores, strategically embedded with nitrogen sites, serve as a stronghold, capturing and immobilizing bromine and polybromide anions, significantly reducing their undesirable effects. Furthermore, we enhanced the electrochemical performance of the NMC/GF electrode by modifying it to be ultrahydrophilic. Abundant oxygen and nitrogen functional groups were incorporated onto the electrode, resulting in an amplified affinity with the aqueous electrolyte. This modification led to improved bromine redox reaction kinetics. Demonstrating an excellent Coulombic efficiency surpassing 96 % and an energy efficiency of over 76 % at a current density of 20 mA cm−2 with a high-rate areal capacity of 2 mAh cm−2, this novel positive electrode achieves a previously unattained milestone; cyclability unprecedentedly extended to 10,000 cycles. The development of NMC/GF positive electrodes further advances the FLZBB system, and large-area scale-up research of these carbon electrodes makes looking forward to practical uses in energy storage systems.

Tin Modified Carbon Nanofibers as an Effective Catalytic Electrode for Bromine Redox Reactions in Static Zinc‐bromine Batteries

AbstractZinc‐bromine batteries (ZBBs) have emerged as a compelling solution for large‐scale energy storage, yet they confront significant technical challenges impeding widespread commercialization. The electrochemical processes within ZBBs rely on a stoichiometric mechanism, where the bromine reaction at the cathode drives the zinc plating reaction on the anode. However, the sluggish electrochemical kinetics of Br2/Br− redox reactions lead to substantial electrochemical polarization, resulting in interruptions in zinc plating and significant voltage losses in ZBBs. This study introduces a new solution to address these challenges by leveraging carbon nanofiber decorated with tin nanoparticles as an efficient catalyst. The catalyst serves to enhance the Br2/Br– redox reaction, effectively reducing voltage losses in ZBBs. When implemented in static ZBB configurations, the Sn/CNF catalysts demonstrate exceptional long‐term stability, achieving an impressive 3000 cycles with minimal voltage loss. In contrast, ZBBs utilizing SnO2 based catalysts experience a substantially higher voltage loss of 736 mV, along with limited and unstable cycling performance. These findings signify a promising approach for the development of catalytic electrodes, paving the way for high‐performance ZBBs with improved efficiency and cycling durability.

Recent Advances in Bromine Complexing Agents for Zinc–Bromine Redox Flow Batteries

The development of energy storage systems (ESS) has become an important area of research due to the need to replace the use of fossil fuels with clean energy. Redox flow batteries (RFBs) provide interesting features, such as the ability to separate the power and battery capacity. This is because the electrolyte tank is located outside the electrochemical cell. Consequently, it is possible to design each battery according to different needs. In this context, zinc–bromine flow batteries (ZBFBs) have shown suitable properties such as raw material availability and low battery cost. To avoid the corrosion and toxicity caused by the free bromine (Br2) generated during the charging process, it is necessary to use bromine complexing agents (BCAs) capable of creating complexes. As an overview, the different BCAs used have been listed to compare their behavior when used in electrolytes in ZBFBs. In addition, the coulombic and energy efficiencies obtained have been compared.

Influence of strong bromine binding complexing agent in electrolytes on the performance of hydrogen/bromine redox flow batteries

1-n-Hexylpyridin-1-ium bromide [C6Py]Br is investigated in this work as bromine complexing agent (BCA) in aqueous bromine electrolytes on its influence on hydrogen bromine redox flow battery (H2/Br2-RFB) performance. [C6Py]+-cations bind bromine of aqueous polybromide solutions safely in an additional fused salt phase limiting the vapor pressure of Br2. Dissolved in aqueous electrolyte solutions, however, [BCA]+ cations drastically lower PFSA membranes' conductivity in the H2/Br2-RFB. In this work the combination of the very strong bromine-binding [C6Py]+cation and an excess of bromine in the electrolyte lead to an almost complete absorption of 99.6 mol% [C6Py]+ into the fused salt within the electrolyte's operation range. In comparison to similar application of short side chain 1-ethylpyridinium bromide, adverse effects are stronger compensated by use of [C6Py]Br. Increases in membrane resistance of the membrane in contact with [C6Py]+ cations are reversible in contrast for contact with [C2Py]+ cations. Electrolytes are cycled for at least 12 cycles and offer a stable useable capacity of 176.7 Ah L−1 and reach and stable discharge energy densities of 138.91 Wh L−1. Strong bromine binding properties between [C6Py]+ cations and polybromides are confirmed by DFT studies. In contrast to [C2Py]+ electrolytes, the long-chain [C6Py]+ cation in electrolytes has a higher cycling stability or a low decrease in capacity and energy density.

Sulfonated Anthraquinone-Based Ionic Complexes as a Promising Organic Negolyte for Redox-Flow Batteries

Due to its high solubility and fast kinetics of redox reactions, anthraquinone-2,7-disulfonic acid is a promising electroactive molecule for redox-flow-battery electrolytes and other energy applications. However, its widespread use is currently limited, primarily due to its tendency to chemical side-reactions and the formation of quinhydrone complexes between the molecule’s different redox-forms. The possibility of overcoming these shortcomings by using a simple anthraquinone-2,7-disulfonic acid functionalization with the poly(diallyldimethylammonium) polycation is studied. The ionic complexes are shown to be formed in this mixture, which leads to the suppression of the quinhydrone compound formation. At the same time, the poly(diallyldimethylammonium)/anthraquinone-2,7-disulfonic acid mixtures retain their redox activity and can be used as a negolyte in anthraquinone–bromine redox flow batteries, while all key characteristics of such a battery are comparable with those of anthraquinone–bromine redox flow batteries which used anthraquinone-2,7-disulfonic acid without any additives. The poly(diallyldimethylammonium)/anthraquinone- 2,7‑disulfonic acid-based battery (0.1 M anthraquinone-2,7-disulfonic acid) has the power density of 105 and 65 mW/cm2 for the battery state-of-charge values 100% and 50%, respectively; the energy efficiency for five charging–discharging cycles, 57.4%. In the future, the composition of the poly(diallyldimethylammonium)/anthraquinone-2,7-disulfonic acid ionic complexes can be optimized, in order to maintain good kinetics and solubility of anthraquinone-2,7-disulfonic acid and at the same time reduce the intensity of chemical side-reactions, including quinhydrone-complexes formation.

Operational Parameter Analysis and Performance Optimization of Zinc–Bromine Redox Flow Battery

Zinc–bromine redox flow battery (ZBFB) is one of the most promising candidates for large-scale energy storage due to its high energy density, low cost, and long cycle life. However, numerical simulation studies on ZBFB are limited. The effects of operational parameters on battery performance and battery design strategy remain unclear. Herein, a 2D transient model of ZBFB is developed to reveal the effects of electrolyte flow rate, electrode thickness, and electrode porosity on battery performance. The results show that higher positive electrolyte flow rates can improve battery performance; however, increasing electrode thickness or porosity causes a larger overpotential, thus deteriorating battery performance. On the basis of these findings, a genetic algorithm was performed to optimize the batter performance considering all the operational parameters. It is found that the battery energy efficiency can reach 79.42% at a current density of 20 mA cm−2. This work is helpful to understand the energy storage characteristics and high-performance design of ZBFB operating at various conditions.

Laser ablated uniform deposition of bismuth oxide film as efficient anode for zinc based flow battery

Zinc based redox flow batteries are the most proficient and attractive candidature for large scale energy storage applications. However, zinc dendritic formation and inhomogeneous deposition of zinc hamper the cyclability of zinc-based flow batteries. Herein, we have successfully decorated Bi2O3 on the felt by using the pulsed laser deposition (PLD) technique and tested it as a negative electrode in zinc bromine redox flow battery. The Bi2O3 felt provides more robust nucleation sites for zinc nuclei, lowers the potential of hydrogen evolution reaction, minimizes the surface diffusion of zinc, lowers zinc nucleation overpotential, and triggers homogenous zinc deposits. Compared to pristine (57.7 %), Bi2O3 felt exhibited an energy efficiency of 70.6 % at 100 mA cm−2. Interestingly, the morphological evolution of zinc deposits demonstrates that zinc deposition on the Bi2O3 felt is more homogeneous than pristine at an initial time (30 sec of charging at 20 mA cm−2). Moreover, Bi2O3 felt shows a stable long cycling performance over 200 cycles with minimized charge discharge overpotential and exhibited an avg. coulombic efficiency of 96.78 % which is superior than pristine. Thus, Bi2O3 felt is a prominent anode material for improving the electrochemical performance of zinc based redox flow batteries.

Synthesis and characterization of highly durable hydrocarbon-based composite membrane for zinc-bromine redox flow battery

Low-cost, durable, and high-performance membranes are urgent requirements for zinc bromine redox flow battery (ZBFB) applications. Sulfonated poly (ether ether ketone), SPEEK is a low-cost, ion-exchange membrane with excellent ionic conductivity, but its backbone is susceptible to the harsh bromine environment. Herein, the successful incorporation of a multifunctional nanofiller, perovskite-structured cerium titanate nanoparticles dispersed on smooth carbon nanofibers (p-CT/CNF) with varying carbon content into the polymer matrix protects the SPEEK backbone, reduces the crossover of active species and improves the selectivity of the composite membrane. At high current density of 100 mA cm−2, the SP-p-CT350 membrane in ZBFB shows an energy efficiency of 73.34% compared to pristine SPEEK and SP-p-CT320 with 70.32 and 69.71%, respectively. Interestingly, the excellent dispersion of the nanofiller notably reduces the self-discharge rate of SP-p-CT350, retaining the OCV at 1.70 V for 117 h which is 1.86 and 1.75 times greater than pristine SPEEK and SP-p-CT320. Furthermore, with the effect of loading to determine the durability of the SP-p-CT350 membrane, SP-p-CT350 with a nanofiller loading of 0.5 wt% demonstrates stable battery performance across 500 cycles at a current density of 40 mA cm−2 with an outstanding energy efficiency of 81.13%.

Boosting aqueous non-flow zinc–bromine batteries with a two-dimensional metal–organic framework host: an adsorption-catalysis approach

We develop a high-performance aqueous non-flow zinc–bromine battery with nickel polyphthalocyanine as a cathode host, where the atomically dispersed Ni–N4 sites enable strong bromine adsorption and efficient bromine redox reactions.

Ultralow platinum loading for redox-flow battery by electrospinning the electrocatalyst and the ionomer in core-shell fibers

Hydrogen Bromine Redox Flow Batteries (HBRFB) are promising candidates for large scale energy storage, having an excellent balance of system, inexpensive and abundant electrolytes, high power density and near zero kinetic limitations. However, they suffer from corrosion of the hydrogen electrode due to bromine species crossover, which requires a high loading of precious group metal (PGM) electrocatalyst. Herein, a standard catalyst has been used in an electrospun (ES) fiber mat electrode, allowing for a significant (six-fold) reduction in platinum loading from 0.3 mgPt/cm2 down to 0.05 mgPt/cm2. At this very low loading, the electrospun electrode attained an impressive specific power of 11.5 W/mgPt, and exhibited excellent durability, with constant power output for 140 charge/discharge cycles. The excellent performance of the electrospun hydrogen electrode is attribute to its unique core-shell nanofiber structure, which improves the stability of the catalyst by preventing bromide species from reaching the catalyst surface.

Enhanced Surface Area Carbon Cathodes for the Hydrogen–Bromine Redox Flow Battery

The hydrogen–bromine redox flow battery is a promising energy storage technology with the potential for capital costs as low as 220 $ kWh−1 and high operational power densities in excess of 1.4 W cm−2. In this work, enhanced surface area bromine electrodes incorporating carbon black (CB) and graphene nanoplatelets (GnPs) on carbon paper and carbon cloth substrates were investigated, and the effect of electrolyte concentration on performance of the electrodes was studied. Carbon-black-modified electrodes are found to possess the largest electrochemically active surface areas, i.e., up to 11 times that of unmodified materials, while GnP electrodes are shown to have superior kinetic activity towards the bromine electrode reaction. In terms of performance, lower electrolyte concentrations are found to favour the improved kinetic parameters associated with graphene nanoplatelet electrodes, while highly concentrated electrolytes favour the larger electrochemically active surface area of carbon black electrodes. The optimal performance was achieved on a carbon-black-modified carbon cloth electrode in a 6 M HBr/2 M Br2 electrolyte concentration, with polarisation current densities approaching 1.6 A cm−2 at overpotentials of ±400 mV, and mean overpotentials of 364 mV during oxidation and 343 mV during reduction, resulting from bromine oxidation/reduction cycling tests at ±1.5 A cm−2.

Resistance Breakdown of a Membraneless Hydrogen-Bromine Redox Flow Battery.

A key bottleneck to society’s transition to renewable energy is the lack of cost-effective energy storage systems. Hydrogen–bromine redox flow batteries are seen as a promising solution, due to the use of low-cost reactants and highly conductive electrolytes, but market penetration is prevented due to high capital costs, for example due to costly membranes to prevent bromine crossover. Membraneless hydrogen–bromine cells relying on colaminar flows have thus been investigated, showing high power density nearing 1 W/cm2. However, no detailed breakdown of resistance losses has been performed to-date, a knowledge gap which impedes further progress. Here, we characterize such a battery, showing the main sources of loss are the porous cathode, due to both Faradaic and Ohmic losses, followed by Ohmic losses in the electrolyte channel, with all other sources relatively minor contributors. We further develop and fit analytical expressions for the impedance of porous electrodes in high power density electrochemical cells to impedance measurements from our battery, which enabled the detailed cell resistance breakdown and determination of important electrode parameters such as volumetric exchange current density and specific capacitance. The insights developed here will enable improved engineering designs to unlock exceptionally high-power density membraneless flow batteries.

Adsorption of bromine complexing agents on platinum electrocatalysts and prevention through polydopamine coatings

Bromine complexing agents (BCAs) are seen as a promising route to mitigate the potential health and environmental risks of the bromine-based redox-flow batteries, like the hydrogen bromine redox flow battery (H2–Br2 RFB). The most studied BCAs are based on the pyridinium anion, which may adsorb and inhibit the Pt catalyst required in the H2–Br2 RFB system for the hydrogen reactions. Herein the effect of two BCAs (ethyl-pyridinium bromide and hexyl-pyridinium bromide) on a Pt electrocatalyst are studied, along with a potential methodology to prevent adsorption of the BCA through a polydopamine (PDA) coating. The results show that the pyridinium anion is adsorbed on Pt throughout a large potential range (−0.02 to 1.0 V), reducing the availability of the surface for the adsorption of other species. The PDA coating prevented this adsorption, but itself experiences adsorption of the BCA leading to some reduction in its porosity.