Electrolytes For Redox Flow Batteries Research Articles

Inkjet-printed microband electrodes for a cost-efficient state-of-charge monitoring in redox flow batteries

A readily available prototyping process for the fabrication of low-cost microband electrodes is introduced, which are applicable for the accurate amperometric state-of-charge (SOC) measurement in redox flow battery (RFB) electrolytes. For this purpose, an inexpensive and straightforward inkjet printing of conductive platinum-based and insulating polymer-based inks was investigated. The overall inkjet-printed microband electrode performance in 0.4 M ferri-/ferrocyanide with 0.5 M KCl as supporting electrolyte were compared to sputter-coated microband electrodes and commercial disk microelectrodes using an SOC measurement method based on steady-state amperometry. Absolute root-mean-square deviations (RMSD) are below 1.04% SOC for the printed microband electrodes. The low material costs of about €2.52 (USD2.86) for the presented prototype and the simplicity of the fabrication process could facilitate a widespread application of the amperometric SOC measurement in RFBs.

State of Charge and Capacity Tracking in Vanadium Redox Flow Battery Systems

The vanadium redox flow battery electrolyte is prone to several capacity loss mechanisms, which must be mitigated to preserve electrolyte health and battery performance. This study investigates a simple and effective technique for the recovery of capacity loss arising from symmetrical mechanisms via automatic electrolyte rebalancing. However, chemical or electrochemical techniques must be used to mitigate capacity loss from asymmetrical mechanisms (e.g., air oxidation of V2+), which requires knowledge of the oxidation states present in the electrolytes. As such, this study assesses the suitability of SOC tracking via electrolyte absorption for independent monitoring of the anolyte and catholyte within an existing VRFB system. Testing is performed over cycling of a 40 cell, 2.5 kW with 40 L of electrolyte. Optical monitoring is performed using a custom-made flow cell with optical paths (interior cavity thicknesses) ranging from 1/4″ to 1/16″. Light transmitted through the cell by a 550 lumen white light source is monitored by a simple photodiode. The electrolyte rebalancing mechanism displayed success in recovering symmetrical capacity losses, while optical monitoring was unsuccessful due to the high absorbance of the electrolyte. Potential improvements to the monitoring system are presented to mitigate this issue.

Phoenicin Switch: Discovering the Trigger for Radical Phoenicin Production in Multiple Wild-Type Penicillium Species.

Society faces the challenge of storing energy from sustainable sources in inexpensive, nontoxic ways that do not deplete the limited resources of Earth. In this regard, quinone redox flow batteries have been proposed as ideal; however, industrially used quinones have traditionally been synthesized from fossil fuels. Therefore, we investigated the production of phoenicin (compound 1), a deep violet dibenzoquinone produced by certain Penicillium species, for its industrial potential. Strains grew as surface cultures on customized growth media with varying production parameters, and phoenicin production was assessed by ultrahigh-performance liquid chromatography-diode array detection-quadrupole time of flight mass spectrometry (UHPLC-DAD-QTOF MS) analysis of the supernatant. Phoenicin production was reliant on the sucrose concentration, and by varying that, we produced 4.94 ± 0.56 g/L phoenicin on a Czapek yeast autolysate broth (CY)-based medium with Penicillium phoeniceum (CBS 249.32) as the production host, with 71.91% phoenicin purity in the resulting medium broth. Unexpectedly, metabolites corresponding to phoenicin polymers were tentatively identified in P. phoeniceum, of which the dimer (diphoenicin) was a major chromatographic peak. An MS-based metabolomics study was conducted on P. atrosanguineum using feature-based molecular networking and multivariate statistics, and it was found that few or no known secondary metabolites besides phoenicin were secreted into the growth medium. Finally, the effects of sucrose, sodium nitrate, and yeast extract (YE) in the growth medium were investigated in a 23 full factorial design. The results indicated an optimal sucrose concentration of 92.87 g/L on CY when NaNO3 and YE were fixed at 3 and 5 g/L, respectively. IMPORTANCE This work was undertaken to explore the production of fungal quinones in wild-type strains for use as electrolytes in redox flow batteries. As society converts energy production in a more sustainable direction, it becomes increasingly more important to store sustainable energy in smart ways. Conventional battery technologies imply the use of highly toxic, expensive, and rare metals; thus, quinone redox flow batteries have been proposed to be a desirable alternative. In this study, we explored the possibility of producing the fungal quinone phoenicin in Penicillium spp. by changing the growth parameters. The production of other secondary metabolites and known mycotoxins was also investigated in a metabolomics study. It was shown that phoenicin production was activated by optimizing the carbon concentration of the medium, resulting in high titers and purity of the single metabolite.

A low-cost amperometric sensor for the combined state-of-charge, capacity, and state-of-health monitoring of redox flow battery electrolytes

• Simultaneous state-of-charge, capacity, and state-of-health measurement on half-cell level. • Temperature-independent, concentration-independent, calibration-free, and cost-efficient. • Reduced absolute state-of-charge measurement error to <0.5% over complete range. • Electrolyte capacity and state-of-health are monitored with relative errors of <2% • Cost-efficient microcontroller-based measurement unit is presented and characterized. We recently introduced an amperometric, temperature-independent, and calibration-free method for the measurement of the state-of-charge (SOC) of redox flow battery (RFB) electrolytes. In the study at hand, the measurement accuracy of the method is re-evaluated and significantly improved. The absolute root-mean-square deviation (RMSD) is reduced from ∼ 5% to below 0.5% over the complete SOC range. Based on this enhanced measurement accuracy, a new approach for the online co-estimation of an electrolyte’s capacity and its state-of-health (SOH) is proposed and experimentally evaluated. In an operating RFB, relative RMSDs of 0.7 and 1.4% are obtained for the capacities of the catholyte and the anolyte, respectively. Utilizing this capacity measurement, SOH values with absolute RMSDs between 0.6 and 2.1% can be achieved. Furthermore, a low-cost microcontroller-based measurement unit (MMU) prototype was constructed and characterized. Based on the component prices and possible cost optimizations, total material costs of below 40 EUR ($49) for two MMUs are calculated. In addition, a preliminary investigation of a low-cost bipolar, backfilled microelectrode (BBME) for material costs of below 2 EUR ($2) is presented, its working principle demonstrated, and pathways for mitigating its stability issues are discussed. The methodological enhancements proposed in this study result in unprecedented measurement accuracies for the simultaneous SOC and SOH monitoring of both electrolytes in an operating RFB. The improved amperometric method stands out for its wide applicability, viable implementation costs, temperature as well as concentration independence, and excellent accuracy level. It, thus, has the potential to facilitate the RFB electrolyte development, improve the operational safety of RFBs, and optimize their operational performance.

Layer Shape LiFePO4 Obtained by Powder Extrusion Molding as Solid Boosters for Ferro/Ferricyanide Catholyte in Semisolid Redox Flow Battery: Effect of Porosity and Shape

AbstractPowder extrusion molding is proposed to fabricate ceramic LiFePO4 layers (0.5–1.0 mm thickness) as solid booster for ferricyanide electrolyte in semisolid redox flow battery. In some extruded layers, the binder is partially decomposed, while in others it is completely removed and, afterwards, the material is sintered, so materials with different porosity and dimensions are obtained. After characterizing the materials, the kinetics for the reaction with ferricyanide is evaluated, being the binder‐less materials the ones which react faster and reach larger degrees of oxidation. For the material with 1.0 mm thick comparable results to the ones already published are obtained (69 % capacity for LiFePO4 compared to the theoretical value). In the case of the 0.5 mm thick sintered solid, an outstanding performance is achieved, reaching almost the theoretical capacity (94 %) with a very high coulombic efficiency (&gt;99 %) at 1 mA cm−2, results that were only obtained at much lower current densities in previous works.

Comparative kinetic analysis of redox flow battery electrolytes: From micro-fibers to macro-felts

In the context of new aqueous organic electrolytes development for redox flow batteries, two different approaches of charge transfer kinetic constant determination on carbon-based felts are compared. The first one consists in direct electrochemical measurement on centimetric pieces of felts, referred to as macro-felts, and the second is based on electrochemical measurement on carbon fibers extracted from felts and conditioned as microelectrodes, referred to as micro-fibers. Quantitative cyclic voltammetry (CV) involving experimental data fitting or simulation and electrochemical impedance spectroscopy (EIS) are carried out on the two supports, with two typical aqueous organic electrolytes, and determined values for charge transfer kinetic constants are compared. k0 values analyzed from micro-fibers are systematically lower than that analyzed from macro-felts where the differences may reach ca. two orders of magnitude in some cases. CV and EIS analysis on micro-fibers show very good consistency. With the simplicity of physical analysis, micro-fibers are considered as a reliable and powerful tool for kinetic determination, especially when confronted to fast kinetics.

Rationally Designed Ternary Deep Eutectic Solvent Enabling Higher Performance for Non-Aqueous Redox Flow Batteries

Redox flow batteries hold promise as large-scale energy storage systems for off-grid electrification. The electrolyte is one of the key components of redox batteries. Inspired by the mechanism involved in solvents for extraction, a ternary deep eutectic solvent (DES) is demonstrated, in which glycerol is introduced into the original binary ethaline DES. Redox pairs (active substance) dissolved in the solvent have low charge transfer resistance. The results show that the viscosity of the solvent with the ratio of choline chloride to ethylene glycol to glycerol of 1:2:0.5 decreases from 51.2 mPa·s to 40.3 mPa·s after adding the redox pair, implying that the mass transfer resistance of redox pairs in this solvent is reduced. Subsequent cyclic voltammetry and impedance tests show that the electrochemical performance with the ternary DES as the electrolyte in redox flow batteries is improved. When the ratio of 1:2:0.5 ternary DES is used as the electrolyte, the power density of the battery (9.01 mW·cm−2) is 38.2% higher than that of the binary one (6.52 mW·cm−2). Fourier transform infrared spectroscopy further indicates that the introduction of glycerol breaks the hydrogen bond network of the solvent environment where the redox pair is located, unraveling the hydrogen bond supramolecular complex. Rational solvent design is an effective strategy to enhance the electrochemical performance of redox batteries.

Microemulsions: Breakthrough Electrolytes for Redox Flow Batteries.

Aqueous and non-aqueous redox flow batteries (RFBs) have limited energy and current densities, respectively, due to the nature of the electrolytes. New approaches to electrolyte design are needed to improve the performance of RFBs. In this work, we combined a highly conductive aqueous phase and an organic redox-active phase in a microemulsion to formulate a novel RFB electrolyte. As a proof-of-concept, we demonstrate an RFB using this microemulsion electrolyte with maximum current density of 17.5 mA·cm−2 with a 0.19 M posolyte and 0.09 M negolyte at a flow rate of only ∼2.5 ml·min−1, comparable to early vanadium electrolyte RFBs at similar flow rates on a per molar basis. The novel active negolyte component is an inexpensive oil-soluble vitamin (K3). By combining aqueous and organic phases, the solvent potential window and energy density may be increased without sacrificing current density and new redox couples may be accessed. Microemulsion electrolytes show great promise for improved performance and increased energy densities in aqueous RFBs but the path forward is complex. We end with discussion of areas that need work to achieve the potential of these electrolytes.

Bismuth Electrocatalyst Enabling Reversible Redox Kinetics of a Chelated Chromium Flow Battery Anolyte

Metal electrocatalysts have been reported to improve the electron transfer kinetics of aqueous redox flow battery electrolytes on various types of carbon electrodes. In this work, we electrodeposited bismuth metal onto a carbon paper anode of a redox flow battery containing our previously reported polyaminocarboxylate-chelated chromium electrolyte. Depositing 0.58 mg cm–2 of bismuth metal enabled an electrochemically reversible electron transfer for the Cr(II)/Cr(III) couple, resulting in a 3.9% voltage efficiency increase over ten cycles at 100 mA cm–2 across an 80% state of charge window, while maintaining >99% current efficiency. The bismuth electrocatalyst provided other improvements, such as a 13% increase in average discharge power density when cycling at 80% energy efficiency, along with a 60% decrease in charge transfer resistance and 12% decrease in the full cell area specific resistance. A chelated bismuth complex was also utilized as a bismuth source for electrodeposition, providing an example of how polyaminocarboxylate ligands can be further implemented into efforts towards improving the energy efficiency of aqueous redox flow batteries.

Stability of TMA-TEMPO-based aqueous electrolytes for redox-flow batteries

The TEMPO scaffold is one of the most prominent used posolyte systems in organic redox flow batteries (RFBs). While the aminoxyl radical is well known for his extraordinary stability, there are only a few studies investigating the stability of the respective oxoammonium cation. In this study, we utilize battery experiments to quantify the fade rate of the oxoammonium cation derived from N,N,N-2,2,6,6-heptamethylpiperidinyloxy-4-ammonium chloride (TMA-TEMPO) in correlation with temperature and time. The observed capacity decay is mostly caused by a deactivation of the oxidized TMA-TEMPO yielding the corresponding hydroxylamine, which can mostly be regenerated by reoxidation. Additionally, unbalanced compositionally symmetric flow cells are used to compare the fade rate at different temperatures combined with varying hold times showing a strong dependency on temperature and residence time in high states of charge. The acquired results are used for a use-oriented cycling program comprising a single cycle per day. Furthermore, GC-HRMS and isotopic labeling are used to analyze the volatile decomposition products of heated and oxidized TMA-TEMPO, identifying key intermediates of the decomposition mechanism and the role of an aqueous environment.

Development of economical and highly efficient electrolyte using vanadium pentoxide for vanadium redox flow battery.

Vanadium pentoxide can be an inexpensive replacement to vanadium sulfate in synthesizing vanadium redox flow battery (VRFB) electrolytes. In this study, VRFB electrolyte is synthesized from vanadium pentoxide using an indigenously developed process and setup. In order to have the same performance as that of vanadium sulfate, the supporting electrolyte environment constituted by H+ and sulfate ion is replicated based on the calculations from standard synthesis mechanisms. The calculations reveal that 4M H2SO4 is required while preparing 1.5M Vn+ electrolyte from V2O5 to replicate 1.5M Vn+ in 2.5M H2SO4 from VOSO4. The effect of variation of sulfuric acid concentration is explored using thermal stability testing, which shows stable V(V) electrolytes for more than 30days for 4M H2SO4 concentration. Furthermore, the electrochemical performance of developed electrolyte from vanadium pentoxide shows similar charge-discharge profile, yet 1/5 the cost as compared to vanadium sulfate.

Family Tree for Aqueous Organic Redox Couples for Redox Flow Battery Electrolytes: A Conceptual Review.

Redox flow batteries (RFBs) are an increasingly attractive option for renewable energy storage, thus providing flexibility for the supply of electrical energy. In recent years, research in this type of battery storage has been shifted from metal-ion based electrolytes to soluble organic redox-active compounds. Aqueous-based organic electrolytes are considered as more promising electrolytes to achieve “green”, safe, and low-cost energy storage. Many organic compounds and their derivatives have recently been intensively examined for application to redox flow batteries. This work presents an up-to-date overview of the redox organic compound groups tested for application in aqueous RFB. In the initial part, the most relevant requirements for technical electrolytes are described and discussed. The importance of supporting electrolytes selection, the limits for the aqueous system, and potential synthetic strategies for redox molecules are highlighted. The different organic redox couples described in the literature are grouped in a “family tree” for organic redox couples. This article is designed to be an introduction to the field of organic redox flow batteries and aims to provide an overview of current achievements as well as helping synthetic chemists to understand the basic concepts of the technical requirements for next-generation energy storage materials.

On the challenges of materials and electrochemical characterization of concentrated electrolytes for redox flow batteries

We highlight the status of, and propose future approaches for, rheological, electrochemical, and spectroscopic characterization of concentrated redoxmer electrolytes for energy storage, with an emphasis on nonaqueous redox flow batteries.

High Purity Vanadium Oxysulfate Electrolyte for Vanadium Redox Flow Battery Prepared from Vanadium Slag Calcified Roasting Acid Leaching Solution by Two-Stage Solvent Extraction

High Purity Vanadium Oxysulfate Electrolyte for Vanadium Redox Flow Battery Prepared from Vanadium Slag Calcified Roasting Acid Leaching Solution by Two-Stage Solvent Extraction

Evaluation of negolyte properties of supramolecular binary complexes based on viologen-cucurbit[7]urils

Viologen-based redox materials have become popular as electrolytes for aqueous organic redox flow batteries (AORFBs) in recent years because of their reversible nature.

All-organic non-aqueous redox flow batteries with advanced composite polymer-ceramic Li-conductive membrane

Composite membranes based on polyvinylidene fluoride (PVdF) binder and Li1.4Al0.4Ge0.2Ti1.4(PO4)3 (LAGTP) ceramic filler as prospective solid electrolytes for non-aqueous redox flow batteries were investigated. Membrane fabrication details and thorough material characterization is provided to show improved performance. Studied membranes possess high Li-ion conductivity of (2.7 ± 0.6)•10−4 S cm−1, uniform microstructure, and excellent stability towards acetonitrile. Moreover, a new redox flow battery configuration is demonstrated with designed composite membranes in all-organic non-aqueous redox flow batteries. For the comparison, commercial Neosepta AHA anion-exchange membranes were evaluated. Triarylamine-based catholyte and viologen-based anolyte materials, which were recently designed in our laboratory, were used as redox couples. The comparison revealed lower resistance, but faster crossover of composite PVdF + LAGTP membrane (permeability rates < 10-5 cm2 min-1); still, this is considered as acceptable for application in flow batteries. H-cells assembled with novel composite membrane exhibit Coulombic efficiency of over 97% and high charge-discharge cycling stability: after the initial 15 cycles, the capacity stabilized at 37 mA h L−1 corresponding to 70% utilization of active materials. The membrane proposed exhibits a beneficial combination of functional characteristics that allows considering it as a credible alternative to the contemporary available polymeric commercial membranes for all-organic redox flow batteries.

Supramolecular Viologen–Cyclodextrin Electrolytes for Aqueous Organic Redox Flow Batteries

Along with a primary modification of redox active materials, an additional introduction of secondary noncovalent interactions can synergistically enhance bulk properties of electrolytes for redox flow batteries. Herein, we highlight the host–guest complex formation between tailored viologens and highly water soluble (2-hydroxypropyl)-β-cyclodextrin as a key electrolyte interaction to modulate relevant electrochemical properties of aqueous redox flow batteries (AORFBs). The cyclodextrin-modified AORFB anolytes demonstrated a complex interrelation of molecular structure and inherent binding activity as well as bulk electrochemical stability of the anolyte. The screening of different combinations of viologen substituents in the presence of cyclodextrin enabled an electrochemically stable AORFB performance for more than 500 cycles with a temporary capacity fade rate of 0.26%/day at high energy (>70%) and Coulombic (>99.7%) efficiencies. A selective interplay of supporting electrolytes and engineered redox active materials is a promising strategy for enhanced energy characteristics of AORFB electrolytes.

(Invited) Characterizing Redox Flow Battery Electrolytes Using Microelectrodes

Electrochemical energy storage is anticipated to play an important role in decarbonizing the electric power sector by facilitating the deployment of intermittent renewable power sources (e.g., solar photovoltaics, wind) and supporting an aging grid infrastructure [1]. Redox flow batteries (RFBs) are a promising electrochemical technology for energy-intensive grid storage, but further cost reductions are needed for widespread adoption, spurring research efforts into new redox chemistries and reactor designs. The recent emergence of engineered molecules offers intriguing new pathways to low cost energy storage through tunable molecular structures and inexpensive synthesis routes [2]. While the rapid and continued advancement of these redox couples is exciting, iterative design-test-improve cycles are slowed as molecules become increasingly robust and failure modes become more subtle, challenging traditional methodologies. Thus, there is a growing need for sensitive diagnostic techniques capable of evaluating materials performance under conditions that mimic those expected in practical embodiments [3]. In this talk, I will describe our recent efforts to develop voltammetric techniques to characterize candidate redox electrolytes, quantify electrochemical properties, and monitor electrolyte stability [4]. We primarily leverage microelectrodes, which offer several distinct advantages over traditional macroelectrodes, such as differentiation between oxidative and reductive signals and minimization of ohmic and capacitive distortions. Microelectrodes also yield more reliable electrochemical characterizations of electrolytes with high active species concentrations and varying states of charge. I will highlight efforts to track electrolyte state of charge and state of health within operating flow cells and to develop flexible modeling frameworks to assess electrolytes across a wide range of conditions. Incorporation of these techniques into experimental campaigns may aid in the development of next-generation RFB technologies.

Fungal quinones: diversity, producers, and applications of quinones from Aspergillus, Penicillium, Talaromyces, Fusarium, and Arthrinium.

Quinones represent an important group of highly structurally diverse, mainly polyketide-derived secondary metabolites widely distributed among filamentous fungi. Many quinones have been reported to have important biological functions such as inhibition of bacteria or repression of the immune response in insects. Other quinones, such as ubiquinones are known to be essential molecules in cellular respiration, and many quinones are known to protect their producing organisms from exposure to sunlight. Most recently, quinones have also attracted a lot of industrial interest since their electron-donating and -accepting properties make them good candidates as electrolytes in redox flow batteries, like their often highly conjugated double bond systems make them attractive as pigments. On an industrial level, quinones are mainly synthesized from raw components in coal tar. However, the possibility of producing quinones by fungal cultivation has great prospects since fungi can often be grown in industrially scaled bioreactors, producing valuable metabolites on cheap substrates. In order to give a better overview of the secondary metabolite quinones produced by and shared between various fungi, mainly belonging to the genera Aspergillus, Penicillium, Talaromyces, Fusarium, and Arthrinium, this review categorizes quinones into families such as emodins, fumigatins, sorbicillinoids, yanuthones, and xanthomegnins, depending on structural similarities and information about the biosynthetic pathway from which they are derived, whenever applicable. The production of these quinone families is compared between the different genera, based on recently revised taxonomy. KEY POINTS: • Quinones represent an important group of secondary metabolites widely distributed in important fungal genera such as Aspergillus, Penicillium, Talaromyces, Fusarium, and Arthrinium. • Quinones are of industrial interest and can be used in pharmacology, as colorants and pigments, and as electrolytes in redox flow batteries. • Quinones are grouped into families and compared between genera according to the revised taxonomy.

Flow battery electrolyte from carbon black incineration fly ash: A feasibility study of an environment friendly disposal process.

Fly ash represents a kind of finely divided solid waste which is derived from industrial or municipal waste incineration and contains various metal elements. In this work, we focus on the waste-to-resource conversion of one fly ash which is generated from the incineration of petroleum coke gasification waste. The leaching behaviors and waste conversion of this fly ash to value-added products under different treatments were investigated. The majority of the identified elements in leachate demonstrated different leaching patterns as the species of leached element from fly ashes depend on the chemical properties of leaching agents. Moreover, A pathway is developed to harvest toxic vanadium from this fly ash, and the vanadium-containing leachate can be further converted into electrolyte for vanadium redox flow battery (VRFB). The vanadium electrolyte was synthesized by using fly ash leachate as the resource materials in two different ways afterwards: reducing vanadium in the leachate directly (electrolyte from leachate) and synthesizing V2O5 from leachate as the intermediate product (electrolyte from leachate-derived V2O5). The electrochemical behavior and performance of these electrolytes were analyzed to investigate the feasibility of these approaches. The measurement of electrochemical performance proves that the electrolyte from leachate-derived V2O5 is comparable to the standard electrolyte in terms of columbic efficiency (CE), energy efficiency (EE) and stability. Based on experimental results, our research provides a potential solution for the establishment of vanadium flow battery plant. Cost-benefit analysis proves that the payback period of electrolyte synthesized from alkaline leachate and leachate-derived V2O5 is 2.1years and 1.0year, respectively.