A biomimetic redox flow battery based on flavin mononucleotide

Rechargeable redox flow batteries: flow fields, stacks and design considerations

Rechargeable redox flow batteries are being developed for medium and large-scale stationary energy storage applications. Flow batteries could play a significant role in maintaining the stability of the electrical grid in conjunction with intermittent renewable energy. However, they are significantly different from conventional batteries in operating principle. Recent contributions on flow batteries have addressed various aspects, including electrolyte, electrode, membrane, cell design, etc. In this review, we focus on the less-discussed practical aspects of devices, such as flow fields, stack and design considerations for developing high performance large-scale flow batteries. Finally, we provide suggestions for further studies on developing advanced flow batteries and large-scale flow battery stacks.

Raising the redox potential in carboxyphenolate-based positive organic materials via cation substitution

Meeting the ever-growing demand for electrical storage devices requires both superior and “greener” battery technologies. Nearly 40 years after the discovery of conductive polymers, long cycling stability in lithium organic batteries has now been achieved. However, the synthesis of high-voltage lithiated organic cathode materials is rather challenging, so very few examples of all-organic lithium-ion cells currently exist. Herein, we present an inventive chemical approach leading to a significant increase of the redox potential of lithiated organic electrode materials. This is achieved by tuning the electronic effects in the redox-active organic skeleton thanks to the permanent presence of a spectator cation in the host structure exhibiting a high ionic potential (or electronegativity). Thus, substituting magnesium (2,5-dilithium-oxy)-terephthalate for lithium (2,5-dilithium-oxy)-terephthalate enables a voltage gain of nearly +800 mV. This compound being also able to act as negative electrode via the carboxylate functional groups, an all-organic symmetric lithium-ion cell exhibiting an output voltage of 2.5 V is demonstrated.

Organic electrode materials could enable novelty chemistry required by the new generation of batteries. Here the authors show the synthesis and electrochemical performance of Mg(Li₂)-p-DHT as a lithiated cathode material that cycles at 3.4 V due to the presence of a spectator cation in the host structure.

Negatively charged nanoporous membrane for a dendrite-free alkaline zinc-based flow battery with long cycle life

Alkaline zinc-based flow batteries are regarded to be among the best choices for electric energy storage. Nevertheless, application is challenged by the issue of zinc dendrite/accumulation. Here, we report a negatively charged nanoporous membrane for a dendrite-free alkaline zinc-based flow battery with long cycle life. Free of zinc dendrite/accumulation, stable performance is afforded for ∼240 cycles at current densities ranging from 80 to 160 mA cm^-2 using the negatively charged nanoporous membrane. Furthermore, 8 h and 7 h plating/stripping processes at 40 mA cm^-2 yield an average energy efficiency of 91.92% and an areal discharge capacity above 130 mAh cm^-2. A peak power density of 1056 mW cm^-2 is achieved at 1040 mA cm^-2. This study may provide an effective way to address the issue of zinc dendrite/accumulation for zinc-based batteries and accelerate the advancement of these batteries.

Design and Mechanisms of Asymmetric Supercapacitors

Ongoing technological advances in diverse fields including portable electronics, transportation, and green energy are often hindered by the insufficient capability of energy-storage devices. By taking advantage of two different electrode materials, asymmetric supercapacitors can extend their operating voltage window beyond the thermodynamic decomposition voltage of electrolytes while enabling a solution to the energy storage limitations of symmetric supercapacitors. This review provides comprehensive knowledge to this field. We first look at the essential energy-storage mechanisms and performance evaluation criteria for asymmetric supercapacitors to understand the wide-ranging research conducted in this area. Then we move to the recent progress made for the design and fabrication of electrode materials and the overall structure of asymmetric supercapacitors in different categories. We also highlight several key scientific challenges and present our perspectives on enhancing the electrochemical performance of future asymmetric supercapacitors.

Novel Riboflavin-Inspired Conjugated Bio-Organic Semiconductors

Flavins are known to be extremely versatile, thus enabling routes to innumerable modifications in order to obtain desired properties. Thus, in the present paper, the group of bio-inspired conjugated materials based on the alloxazine core is synthetized using two efficient novel synthetic approaches providing relatively high reaction yields. The comprehensive characterization of the materials, in order to evaluate the properties and application potential, has shown that the modification of the initial alloxazine core with aromatic substituents allows fine tuning of the optical bandgap, position of electronic orbitals, absorption and emission properties. Interestingly, the compounds possess multichromophoric behavior, which is assumed to be the results of an intramolecular proton transfer.

Ion conducting membranes for aqueous flow battery systems

Flow batteries, aqueous flow batteries in particular, are the most promising candidates for stationary energy storage to realize the wide utilization of renewable energy sources. To meet the requirement of large-scale energy storage, there has been a growing interest in aqueous flow batteries, especially in novel redox couples and flow-type systems. However, the development of aqueous flow battery technologies is at an early stage and their performance can be further improved. As a key component of a flow battery, the membrane has a significant effect on battery performance. Currently, the membranes used in aqueous flow battery technologies are very limited. In this feature article, we first cover the application of porous membranes in vanadium flow battery technology, and then the membranes in most recently reported aqueous flow battery systems. Meanwhile, we hope that this feature article will inspire more efforts to design and prepare membranes with outstanding performance and stability, and then accelerate the development of flow batteries for large scale energy storage applications.

Toward a Low-Cost Alkaline Zinc-Iron Flow Battery with a Polybenzimidazole Custom Membrane for Stationary Energy Storage

Alkaline zinc-iron flow battery is a promising technology for electrochemical energy storage. In this study, we present a high-performance alkaline zinc-iron flow battery in combination with a self-made, low-cost membrane with high mechanical stability and a 3D porous carbon felt electrode. The membrane could provide high hydroxyl ion conductivity while resisting zinc dendrites well owing to its high mechanical stability. The 3D porous carbon felt could serve as a guidance for the zinc stripping/plating, which can effectively suppress zinc dendrite/accumulation as well. Thus this battery demonstrates a coulombic efficiency of 99.5% and an energy efficiency of 82.8% at 160 mA cm⁻², which is the highest value among recently reported flow battery systems. The battery can stably run for more than 500 cycles, showing very good stability. Most importantly, the practicability of this battery is confirmed by assembling a kilowatt cell stack with capital cost under $90/kWh.

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An alkaline zinc-iron flow battery is presented for stationary energy storage

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A battery with self-made membrane shows a CE of 99.49% and an EE of 82.78% at 160 mA cm⁻²

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The self-made membrane shows excellent mechanical and chemical stability

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A kilowatt cell stack with a capital cost under $90/kWh has been demonstrated

Porphyrin-Based Symmetric Redox-Flow Batteries towards Cold-Climate Energy Storage

Electrochemical energy storage with redox-flow batteries (RFBs) under subzero temperature is of great significance for the use of renewable energy in cold regions. However, RFBs are generally used above 10 °C. Herein we present non-aqueous organic RFBs based on 5,10,15,20-tetraphenylporphyrin (H₂ TPP) as a bipolar redox-active material (anode: [H₂ TPP]^2- /H₂ TPP, cathode: H₂ TPP/[H₂ TPP]²⁺ ) and a Y-zeolite-poly(vinylidene fluoride) (Y-PVDF) ion-selective membrane with high ionic conductivity as a separator. The constructed RFBs exhibit a high volumetric capacity of 8.72 Ah L^-1 with a high voltage of 2.83 V and excellent cycling stability (capacity retention exceeding 99.98 % per cycle) in the temperature range between 20 and -40 °C. Our study highlights principles for the design of RFBs that operate at low temperatures, thus offering a promising approach to electrochemical energy storage under cold-climate conditions.

Releasing iron from ferritin protein nanocage by reductive method: The role of electron transfer mediator

BACKGROUND

Ferritin detoxifies excess of free Fe(II) and concentrates it in the form of ferrihydrite (Fe₂O₃·xH₂O) mineral. When in need, ferritin iron is released for cellular metabolic activities. However, the low solubility of Fe(III) at neutral pH, its encapsulation by stable protein nanocage and presence of dissolved O₂ limits in vitro ferritin iron release.

METHODS

Physiological reducing agent, NADH (E_1/2 = -330 mV) was inefficient in releasing the ferritin iron (E_1/2 = +183 mV), when used alone. Thus, current work investigates the role of low concentration (5-50 μM) of phenazine based electron transfer (ET) mediators such as FMN, PYO - a redox active virulence factor secreted by Pseudomonas aeruginosa and PMS towards iron mobilization from recombinant frog M ferritin.

RESULTS

The presence of dissolved O₂, resulting in initial lag phase and low iron release in FMN, had little impact in case of PMS and PYO, reflecting their better ET relay ability that facilitates iron mobilization. The molecular modeling as well as fluorescence studies provided further structural insight towards interaction of redox mediators on ferritin surface for electron relay.

CONCLUSIONS

Reductive mobilization of iron from ferritin is dependent on the relative rate of NADH oxidation, dissolved O₂ consumption and mineral core reduction, which in turn depends on E_1/2 of these mediators and their interaction with ferritin.

GENERAL SIGNIFICANCE

The current mechanism of in vitro iron mobilization from ferritin by using redox mediators involves different ET steps, which may help to understand the iron release pathway in vivo and to check microbial growth.

Harnessing the Periplasm of Bacterial Cells To Develop Biocatalysts for the Biosynthesis of Highly Pure Chemicals

Although biocatalytic transformation has shown great promise in chemical synthesis, there remain significant challenges in controlling high selectivity without the formation of undesirable by-products. For instance, few attempts to construct biocatalysts for de novo synthesis of pure flavin mononucleotide (FMN) have been successful, due to riboflavin (RF) accumulating in the cytoplasm and being secreted with FMN. To address this problem, we show here a novel biosynthesis strategy, compartmentalizing the final FMN biosynthesis step in the periplasm of an engineered Escherichia coli strain. This construct is able to overproduce FMN with high specificity (92.4% of total excreted flavins). Such a biosynthesis approach allows isolation of the final biosynthesis step from the cytoplasm to eliminate undesirable by-products, providing a new route to develop biocatalysts for the synthesis of high-purity chemicals.IMPORTANCE The periplasm of Gram-negative bacterial hosts is engineered to compartmentalize the final biosynthesis step from the cytoplasm. This strategy is promising for the overproduction of high-value products with high specificity. We demonstrate the successful implementation of this strategy in microbial production of highly pure FMN.

Molecular engineering of organic electroactive materials for redox flow batteries

With high scalability and independent control over energy and power, redox flow batteries (RFBs) stand out as an important large-scale energy storage system.

Molecular Engineering with Organic Carbonyl Electrode Materials for Advanced Stationary and Redox Flow Rechargeable Batteries

Organic carbonyl electrode materials that have the advantages of high capacity, low cost and being environmentally friendly, are regarded as powerful candidates for next-generation stationary and redox flow rechargeable batteries (RFBs). However, low carbonyl utilization, poor electronic conductivity and undesired dissolution in electrolyte are urgent issues to be solved. Here, we summarize a molecular engineering approach for tuning the capacity, working potential, concentration of active species, kinetics, and stability of stationary and redox flow batteries, which well resolves the problems of organic carbonyl electrode materials. As an example, in stationary batteries, 9,10-anthraquinone (AQ) with two carbonyls delivers a capacity of 257 mAh g^-1 (2.27 V vs Li⁺ /Li), while increasing the number of carbonyls to four with the formation of 5,7,12,14-pentacenetetrone results in a higher capacity of 317 mAh g^-1 (2.60 V vs Li⁺ /Li). In RFBs, AQ, which is less soluble in aqueous electrolyte, reaches 1 M by grafting -SO₃ H with the formation of 9,10-anthraquinone-2,7-disulphonic acid, resulting in a power density exceeding 0.6 W cm^-2 with long cycling life. Therefore, through regulating substituent groups, conjugated structures, Coulomb interactions, and the molecular weight, the electrochemical performance of carbonyl electrode materials can be rationally optimized. This review offers fundamental principles and insight into designing advanced carbonyl materials for the electrodes of next-generation rechargeable batteries.

The Promise of Environmentally Benign Redox Flow Batteries by Molecular Engineering

Green redox flow batteries: The development of environmentally benign sustainable energy storage systems is eagerly awaited. Organic and organometallic-based electroactive materials are green alternatives to realize this goal. Using rational molecular design and function-oriented organic synthesis, a general design principle is presented to build high-performance green redox flow batteries.