Two extremely stable anthraquinone negolytes were synthesized from inexpensive precursors that potentially decrease the mass production cost. The carbon-linked anthraquinones eliminate S N 2 or S N Ar side reactions. Pairing with a Fe(CN) 6 3À/4À posolyte, they exhibited an open-circuit voltage of 1.0 V. By operating at pH 14, a record low capacity fade rate of <1% per year was demonstrated.
A highly stable phosphonate‐functionalized viologen is introduced as the redox‐active material in a negative potential electrolyte for aqueous redox flow batteries (ARFBs) operating at nearly neutral pH. The solubility is 1.23 m and the reduction potential is the lowest of any substituted viologen utilized in a flow battery, reaching −0.462 V versus SHE at pH = 9. The negative charges in both the oxidized and the reduced states of 1,1′‐bis(3‐phosphonopropyl)‐[4,4′‐bipyridine]‐1,1′‐diium dibromide (BPP−Vi) effect low permeability in cation exchange membranes and suppress a bimolecular mechanism of viologen decomposition. A flow battery pairing BPP−Vi with a ferrocyanide‐based positive potential electrolyte across an inexpensive, non‐fluorinated cation exchange membrane at pH = 9 exhibits an open‐circuit voltage of 0.9 V and a capacity fade rate of 0.016% per day or 0.00069% per cycle. Overcharging leads to viologen decomposition, causing irreversible capacity fade. This work introduces extremely stable, extremely low‐permeating and low reduction potential redox active materials into near neutral ARFBs.
hybrid RFBs electrodeposit at least one active species, e.g., lithium, aluminum, or zinc, onto nonflowing electrodes. The metal deposition process usually occurs on the negative electrode side. Although many hybrid RFBs utilize nonaqueous electrolytes to attain high working potential, a zinc-based hybrid system can attain a relatively high working potential in a nonflammable, lower-cost aqueous electrolyte. This is because the zinc/zincate redox couple, Zn/[Zn(OH) 4 ] 2− , in a pH 14 alkaline solution has the advantage of a large negative redox potential of −1.23 V versus the standard hydrogen electrode (SHE). An example is the alkaline zincferricyanide hybrid RFB, which was first reported in the 1970s and is still under development. [3] However, the low solubility of the [Fe(CN) 6 ] 3− /[Fe(CN) 6 ] 4− couple at high pH limits the energy density and constrains practical implementation. [4] In addition, acidic zinc-bromine hybrid RFBs have been widely studied and are being commercialized; however, the toxicity and corrosivity of bromine limits widespread deployment. [1] Recently, redox-active organic and organometallic molecules have been widely studied for their promise of enabling the development of inexpensive flow batteries. [5][6][7] These molecules exhibit structural diversity and broad tunability, permitting the engineering of solubility, redox potential, kinetics, and stability. Many different types of molecules, including quinones, [8][9][10][11][12] phenazines, [13,14] viologens, [7,[15][16][17][18][19] alloxazines, [20] and (2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl, [13,15,16,21,22] have demonstrated good electrochemical performance as redox-active materials in aqueous organic redox flow batteries (AORFBs). Most of these molecules exhibit low reduction potentials and consequently have been explored as negolyte (negative electrolyte) materials. Some exceptions are tetrachloro-1,4 benzoquinone and 4,5-dihydroxybenzene-1,3-disulfonic acid, which have high positive reduction potentials of >0.8 V versus SHE in acidic solution. [9,11,23] Thus, by pairing high potential organic molecules such as these with the Zn/[Zn(OH) 4 ] 2− redox couple, a new type of hybrid RFB can be designed to achieve a high cell voltage.However, it is difficult to pair an alkaline electrolyte and an acidic electrolyte within conventional single-membrane RFBs due to H + or OH − crossover. Recently, ceramic membranes and bipolar polymer membranes have been introduced into singlemembrane pH-differential flow cells, but the high resistance of these membranes has severely limited the current density. [24,25] Water-soluble redox-active organic molecules have attracted extensive attention as electrical energy storage alternatives to redox-active metals that are low in abundance and high in cost. Here an aqueous zinc-organic hybrid redox flow battery (RFB) is reported with a positive electrolyte comprising a functionalized 1,4-hydroquinone bearing four (dimethylamino)methyl groups dissolved in sulfuric acid. By utilizing a three-electrolyte...
Aqueous organic redox flow batteries (AORFBs) have recently gained significant attention as a potential candidate for grid-scale electrical energy storage. Successful implementation of this technology will require redox-active organic molecules with many desired properties. Here we introduce a naphthoquinone dimer, bislawsone, as the redox-active material in a negative potential electrolyte (negolyte) for an AORFB. This dimerization strategy substantially improves the performance of the electrolyte versus that of the lawsone monomer in terms of solubility, stability, reversible capacity, permeability, and cell voltage. An AORFB pairing bislawsone with a ferri/ferrocyanide positive electrolyte delivers an open-circuit voltage of 1.05 V and cycles at a current density of 300 mA/cm 2 with a negolyte concentration of 2 M electrons in alkaline solution. We determined the degradation mechanism for the naphthoquinone-based electrolyte using chemical analysis and predicted theoretically electrolytes based on naphthoquinones that will be even more stable.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.