A New Michael-Reaction-Resistant Benzoquinone for Aqueous Organic Redox Flow Batteries

Abstract

We report here the synthesis, characterization and properties of 3,6-dihydroxy-2,4-dimethylbenzenesulfonic acid (DHDMBS) as a new positive side electrolyte material for aqueous organic redox flow batteries (ORBAT). We have synthesized this material in pure form in high yield and confirmed its structure. We have determined that the standard reduction potential, the rate constant of the redox reaction, and the diffusion coefficient are ideally suited for use in ORBAT. Specifically, DHDMBS overcomes the major issue of Michael reaction with water faced with 4,5-dihydroxybenzene-1,3-disulfonic acid (BQDS) and similar unsubstituted benzoquinones in the selection of positive electrolyte materials. DHDMBS can be synthesized relatively inexpensively. We have demonstrated the chemical stability of DHDMBS to repeated electrochemical cycling through NMR and electrochemical studies proving the absence of products of the Michael reaction. A flow cell with DHDMBS and anthraquinone-2,7-disulfonic acid has now been shown to operate close to 100% coulombic efficiency for over 25 cycles when continuously cycled at 100 mA/cm 2 , and can sustain current densities as high as 500 mA/cm 2 without noticeable chemical degradation. However, there was a slow decrease in the capacity of the flow cell attributable to the crossover of DHDMBS from the positive side of the cell. Thus, the present study has shown DHDMBS as a promising candidate for the positive side material for an all-organic aqueous redox flow battery in acidic media, and our future efforts will focus on understanding the crossover of DHDMBS and the effects of long-term cycling. As intermittent renewable energy sources based on solar photovoltaics and wind turbines are installed worldwide, electrical energy storage facilities will be of paramount importance to maintain the stability of the electricity grid and to meet the growing demand for clean energy. Rechargeable batteries have shown promise in meeting this large energy storage demand, because of their high efficiency and scalability.1-3 Redox flow batteries (RFBs) are especially attractive for stationary applications due to their scalability and their inherent ability to address the power and energy requirements independently.4,5 However, none of today's battery technologies can meet the demands of robustness, low-cost, and environmental-friendliness simultaneously. 6 Recently, flow batteries based on aqueous solutions of simple watersoluble organic redox couples, or ORBAT, have become the subject of great interest because of their prospect of offering such a gridscale energy storage solution. Thus, the investigation into simple organic molecules that can be readily synthesized or procured for use in ORBAT has grown significantly. 7-12Specifically, we and others have found that quinone-and anthraquinone-based molecules have the essential electrochemical characteristics for the design of ORBAT. [13][14][15][16][17][18][19] We first reported the properties of an "all-quinone" organic redox flow battery in 2014 in which the ...

A High Voltage Aqueous Zinc–Organic Hybrid Flow Battery

“…This has been identified as a major decomposition pathway for many benzoquinones with unprotected carbons on the aryl ring. [11,30] However, this reaction is suppressed in FQ by replacing all C-H bonds with substituents. FQ is thus not susceptible to decomposition via this mechanism.…”

Comparison of Quinone‐Based Catholytes for Aqueous Redox Flow Batteries and Demonstration of Long‐Term Stability with Tetrasubstituted Quinones

“…Hydroquinones 1 and 2 are commercially available as the sodium and potassium salts, respectively, and compounds 3 , 4 , 5 , and 8 were synthesized according to literature procedures (in some cases, with modifications; see Supporting Information). [ 14,23,24 ] Hydroquinones 6 and 7 were synthesized by addition of sodium mercaptoethanesulfonate to benzoquinone. The tris‐thioether compound 6 is an analogue of the major byproduct formed during the previously reported synthesis of 4 , [ 22 ] and it was produced by attempting the synthesis of 5 at elevated temperature (see Supporting Information).…”

“…The observed peak power densities are superior to those reported for other all‐quinone redox flow batteries and are within an order of magnitude of the state‐of‐the‐art for inorganic flow batteries. [ 14,34 ]…”

“…Anthraquinone derivatives, such as anthraquinone‐2,7‐disulfonate (AQDS), have proven to be quite effective as low‐potential (anodic) electrolytes, and they have been paired with both organic and inorganic high‐potential (cathodic) electrolytes in aqueous RFBs. [ 10,13–19 ] The lower stability of high potential quinones has limited the utility of quinone‐based catholytes, as revealed by studies with the parent benzoquinone, [ 20 ] as well as benzoquinones bearing substitutents that increase their aqueous solubility [ 14–18 ] (inter alia, compounds 1 – 3 in Scheme 2 ). Benzoquinones are reactive electrophiles, and they are capable of undergoing Michael addition with various nucleophiles, including water, as well as oligomerization.…”

“…Benzoquinones are reactive electrophiles, and they are capable of undergoing Michael addition with various nucleophiles, including water, as well as oligomerization. [ 14,15,21 ] Recognition of this issue provided the basis for Narayanan and co‐workers to develop the trisubstituted quinone 3 , which exhibits considerably improved stability relative to previously reported derivatives 1 and 2 (Scheme 2). [ 14 ]…”