Designing for conjugate addition: an amine functionalised quinone anolyte for redox flow batteries

Abstract

Redox flow batteries (RFBs) are promising grid-level electrical storage systems. The key to this emerging technology is the development of cheap, highly soluble, and high energy-density inorganic and organic electrolytes....

On the Capacity and Stability of a Biosynthesized Bis-quinone Flow Battery Negolyte

“…Ions matching the accurate mass of a phoenicin dimer, trimer (9), tetramers (11), and pentamer (12) were observed. Additionally, ions corresponding to the dimer, trimer, and tetramer with an additional hydroxyl group were observed (7,8,10). Thus, we observed masses corresponding to phoenicin with additional hydroxyl groups and different stages of polymerization.…”

“…10−12 Besides benzoquinones, the anthraquinones, which have a multicyclic aromatic structure, have attracted the most attention with one of the most investigated quinones as RFB negolyte being the 9,10anthraquinone-2,7-disulfonic acid (AQDS). 7,11,13,14 Even AQDS, which shows reasonable stability, possibly due to having two additional aromatic rings, 10 aggregates when dissolved by dimerization with its hydroquinone form producing a quinhydrone, or by dimerizing with another AQDS molecule. 8,15 It has been shown that the storage capacity of the self-dimerized AQDS is less than the two electrons per molecule of AQDS that is usually reported.…”

“…Research in aqueous organic redox flow batteries (AORFB) is aiming at overcoming the drawback of lithium batteries and vanadium RFBs for large-scale energy storage, which suffer from electrolyte materials that are expensive, dangerous, environmentally unfriendly, and geographically mined outside of the European Union and therefore may potentially be used in geopolitical conflicts. − With their high availability and biodegradability, organic electrolytes offer a possible solution to abundant and sustainable battery chemistry. , Especially quinones have gained a lot of interest as negolyte materials, most of them being capable of reversible redox chemistry involving two electrons per molecule. , Most of the quinones investigated suffer from low stability and the self-association of the organic molecules has been seen, resulting in the formation of dimers. , Stability issues among quinones mostly occur from degradation, e.g., Michael addition, dimerization, and nucleophilic substitution. , Benzoquinones are the simplest quinone form, having one aromatic ring with two carbonyl groups. These are well known for being prone to Michael addition with nucleophiles such as water, producing hydroquinone by the addition of hydroxyl groups to the unsubstituted carbon atoms. − Besides benzoquinones, the anthraquinones, which have a multicyclic aromatic structure, have attracted the most attention with one of the most investigated quinones as RFB negolyte being the 9,10-anthraquinone-2,7-disulfonic acid (AQDS). ,,, Even AQDS, which shows reasonable stability, possibly due to having two additional aromatic rings, aggregates when dissolved by dimerization with its hydroquinone form producing a quinhydrone, or by dimerizing with another AQDS molecule. , It has been shown that the storage capacity of the self-dimerized AQDS is less than the two electrons per molecule of AQDS that is usually reported . Recently, some anthraquinones such as 4,4′-((9,10-anthraquinone-2,6-diyl)­dioxy)­dibutyrate (2,6-DBEAQ), ((9,10-dioxo-9,10-dihydroanthracene-2,6-diyl)­bis­(oxy))­bis­(propane-3,1-diyl) (2,6-DPPEAQ) and 3,3′-(9,10-anthraquinone-diyl)­bis­(3-methylbutanoic acid) (DPivOHAQ), and 4,4′-(9,10-anthraquinone-diyl)­dibutanoic acid (DBAQ) have shown good cycling stability with a capacity fade rate of 0.05% day –1 or lower, wherein DPivOHAQ yielded a record low capacity fade rate of less than 1% per year.…”

Triarylamines as Catholytes in Aqueous Organic Redox Flow Batteries

“…The target solubility for organic electrolytes in aqueous RFBs for a commercially viable system is 2 m , but the vast majority of currently explored organic electrolytes struggle to meet this [6] . This balance between solubility and stability is a difficult tightrope to traverse, especially since the mere introduction of a solubilising functionality onto the anolyte or catholyte framework can result in decreased cycling stability or complete loss of electrochemical activity [7–9] . Nonetheless, the overall advantages of safety (due to the aqueous electrolyte), cost, and fast kinetics make the development of aqueous organic RFBs (AORFBs) an important area of study.…”

Demonstrating the Use of a Fungal Synthesized Quinone in a Redox Flow Battery

“…[18] As opposed to vanadium-based RFB systems, AORFBs employ electrolytes based on organic redox-active species from earth-abundant elements. [19] Among the most well-investigated compounds for AORFBs are quinones, which includes systems using anthraquinones, [20][21][22][23][24] benzoquinones, [5,25,26] and naphtoquinones, [27,28] viologens, [29][30][31][32] TEMPO-based (2,2,6,6tetramethylpiperidine-1-oxyl) organic radicals, [33][34][35][36] and ferrocenes, [6,37] as well as others. [38][39][40][41] The high interest in quinones as active materials in RFB electrolytes is based on both their ability to feature reversible two-electron redox reactions [42] and their structural diversity.…”