Alkaline Quinone Flow Battery with Long Lifetime at pH 12

Abstract

This work demonstrates a new, organic redox-flow battery (RFB) that outlives its predecessors, offering the longest-lived high-performance organic flow battery to date. It appears to be the first aqueous-soluble organic RFB chemistry to meet all the technical criteria for commercialization. The potential low reactant and membrane costs of this chemistry offer the potential for RFBs of this type to be used cost effectively at the gigawatt scale in order to enable massive penetration of intermittent renewable electricity.

A Phosphonate‐Functionalized Quinone Redox Flow Battery at Near‐Neutral pH with Record Capacity Retention Rate

“…[6a,c,d] Recently, we reported a negative electrolyte (negolyte) comprising 4,4-((9,10-anthraquinone-2,6-diyl)dioxy) dibutyrate (2,6-DBEAQ), [9] that combines high chemical stability with an OCV of ≥1.0 V against a potassium ferri/ferrocyanide positive electrolyte (posolyte). Among the most promising solutions are redox-flow batteries (RFBs), which store the electro-active chemical species separately from the power-generating electrode stack, through which the reactants are pumped during operation.…”

“…[6a,c,d] Recently, we reported a negative electrolyte (negolyte) comprising 4,4-((9,10-anthraquinone-2,6-diyl)dioxy) dibutyrate (2,6-DBEAQ), [9] that combines high chemical stability with an OCV of ≥1.0 V against a potassium ferri/ferrocyanide positive electrolyte (posolyte). Due to the generally low chemical stability of these reactants, most existing systems experience high temporal capacity fade rates on the order of 0.1-10% per day, which limits their long-term use and renders most of these chemistries unsuitable for commercialization.…”

“…[9] Notably, cleavage of a second γ-hydroxybutyrate moiety leads to 2,6-dihydroxyanthraquione (2,6-DHAQ), whose capacity fade rate has been reported as 5% per day. Chemical stability studies at elevated temperature indicate that the oxidized form of 2,6-DBEAQ is susceptible to decomposition by γ-hydroxybutyrate cleavage (Scheme 1), as confirmed by 1 H NMR.…”

“…Chemical stability studies at elevated temperature indicate that the oxidized form of 2,6-DBEAQ is susceptible to decomposition by γ-hydroxybutyrate cleavage (Scheme 1), as confirmed by 1 H NMR. [9] Noting the influence of pH on the degradation rate and that both hydroxide and carboxylate may act as nucleophiles in the decomposition (Scheme 1), we therefore expect further enhancement in stability either by operating at lower pH conditions or by suppressing carboxylate-mediated intramolecular nucleophilic substitution. [9,11] The rate of 2,6-DBEAQ decomposition has been shown to be considerably slower at pH 12 relative to pH 14 at 95 °C and 0.1 m concentration ( Figure 1E,F and Figure S8, Supporting Information).…”

“…To examine the pH reversibility and cycling stability, a cell was assembled with a negolyte comprising 0.1 m of the tetrapotassium salt of 2,6-DPPEAQ in 1 m KCl, the pH of which was monitored by a pH probe immersed in the solution, and a posolyte comprising 0.1 m K 4 Fe(CN) 6 and 0.01 m K 3 Fe(CN) 6 in 1 m KCl, separated by a Fumasep E-620 (K) membrane ( Figure 2B,C). 2019, 9,1900039 Figure 1. Operating at pH values as low as 9 enhances the stability not only of the negolyte but also of the posolyte, as the decomposition rate of ferricyanide, which is typically used as a posolyte species in alkaline batteries, is increased at high pH.…”