Please cite this article in press as: Wu et al., Extremely Stable Anthraquinone Negolytes Synthesized from Common Precursors, Chem (2020),
Article
Extremely Stable Anthraquinone Negolytes
Synthesized from Common Precursors
Min Wu,1 Yan Jing,2 Andrew A. Wong,1 Eric M. Fell,1 Shijian Jin,1 Zhijiang Tang,1 Roy G. Gordon,1,2,
*
SUMMARY
The Bigger Picture
The cost of solar and wind
Synthetic cost and long-term stability remain two of the most challenging bar-
riers for the utilization of redox-active organic molecules in redox flow batteries
for grid-scale energy storage. Starting from potentially inexpensive 9,10-dihy-
droanthracene, we developed a new synthetic approach for two extremely sta-
ble anthraquinone negolytes, i.e., 3,30-(9,10-anthraquinone-diyl)bis(3-methyl-
butanoic acid) (DPivOHAQ) and 4,40-(9,10-anthraquinone-diyl)dibutanoic acid
(DBAQ). Pairing with a ferrocyanide posolyte at pH 12, DPivOHAQ and DBAQ
can transfer up to 1.4 and 2 M electrons with capacity fade rates of 0.014%
per day and 0.0084% per day, respectively, and exhibit 1.0 V of open-circuit
voltage. By adjusting the supporting electrolytes to pH 14, DPivOHAQ ex-
hibited a record low capacity fade rate of <1% per year. We attribute the capac-
ity loss of these flow batteries primarily to the formation of anthrone, which can
be suppressed by increasing the pH of the electrolyte and reversed by exposure
to air.
electricity is decreasing so rapidly
that a grid-scale energy storage
technology will become essential.
Aqueous organic redox flow
batteries are a potentially safe,
inexpensive substitute for lithium-
ion batteries and vanadium flow
batteries for large-scale energy
storage. Here, we report a new
synthetic strategy for two
extremely stable anthraquinone
negolyte (negative electrolyte)
molecules starting from
inexpensive precursors that
potentially decrease the cost
when scaled up. Additionally, we
demonstrate that an
INTRODUCTION
The cost of solar and wind electricity has dropped so precipitously that the main bar-
rier to widespread implementation is their intrinsic intermittency.1–3 A safe, low-cost,
large-scale electrical energy storage system could enable grid-scale adoption of re-
newables. Among the numerous proposed technologies, redox flow batteries (RFBs)
have been recognized as a potentially viable strategy to address the intermittency of
renewable energy.2–4 Compared with conventional stationary rechargeable batte-
ries (e.g., lithium-ion batteries and lead-acid batteries), RFBs use redox-active mate-
rials dissolved in liquid supporting electrolytes that are stored in external tanks and
separated from the power generation stack. This separation allows for the decou-
pling of energy capacity from output power capacity, thereby providing the possibil-
ity of low-cost long-duration discharge.2–4
anthraquinone negolyte is more
stable running at pH 14 than at pH
12, and is expected to be more
stable in alkaline solution than in
acidic or neutral conditions.
3ꢀ/4ꢀ
Paired with a Fe(CN)6
positive electrolyte, the
anthraquinone cell exhibited a
record low capacity fade rate of
<1% per year. The new synthetic
strategy for these highly stable
anthraquinone negolytes might
facilitate the commercialization of
anthraquinone-based flow
batteries.
Aqueous RFBs, featuring non-flammable electrolytes, are particularly suitable for storing
massive amounts of electricity. Aqueous vanadium RFBs are the most widely studied and
adopted systems, but are hindered by the high cost of vanadium.3–5 In contrast, redox-
active organic molecules comprising earth abundant elements such as carbon (C),
hydrogen (H), oxygen (O), and nitrogen (N) have the potential to be inexpensive alterna-
tives to vanadium.6–13 Additionally, the structural diversity and tunability of organics
enable chemists to design organics with essential properties such as high aqueous solu-
bility, high chemical stability, fast kinetics, and appropriate redox potential.6,8–12,14,15
Recently, water-soluble anthraquinones 4,40-([9,10-anthraquinone-2,6-diyl]dioxy)di-
butyrate (2,6-DBEAQ) and (([9,10-dioxo-9,10-dihydroanthracene-2,6-diyl]bis[oxy])
Chem 6, 1–11, June 11, 2020 ª 2020 Elsevier Inc.
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