An official website of the United States government
Abstract 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 1.23mand 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.
more »
« less
Highly Stable, Low Redox Potential Quinone for Aqueous Flow Batteries**
Abstract Aqueous organic redox flow batteries are promising candidates for large‐scale energy storage. However, the design of stable and inexpensive electrolytes is challenging. Here, we report a highly stable, low redox potential, and potentially inexpensive negolyte species, sodium 3,3′,3′′,3′′′‐((9,10‐anthraquinone‐2,6‐diyl)bis(azanetriyl))tetrakis(propane‐1‐sulfonate) (2,6‐N‐TSAQ), which is synthesized in a single step from inexpensive precursors. Pairing 2,6‐N‐TSAQ with potassium ferrocyanide at pH=14 yielded a battery with the highest open‐circuit voltage, 1.14 V, of any anthraquinone‐based cell with a capacity fade rate <10 %/yr. When 2,6‐N‐TSAQ was cycled at neutral pH, it exhibited two orders of magnitude higher capacity fade rate. The great difference in anthraquinone cycling stability at different pH is interpreted in terms of the thermodynamics of the anthrone formation reaction. This work shows the great potential of organic synthetic chemistry for the development of viable flow battery electrolytes and demonstrates the remarkable performance improvements achievable with an understanding of decomposition mechanisms.
more »
« less
- Award ID(s):
- 1914543
- PAR ID:
- 10395060
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Batteries & Supercaps
- Volume:
- 5
- Issue:
- 6
- ISSN:
- 2566-6223
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract An iron complex, tris(4,4′‐bis(hydroxymethyl)‐2,2′‐bipyridine) iron dichloride is reported, which operates at near‐neutral pH with a redox potential of 0.985 V versus SHE. This high potential compound is employed in the posolyte of an aqueous flow battery, paired with bis(3‐trimethylammonio)propyl viologen tetrachloride in the negolyte, exhibiting an open‐circuit voltage of 1.3 V at near‐neutral pH. It demonstrates excellent cycling performance with a low temporal capacity fade rate of 0.07% per day over 35 days of cycling. The extended cycling lifetime is the result of low permeability and improved structural stability of the newly developed iron complex compared to that of the iron tris(bipyridine) complex. The combination of high redox potential and low capacity fade rate compares favorably with those of all previously demonstrated organic and organometallic aqueous posolytes. Extensive investigation into the possible degradation mechanisms, including post‐mortem chemical and electrochemical analyses, indicates that stepwise ligand dissociations of the iron complex are responsible for the reported capacity loss during cell cycling. This investigation provides unprecedented insight to guide further improvements of such metalorganic compounds for energy storage and conversion applications.more » « less
-
Abstract Aqueous organic redox flow batteries (AORFBs) have received increasing attention as an emergent battery technology for grid‐scale renewable energy storage. However, physicochemical properties of redox‐active organic electrolytes remain fine refinement to maximize their performance in RFBs. Herein, we report a carboxylate functionalized viologen derivative, N,N′‐dibutyrate‐4,4′‐bipyridinium,(CBu)2V, as a highly stable, high capacity anolyte material under near pH neutral conditions.(CBu)2Vcan achieve solubility of 2.1 M and display a reversible, kinetically fast reduction at −0.43 V vs NHE at pH 9. DFT studies revealed that the high solubility of(CBu)2Vis attributed to its high molecular polarity while its negative reduction potential is benefitted from electron‐donating carboxylate groups. A 0.89 V (CBu)2V/(NH)4Fe(CN)6AORFB demonstrated exceptional energy storage performance, specifically, 100 % capacity retention with a discharge energy density of 9.5 Wh L−1for 1000 cycles, power densities of up to 85 mW cm−2, and an energy efficiency of 70 % at 60 mA cm−2.(CBu)2Vnot only represents the most capacity dense viologen with pendant ionic groups and also exhibits the longest (1200 hours or 50 days) and the most stable flow battery performance to date.more » « less
-
Abstract Organic redox-active molecules are attractive as redox-flow battery (RFB) reactants because of their low anticipated costs and widely tunable properties. Unfortunately, many lab-scale flow cells experience rapid material degradation (from chemical and electrochemical decay mechanisms) and capacity fade during cycling (>0.1%/day) hindering their commercial deployment. In this work, we combine ultraviolet-visible spectrophotometry and statistical inference techniques to elucidate the Michael attack decay mechanism for 4,5-dihydroxy-1,3-benzenedisulfonic acid (BQDS), a once-promising positive electrolyte reactant for aqueous organic redox-flow batteries. We use Bayesian inference and multivariate curve resolution on the spectroscopic data to derive uncertainty-quantified reaction orders and rates for Michael attack, estimate the spectra of intermediate species and establish a quantitative connection between molecular decay and capacity fade. Our work illustrates the promise of using statistical inference to elucidate chemical and electrochemical mechanisms of capacity fade in organic redox-flow battery together with uncertainty quantification, in flow cell-based electrochemical systems.more » « less
-
Abstract Redox‐active anthraquinone molecules represent promising anolyte materials in aqueous organic redox flow batteries (AORFBs). However, the chemical stability issue and corrosion nature of anthraquinone‐based anolytes in reported acidic and alkaline AORFBs constitute a roadblock for their practical applications in energy storage. A feasible strategy to overcome these issues is migrating to pH‐neutral conditions and employing soluble AQDS salts. Herein, we report the 9,10‐anthraquinone‐2,7‐disulfonic diammonium saltAQDS(NH4)2, as an anolyte material for pH‐neutral AORFBs with solubility of 1.9 min water, which is more than 3 times that of the corresponding sodium salt. Paired with an NH4I catholyte, the resulting pH‐neutral AORFB with an energy density of 12.5 Wh L−1displayed outstanding cycling stability over 300 cycles. Even at the pH‐neutral condition, theAQDS(NH4)2 /NH4I AORFB delivered an impressive energy efficiency of 70.6 % at 60 mA cm−2and a high power density of 91.5 mW cm−2at 100 % SOC. The present AQDS(NH4)2flow battery chemistry opens a new avenue to apply anthraquinone molecules in developing low‐cost and benign pH‐neutral flow batteries for scalable energy storage.more » « less
