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Nonaqueous redox flow batteries (NARFBs) offer a promising solution for large-scale storage of renewable energy. However, crossover of redox active molecules between the two sides of the cell is a major factor limiting their development, as most selective separators are designed for deployment in water, rather than organic solvents. This report describes a systematic investigation of the crossover rates of redox active organic molecules through an anion exchange separator under RFB-relevant non-aqueous conditions (in acetonitrile/KPF6) using a combination of experimental and computational methods. A structurally diverse set of neutral and cationic molecules was selected, and their rates of crossover were determined experimentally with the organic solvent-compatible anion exchange separator Fumasep FAP-375-PP. The resulting data were then fit to various descriptors of molecular size, charge, and hydrophobicity (overall charge, solution diffusion coefficient, globularity, dynamic volume, dynamic surface area, clogP). This analysis resulted in multiple statistical models of crossover rates for this separator. These models were then used to predict tether groups that dramatically slow the crossover of small organic molecules in this system.
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Metal-free polypeptide redox flow batteries
Non-aqueous organic redox flow batteries (NAORFBs) are considered emerging large-scale energy storage systems due to their larger voltage window as compared to aqueous systems and their metal-free nature. However, low solubility, sustainability, and crossover of redox materials remain major challenges for the development of NAORFBs. Here, we report the use of redox active α-helical polypeptides suitable for NAORFBs. The polypeptides exhibit less crossover than small molecule analogs for both Daramic 175 separator and FAPQ 375 PP membrane, with FAPQ 375 PP preventing crossover most effectivley. Polypeptide NAORFBs assembled with a TEMPO-based polypeptide catholyte and viologen-based polypeptide anolyte exhibit low capacity fade ( ca. 0.1% per cycle over 500 cycles) and high coulombic efficiency (>99.5%). The polypeptide NAORFBs exhibit an output voltage of 1.1 V with a maximum capacity of 0.53 A h L −1 (39% of the theoretical capacity). After 500 charge–discharge cycles, 60% of the initial capacity was retained. Post cycling analysis using spectral and electrochemical methods demonstrate that the polypeptide backbone and the ester side chain linkages are stable during electrochemical cycling. Taken together, these polypeptides offer naturally-derived, deconstructable platforms for addressing the needs of metal-free energy storage.
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- PAR ID:
- 10349356
- Date Published:
- Journal Name:
- Materials Advances
- Volume:
- 3
- Issue:
- 16
- ISSN:
- 2633-5409
- Page Range / eLocation ID:
- 6558 to 6565
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d2ma00498d
