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A biomimetic high-capacity phenazine-based anolyte for aqueous organic redox flow batteries


Aqueous soluble organic (ASO) redox-active materials have recently attracted significant attention as alternatives to traditional transition metal ions in redox flow batteries (RFB). However, reported reversible capacities of ASO are often substantially lower than their theoretical values based on the reported maximum solubilities. Here, we describe a phenazine-based ASO compound with an exceptionally high reversible capacity that exceeds 90% of its theoretical value. By strategically modifying the phenazine molecular structure, we demonstrate an increased solubility from near-zero with pristine phenazine to as much as 1.8 M while also shifting its redox potential by more than 400 mV. An RFB based on a phenazine derivative (7,8-dihydroxyphenazine-2-sulfonic acid) at its near-saturation concentration exhibits an operating voltage of 1.4 V with a reversible anolyte capacity of 67 Ah l−1 and a capacity retention of 99.98% per cycle over 500 cycles.

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Fig. 1: Molecular structure and computationally predicted properties of phenazine derivatives.
Fig. 2: Coulombic potential map of phenazine and candidates with highest calculated solvation energy.
Fig. 3: NMR spectra of DHPS at low and high concentrations.
Fig. 4: Cyclic voltammograms of selected phenazine derivatives.
Fig. 5: Low-concentration flow battery performance.
Fig. 6: High-concentration flow battery performance.

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The authors would like to acknowledge financial support from the US Department of Energy's Office of Electricity Delivery and Energy Reliability (under Contract No. 57558). The mass spectrometry measurements, NMR measurements and theoretical calculations were performed at the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the US Department of Energy's Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. We thank A. Andersen (Environmental Molecular Sciences Laboratory) for helpful discussions regarding redox potential calculations and R. Chu (Environmental Molecular Sciences Laboratory) for performing mass spectrometry analysis. Pacific Northwest National Laboratory is a multi-programme national laboratory operated by Battelle for the US Department of Energy under contract DE-AC05-76RL01830. X.W. thanks Indiana University-Purdue University Indianapolis for providing research startup funding support during the manuscript review process.

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X.W. and W.W. conceived the research. A.H., V.M., X.W. and W.W. designed the experiments. A.H., Z.N. and B. L. performed the experiments and measurements. V.M. performed DFT calculations and NMR. All authors discussed the results. D.R., J.L. and V.S. revised the manuscript. A.H., V.M., X.W. and W.W. wrote the paper with input from all authors.

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Correspondence to Xiaoliang Wei or Wei Wang.

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Supplementary Figures 1–9, Supplementary Tables 1–3, Supplementary References

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Hollas, A., Wei, X., Murugesan, V. et al. A biomimetic high-capacity phenazine-based anolyte for aqueous organic redox flow batteries. Nat Energy 3, 508–514 (2018).

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