Non-Aqueous Redox Flow Battery Material with High Current Density: MEEPT

Odom et al. have recently developed 10-[2-(2-methoxyethoxy)ethyl]-10H-phenothiazine (MEEPT, 1) which features a redox active phenothiazine core and an alkoxy chain to increase solubility in non-aqueous media.
1 acts as a catholyte material for a non-aqueous redox flow battery (RFB), and is miscible with non-aqueous organic solvents to provide electrolyte solutions with high concentration. In addition, 1 shows high current density and long duration cycling for further development of a non-aqueous RFB.¹⁾

Figure 1. Electrochemical and Spectral Properties of MEEPT/MEEPT⁺

(a) Cyclic voltammogram of MEEPT at 10 mM in 0.1 M TBAPF₆ in DCM recorded at scan rates from 10 to 500 mV/s. (b) UV-vis spectra of MEEPT-SbCl₆ at 0.15 mM in acetonitrile for up to 24 h after dissolution. (These graphical materials were provided by Prof. Odom.)

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Glossary: Redox flow battery
Redox flow batteries (RFB) have long duration cycling by charge/discharge, which may have applications for grid level energy storage. RFB may be useful for large energy storage by increasing battery scale; however, it cannot be compact due to low energy density. Aqueous RFB’s using vanadium ion and water-soluble organic active materials in particular have received much attention.^1,2) Alternatively, organic solvents (e.g. acetonitrile, carbonate) can be expected to improve solubility of organic active materials to increase energy density.³⁾

1) M. Skyllas-Kazacos, L. Cao, M. Kazacos, N. Kausar, A. Mousa, ChemSusChem 2016, 9, 1521. (DOI: 10.1002/cssc.201600102) 2) E. S. Beh, D. De Porcellinis, R. L. Gracia, K. T. Xia, R. G. Gordon, M. J. Aziz, ACS Energy Lett. 2017, 2, 639. (DOI: 10.1021/acsenergylett.7b00019) 3) J. Winsberg, T. Hagemann, T. Janoschka, M. D. Hager, U. S. Schubert, Angew. Chem. Int. Ed. 2017, 56, 686. (DOI: 10.1002/anie.201604925)

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