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Aqueous Symmetrical Redox Flow Batteries Based Upon a pH-Responsive Cobalt Complex

preprint
submitted on 07.12.2019 and posted on 16.12.2019 by Hao Wang, Sayed Youssef Sayed, Yuqiao Zhou, Brian Olsen, Erik J. Luber, Jillian Buriak
Aqueous symmetric redox flow batteries (RFB) are of great interest due to the non-flammability and high conductivity of the solvent, and avoidance of irreversible anolyte crossover seen in asymmetric cells. In this work, we introduce a simple octahedral Co(II) complex, termed BCPIP-Co(II), that has 4 appended carboxylic groups on the ligand periphery that render it both water-soluble and pH-sensitive in the range of pH 1.5 - 5.5. The complex has reversible BCPIP-Co(II-III) and BCPIP-Co(II-I) redox couples within the water splitting window, as well as fast kinetics. The overall charge of the complex varies from +3 to -3, resulting from the level of deprotonation of the carboxylic acid moieties and the oxidation state of the cobalt metal center, both of which affect the resulting redox properties. BCPIP-Co(II) was then incorporated, as both the posolyte and negolyte, into a symmetric aqueous RFB, demonstrating Coulombic efficiencies >99% for up to 100 cycles.

Funding

Climate Change Innovation Technology Framework

Alberta Innovates Technology Futures (grant number CTDP-G2018000919)

Graduate scholarship from Alberta Innovates Technology Futures to HW

NSERC (grant numbers RGPIN-2014-05195 and RGPIN-2019-04346)

Future Energy Systems of the University of Alberta (https://futureenergysystems.ca; grant number T12-P04)

Alberta Innovates Technology Futures Industry Chair, (grant number AITF iCORE IC50- T1 G2013000198)

Western Economic Diversification (WD, grant number 000014328)

Canada Research Chairs program (CRC 207142)

History

Email Address of Submitting Author

jburiak@ualberta.ca

Institution

University of Alberta

Country

Canada

ORCID For Submitting Author

0000-0002-9567-4328

Declaration of Conflict of Interest

None

Version Notes

First version

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