A Sulfonate-Functionalized Viologen Enabling Neutral Cation Exchange, Aqueous Organic Redox Flow Batteries toward Renewable Energy Storage
2018-02-13T00:00:00Z (GMT) by
Redox flow batteries using synthetically tunable and resource abundant organic molecules have gained increasing attention for large-scale energy storage. Herein we report a sulfonate-functionalized viologen molecule, 1,1′-bis(3-sulfonatopropyl)-4,4′-bipyridinium, <b>(SPr)</b><sub><b>2</b></sub><b>V</b>, as an anolyte in neutral aqueous organic redox flow batteries (AORFBs) functioning through a cation charge-transfer mechanism. Demonstrated <b>(SPr)</b><sub><b>2</b></sub><b>V</b>/KI AORFBs manifested high current performance from 40 to 100 mA/cm<sup>2</sup> with up to 71% energy efficiency. In extended cycling studies, the <b>(SPr)</b><sub><b>2</b></sub><b>V</b>/KI redox flow battery delivered stable cycling performance at 60 mA/cm<sup>2</sup>, up to 67% energy efficiency, and 99.99% capacity retention per cycle. Density functional theory modeling of the electrostatic charge surface of <b>(SPr)</b><sub><b>2</b></sub><b>V</b> and its charged state, <b>[(SPr)</b><sub><b>2</b></sub><b>V]</b><sup><b>–1</b></sup>, suggests charge repulsion and size exclusion enable their compatibility with a cation exchange membrane. The present findings expand the battery design of neutral viologen AORFBs and represent an attractive RFB technology for sustainable and benign renewable energy storage.