Cyclodextrin to boost flow battery

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Redox flow batteries have a unique architecture that potentially enables cost-effective long-duration energy storage to address the intermittency introduced by increased renewable integration for the decarbonization of the electric power sector. Targeted molecular engineering has demonstrated electrochemical reversibility in natively redox-inactive ketone molecules in aqueous electrolytes. However, the kinetics of fluorenone-based flow batteries continue to be limited by slow alcohol oxidation. We show how strategically designed proton regulators can accelerate alcohol oxidation and thus enhance battery kinetics. Fluorenone-based flow batteries with the organic additive β-cyclodextrin demonstrate enhanced rate capability, high capacity, and long cycling. This study opens a new avenue to improve the kinetics of aqueous organic flow batteries by modulating the reaction pathway with a homogeneous catalyst.

The researchers at Pacific  NorthWest  National Laboratory to boost battery longevity and capacity. In a series of experiments, the scientists optimized the ratio of chemicals in the system until it achieved 60 percent more peak power. Then they cycled the battery over and over for more than a year, only stopping the experiment when the plastic tubing failed. During all that time, the flow battery barely lost any of its activity to recharge. This is the first laboratory-scale flow battery experiment to report more than a year of continuous use with minimal loss of capacity. 

Beta-cyclodextrin was used first to improve the water solubility of fluorenon, but surprisingly it has a catalytic effect: accepts positively charged protons, which helps balance out the movement of negative electrons as the battery discharges thus speeding up the battery. This new advance makes the battery design a candidate for scale up.

Ruozhu Feng, Ying Chen, Xin Zhang, Sharon Hammes-Schiffer, Yuyan Shao, Wei Wang (2023) Proton-regulated alcohol oxidation for high-capacity ketone-based flow battery anolyte. Joule 7, 1609-1622.

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