Symmetric redox flow battery based on Blatter radicals

A Dutch-Danish research group has provided a proof of concept for the use of Blatter radicals in electrochemical energy-storage applications. It tested these compounds in a small electrochemical cell that was found to remain stable over 275 charge/discharge cycles.

Blatter radicals are organic compounds that have remarkable electronic and magnetic properties, strong chemical and thermal stability and reversible redox properties. All these characteristics make them potentially suitable for several applications, including their use in redox flow batteries.

A Dutch-Danish research team has used these compounds, which are also known as 1,2,4-benzotriazin-4-yl radicals, to build a prototype of a symmetric redox flow battery for applications in stationary storage. “Blatter radicals combine tunable redox potentials and high stability in all relevant redox states necessary for application as redox-active components in redox flow batteries,” the academics stated.

The scientists selected a single molecule that is intrinsically stable and that can accept or donate electrons, which means it can be used on both sides of the battery and, at the same time, show how minimal capacity fade during battery cycling.

The Blatter radical used in the experiments, that can act as electron donor and acceptor.

Image: E. Otten, University of Groningen

The special compound was used in a small electrochemical cell and was found to remain stable over 275 charge/discharge cycles. “We need to bring this up to thousands of cycles; however, our experiments are a proof of concept. It is possible to make a symmetrical flow battery that has good stability,” said Edwin Otten, Associate Professor of Molecular Inorganic Chemistry at the University of Groningen.

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“Another advantage of our symmetrical design is that it is not a big problem if some of our compound crosses the membrane during use,” explained Otten. “This could result in a slightly higher volume in one of the tanks but any imbalance is easily restored by simply reversing the polarity,”

A full description of the battery technology can be found in the study Blatter Radicals as Bipolar Materials for Symmetrical Redox-Flow Batteries, published in ACS Publications. The research group includes scientists from the University of Groningen and the University of Eindhoven in the Netherlands, as well as from the Technical University of Denmark. “We have shown that 1,2,4-benzotriazin-4-yl radicals combine bipolar electrochemistry with high chemical stability in all states of charge, which renders these compounds promising energy-storage materials for symmetric redox-flow batteries,” it concluded.

Looking forward, the academics are planning to develop a water-soluble version of the Blatter radicals.

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