Aqueous electrolyte for high temperature redox flow battery designs

September 25, 2020 // By Nick Flaherty
Test lab for ferrocene flow battery aqueous electrolyte
Researchers in Germany have used a ferrocene co-polymer electrolyte that can operate up to 60ºC and more efficiently than other materials

Researchers at the Friedrich Schiller University in Jena, Germany have developed a polymer electrolyte for redox flow batteries that operates at higher temperatures, opening up storage battery applications around the world.

"In this type of battery, the energy-storing components are dissolved in a solvent and can therefore be stored at a decentralised location, which allows the battery to be scaled as required, from a few millilitres to several cubic metres of electrolyte solution," said Prof. Dr Ulrich S. Schubert of the Center for Energy and Environmental Chemistry Jena (CEEC Jena) at the Friedrich Schiller University.

Redox flow batteries, often using vanadium, generally have a great potential to become an important means of energy storage in the future but suffer from two weaknesses that have prevented their widespread use. The first was the frequent usage of environmentally hazardous and toxic heavy metal salts, such as vanadium dissolved in sulfuric acid, as electrolytes. The other problem was the restriction of the batteries to a maximum working temperature of 40ºC, which means an elaborate cooling system is needed. The new electrolyte based on a ferrocene co-polymer tackles both these challenges.

"We have designed a new type of polymer that is soluble in water, which makes it suitable for use in an aqueous electrolyte, and that contains iron, which provides the ability to store electricity," said Schubert. "At the same time, the polymer can cope with a significantly higher temperature of up to 60ºC, so that the additional expense for a sensitive temperature management is eliminated." Test with the electrolyte by the Jena researchers discovered that it also works more efficiently than its predecessors with a coulombinc efficiency of over 99.8 percent, a key figure when the electrolyte is used over and over again.

All this means that electricity can be stored in a non-hazardous, water-based solution, which is then stored temporarily in tanks, and the electricity in the battery can be used

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