The widespread deployment of renewable energies such as wind and solar has increased the demand for energy storage. Redox-flow batteries are scalable energy-storage devices that are one of the most promising scalable electricity-storage systems to address the intermittency issues of renewable energy sources.

Researchers from the P.G. and Research Department of Chemistry at Christ College in Kerala, India, have claimed to have developed a dendrite-free zinc-iron redox flow battery. The paper, titled A Dendrite Free Zn-Fe Hybrid Redox Flow Battery for Renewable Energy Storage”, was published in the Energy Storage journal.

Previously, redox-flow batteries have used materials like vanadium, copper, iron, and lead. According to the researchers, none of these were suitable for commercialization due to factors such as high costs, toxicity, low energy efficiency, low cell voltage, hydrogen evolution, and coulombic loss, to name a few.

Researchers have now come up with a dendrite-free zinc-iron redox-flow battery. The abundance and relatively lower costs make zinc a viable option to commercialize the production of redox flow batteries.

The researchers fabricated a novel zinc-iron hybrid redox flow battery (Zn/Fe hybrid RFB), in which Zn/Zn(II) redox acted as the negative redox material and Fe(II)/Fe(III) redox as the positive redox material. A self-made anion exchange membrane separated the two redox couples. Densified graphite sheets were used for the electrodes; cell housings were made of acrylic sheets. Researchers stated that zinc and iron are advantageous elements for energy storage due to their low cost and abundance. Due to its rapid kinetics, ferric/ferrous chloride redox pair, used in various flow battery systems, is promising as active material on the battery’s positive side.

The battery supposedly delivered an average discharge voltage of 1.34V at 25 mA cm-2 approximately, with a high average coulombic efficiency of 92%, voltage efficiency of 85%, and energy efficiency of 78.2% over 30 cycles at 298 Kelvin.

According to the researchers, this version of a zinc-iron hybrid redox flow battery is notable because it overcame serious drawbacks that many previous iterations of zinc-based redox flow batteries had reported by achieving homogenous zinc coatings and no dendrite growth on zinc electrodes after repeated galvanostatic charge and discharge cycles.

Previously, researchers at TU Graz University claimed that they had developed a redox flow battery that utilizes conventional vanillin instead of liquid electrolyte, making the battery more environmentally friendly.

Researchers at Friedrich Schiller University said that they had developed a new polymer electrolyte for redox flow batteries that enhances its efficiency and heat-resistance capacity.