Indian Scientists Make Dendrite-free Zinc-iron Redox Flow Battery

Indian scientists have created a redox flow battery based on zinc and iron, which showed strong storage characteristics and no signs of degradation over 30 charge-discharge cycles. Additionally, the battery did not show any signs of dendrite formation, overcoming one of the key challenges for redox-flow batteries based on these low-cost, abundant materials.

The researchers described their invention in the paper “A Dendrite Free Zn-Fe Hybrid Redox Flow Battery for Renewable Energy Storage,” published in the journal Energy Storage. The full paper can be accessed here.

About two thirds of global greenhouse emissions is caused by burning of fossil fuels for energy purposes and this has spurred great research interest to develop renewable energy technologies based on wind, solar power etc. Redox Flow Batteries (RFB) are receiving wide attention as scalable energy-storage systems to address the intermittency issues of renewable energy sources.

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However, for widespread commercialization, the redox flow batteries should be economically viable and environmentally friendly. Zinc based batteries are good choice for energy storage devices because zinc is earth abundant and zinc metal has a moderate specific capacity of 820 mA hg−1 and high volumetric capacity of 5851 mA h cm−3. In their paper, the scientists demonstrate a zinc-iron (Zn-Fe) hybrid RFB employing Zn/Zn(II) and Fe(II)/Fe(III) redox couples as positive and negative redox systems, respectively, separated by a self-made anion exchange membrane (AEM).

The battery, say the scientists, delivers a good discharge voltage of approximately 1.34 V at 25 mA cm−2, with a coulombic efficiency (CE) of 92%, voltage efficiency (VE) of 85% and energy efficiency (EE) of ~78% for 30 charge-discharge cycles. Repeated galvanostatic charge/discharge cycles show no degradation in performance, confirming the excellent stability of the system.

A key advancement in the present Zn-Fe hybrid redox flow battery with AEM separator is that no dendrite growth was observed on zinc electrode on repeated charge-discharge cycles, which was the serious drawback of many previously reported zinc based redox flow batteries.

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This study’s results show that the operating conditions are crucial impact factors for the cell performance and the Zn-Fe RFB can exhibit good performance at low concentration (1 M) and at low current density (15 mA cm-2). “Thus, we have successfully demonstrated working of a high efficiency and stable Zn-Fe hybrid redox flow battery with no dendrite growth during zinc deposition by optimizing charge-discharge conditions and employing an anion exchange membrane as separator,” conclude the scientists.

The paper was co-authored by C. B. Jeena, P. J. Elsa, P. P. Moly, K. J. Ambily, and V. T. Joy, and the research was supported by the P.G. and Research Department of Chemistry, Christ College, Kerala.