Improvement in the Performance of an Fe/Fe^II Electrode in an All‐Iron Redox Flow Battery by the addition of Zn^II ions

Abstract

Redox flow batteries are the most promising large‐scale energy storage technologies for solving intermittency issues of renewable energy sources such as wind, solar, etc. They have favorable features over other battery technologies like high energy efficiency, intrinsic safety, independent scaling, and a long lifetime. Among various RFBs, all‐Iron redox flow batteries are an attractive choice because iron is the second most abundant metal in earth's crust, is cheap and ecofriendly. However, low charging efficiency, parasitic hydrogen evolution reaction (HER) at the negative Fe/FeII electrode, self‐discharge by electrolyte cross‐over, and poor cycle‐life (due to ferric hydroxide precipitation) are the major technical challenges to be overcome for the successful commercialization of all‐iron redox flow batteries. Herein, we report an all‐iron redox flow battery containing Fe/FeII and FeIII/FeII redox couples separated by a self‐made anion exchange membrane. We also examined the impact of adding ZnII ions on the electrochemical performance of the Fe/FeII redox couple. The coulombic efficiency, voltage efficiency and energy efficiency of the cell with 0.03 m ZnCl2 was found to be greater (90 %, 70.96 % and 63.86 %) than those of the cell without ZnCl2 (80 %, 62.06 % and 49.64 %). The results reveal that the addition of small amounts of ZnII ions to the Fe/FeII electrode suppresses the hydrogen evolution reaction and increase the cell performance.

A Review on the Recent Advances in Battery Development and Energy Storage Technologies

“…As a result, the Coulombic efciency (CE) as well as battery capacity are permanently lost, which afects RFBs' overall performance. A self-made anion exchange membrane separates the two redox couples in a zinc-iron hybrid redox fow battery (Zn/Fe hybrid RFB), which uses Zn/Zn (II) and Fe(II)/Fe(III) redox couples as negative and positive redox materials, respectively [218]. Because of their low cost as well as abundance, zinc and iron are the two best elements for energy storage.…”

“…Sheets of densifed graphite have been used as the electrodes, while acrylic sheets have been used as the cell housings [213]. Te Fe 2+ ions at the negative electrode pick up these electrons during battery charging and electrodeposit them as metallic Fe; the Fe 2+ ions at the positive electrode release the electrons and oxidize to become Fe 3+ ions [218]. Chloride ions pass across the anion exchange membrane from the negative electrolyte into the positive electrolyte to maintain charge neutrality.…”

Review—Flow Batteries from 1879 to 2022 and Beyond

“…We shall mention in passing all-iron hybrid flow batteries (AIHFBs), based on the chemistry shown in Eqs. This chemistry has a record-low capital cost of energy, 366,367 and not surprisingly it attracted attention of some developers, such as those in the USA (CWRU,, 15,20,368,369 LBNL, 367 USC, 370 UCSD, 371 Honeywell, 372 ), in India, [373][374][375][376][377][378] in China, 375,379,380 and in Germany. [381][382][383] Typically, carbon felts are used as insoluble posodes and negodes in such batteries, and the operating current densities are 10, 384 20, 371 25, 378 50, 368,374,376 100 mA cm −2 during charge and 10, 383 20, 372 50 369,375,382,386 -100 368,370,374,377,382 mA cm −2 during discharge.…”

A Double‐ligand Chelating Strategy to Iron Complex Anolytes with Ultrahigh Cyclability for Aqueous Iron Flow Batteries

“…[9] Techno-economic modeling has implicated all-iron flow batteries (AIFBs) as a desirable technology for next-generation large-scale energy storage devices. [10] The first AIFB was built as early as 1981, using Fe 3 + /Fe 2 + as the cathodic redox couple and Fe 2 + /Fe 0 as the anodic redox couple. [11] As solid metallic iron formates at anodes in the charge reaction, the energy and power are no longer wholly decoupled.…”

“…The global reserves of iron (400 billion tons) are over 25,000 times than vanadium (15 million tons) [9] . Techno‐economic modeling has implicated all‐iron flow batteries (AIFBs) as a desirable technology for next‐generation large‐scale energy storage devices [10] . The first AIFB was built as early as 1981, using Fe 3+ /Fe 2+ as the cathodic redox couple and Fe 2+ /Fe 0 as the anodic redox couple [11] .…”