Volume 63, Issue 9 e202316593
Research Article

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

Shaocong Wang

Shaocong Wang

State Key Laboratory of Organic-Inorganic Composites, College of Chemical Engineering, Beijing University of Chemical Technology, Beijing, 100029 P. R. China

These authors contributed equally to this work.

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Long Ma

Long Ma

State Key Laboratory of Organic-Inorganic Composites, College of Chemical Engineering, Beijing University of Chemical Technology, Beijing, 100029 P. R. China

These authors contributed equally to this work.

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Shiyang Niu

Shiyang Niu

State Key Laboratory of Organic-Inorganic Composites, College of Chemical Engineering, Beijing University of Chemical Technology, Beijing, 100029 P. R. China

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Shibo Sun

Shibo Sun

State Key Laboratory of Organic-Inorganic Composites, College of Chemical Engineering, Beijing University of Chemical Technology, Beijing, 100029 P. R. China

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Yong Liu

Yong Liu

State Key Laboratory of Organic-Inorganic Composites, College of Chemical Engineering, Beijing University of Chemical Technology, Beijing, 100029 P. R. China

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Prof. Yuanhui Cheng

Corresponding Author

Prof. Yuanhui Cheng

State Key Laboratory of Organic-Inorganic Composites, College of Chemical Engineering, Beijing University of Chemical Technology, Beijing, 100029 P. R. China

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First published: 07 January 2024
Citations: 16

Graphical Abstract

A double-ligand chelating strategy was proposed to design Fe(TEA)MM complex as anolyte materials with high binding energy, robust coordination structure, highly electrochemical activity and good reversibility. All iron flow batteries based on Fe(TEA)MM anolytes and Fe(CN)6 catholytes reach a low capital cost of $ 33.2 kWh−1 and record-breaking cycling stability without detectable energy efficiency and capacity decay during 1400 cycles.

Abstract

Aqueous all-iron flow batteries (AIFBs) are attractive for large-scale and long-term energy storage due to their extremely low cost and safety features. To accelerate commercial application, a long cyclable and reversible iron anolyte is expected to address the critical barriers, namely iron dendrite growth and hydrogen evolution reaction (HER). Herein, we report a robust iron complex with triethanolamine (TEA) and 2-methylimidazole (MM) double ligands. By introducing two ligands into one iron center, the binding energy of the complex increases, making it more stable in the charge-discharge reactions. The Fe(TEA)MM complex achieves reversible and stable redox between Fe3+ and Fe2+, without metallic iron growth and HER. AIFBs based on this anolyte perform a high energy efficiency of 80.5 % at 80 mA cm−2 and exhibit a record durability among reported AIFBs. The efficiency and capacity retain nearly 100 % after 1,400 cycles. The capital cost of this AIFB is $ 33.2 kWh−1 (e.g., 20 h duration), cheaper than Li-ion battery and vanadium flow battery. This double-ligand chelating strategy not only solves the current problems faced by AIFBs, but also provides an insight for further improving the cycling stability of other flow batteries.

Conflict of interest

The authors declare no conflict of interest.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

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