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- In relation to this article, we declare that there is no conflict of interest.
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Received April 30, 2024
Accepted May 27, 2024
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This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/bync/3.0) which permits
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The Performance of All Iron-Based Redox Flow Batteries Enhanced by Carbon Nanotube Catalysts
Abstract
Carbon nanotubes (CNTs) are applied as catalysts to improve redox reaction of iron and 2,2-bis(hydroxymethyl)-2,2',2''-
nitrilotriethanol (Fe(BIS–TRIS)) complex as negolyte of iron-based fl ow batteries (FBs). Especially, multi-walled CNT
(MWCNT) and carboxylic acid-functionalized MWCNT (CACNT) are adopted as the catalysts. Eff ects of the catalysts are
electrochemically analyzed. CACNT is expected to have a better performance than MWCNT due to its abundant hydrophilic
functional groups. However, MWCNT is more eff ective catalyst than CACNT for improving redox reactivity of Fe(BIS–
TRIS). This is because carboxylic acid groups of CACNT are deprotonated to form COO − ions in aqueous electrolytes. FB
single cell tests show that energy effi ciency (EE) is 80.2% without catalyst at 80 mA cm −2 , but the EE increases when catalyst
is doped at negative electrode. When MWCNT and CACNT are doped, EE is 84.0 and 83.5%. The lower performance of
CACNT is because of electrostatic repulsion occurring between anionic Fe(BIS–TRIS) molecules and COO − ions. Therefore,
a larger overpotential is formed in the case of CACNT than MWCNT. This means when electrode is treated by catalyst,
interaction of active material and catalyst should be considered.
