Graduate School of Energy and Environment , Seoul National University of Science and Technology , 232 Gongneung-ro , Nowon-gu, Seoul 01811 , Republic of Korea.
ACS Appl Mater Interfaces. 2018 Oct 31;10(43):36882-36891. doi: 10.1021/acsami.8b10952. Epub 2018 Oct 18.
Alloxazine and ferrocyanide are suggested as the redox couple for an aqueous organic redox flow battery (AORFB). Alloxazine is further modified by carboxylic acid (COOH) groups (alloxazine-COOH) to increase the aqueous solubility and to pursue a desirable shift in the redox potential. For obtaining a better AORFB performance, the overall redox reactivity of AORFB should be improved by the enhancement of the rate-determining reaction of the redox couple. A carboxylic acid-doped carbon nanotube (CA-CNT) catalyst is considered for increasing the reactivity. The utilization of CA-CNT allows for the induction of a better redox reactivity of alloxazine-COOH because of the role of COOH within alloxazine-COOH as a proton donor, the fortified hydrophilic attribute of alloxazine-COOH, and the increased number of active sites. With the assistance of these attributes, the mass transfer of aqueous alloxazine-COOH molecules can be promoted. However, CA-CNT does not have an effect on the increase of the redox reactivity of ferrocyanide because the redox reaction is not affected by the same influence of protons that the redox reactivity of alloxazine-COOH is affected by. Such a behavior is proven by measuring the electron transfer rate constant and diffusivity. With regard to AORFB full cell testing, when CA-CNT is used as a catalyst for the negative electrode, the performance of the AORFB increases. Specifically, the charge-discharge overpotential and infrared drop potential are improved. As a result, the voltage efficiency affected by the potentials increases to 64%. Furthermore, the discharging capacity reaches 26.7 A h·L, and the state of charge attains 83% even after 30 cycles.
吖嗪和亚铁氰化物被建议作为水有机氧化还原流电池（AORFB）的氧化还原对。吖嗪通过羧酸（COOH）基团进一步修饰（吖嗪-COOH），以提高其在水中的溶解度并寻求氧化还原电位的理想变化。为了获得更好的 AORFB 性能，应通过增强氧化还原对的速率决定反应来提高 AORFB 的整体氧化还原反应性。考虑使用羧酸掺杂的碳纳米管（CA-CNT）催化剂来提高反应性。由于 CA-CNT 的使用，吖嗪-COOH 的更好氧化还原反应性得以诱导，这是因为 COOH 在吖嗪-COOH 中作为质子供体的作用、吖嗪-COOH 增强的亲水性以及增加的活性位点的数量。借助这些属性，可以促进水合吖嗪-COOH 分子的质量转移。然而，CA-CNT 对增加亚铁氰化物的氧化还原反应性没有影响，因为氧化还原反应不受质子影响，而这种影响会影响吖嗪-COOH 的氧化还原反应性。通过测量电子转移速率常数和扩散系数可以证明这种行为。在 AORFB 全电池测试方面，当 CA-CNT 用作负极的催化剂时，AORFB 的性能会提高。具体来说，充放电过电势和红外降电势得到改善。因此，受电位影响的电压效率提高到 64%。此外，即使经过 30 次循环，放电容量仍达到 26.7 A h·L，且荷电状态达到 83%。
